diff --git a/doc/examples.qbk b/doc/examples.qbk
index aafc1721..c238f80c 100644
--- a/doc/examples.qbk
+++ b/doc/examples.qbk
@@ -398,10 +398,15 @@ Boost.Asio's asynchronous operations.
 
 [heading Handler Tracking]
 
-This example shows how to implement custom handler tracking.
+This example header file shows how to implement custom handler tracking.
 
 * [@boost_asio/example/cpp11/handler_tracking/custom_tracking.hpp]
 
+This example program shows how to include source location information in
+the handler tracking output.
+
+* [@boost_asio/example/cpp11/handler_tracking/async_tcp_echo_server.cpp]
+
 
 [heading HTTP Server]
 
diff --git a/doc/net_ts.qbk b/doc/net_ts.qbk
index 32ab46d9..4ffee0ad 100644
--- a/doc/net_ts.qbk
+++ b/doc/net_ts.qbk
@@ -44,14 +44,14 @@ below shows the new Networking TS interfaces and the facilities they replace:
     ExecutionContext].]
   ]
   [
-    [[link boost_asio.reference.dispatch `post`]]
+    [[link boost_asio.reference.post `post`]]
     [[link boost_asio.reference.io_context.post `io_service::post`]]
-    [The `dispatch` free function can be used to submit functions to any [link
+    [The `post` free function can be used to submit functions to any [link
     boost_asio.reference.Executor1 Executor] or [link boost_asio.reference.ExecutionContext
     ExecutionContext].]
   ]
   [
-    [[link boost_asio.reference.dispatch `defer`]]
+    [[link boost_asio.reference.defer `defer`]]
     [[link boost_asio.reference.io_context.post `io_service::post`] when the [link
     boost_asio.reference.asio_handler_is_continuation `asio_handler_is_continuation`]
     hook returns true]
diff --git a/doc/overview/coroutines_ts.qbk b/doc/overview/coroutines_ts.qbk
index 7638e72d..04a07774 100644
--- a/doc/overview/coroutines_ts.qbk
+++ b/doc/overview/coroutines_ts.qbk
@@ -14,12 +14,7 @@ boost_asio.reference.co_spawn `co_spawn()`] function. These facilities allow pro
 to implement asynchronous logic in a synchronous manner, in conjunction with
 the `co_await` keyword, as shown in the following example:
 
-  boost::asio::co_spawn(executor,
-      [socket = std::move(socket)]() mutable
-      {
-        return echo(std::move(socket));
-      },
-      boost::asio::detached);
+  boost::asio::co_spawn(executor, echo(std::move(socket)), boost::asio::detached);
 
   // ...
 
@@ -46,10 +41,12 @@ execute. For example, a server's per-client object may consist of multiple
 coroutines; they should all run on the same `strand` so that no explicit
 synchronisation is required.
 
-The second argument is a nullary function object that returns a [link
-boost_asio.reference.awaitable `boost::asio::awaitable<R>`],
-where `R` is the type of return value produced by the coroutine. In the above
-example, the coroutine returns `void`.
+The second argument is an [link boost_asio.reference.awaitable `awaitable<R>`],
+that is the result of the coroutine's entry point function, and in the above
+example is the result of the call to `echo`. (Alternatively, this argument can
+be a function object that returns the [link boost_asio.reference.awaitable
+`awaitable<R>`].) The template parameter `R` is the type of return value
+produced by the coroutine. In the above example, the coroutine returns `void`.
 
 The third argument is a completion token, and this is used by `co_spawn()` to
 produce a completion handler with signature `void(std::exception_ptr, R)`. This
diff --git a/doc/overview/handler_tracking.qbk b/doc/overview/handler_tracking.qbk
index fad1ef59..5cb34ce9 100644
--- a/doc/overview/handler_tracking.qbk
+++ b/doc/overview/handler_tracking.qbk
@@ -18,30 +18,31 @@ asynchronous operations are chained together, or what the pending asynchronous
 operations are. As an illustration, here is the output when you run the HTTP
 Server example, handle a single request, then shut down via Ctrl+C:
 
-  @asio|1512254357.979980|0*1|signal_set@0x7ffeaaaa20d8.async_wait
-  @asio|1512254357.980127|0*2|socket@0x7ffeaaaa20f8.async_accept
-  @asio|1512254357.980150|.2|non_blocking_accept,ec=asio.system:11
-  @asio|1512254357.980162|0|resolver@0x7ffeaaaa1fd8.cancel
-  @asio|1512254368.457147|.2|non_blocking_accept,ec=system:0
-  @asio|1512254368.457193|>2|ec=system:0
-  @asio|1512254368.457219|2*3|socket@0x55cf39f0a238.async_receive
-  @asio|1512254368.457244|.3|non_blocking_recv,ec=system:0,bytes_transferred=141
-  @asio|1512254368.457275|2*4|socket@0x7ffeaaaa20f8.async_accept
-  @asio|1512254368.457293|.4|non_blocking_accept,ec=asio.system:11
-  @asio|1512254368.457301|<2|
-  @asio|1512254368.457310|>3|ec=system:0,bytes_transferred=141
-  @asio|1512254368.457441|3*5|socket@0x55cf39f0a238.async_send
-  @asio|1512254368.457502|.5|non_blocking_send,ec=system:0,bytes_transferred=156
-  @asio|1512254368.457511|<3|
-  @asio|1512254368.457519|>5|ec=system:0,bytes_transferred=156
-  @asio|1512254368.457544|5|socket@0x55cf39f0a238.close
-  @asio|1512254368.457559|<5|
-  @asio|1512254371.385106|>1|ec=system:0,signal_number=2
-  @asio|1512254371.385130|1|socket@0x7ffeaaaa20f8.close
-  @asio|1512254371.385163|<1|
-  @asio|1512254371.385175|>4|ec=asio.system:125
-  @asio|1512254371.385182|<4|
-  @asio|1512254371.385202|0|signal_set@0x7ffeaaaa20d8.cancel
+  @asio|1589424178.741850|0*1|signal_set@0x7ffee977d878.async_wait
+  @asio|1589424178.742593|0*2|socket@0x7ffee977d8a8.async_accept
+  @asio|1589424178.742619|.2|non_blocking_accept,ec=asio.system:11
+  @asio|1589424178.742625|0|resolver@0x7ffee977d760.cancel
+  @asio|1589424195.830382|.2|non_blocking_accept,ec=system:0
+  @asio|1589424195.830413|>2|ec=system:0
+  @asio|1589424195.830473|2*3|socket@0x7fa71d808230.async_receive
+  @asio|1589424195.830496|.3|non_blocking_recv,ec=system:0,bytes_transferred=151
+  @asio|1589424195.830503|2*4|socket@0x7ffee977d8a8.async_accept
+  @asio|1589424195.830507|.4|non_blocking_accept,ec=asio.system:11
+  @asio|1589424195.830510|<2|
+  @asio|1589424195.830529|>3|ec=system:0,bytes_transferred=151
+  @asio|1589424195.831143|3^5|in 'async_write' (./../../../boost/asio/impl/write.hpp:330)
+  @asio|1589424195.831143|3*5|socket@0x7fa71d808230.async_send
+  @asio|1589424195.831186|.5|non_blocking_send,ec=system:0,bytes_transferred=1090
+  @asio|1589424195.831194|<3|
+  @asio|1589424195.831218|>5|ec=system:0,bytes_transferred=1090
+  @asio|1589424195.831263|5|socket@0x7fa71d808230.close
+  @asio|1589424195.831298|<5|
+  @asio|1589424199.793770|>1|ec=system:0,signal_number=2
+  @asio|1589424199.793781|1|socket@0x7ffee977d8a8.close
+  @asio|1589424199.793809|<1|
+  @asio|1589424199.793840|>4|ec=asio.system:125
+  @asio|1589424199.793854|<4|
+  @asio|1589424199.793883|0|signal_set@0x7ffee977d878.cancel
 
 Each line is of the form:
 
@@ -74,6 +75,13 @@ The `<action>` takes one of the following forms:
     usually the case for any unfinished asynchronous operations when the
     `io_context` is destroyed.]
   ]
+  [
+    [n^m]
+    [The handler number `n` is about to create a new asynchronous operation with
+    completion handler number `m`. The `<description>` contains source location
+    information to help identify where in the program the asynchronous operation
+    is being started.]
+  ]
   [
     [n*m]
     [The handler number `n` created a new asynchronous operation with completion
@@ -105,6 +113,53 @@ As shown above, Each handler is assigned a numeric identifier. Where the
 handler tracking output shows a handler number of 0, it means that the action
 was performed outside of any handler.
 
+[heading Adding Location Information]
+
+[c++]
+Programs may augment the handler tracking output's location information by
+using the macro `BOOST_ASIO_HANDLER_LOCATION` in the source code. For example:
+
+  #define HANDLER_LOCATION \
+    BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, __func__))
+
+  // ...
+
+  void do_read()
+  {
+    HANDLER_LOCATION;
+
+    auto self(shared_from_this());
+    socket_.async_read_some(boost::asio::buffer(data_, max_length),
+        [this, self](boost::system::error_code ec, std::size_t length)
+        {
+          HANDLER_LOCATION;
+
+          if (!ec)
+          {
+            do_write(length);
+          }
+        });
+  }
+
+[teletype]
+With the additional location information available, the handler tracking output
+may include a call stack of source locations:
+
+  @asio|1589423304.861944|>7|ec=system:0,bytes_transferred=5
+  @asio|1589423304.861952|7^8|in 'async_write' (./../../../boost/asio/impl/write.hpp:330)
+  @asio|1589423304.861952|7^8|called from 'do_write' (handler_tracking/async_tcp_echo_server.cpp:62)
+  @asio|1589423304.861952|7^8|called from 'operator()' (handler_tracking/async_tcp_echo_server.cpp:51)
+  @asio|1589423304.861952|7*8|socket@0x7ff61c008230.async_send
+  @asio|1589423304.861975|.8|non_blocking_send,ec=system:0,bytes_transferred=5
+  @asio|1589423304.861980|<7|
+
+Furthermore, if `std::source_location` or `std::experimental::source_location`
+are available, the [link boost_asio.reference.use_awaitable_t `use_awaitable_t`]
+token (when default-constructed or used as a default completion token) will
+also cause handler tracking to output a source location for each newly created
+asynchronous operation. A `use_awaitable_t` object may also be explicitly
+constructed with location information.
+
 [heading Visual Representations]
 
 The handler tracking output may be post-processed using the included
@@ -137,6 +192,12 @@ preprocessor macros:
     [`BOOST_ASIO_HANDLER_TRACKING_INIT(args)`]
     [An expression that is used to initialise the tracking mechanism.]
   ]
+  [
+    [`BOOST_ASIO_HANDLER_LOCATION(args)`]
+    [A variable declaration that is used to define a source code location.
+    `args` is a parenthesised function argument list containing the file
+    name, line number, and function name.]
+  ]
   [
     [`BOOST_ASIO_HANDLER_CREATION(args)`]
     [An expression that is called on creation of an asynchronous operation.
@@ -214,7 +275,7 @@ preprocessor macros:
 
 [heading See Also]
 
-[link boost_asio.examples.cpp11_examples.handler_tracking Custom handler tracking
-example].
+[link boost_asio.examples.cpp11_examples.handler_tracking Handler tracking
+examples].
 
 [endsect]
diff --git a/doc/quickref.xml b/doc/quickref.xml
index cf478be2..3228079a 100644
--- a/doc/quickref.xml
+++ b/doc/quickref.xml
@@ -9,6 +9,135 @@
 -->
 
 <informaltable frame="all">
+  <tgroup cols="4">
+    <colspec colname="a"/>
+    <colspec colname="b"/>
+    <colspec colname="c"/>
+    <colspec colname="d"/>
+    <thead>
+      <row>
+        <entry valign="center" namest="a" nameend="a">
+          <bridgehead renderas="sect2">Properties</bridgehead>
+        </entry>
+        <entry valign="center" namest="b" nameend="d">
+          <bridgehead renderas="sect2">Execution</bridgehead>
+        </entry>
+      </row>
+    </thead>
+    <tbody>
+      <row>
+        <entry valign="top">
+          <bridgehead renderas="sect3">Customisation Points</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.prefer">prefer</link></member>
+            <member><link linkend="boost_asio.reference.query">query</link></member>
+            <member><link linkend="boost_asio.reference.require">require</link></member>
+            <member><link linkend="boost_asio.reference.require_concept">require_concept</link></member>
+          </simplelist>
+          <bridgehead renderas="sect3">Traits</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.can_prefer">can_prefer</link></member>
+            <member><link linkend="boost_asio.reference.can_query">can_query</link></member>
+            <member><link linkend="boost_asio.reference.can_require">can_require</link></member>
+            <member><link linkend="boost_asio.reference.can_require_concept">can_require_concept</link></member>
+            <member><link linkend="boost_asio.reference.is_nothrow_prefer">is_nothrow_prefer</link></member>
+            <member><link linkend="boost_asio.reference.is_nothrow_query">is_nothrow_query</link></member>
+            <member><link linkend="boost_asio.reference.is_nothrow_require">is_nothrow_require</link></member>
+            <member><link linkend="boost_asio.reference.is_nothrow_require_concept">is_nothrow_require_concept</link></member>
+            <member><link linkend="boost_asio.reference.prefer_result_type">prefer_result_type</link></member>
+            <member><link linkend="boost_asio.reference.query_result_type">query_result_type</link></member>
+            <member><link linkend="boost_asio.reference.require_result_type">require_result_type</link></member>
+            <member><link linkend="boost_asio.reference.require_concept_result_type">require_concept_result_type</link></member>
+          </simplelist>
+        </entry>
+        <entry valign="top">
+          <bridgehead renderas="sect3">Concepts</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.Executor1">Executor</link></member>
+          </simplelist>
+          <bridgehead renderas="sect3">Customisation Points</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.execution__execute">execution::execute</link></member>
+          </simplelist>
+          <bridgehead renderas="sect3">Class Templates</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.execution__any_executor">execution::any_executor</link></member>
+          </simplelist>
+          <bridgehead renderas="sect3">Classes</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.execution__bad_executor">execution::bad_executor</link></member>
+            <member><link linkend="boost_asio.reference.execution__invocable_archetype">execution::invocable_archetype</link></member>
+          </simplelist>
+          <bridgehead renderas="sect3">Traits</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.execution__is_executor">execution::is_executor</link></member>
+            <member><link linkend="boost_asio.reference.execution__can_execute">execution::can_execute</link></member>
+          </simplelist>
+        </entry>
+        <entry valign="top">
+          <bridgehead renderas="sect3">Properties</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.execution__allocator_t">execution::allocator_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t">execution::blocking_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t__possibly_t">execution::blocking_t::possibly_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t__always_t">execution::blocking_t::always_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t__never_t">execution::blocking_t::never_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_adaptation_t">execution::blocking_adaptation_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_adaptation_t__disallowed_t">execution::blocking_adaptation_t::disallowed_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_adaptation_t__allowed_t">execution::blocking_adaptation_t::allowed_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t">execution::bulk_guarantee_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t">execution::bulk_guarantee_t::unsequenced_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t__sequenced_t">execution::bulk_guarantee_t::sequenced_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t__parallel_t">execution::bulk_guarantee_t::parallel_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__context_t">execution::context_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__context_as_t">execution::context_as_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t">execution::mapping_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t__thread_t">execution::mapping_t::thread_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t__new_thread_t">execution::mapping_t::new_thread_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t__other_t">execution::mapping_t::other_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__occupancy_t">execution::occupancy_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__outstanding_work_t">execution::outstanding_work_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__outstanding_work_t__untracked_t">execution::outstanding_work_t::untracked_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__outstanding_work_t__tracked_t">execution::outstanding_work_t::tracked_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__prefer_only">execution::prefer_only</link></member>
+            <member><link linkend="boost_asio.reference.execution__relationship_t">execution::relationship_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__relationship_t__fork_t">execution::relationship_t::fork_t</link></member>
+            <member><link linkend="boost_asio.reference.execution__relationship_t__continuation_t">execution::relationship_t::continuation_t</link></member>
+          </simplelist>
+        </entry>
+        <entry valign="top">
+          <bridgehead renderas="sect3">Property Objects</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.execution__allocator">execution::allocator</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking">execution::blocking</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t.possibly">execution::blocking.possibly</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t.always">execution::blocking.always</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_t.never">execution::blocking.never</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_adaptation">execution::blocking_adaptation</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_adaptation_t.disallowed">execution::blocking_adaptation.disallowed</link></member>
+            <member><link linkend="boost_asio.reference.execution__blocking_adaptation_t.allowed">execution::blocking_adaptation.allowed</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee">execution::bulk_guarantee</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t.unsequenced">execution::bulk_guarantee.unsequenced</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t.sequenced">execution::bulk_guarantee.sequenced</link></member>
+            <member><link linkend="boost_asio.reference.execution__bulk_guarantee_t.parallel">execution::bulk_guarantee.parallel</link></member>
+            <member><link linkend="boost_asio.reference.execution__context">execution::context</link></member>
+            <member><link linkend="boost_asio.reference.execution__context_as">execution::context_as</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping">execution::mapping</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t.thread">execution::mapping.thread</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t.new_thread">execution::mapping.new_thread</link></member>
+            <member><link linkend="boost_asio.reference.execution__mapping_t.other">execution::mapping.other</link></member>
+            <member><link linkend="boost_asio.reference.execution__occupancy">execution::occupancy</link></member>
+            <member><link linkend="boost_asio.reference.execution__outstanding_work">execution::outstanding_work</link></member>
+            <member><link linkend="boost_asio.reference.execution__outstanding_work_t.untracked">execution::outstanding_work.untracked</link></member>
+            <member><link linkend="boost_asio.reference.execution__outstanding_work_t.tracked">execution::outstanding_work.tracked</link></member>
+            <member><link linkend="boost_asio.reference.execution__relationship">execution::relationship</link></member>
+            <member><link linkend="boost_asio.reference.execution__relationship_t.fork">execution::relationship.fork</link></member>
+            <member><link linkend="boost_asio.reference.execution__relationship_t.continuation">execution::relationship.continuation</link></member>
+          </simplelist>
+        </entry>
+      </row>
+    </tbody>
+  </tgroup>
   <tgroup cols="4">
     <colspec colname="a"/>
     <colspec colname="b"/>
@@ -26,6 +155,7 @@
         <entry valign="top">
           <bridgehead renderas="sect3">Classes</bridgehead>
           <simplelist type="vert" columns="1">
+            <member><link linkend="boost_asio.reference.any_io_executor">any_io_executor</link></member>
             <member><link linkend="boost_asio.reference.bad_executor">bad_executor</link></member>
             <member><link linkend="boost_asio.reference.coroutine">coroutine</link></member>
             <member><link linkend="boost_asio.reference.detached_t">detached_t</link></member>
@@ -36,16 +166,18 @@
             <member><link linkend="boost_asio.reference.executor_arg_t">executor_arg_t</link></member>
             <member><link linkend="boost_asio.reference.invalid_service_owner">invalid_service_owner</link></member>
             <member><link linkend="boost_asio.reference.io_context">io_context</link></member>
-            <member><link linkend="boost_asio.reference.io_context__executor_type">io_context::executor_type</link></member>
+            <member><link linkend="boost_asio.reference.io_context.executor_type">io_context::executor_type</link></member>
             <member><link linkend="boost_asio.reference.io_context__service">io_context::service</link></member>
             <member><link linkend="boost_asio.reference.io_context__strand">io_context::strand</link></member>
             <member><link linkend="boost_asio.reference.io_context__work">io_context::work</link> (deprecated)</member>
+            <member><link linkend="boost_asio.reference.multiple_exceptions">multiple_exceptions</link></member>
             <member><link linkend="boost_asio.reference.service_already_exists">service_already_exists</link></member>
+            <member><link linkend="boost_asio.reference.static_thread_pool">static_thread_pool</link></member>
             <member><link linkend="boost_asio.reference.system_context">system_context</link></member>
             <member><link linkend="boost_asio.reference.system_executor">system_executor</link></member>
             <member><link linkend="boost_asio.reference.this_coro__executor_t">this_coro::executor_t</link></member>
             <member><link linkend="boost_asio.reference.thread_pool">thread_pool</link></member>
-            <member><link linkend="boost_asio.reference.thread_pool__executor_type">thread_pool::executor_type</link></member>
+            <member><link linkend="boost_asio.reference.thread_pool.executor_type">thread_pool::executor_type</link></member>
             <member><link linkend="boost_asio.reference.yield_context">yield_context</link></member>
           </simplelist>
         </entry>
@@ -53,9 +185,9 @@
           <bridgehead renderas="sect3">Free Functions</bridgehead>
           <simplelist type="vert" columns="1">
             <member><link linkend="boost_asio.reference.execution_context.add_service">add_service</link></member>
-            <member><link linkend="boost_asio.reference.asio_handler_allocate">asio_handler_allocate</link></member>
-            <member><link linkend="boost_asio.reference.asio_handler_deallocate">asio_handler_deallocate</link></member>
-            <member><link linkend="boost_asio.reference.asio_handler_invoke">asio_handler_invoke</link></member>
+            <member><link linkend="boost_asio.reference.asio_handler_allocate">asio_handler_allocate</link> (deprecated)</member>
+            <member><link linkend="boost_asio.reference.asio_handler_deallocate">asio_handler_deallocate</link> (deprecated)</member>
+            <member><link linkend="boost_asio.reference.asio_handler_invoke">asio_handler_invoke</link> (deprecated)</member>
             <member><link linkend="boost_asio.reference.asio_handler_is_continuation">asio_handler_is_continuation</link></member>
             <member><link linkend="boost_asio.reference.async_compose">async_compose</link></member>
             <member><link linkend="boost_asio.reference.async_initiate">async_initiate</link></member>
@@ -80,11 +212,14 @@
             <member><link linkend="boost_asio.reference.async_completion">async_completion</link></member>
             <member><link linkend="boost_asio.reference.awaitable">awaitable</link></member>
             <member><link linkend="boost_asio.reference.basic_io_object">basic_io_object</link></member>
+            <member><link linkend="boost_asio.reference.basic_system_executor">basic_system_executor</link></member>
             <member><link linkend="boost_asio.reference.basic_yield_context">basic_yield_context</link></member>
             <member><link linkend="boost_asio.reference.executor_binder">executor_binder</link></member>
             <member><link linkend="boost_asio.reference.executor_work_guard">executor_work_guard</link></member>
+            <member><link linkend="boost_asio.reference.io_context__basic_executor_type">io_context::basic_executor_type</link></member>
             <member><link linkend="boost_asio.reference.redirect_error_t">redirect_error_t</link></member>
             <member><link linkend="boost_asio.reference.strand">strand</link></member>
+            <member><link linkend="boost_asio.reference.thread_pool__basic_executor_type">thread_pool::basic_executor_type</link></member>
             <member><link linkend="boost_asio.reference.use_awaitable_t">use_awaitable_t</link></member>
             <member><link linkend="boost_asio.reference.use_future_t">use_future_t</link></member>
           </simplelist>
diff --git a/doc/reference.dox b/doc/reference.dox
index 6db85872..a77ccdf1 100644
--- a/doc/reference.dox
+++ b/doc/reference.dox
@@ -81,6 +81,7 @@ INPUT                  = ./../../../boost/asio.hpp \
                          ./../../../boost/asio/posix \
                          ./../../../boost/asio/ssl \
                          ./../../../boost/asio/windows \
+                         ./../../../boost/asio/execution \
                          ./noncopyable_dox.txt \
                          ./std_exception_dox.txt
 FILE_PATTERNS          = 
@@ -221,7 +222,8 @@ PREDEFINED             = GENERATING_DOCUMENTATION \
                          BOOST_ASIO_MUTABLE_BUFFER=mutable_buffer \
                          BOOST_ASIO_SYNC_OP_VOID=void \
                          BOOST_ASIO_STRING_VIEW_PARAM=string_view \
-                         BOOST_ASIO_UNUSED_VARIABLE=
+                         BOOST_ASIO_UNUSED_VARIABLE= \
+                         BOOST_ASIO_UNSPECIFIED(e)=unspecified
 EXPAND_AS_DEFINED      = 
 SKIP_FUNCTION_MACROS   = YES
 #---------------------------------------------------------------------------
diff --git a/doc/reference.qbk b/doc/reference.qbk
index 86c50785..12182f9f 100644
--- a/doc/reference.qbk
+++ b/doc/reference.qbk
@@ -64,13 +64,138 @@
 
 
 
+[section:any_io_executor any_io_executor]
+
+[indexterm1 boost_asio.indexterm.any_io_executor..any_io_executor] 
+Polymorphic executor type for use with I/O objects. 
+
+
+  typedef execution::any_executor<...> any_io_executor;
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__any_executor.any_executor [*any_executor]]]
+    [Default constructor. 
+     [hr]
+     Copy constructor. 
+     [hr]
+     Move constructor. 
+     [hr]
+     Construct to point to the same target as another any_executor. 
+     [hr]
+     Construct a polymorphic wrapper for the specified executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.context [*context]]]
+    [Obtain the underlying execution context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.execute [*execute]]]
+    [Execute the function on the target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_bool [*operator bool]]]
+    [Determine whether the wrapper has a target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_eq_ [*operator=]]]
+    [Assignment operator. 
+     [hr]
+     Move assignment operator. 
+     [hr]
+     Assignment operator to create a polymorphic wrapper for the specified executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.prefer [*prefer]]]
+    [Obtain a polymorphic wrapper with the specified property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.query [*query]]]
+    [Obtain the value associated with the specified property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.require [*require]]]
+    [Obtain a polymorphic wrapper with the specified property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.target [*target]]]
+    [Get a pointer to the target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.target_type [*target_type]]]
+    [Get the type of the target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor._any_executor [*~any_executor]]]
+    [Destructor. ]
+  ]
+  
+]
+
+[heading Related Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_not__eq_ [*operator!=]]]
+    [Inequality operator. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_eq__eq_ [*operator==]]]
+    [Equality operator. ]
+  ]
+  
+]
+
+
+The `any_io_executor` type is a polymorphic executor that supports the set of properties required by I/O objects. It is defined as the [link boost_asio.reference.execution__any_executor `execution::any_executor`] class template parameterised as follows: 
+
+   execution::any_executor<
+     execution::context_as_t<execution_context&>,
+     execution::blocking_t::never_t,
+     execution::prefer_only<execution::blocking_t::possibly_t>,
+     execution::prefer_only<execution::outstanding_work_t::tracked_t>,
+     execution::prefer_only<execution::outstanding_work_t::untracked_t>,
+     execution::prefer_only<execution::relationship_t::fork_t>,
+     execution::prefer_only<execution::relationship_t::continuation_t>
+   > 
+
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/any_io_executor.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
 [section:asio_handler_allocate asio_handler_allocate]
 
 [indexterm1 boost_asio.indexterm.asio_handler_allocate..asio_handler_allocate] 
-Default allocation function for handlers. 
+(Deprecated: Use the [link boost_asio.reference.associated_allocator `associated_allocator`] trait.) Default allocation function for handlers. 
 
 
-  void * asio_handler_allocate(
+  asio_handler_allocate_is_deprecated asio_handler_allocate(
       std::size_t size,
       ... );
 
@@ -126,7 +251,7 @@ All temporary objects associated with a handler will be deallocated before the u
 Default deallocation function for handlers. 
 
 
-  void asio_handler_deallocate(
+  asio_handler_deallocate_is_deprecated asio_handler_deallocate(
       void * pointer,
       std::size_t size,
       ... );
@@ -152,14 +277,14 @@ The default implementation of these allocation hooks uses `operator new` and `op
 [section:asio_handler_invoke asio_handler_invoke]
 
 [indexterm1 boost_asio.indexterm.asio_handler_invoke..asio_handler_invoke] 
-Default invoke function for handlers. 
+(Deprecated: Use the [link boost_asio.reference.associated_executor `associated_executor`] trait.) Default invoke function for handlers. 
 
 
 Default handler invocation hook used for non-const function objects. 
 
   template<
       typename Function>
-  void ``[link boost_asio.reference.asio_handler_invoke.overload1 asio_handler_invoke]``(
+  asio_handler_invoke_is_deprecated ``[link boost_asio.reference.asio_handler_invoke.overload1 asio_handler_invoke]``(
       Function & function,
       ... );
   ``  [''''&raquo;''' [link boost_asio.reference.asio_handler_invoke.overload1 more...]]``
@@ -168,7 +293,7 @@ Default handler invocation hook used for const function objects.
 
   template<
       typename Function>
-  void ``[link boost_asio.reference.asio_handler_invoke.overload2 asio_handler_invoke]``(
+  asio_handler_invoke_is_deprecated ``[link boost_asio.reference.asio_handler_invoke.overload2 asio_handler_invoke]``(
       const Function & function,
       ... );
   ``  [''''&raquo;''' [link boost_asio.reference.asio_handler_invoke.overload2 more...]]``
@@ -219,7 +344,7 @@ Default handler invocation hook used for non-const function objects.
 
   template<
       typename Function>
-  void asio_handler_invoke(
+  asio_handler_invoke_is_deprecated asio_handler_invoke(
       Function & function,
       ... );
 
@@ -237,7 +362,7 @@ Default handler invocation hook used for const function objects.
 
   template<
       typename Function>
-  void asio_handler_invoke(
+  asio_handler_invoke_is_deprecated asio_handler_invoke(
       const Function & function,
       ... );
 
@@ -5439,7 +5564,7 @@ The return type of a coroutine or asynchronous operation.
 
   template<
       typename T,
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class awaitable
 
 
@@ -12431,7 +12556,7 @@ Provides waitable timer functionality.
   template<
       typename Time,
       typename ``[link boost_asio.reference.TimeTraits TimeTraits]`` = boost::asio::time_traits<Time>,
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_deadline_timer
 
 
@@ -14175,63 +14300,6 @@ The type of the executor associated with the object.
   typedef boost::asio::io_context::executor_type executor_type;
 
 
-[heading Member Functions]
-[table
-  [[Name][Description]]
-
-  [
-    [[link boost_asio.reference.io_context__executor_type.context [*context]]]
-    [Obtain the underlying execution context. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.defer [*defer]]]
-    [Request the io_context to invoke the given function object. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.dispatch [*dispatch]]]
-    [Request the io_context to invoke the given function object. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.on_work_finished [*on_work_finished]]]
-    [Inform the io_context that some work is no longer outstanding. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.on_work_started [*on_work_started]]]
-    [Inform the io_context that it has some outstanding work to do. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.post [*post]]]
-    [Request the io_context to invoke the given function object. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.running_in_this_thread [*running_in_this_thread]]]
-    [Determine whether the io_context is running in the current thread. ]
-  ]
-  
-]
-
-[heading Friends]
-[table
-  [[Name][Description]]
-
-  [
-    [[link boost_asio.reference.io_context__executor_type.operator_not__eq_ [*operator!=]]]
-    [Compare two executors for inequality. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.io_context__executor_type.operator_eq__eq_ [*operator==]]]
-    [Compare two executors for equality. ]
-  ]
-  
-]
-
 
 [heading Requirements]
 
@@ -27194,7 +27262,7 @@ Provides serial port functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_serial_port :
     public serial_port_base
 
@@ -29243,7 +29311,7 @@ Provides signal functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_signal_set
 
 
@@ -50486,6 +50554,707 @@ Get the size of the input sequence.
 
 
 
+[endsect]
+
+[section:basic_system_executor basic_system_executor]
+
+
+An executor that uses arbitrary threads. 
+
+
+  template<
+      typename Blocking,
+      typename Relationship,
+      typename Allocator>
+  class basic_system_executor
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.basic_system_executor.basic_system_executor [*basic_system_executor]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.context [*context]]]
+    [Obtain the underlying execution context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.defer [*defer]]]
+    [Request the system executor to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.dispatch [*dispatch]]]
+    [Request the system executor to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.execute [*execute]]]
+    [Oneway execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.on_work_finished [*on_work_finished]]]
+    [Inform the executor that some work is no longer outstanding. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.on_work_started [*on_work_started]]]
+    [Inform the executor that it has some outstanding work to do. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.post [*post]]]
+    [Request the system executor to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.query [*query]]]
+    [Query the current value of the allocator property. 
+     [hr]
+     Query the occupancy (recommended number of work items) for the system context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.query__static [*query]]]
+    [Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.always property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.basic_system_executor.operator_not__eq_ [*operator!=]]]
+    [Compare two executors for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.operator_eq__eq_ [*operator==]]]
+    [Compare two executors for equality. ]
+  ]
+  
+]
+
+The system executor represents an execution context where functions are permitted to run on arbitrary threads. When the blocking.never property is established, the system executor will schedule the function to run on an unspecified system thread pool. When either blocking.possibly or blocking.always is established, the executor invokes the function immediately. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/system_executor.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:basic_system_executor basic_system_executor::basic_system_executor]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.basic_system_executor..basic_system_executor..basic_system_executor] 
+Default constructor. 
+
+
+  basic_system_executor();
+
+
+
+[endsect]
+
+
+
+[section:context basic_system_executor::context]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.context..context..basic_system_executor] 
+Obtain the underlying execution context. 
+
+
+  system_context & context() const;
+
+
+
+[endsect]
+
+
+
+[section:defer basic_system_executor::defer]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.defer..defer..basic_system_executor] 
+Request the system executor to invoke the given function object. 
+
+
+  template<
+      typename Function,
+      typename OtherAllocator>
+  void defer(
+      Function && f,
+      const OtherAllocator & a) const;
+
+
+This function is used to ask the executor to execute the given function object. The function object will never be executed inside this function. Instead, it will be scheduled to run on an unspecified system thread pool.
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[f][The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
+``
+   void function(); 
+``
+]]
+
+[[a][An allocator that may be used by the executor to allocate the internal storage needed for function invocation. ]]
+
+]
+
+
+
+
+[endsect]
+
+
+
+[section:dispatch basic_system_executor::dispatch]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.dispatch..dispatch..basic_system_executor] 
+Request the system executor to invoke the given function object. 
+
+
+  template<
+      typename Function,
+      typename OtherAllocator>
+  void dispatch(
+      Function && f,
+      const OtherAllocator & a) const;
+
+
+This function is used to ask the executor to execute the given function object. The function object will always be executed inside this function.
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[f][The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
+``
+   void function(); 
+``
+]]
+
+[[a][An allocator that may be used by the executor to allocate the internal storage needed for function invocation. ]]
+
+]
+
+
+
+
+[endsect]
+
+
+
+[section:execute basic_system_executor::execute]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.execute..execute..basic_system_executor] 
+Oneway execution function. 
+
+
+  template<
+      typename Function>
+  void execute(
+      Function && f) const;
+
+
+
+[endsect]
+
+
+
+[section:on_work_finished basic_system_executor::on_work_finished]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.on_work_finished..on_work_finished..basic_system_executor] 
+Inform the executor that some work is no longer outstanding. 
+
+
+  void on_work_finished() const;
+
+
+For the system executor, this is a no-op. 
+
+
+[endsect]
+
+
+
+[section:on_work_started basic_system_executor::on_work_started]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.on_work_started..on_work_started..basic_system_executor] 
+Inform the executor that it has some outstanding work to do. 
+
+
+  void on_work_started() const;
+
+
+For the system executor, this is a no-op. 
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ basic_system_executor::operator!=]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.operator_not__eq_..operator!=..basic_system_executor] 
+Compare two executors for inequality. 
+
+
+  friend bool operator!=(
+      const basic_system_executor & ,
+      const basic_system_executor & );
+
+
+Two executors are equal if they refer to the same underlying [link boost_asio.reference.io_context `io_context`]. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/system_executor.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ basic_system_executor::operator==]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.operator_eq__eq_..operator==..basic_system_executor] 
+Compare two executors for equality. 
+
+
+  friend bool operator==(
+      const basic_system_executor & ,
+      const basic_system_executor & );
+
+
+Two executors are equal if they refer to the same underlying [link boost_asio.reference.io_context `io_context`]. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/system_executor.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
+[section:post basic_system_executor::post]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.post..post..basic_system_executor] 
+Request the system executor to invoke the given function object. 
+
+
+  template<
+      typename Function,
+      typename OtherAllocator>
+  void post(
+      Function && f,
+      const OtherAllocator & a) const;
+
+
+This function is used to ask the executor to execute the given function object. The function object will never be executed inside this function. Instead, it will be scheduled to run on an unspecified system thread pool.
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[f][The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
+``
+   void function(); 
+``
+]]
+
+[[a][An allocator that may be used by the executor to allocate the internal storage needed for function invocation. ]]
+
+]
+
+
+
+
+[endsect]
+
+
+[section:query basic_system_executor::query]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.query..query..basic_system_executor] 
+Query the current value of the `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr Allocator ``[link boost_asio.reference.basic_system_executor.query.overload1 query]``(
+      execution::allocator_t< OtherAllocator > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query.overload1 more...]]``
+
+  constexpr Allocator ``[link boost_asio.reference.basic_system_executor.query.overload2 query]``(
+      execution::allocator_t< void > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query.overload2 more...]]``
+
+
+Query the occupancy (recommended number of work items) for the system context. 
+
+
+  std::size_t ``[link boost_asio.reference.basic_system_executor.query.overload3 query]``(
+      execution::occupancy_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query.overload3 more...]]``
+
+
+[section:overload1 basic_system_executor::query (1 of 3 overloads)]
+
+
+Query the current value of the `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr Allocator query(
+      execution::allocator_t< OtherAllocator > ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload2 basic_system_executor::query (2 of 3 overloads)]
+
+
+Query the current value of the `allocator` property. 
+
+
+  constexpr Allocator query(
+      execution::allocator_t< void > ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload3 basic_system_executor::query (3 of 3 overloads)]
+
+
+Query the occupancy (recommended number of work items) for the system context. 
+
+
+  std::size_t query(
+      execution::occupancy_t ) const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+[section:query__static basic_system_executor::query]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.query__static..query..basic_system_executor] 
+Query the current value of the `mapping` property. 
+
+
+  static constexpr execution::mapping_t ``[link boost_asio.reference.basic_system_executor.query__static.overload1 query]``(
+      execution::mapping_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query__static.overload1 more...]]``
+
+
+Query the current value of the `context` property. 
+
+
+  static system_context & ``[link boost_asio.reference.basic_system_executor.query__static.overload2 query]``(
+      execution::context_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query__static.overload2 more...]]``
+
+
+Query the current value of the `blocking` property. 
+
+
+  static constexpr execution::blocking_t ``[link boost_asio.reference.basic_system_executor.query__static.overload3 query]``(
+      execution::blocking_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query__static.overload3 more...]]``
+
+
+Query the current value of the `relationship` property. 
+
+
+  static constexpr execution::relationship_t ``[link boost_asio.reference.basic_system_executor.query__static.overload4 query]``(
+      execution::relationship_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.query__static.overload4 more...]]``
+
+
+[section:overload1 basic_system_executor::query (1 of 4 overloads)]
+
+
+Query the current value of the `mapping` property. 
+
+
+  static constexpr execution::mapping_t query(
+      execution::mapping_t );
+
+
+
+[endsect]
+
+
+
+[section:overload2 basic_system_executor::query (2 of 4 overloads)]
+
+
+Query the current value of the `context` property. 
+
+
+  static system_context & query(
+      execution::context_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 basic_system_executor::query (3 of 4 overloads)]
+
+
+Query the current value of the `blocking` property. 
+
+
+  static constexpr execution::blocking_t query(
+      execution::blocking_t );
+
+
+
+[endsect]
+
+
+
+[section:overload4 basic_system_executor::query (4 of 4 overloads)]
+
+
+Query the current value of the `relationship` property. 
+
+
+  static constexpr execution::relationship_t query(
+      execution::relationship_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+[section:require basic_system_executor::require]
+
+[indexterm2 boost_asio.indexterm.basic_system_executor.require..require..basic_system_executor] 
+Obtain an executor with the `blocking.possibly` property. 
+
+
+  basic_system_executor< execution::blocking_t::possibly_t, Relationship, Allocator > ``[link boost_asio.reference.basic_system_executor.require.overload1 require]``(
+      execution::blocking_t::possibly_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload1 more...]]``
+
+
+Obtain an executor with the `blocking.always` property. 
+
+
+  basic_system_executor< execution::blocking_t::always_t, Relationship, Allocator > ``[link boost_asio.reference.basic_system_executor.require.overload2 require]``(
+      execution::blocking_t::always_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload2 more...]]``
+
+
+Obtain an executor with the `blocking.never` property. 
+
+
+  basic_system_executor< execution::blocking_t::never_t, Relationship, Allocator > ``[link boost_asio.reference.basic_system_executor.require.overload3 require]``(
+      execution::blocking_t::never_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload3 more...]]``
+
+
+Obtain an executor with the `relationship.continuation` property. 
+
+
+  basic_system_executor< Blocking, execution::relationship_t::continuation_t, Allocator > ``[link boost_asio.reference.basic_system_executor.require.overload4 require]``(
+      execution::relationship_t::continuation_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload4 more...]]``
+
+
+Obtain an executor with the `relationship.fork` property. 
+
+
+  basic_system_executor< Blocking, execution::relationship_t::fork_t, Allocator > ``[link boost_asio.reference.basic_system_executor.require.overload5 require]``(
+      execution::relationship_t::fork_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload5 more...]]``
+
+
+Obtain an executor with the specified `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  basic_system_executor< Blocking, Relationship, OtherAllocator > ``[link boost_asio.reference.basic_system_executor.require.overload6 require]``(
+      execution::allocator_t< OtherAllocator > a) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload6 more...]]``
+
+
+Obtain an executor with the default `allocator` property. 
+
+
+  basic_system_executor< Blocking, Relationship, std::allocator< void > > ``[link boost_asio.reference.basic_system_executor.require.overload7 require]``(
+      execution::allocator_t< void > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_system_executor.require.overload7 more...]]``
+
+
+[section:overload1 basic_system_executor::require (1 of 7 overloads)]
+
+
+Obtain an executor with the `blocking.possibly` property. 
+
+
+  basic_system_executor< execution::blocking_t::possibly_t, Relationship, Allocator > require(
+      execution::blocking_t::possibly_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload2 basic_system_executor::require (2 of 7 overloads)]
+
+
+Obtain an executor with the `blocking.always` property. 
+
+
+  basic_system_executor< execution::blocking_t::always_t, Relationship, Allocator > require(
+      execution::blocking_t::always_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload3 basic_system_executor::require (3 of 7 overloads)]
+
+
+Obtain an executor with the `blocking.never` property. 
+
+
+  basic_system_executor< execution::blocking_t::never_t, Relationship, Allocator > require(
+      execution::blocking_t::never_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload4 basic_system_executor::require (4 of 7 overloads)]
+
+
+Obtain an executor with the `relationship.continuation` property. 
+
+
+  basic_system_executor< Blocking, execution::relationship_t::continuation_t, Allocator > require(
+      execution::relationship_t::continuation_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload5 basic_system_executor::require (5 of 7 overloads)]
+
+
+Obtain an executor with the `relationship.fork` property. 
+
+
+  basic_system_executor< Blocking, execution::relationship_t::fork_t, Allocator > require(
+      execution::relationship_t::fork_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload6 basic_system_executor::require (6 of 7 overloads)]
+
+
+Obtain an executor with the specified `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  basic_system_executor< Blocking, Relationship, OtherAllocator > require(
+      execution::allocator_t< OtherAllocator > a) const;
+
+
+
+[endsect]
+
+
+
+[section:overload7 basic_system_executor::require (7 of 7 overloads)]
+
+
+Obtain an executor with the default `allocator` property. 
+
+
+  basic_system_executor< Blocking, Relationship, std::allocator< void > > require(
+      execution::allocator_t< void > ) const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+
 [endsect]
 
 [section:basic_waitable_timer basic_waitable_timer]
@@ -50840,8 +51609,15 @@ Move-construct a [link boost_asio.reference.basic_waitable_timer `basic_waitable
       basic_waitable_timer && other);
   ``  [''''&raquo;''' [link boost_asio.reference.basic_waitable_timer.basic_waitable_timer.overload7 more...]]``
 
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor1]``>
+  ``[link boost_asio.reference.basic_waitable_timer.basic_waitable_timer.overload8 basic_waitable_timer]``(
+      basic_waitable_timer< Clock, WaitTraits, Executor1 > && other,
+      typename enable_if< is_convertible< Executor1, Executor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_waitable_timer.basic_waitable_timer.overload8 more...]]``
 
-[section:overload1 basic_waitable_timer::basic_waitable_timer (1 of 7 overloads)]
+
+[section:overload1 basic_waitable_timer::basic_waitable_timer (1 of 8 overloads)]
 
 
 Constructor. 
@@ -50870,7 +51646,7 @@ This constructor creates a timer without setting an expiry time. The `expires_at
 
 
 
-[section:overload2 basic_waitable_timer::basic_waitable_timer (2 of 7 overloads)]
+[section:overload2 basic_waitable_timer::basic_waitable_timer (2 of 8 overloads)]
 
 
 Constructor. 
@@ -50902,7 +51678,7 @@ This constructor creates a timer without setting an expiry time. The `expires_at
 
 
 
-[section:overload3 basic_waitable_timer::basic_waitable_timer (3 of 7 overloads)]
+[section:overload3 basic_waitable_timer::basic_waitable_timer (3 of 8 overloads)]
 
 
 Constructor to set a particular expiry time as an absolute time. 
@@ -50934,7 +51710,7 @@ This constructor creates a timer and sets the expiry time.
 
 
 
-[section:overload4 basic_waitable_timer::basic_waitable_timer (4 of 7 overloads)]
+[section:overload4 basic_waitable_timer::basic_waitable_timer (4 of 8 overloads)]
 
 
 Constructor to set a particular expiry time as an absolute time. 
@@ -50969,7 +51745,7 @@ This constructor creates a timer and sets the expiry time.
 
 
 
-[section:overload5 basic_waitable_timer::basic_waitable_timer (5 of 7 overloads)]
+[section:overload5 basic_waitable_timer::basic_waitable_timer (5 of 8 overloads)]
 
 
 Constructor to set a particular expiry time relative to now. 
@@ -51001,7 +51777,7 @@ This constructor creates a timer and sets the expiry time.
 
 
 
-[section:overload6 basic_waitable_timer::basic_waitable_timer (6 of 7 overloads)]
+[section:overload6 basic_waitable_timer::basic_waitable_timer (6 of 8 overloads)]
 
 
 Constructor to set a particular expiry time relative to now. 
@@ -51036,7 +51812,7 @@ This constructor creates a timer and sets the expiry time.
 
 
 
-[section:overload7 basic_waitable_timer::basic_waitable_timer (7 of 7 overloads)]
+[section:overload7 basic_waitable_timer::basic_waitable_timer (7 of 8 overloads)]
 
 
 Move-construct a [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] from another. 
@@ -51066,6 +51842,43 @@ Following the move, the moved-from object is in the same state as if constructed
 
 
 
+[endsect]
+
+
+
+[section:overload8 basic_waitable_timer::basic_waitable_timer (8 of 8 overloads)]
+
+
+Move-construct a [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] from another. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor1]``>
+  basic_waitable_timer(
+      basic_waitable_timer< Clock, WaitTraits, Executor1 > && other,
+      typename enable_if< is_convertible< Executor1, Executor >::value >::type *  = 0);
+
+
+This constructor moves a timer from one object to another.
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[other][The other [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] object from which the move will occur.]]
+
+]
+
+
+[heading Remarks]
+      
+Following the move, the moved-from object is in the same state as if constructed using the `basic_waitable_timer(const executor_type&)` constructor. 
+
+
+
+
 [endsect]
 
 
@@ -51733,10 +52546,26 @@ Get the executor associated with the object.
 [endsect]
 
 
-
 [section:operator_eq_ basic_waitable_timer::operator=]
 
 [indexterm2 boost_asio.indexterm.basic_waitable_timer.operator_eq_..operator=..basic_waitable_timer] 
+Move-assign a [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] from another. 
+
+
+  basic_waitable_timer & ``[link boost_asio.reference.basic_waitable_timer.operator_eq_.overload1 operator=]``(
+      basic_waitable_timer && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_waitable_timer.operator_eq_.overload1 more...]]``
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor1]``>
+  enable_if< is_convertible< Executor1, Executor >::value, basic_waitable_timer & >::type ``[link boost_asio.reference.basic_waitable_timer.operator_eq_.overload2 operator=]``(
+      basic_waitable_timer< Clock, WaitTraits, Executor1 > && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.basic_waitable_timer.operator_eq_.overload2 more...]]``
+
+
+[section:overload1 basic_waitable_timer::operator= (1 of 2 overloads)]
+
+
 Move-assign a [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] from another. 
 
 
@@ -51768,6 +52597,44 @@ Following the move, the moved-from object is in the same state as if constructed
 
 
 
+[section:overload2 basic_waitable_timer::operator= (2 of 2 overloads)]
+
+
+Move-assign a [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] from another. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor1]``>
+  enable_if< is_convertible< Executor1, Executor >::value, basic_waitable_timer & >::type operator=(
+      basic_waitable_timer< Clock, WaitTraits, Executor1 > && other);
+
+
+This assignment operator moves a timer from one object to another. Cancels any outstanding asynchronous operations associated with the target object.
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[other][The other [link boost_asio.reference.basic_waitable_timer `basic_waitable_timer`] object from which the move will occur.]]
+
+]
+
+
+[heading Remarks]
+      
+Following the move, the moved-from object is in the same state as if constructed using the `basic_waitable_timer(const executor_type&)` constructor. 
+
+
+
+
+[endsect]
+
+
+[endsect]
+
+
 [section:time_point basic_waitable_timer::time_point]
 
 [indexterm2 boost_asio.indexterm.basic_waitable_timer.time_point..time_point..basic_waitable_timer] 
@@ -52431,7 +53298,7 @@ Associate an object of type `T` with an executor of type `Executor`.
   executor_binder< typename decay< T >::type, Executor > ``[link boost_asio.reference.bind_executor.overload1 bind_executor]``(
       const Executor & ex,
       T && t,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.bind_executor.overload1 more...]]``
 
 Associate an object of type `T` with an execution context's executor. 
@@ -52464,7 +53331,7 @@ Associate an object of type `T` with an executor of type `Executor`.
   executor_binder< typename decay< T >::type, Executor > bind_executor(
       const Executor & ex,
       T && t,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -57513,34 +58380,172 @@ The type of the value pointed to by the iterator.
 
 
 
+[endsect]
+
+[section:can_prefer can_prefer]
+
+
+A type trait that determines whether a `prefer` expression is well-formed. 
+
+
+  template<
+      typename T,
+      typename... Properties>
+  struct can_prefer
+
+
+Class template `can_prefer` is a trait that is derived from `true_type` if the expression `boost::asio::prefer(std::declval<T>(), std::declval<Properties>()...)` is well formed; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/prefer.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+[section:can_query can_query]
+
+
+A type trait that determines whether a `query` expression is well-formed. 
+
+
+  template<
+      typename T,
+      typename Property>
+  struct can_query
+
+
+Class template `can_query` is a trait that is derived from `true_type` if the expression `boost::asio::query(std::declval<T>(), std::declval<Property>())` is well formed; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/query.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+[section:can_require can_require]
+
+
+A type trait that determines whether a `require` expression is well-formed. 
+
+
+  template<
+      typename T,
+      typename... Properties>
+  struct can_require
+
+
+Class template `can_require` is a trait that is derived from `true_type` if the expression `boost::asio::require(std::declval<T>(), std::declval<Properties>()...)` is well formed; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+[section:can_require_concept can_require_concept]
+
+
+A type trait that determines whether a `require_concept` expression is well-formed. 
+
+
+  template<
+      typename T,
+      typename Property>
+  struct can_require_concept
+
+
+Class template `can_require_concept` is a trait that is derived from `true_type` if the expression `boost::asio::require_concept(std::declval<T>(), std::declval<Property>())` is well formed; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require_concept.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
 [endsect]
 
 [section:co_spawn co_spawn]
 
 [indexterm1 boost_asio.indexterm.co_spawn..co_spawn] 
-Spawn a new thread of execution. 
+Spawn a new coroutined-based thread of execution. 
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``,
+      typename T,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload1 co_spawn]``(
+      const Executor & ex,
+      awaitable< T, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< (is_executor< Executor >::value||execution::is_executor< Executor >::value)&&is_convertible< Executor, AwaitableExecutor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload1 more...]]``
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload2 co_spawn]``(
+      const Executor & ex,
+      awaitable< void, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< (is_executor< Executor >::value||execution::is_executor< Executor >::value)&&is_convertible< Executor, AwaitableExecutor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload2 more...]]``
+
+  template<
+      typename ExecutionContext,
+      typename T,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload3 co_spawn]``(
+      ExecutionContext & ctx,
+      awaitable< T, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value &&is_convertible< typename ExecutionContext::executor_type, AwaitableExecutor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload3 more...]]``
+
+  template<
+      typename ExecutionContext,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload4 co_spawn]``(
+      ExecutionContext & ctx,
+      awaitable< void, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value &&is_convertible< typename ExecutionContext::executor_type, AwaitableExecutor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload4 more...]]``
 
   template<
       typename ``[link boost_asio.reference.Executor1 Executor]``,
       typename F,
       typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
-  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload1 co_spawn]``(
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload5 co_spawn]``(
       const Executor & ex,
       F && f,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
-  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload1 more...]]``
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload5 more...]]``
 
   template<
       typename ExecutionContext,
       typename F,
       typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
-  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload2 co_spawn]``(
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.co_spawn.overload6 co_spawn]``(
       ExecutionContext & ctx,
       F && f,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
       typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value >::type *  = 0);
-  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload2 more...]]``
+  ``  [''''&raquo;''' [link boost_asio.reference.co_spawn.overload6 more...]]``
 
 [heading Requirements]
 
@@ -57549,10 +58554,332 @@ Spawn a new thread of execution.
 ['Convenience header: ][^boost/asio.hpp]
 
 
-[section:overload1 co_spawn (1 of 2 overloads)]
+[section:overload1 co_spawn (1 of 6 overloads)]
 
 
-Spawn a new thread of execution. 
+Spawn a new coroutined-based thread of execution. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``,
+      typename T,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` co_spawn(
+      const Executor & ex,
+      awaitable< T, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< (is_executor< Executor >::value||execution::is_executor< Executor >::value)&&is_convertible< Executor, AwaitableExecutor >::value >::type *  = 0);
+
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[ex][The executor that will be used to schedule the new thread of execution.]]
+
+[[a][The [link boost_asio.reference.awaitable `awaitable`] object that is the result of calling the coroutine's entry point function.]]
+
+[[token][The completion token that will handle the notification that the thread of execution has completed. The function signature of the completion handler must be: 
+``
+   void handler(std::exception_ptr, T); 
+``
+]]
+
+]
+
+
+[heading Example]
+  
+
+
+   boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+   {
+     std::size_t bytes_transferred = 0;
+
+     try
+     {
+       char data[1024];
+       for (;;)
+       {
+         std::size_t n = co_await socket.async_read_some(
+             boost::asio::buffer(data), boost::asio::use_awaitable);
+
+         co_await boost::asio::async_write(socket,
+             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+
+         bytes_transferred += n;
+       }
+     }
+     catch (const std::exception&)
+     {
+     }
+
+     co_return bytes_transferred;
+   }
+
+   // ...
+
+   boost::asio::co_spawn(my_executor,
+     echo(std::move(my_tcp_socket)),
+     [](std::exception_ptr e, std::size_t n)
+     {
+       std::cout << "transferred " << n << "\n";
+     });
+
+
+
+
+
+
+
+[endsect]
+
+
+
+[section:overload2 co_spawn (2 of 6 overloads)]
+
+
+Spawn a new coroutined-based thread of execution. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` co_spawn(
+      const Executor & ex,
+      awaitable< void, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< (is_executor< Executor >::value||execution::is_executor< Executor >::value)&&is_convertible< Executor, AwaitableExecutor >::value >::type *  = 0);
+
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[ex][The executor that will be used to schedule the new thread of execution.]]
+
+[[a][The [link boost_asio.reference.awaitable `awaitable`] object that is the result of calling the coroutine's entry point function.]]
+
+[[token][The completion token that will handle the notification that the thread of execution has completed. The function signature of the completion handler must be: 
+``
+   void handler(std::exception_ptr); 
+``
+]]
+
+]
+
+
+[heading Example]
+  
+
+
+   boost::asio::awaitable<void> echo(tcp::socket socket)
+   {
+     try
+     {
+       char data[1024];
+       for (;;)
+       {
+         std::size_t n = co_await socket.async_read_some(
+             boost::asio::buffer(data), boost::asio::use_awaitable);
+
+         co_await boost::asio::async_write(socket,
+             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+       }
+     }
+     catch (const std::exception& e)
+     {
+       std::cerr << "Exception: " << e.what() << "\n";
+     }
+   }
+
+   // ...
+
+   boost::asio::co_spawn(my_executor,
+     echo(std::move(my_tcp_socket)),
+     boost::asio::detached);
+
+
+
+
+
+
+
+[endsect]
+
+
+
+[section:overload3 co_spawn (3 of 6 overloads)]
+
+
+Spawn a new coroutined-based thread of execution. 
+
+
+  template<
+      typename ExecutionContext,
+      typename T,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` co_spawn(
+      ExecutionContext & ctx,
+      awaitable< T, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value &&is_convertible< typename ExecutionContext::executor_type, AwaitableExecutor >::value >::type *  = 0);
+
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[ctx][An execution context that will provide the executor to be used to schedule the new thread of execution.]]
+
+[[a][The [link boost_asio.reference.awaitable `awaitable`] object that is the result of calling the coroutine's entry point function.]]
+
+[[token][The completion token that will handle the notification that the thread of execution has completed. The function signature of the completion handler must be: 
+``
+   void handler(std::exception_ptr); 
+``
+]]
+
+]
+
+
+[heading Example]
+  
+
+
+   boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+   {
+     std::size_t bytes_transferred = 0;
+
+     try
+     {
+       char data[1024];
+       for (;;)
+       {
+         std::size_t n = co_await socket.async_read_some(
+             boost::asio::buffer(data), boost::asio::use_awaitable);
+
+         co_await boost::asio::async_write(socket,
+             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+
+         bytes_transferred += n;
+       }
+     }
+     catch (const std::exception&)
+     {
+     }
+
+     co_return bytes_transferred;
+   }
+
+   // ...
+
+   boost::asio::co_spawn(my_io_context,
+     echo(std::move(my_tcp_socket)),
+     [](std::exception_ptr e, std::size_t n)
+     {
+       std::cout << "transferred " << n << "\n";
+     });
+
+
+
+
+
+
+
+[endsect]
+
+
+
+[section:overload4 co_spawn (4 of 6 overloads)]
+
+
+Spawn a new coroutined-based thread of execution. 
+
+
+  template<
+      typename ExecutionContext,
+      typename ``[link boost_asio.reference.Executor1 AwaitableExecutor]``,
+      typename CompletionToken = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``>
+  ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` co_spawn(
+      ExecutionContext & ctx,
+      awaitable< void, AwaitableExecutor > a,
+      CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
+      typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value &&is_convertible< typename ExecutionContext::executor_type, AwaitableExecutor >::value >::type *  = 0);
+
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[ctx][An execution context that will provide the executor to be used to schedule the new thread of execution.]]
+
+[[a][The [link boost_asio.reference.awaitable `awaitable`] object that is the result of calling the coroutine's entry point function.]]
+
+[[token][The completion token that will handle the notification that the thread of execution has completed. The function signature of the completion handler must be: 
+``
+   void handler(std::exception_ptr); 
+``
+]]
+
+]
+
+
+[heading Example]
+  
+
+
+   boost::asio::awaitable<void> echo(tcp::socket socket)
+   {
+     try
+     {
+       char data[1024];
+       for (;;)
+       {
+         std::size_t n = co_await socket.async_read_some(
+             boost::asio::buffer(data), boost::asio::use_awaitable);
+
+         co_await boost::asio::async_write(socket,
+             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+       }
+     }
+     catch (const std::exception& e)
+     {
+       std::cerr << "Exception: " << e.what() << "\n";
+     }
+   }
+
+   // ...
+
+   boost::asio::co_spawn(my_io_context,
+     echo(std::move(my_tcp_socket)),
+     boost::asio::detached);
+
+
+
+
+
+
+
+[endsect]
+
+
+
+[section:overload5 co_spawn (5 of 6 overloads)]
+
+
+Spawn a new coroutined-based thread of execution. 
 
 
   template<
@@ -57563,29 +58890,103 @@ Spawn a new thread of execution.
       const Executor & ex,
       F && f,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
-
-
-The entry point function object `f` must have the signature:
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 
-   awaitable<void, E> f(); 
+[heading Parameters]
+    
+
+[variablelist
+  
+[[ex][The executor that will be used to schedule the new thread of execution.]]
+
+[[f][A nullary function object with a return type of the form `boost::asio::awaitable<R,E>` that will be used as the coroutine's entry point.]]
+
+[[token][The completion token that will handle the notification that the thread of execution has completed. If `R` is `void`, the function signature of the completion handler must be:]]
+
+]
+
+
+
+   void handler(std::exception_ptr); 
+
+
+Otherwise, the function signature of the completion handler must be: 
+
+   void handler(std::exception_ptr, R); 
+
+
+
+
+
+[heading Example]
+  
+
+
+   boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+   {
+     std::size_t bytes_transferred = 0;
+
+     try
+     {
+       char data[1024];
+       for (;;)
+       {
+         std::size_t n = co_await socket.async_read_some(
+             boost::asio::buffer(data), boost::asio::use_awaitable);
+
+         co_await boost::asio::async_write(socket,
+             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+
+         bytes_transferred += n;
+       }
+     }
+     catch (const std::exception&)
+     {
+     }
+
+     co_return bytes_transferred;
+   }
+
+   // ...
+
+   boost::asio::co_spawn(my_executor,
+     [socket = std::move(my_tcp_socket)]() mutable
+       -> boost::asio::awaitable<void>
+     {
+       try
+       {
+         char data[1024];
+         for (;;)
+         {
+           std::size_t n = co_await socket.async_read_some(
+               boost::asio::buffer(data), boost::asio::use_awaitable);
+
+           co_await boost::asio::async_write(socket,
+               boost::asio::buffer(data, n), boost::asio::use_awaitable);
+         }
+       }
+       catch (const std::exception& e)
+       {
+         std::cerr << "Exception: " << e.what() << "\n";
+       }
+     }, boost::asio::detached);
+
 
 
 
 
-where `E` is convertible from `Executor`. 
 
 
 [endsect]
 
 
 
-[section:overload2 co_spawn (2 of 2 overloads)]
+[section:overload6 co_spawn (6 of 6 overloads)]
 
 
-Spawn a new thread of execution. 
+Spawn a new coroutined-based thread of execution. 
 
 
   template<
@@ -57599,16 +59000,90 @@ Spawn a new thread of execution.
       typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value >::type *  = 0);
 
 
-The entry point function object `f` must have the signature:
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[ctx][An execution context that will provide the executor to be used to schedule the new thread of execution.]]
+
+[[f][A nullary function object with a return type of the form `boost::asio::awaitable<R,E>` that will be used as the coroutine's entry point.]]
+
+[[token][The completion token that will handle the notification that the thread of execution has completed. If `R` is `void`, the function signature of the completion handler must be:]]
+
+]
 
 
 
-   awaitable<void, E> f(); 
+   void handler(std::exception_ptr); 
+
+
+Otherwise, the function signature of the completion handler must be: 
+
+   void handler(std::exception_ptr, R); 
+
+
+
+
+
+[heading Example]
+  
+
+
+   boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+   {
+     std::size_t bytes_transferred = 0;
+
+     try
+     {
+       char data[1024];
+       for (;;)
+       {
+         std::size_t n = co_await socket.async_read_some(
+             boost::asio::buffer(data), boost::asio::use_awaitable);
+
+         co_await boost::asio::async_write(socket,
+             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+
+         bytes_transferred += n;
+       }
+     }
+     catch (const std::exception&)
+     {
+     }
+
+     co_return bytes_transferred;
+   }
+
+   // ...
+
+   boost::asio::co_spawn(my_io_context,
+     [socket = std::move(my_tcp_socket)]() mutable
+       -> boost::asio::awaitable<void>
+     {
+       try
+       {
+         char data[1024];
+         for (;;)
+         {
+           std::size_t n = co_await socket.async_read_some(
+               boost::asio::buffer(data), boost::asio::use_awaitable);
+
+           co_await boost::asio::async_write(socket,
+               boost::asio::buffer(data, n), boost::asio::use_awaitable);
+         }
+       }
+       catch (const std::exception& e)
+       {
+         std::cerr << "Exception: " << e.what() << "\n";
+       }
+     }, boost::asio::detached);
+
 
 
 
 
-where `E` is convertible from `ExecutionContext::executor_type`. 
 
 
 [endsect]
@@ -59944,7 +61419,7 @@ Submits a completion token or function object for execution.
   ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.defer.overload2 defer]``(
       const Executor & ex,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.defer.overload2 more...]]``
 
   template<
@@ -60018,7 +61493,7 @@ Submits a completion token or function object for execution.
   ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` defer(
       const Executor & ex,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
 
 
 This function submits an object for execution using the specified executor. The function object is queued for execution, and is never called from the current thread prior to returning from `defer()`.
@@ -60117,10 +61592,28 @@ Class used to specify that an asynchronous operation is detached.
   class detached_t
 
 
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.detached_t__executor_with_default [*executor_with_default]]]
+    [Adapts an executor to add the detached_t completion token as the default. ]
+  
+  ]
+
+]
+
 [heading Member Functions]
 [table
   [[Name][Description]]
 
+  [
+    [[link boost_asio.reference.detached_t.as_default_on [*as_default_on]]]
+    [Function helper to adapt an I/O object to use detached_t as its default completion token type. ]
+  ]
+  
   [
     [[link boost_asio.reference.detached_t.detached_t [*detached_t]]]
     [Constructor. ]
@@ -60144,6 +61637,23 @@ The [link boost_asio.reference.detached_t `detached_t`] class is used to indicat
 ['Convenience header: ][^boost/asio.hpp]
 
 
+[section:as_default_on detached_t::as_default_on]
+
+[indexterm2 boost_asio.indexterm.detached_t.as_default_on..as_default_on..detached_t] 
+Function helper to adapt an I/O object to use `detached_t` as its default completion token type. 
+
+
+  template<
+      typename T>
+  static decay< T >::type::template rebind_executor< executor_with_default< typename decay< T >::type::executor_type > >::other as_default_on(
+      T && object);
+
+
+
+[endsect]
+
+
+
 [section:detached_t detached_t::detached_t]
 
 [indexterm2 boost_asio.indexterm.detached_t.detached_t..detached_t..detached_t] 
@@ -60158,6 +61668,167 @@ Constructor.
 
 
 
+[endsect]
+
+[section:detached_t__executor_with_default detached_t::executor_with_default]
+
+
+Adapts an executor to add the `detached_t` completion token as the default. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 InnerExecutor]``>
+  struct executor_with_default
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.detached_t__executor_with_default.default_completion_token_type [*default_completion_token_type]]]
+    [Specify detached_t as the default completion token type. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.detached_t__executor_with_default.executor_with_default [*executor_with_default]]]
+    [Construct the adapted executor from the inner executor type. 
+     [hr]
+     Convert the specified executor to the inner executor type, then use that to construct the adapted executor. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/detached.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:default_completion_token_type detached_t::executor_with_default::default_completion_token_type]
+
+[indexterm2 boost_asio.indexterm.detached_t__executor_with_default.default_completion_token_type..default_completion_token_type..detached_t::executor_with_default] 
+Specify `detached_t` as the default completion token type. 
+
+
+  typedef detached_t default_completion_token_type;
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.detached_t__executor_with_default [*executor_with_default]]]
+    [Adapts an executor to add the detached_t completion token as the default. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.detached_t.as_default_on [*as_default_on]]]
+    [Function helper to adapt an I/O object to use detached_t as its default completion token type. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.detached_t.detached_t [*detached_t]]]
+    [Constructor. ]
+  ]
+  
+]
+
+The [link boost_asio.reference.detached_t `detached_t`] class is used to indicate that an asynchronous operation is detached. That is, there is no completion handler waiting for the operation's result. A [link boost_asio.reference.detached_t `detached_t`] object may be passed as a handler to an asynchronous operation, typically using the special value `boost::asio::detached`. For example:
+
+
+
+   my_socket.async_send(my_buffer, boost::asio::detached);
+
+
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/detached.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+[section:executor_with_default detached_t::executor_with_default::executor_with_default]
+
+[indexterm2 boost_asio.indexterm.detached_t__executor_with_default.executor_with_default..executor_with_default..detached_t::executor_with_default] 
+Construct the adapted executor from the inner executor type. 
+
+
+  ``[link boost_asio.reference.detached_t__executor_with_default.executor_with_default.overload1 executor_with_default]``(
+      const InnerExecutor & ex);
+  ``  [''''&raquo;''' [link boost_asio.reference.detached_t__executor_with_default.executor_with_default.overload1 more...]]``
+
+
+Convert the specified executor to the inner executor type, then use that to construct the adapted executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 OtherExecutor]``>
+  ``[link boost_asio.reference.detached_t__executor_with_default.executor_with_default.overload2 executor_with_default]``(
+      const OtherExecutor & ex,
+      typename enable_if< is_convertible< OtherExecutor, InnerExecutor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.detached_t__executor_with_default.executor_with_default.overload2 more...]]``
+
+
+[section:overload1 detached_t::executor_with_default::executor_with_default (1 of 2 overloads)]
+
+
+Construct the adapted executor from the inner executor type. 
+
+
+  executor_with_default(
+      const InnerExecutor & ex);
+
+
+
+[endsect]
+
+
+
+[section:overload2 detached_t::executor_with_default::executor_with_default (2 of 2 overloads)]
+
+
+Convert the specified executor to the inner executor type, then use that to construct the adapted executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 OtherExecutor]``>
+  executor_with_default(
+      const OtherExecutor & ex,
+      typename enable_if< is_convertible< OtherExecutor, InnerExecutor >::value >::type *  = 0);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
 [endsect]
 
 [section:dispatch dispatch]
@@ -60177,7 +61848,7 @@ Submits a completion token or function object for execution.
   ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.dispatch.overload2 dispatch]``(
       const Executor & ex,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.dispatch.overload2 more...]]``
 
   template<
@@ -60249,7 +61920,7 @@ Submits a completion token or function object for execution.
   ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` dispatch(
       const Executor & ex,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
 
 
 This function submits an object for execution using the specified executor. The function object may be called from the current thread prior to returning from `dispatch()`. Otherwise, it is queued for execution.
@@ -62506,6 +64177,6015 @@ Erases `n` bytes from the end of the vector by resizing the vector object. If `n
 [endsect]
 
 
+
+[section:execution__allocator execution::allocator]
+
+[indexterm1 boost_asio.indexterm.execution__allocator..execution::allocator] 
+A special value used for accessing the [link boost_asio.reference.execution__allocator_t `execution::allocator_t`] property. 
+
+
+  constexpr allocator_t< void > allocator;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/allocator.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__allocator_t execution::allocator_t]
+
+
+A property to describe which allocator an executor will use to allocate the memory required to store a submitted function object. 
+
+
+  template<
+      typename ``[link boost_asio.reference.ProtoAllocator ProtoAllocator]``>
+  struct allocator_t
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__allocator_t.allocator_t [*allocator_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__allocator_t.value [*value]]]
+    [Obtain the allocator stored in the allocator_t property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__allocator_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The allocator_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__allocator_t.is_preferable [*is_preferable]]]
+    [The allocator_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__allocator_t.is_requirable [*is_requirable]]]
+    [The allocator_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/allocator.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:allocator_t execution::allocator_t::allocator_t]
+
+[indexterm2 boost_asio.indexterm.execution__allocator_t.allocator_t..allocator_t..execution::allocator_t] 
+Default constructor. 
+
+
+  constexpr allocator_t();
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::allocator_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__allocator_t.is_applicable_property_v..is_applicable_property_v..execution::allocator_t] 
+The [link boost_asio.reference.execution__allocator_t `execution::allocator_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::allocator_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__allocator_t.is_preferable..is_preferable..execution::allocator_t] 
+The [link boost_asio.reference.execution__allocator_t `execution::allocator_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::allocator_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__allocator_t.is_requirable..is_requirable..execution::allocator_t] 
+The [link boost_asio.reference.execution__allocator_t `execution::allocator_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:value execution::allocator_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__allocator_t.value..value..execution::allocator_t] 
+Obtain the allocator stored in the [link boost_asio.reference.execution__allocator_t `execution::allocator_t`] property object. 
+
+
+  constexpr ProtoAllocator value() const;
+
+
+Present only if `ProtoAllocator` is non-void. 
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__any_executor execution::any_executor]
+
+
+Polymorphic executor wrapper. 
+
+
+  template<
+      typename... SupportableProperties>
+  class any_executor
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__any_executor.any_executor [*any_executor]]]
+    [Default constructor. 
+     [hr]
+     Copy constructor. 
+     [hr]
+     Move constructor. 
+     [hr]
+     Construct to point to the same target as another any_executor. 
+     [hr]
+     Construct a polymorphic wrapper for the specified executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.context [*context]]]
+    [Obtain the underlying execution context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.execute [*execute]]]
+    [Execute the function on the target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_bool [*operator bool]]]
+    [Determine whether the wrapper has a target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_eq_ [*operator=]]]
+    [Assignment operator. 
+     [hr]
+     Move assignment operator. 
+     [hr]
+     Assignment operator to create a polymorphic wrapper for the specified executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.prefer [*prefer]]]
+    [Obtain a polymorphic wrapper with the specified property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.query [*query]]]
+    [Obtain the value associated with the specified property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.require [*require]]]
+    [Obtain a polymorphic wrapper with the specified property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.target [*target]]]
+    [Get a pointer to the target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.target_type [*target_type]]]
+    [Get the type of the target executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor._any_executor [*~any_executor]]]
+    [Destructor. ]
+  ]
+  
+]
+
+[heading Related Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_not__eq_ [*operator!=]]]
+    [Inequality operator. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__any_executor.operator_eq__eq_ [*operator==]]]
+    [Equality operator. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/any_executor.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+[section:any_executor execution::any_executor::any_executor]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.any_executor..any_executor..execution::any_executor] 
+Default constructor. 
+
+
+  ``[link boost_asio.reference.execution__any_executor.any_executor.overload1 any_executor]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.any_executor.overload1 more...]]``
+
+
+Copy constructor. 
+
+
+  ``[link boost_asio.reference.execution__any_executor.any_executor.overload2 any_executor]``(
+      const any_executor & e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.any_executor.overload2 more...]]``
+
+
+Move constructor. 
+
+
+  ``[link boost_asio.reference.execution__any_executor.any_executor.overload3 any_executor]``(
+      any_executor && e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.any_executor.overload3 more...]]``
+
+
+Construct to point to the same target as another [link boost_asio.reference.execution__any_executor `execution::any_executor`]. 
+
+
+  template<
+      class... OtherSupportableProperties>
+  ``[link boost_asio.reference.execution__any_executor.any_executor.overload4 any_executor]``(
+      any_executor< OtherSupportableProperties...> e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.any_executor.overload4 more...]]``
+
+
+Construct a polymorphic wrapper for the specified executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  ``[link boost_asio.reference.execution__any_executor.any_executor.overload5 any_executor]``(
+      Executor e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.any_executor.overload5 more...]]``
+
+
+[section:overload1 execution::any_executor::any_executor (1 of 5 overloads)]
+
+
+Default constructor. 
+
+
+  any_executor();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::any_executor::any_executor (2 of 5 overloads)]
+
+
+Copy constructor. 
+
+
+  any_executor(
+      const any_executor & e);
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::any_executor::any_executor (3 of 5 overloads)]
+
+
+Move constructor. 
+
+
+  any_executor(
+      any_executor && e);
+
+
+
+[endsect]
+
+
+
+[section:overload4 execution::any_executor::any_executor (4 of 5 overloads)]
+
+
+Construct to point to the same target as another [link boost_asio.reference.execution__any_executor `execution::any_executor`]. 
+
+
+  template<
+      class... OtherSupportableProperties>
+  any_executor(
+      any_executor< OtherSupportableProperties...> e);
+
+
+
+[endsect]
+
+
+
+[section:overload5 execution::any_executor::any_executor (5 of 5 overloads)]
+
+
+Construct a polymorphic wrapper for the specified executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  any_executor(
+      Executor e);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:context execution::any_executor::context]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.context..context..execution::any_executor] 
+Obtain the underlying execution context. 
+
+
+  automatically_determined context() const;
+
+
+This function is provided for backward compatibility. It is automatically defined when the `SupportableProperties`... list includes a property of type `execution::context_as<U>`, for some type `U`. 
+
+
+[endsect]
+
+
+
+[section:execute execution::any_executor::execute]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.execute..execute..execution::any_executor] 
+Execute the function on the target executor. 
+
+
+  template<
+      typename Function>
+  void execute(
+      Function && f) const;
+
+
+Do not call this function directly. It is intended for use with the [link boost_asio.reference.execution__execute `execution::execute`] customisation point.
+
+For example: 
+
+   execution::any_executor<> ex = ...;
+   execution::execute(ex, my_function_object); 
+
+
+
+
+Throws [link boost_asio.reference.bad_executor `bad_executor`] if the polymorphic wrapper has no target. 
+
+
+[endsect]
+
+
+
+[section:operator_bool execution::any_executor::operator bool]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.operator_bool..operator bool..execution::any_executor] 
+Determine whether the wrapper has a target executor. 
+
+
+  operator bool() const;
+
+
+
+[heading Return Value]
+      
+`true` if the polymorphic wrapper has a target executor, otherwise false. 
+
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::any_executor::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.operator_not__eq_..operator!=..execution::any_executor] 
+Inequality operator. 
+
+
+  bool operator!=(
+      const any_executor< SupportableProperties...> & a,
+      const any_executor< SupportableProperties...> & b);
+
+
+
+[endsect]
+
+
+[section:operator_eq_ execution::any_executor::operator=]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.operator_eq_..operator=..execution::any_executor] 
+Assignment operator. 
+
+
+  any_executor & ``[link boost_asio.reference.execution__any_executor.operator_eq_.overload1 operator=]``(
+      const any_executor & e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.operator_eq_.overload1 more...]]``
+
+
+Move assignment operator. 
+
+
+  any_executor & ``[link boost_asio.reference.execution__any_executor.operator_eq_.overload2 operator=]``(
+      any_executor && e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.operator_eq_.overload2 more...]]``
+
+
+Assignment operator to create a polymorphic wrapper for the specified executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  any_executor & ``[link boost_asio.reference.execution__any_executor.operator_eq_.overload3 operator=]``(
+      Executor e);
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.operator_eq_.overload3 more...]]``
+
+
+[section:overload1 execution::any_executor::operator= (1 of 3 overloads)]
+
+
+Assignment operator. 
+
+
+  any_executor & operator=(
+      const any_executor & e);
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::any_executor::operator= (2 of 3 overloads)]
+
+
+Move assignment operator. 
+
+
+  any_executor & operator=(
+      any_executor && e);
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::any_executor::operator= (3 of 3 overloads)]
+
+
+Assignment operator to create a polymorphic wrapper for the specified executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  any_executor & operator=(
+      Executor e);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:operator_eq__eq_ execution::any_executor::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.operator_eq__eq_..operator==..execution::any_executor] 
+Equality operator. 
+
+
+  bool operator==(
+      const any_executor< SupportableProperties...> & a,
+      const any_executor< SupportableProperties...> & b);
+
+
+
+[endsect]
+
+
+
+[section:prefer execution::any_executor::prefer]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.prefer..prefer..execution::any_executor] 
+Obtain a polymorphic wrapper with the specified property. 
+
+
+  template<
+      typename Property>
+  any_executor prefer(
+      Property ) const;
+
+
+Do not call this function directly. It is intended for use with the [link boost_asio.reference.prefer `prefer`] customisation point.
+
+For example: 
+
+   execution::any_executor<execution::blocking_t::possibly_t> ex = ...;
+   auto ex2 = boost::asio::prefer(ex, execution::blocking.possibly); 
+
+
+
+
+
+[endsect]
+
+
+
+[section:query execution::any_executor::query]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.query..query..execution::any_executor] 
+Obtain the value associated with the specified property. 
+
+
+  template<
+      typename Property>
+  Property::polymorphic_query_result_type query(
+      Property ) const;
+
+
+Do not call this function directly. It is intended for use with the [link boost_asio.reference.query `query`] customisation point.
+
+For example: 
+
+   execution::any_executor<execution::occupancy_t> ex = ...;
+   size_t n = boost::asio::query(ex, execution::occupancy); 
+
+
+
+
+
+[endsect]
+
+
+
+[section:require execution::any_executor::require]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.require..require..execution::any_executor] 
+Obtain a polymorphic wrapper with the specified property. 
+
+
+  template<
+      typename Property>
+  any_executor require(
+      Property ) const;
+
+
+Do not call this function directly. It is intended for use with the [link boost_asio.reference.require `require`] and [link boost_asio.reference.prefer `prefer`] customisation points.
+
+For example: 
+
+   execution::any_executor<execution::blocking_t::possibly_t> ex = ...;
+   auto ex2 = boost::asio::requre(ex, execution::blocking.possibly); 
+
+
+
+
+
+[endsect]
+
+
+[section:target execution::any_executor::target]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.target..target..execution::any_executor] 
+Get a pointer to the target executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  Executor * ``[link boost_asio.reference.execution__any_executor.target.overload1 target]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.target.overload1 more...]]``
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  const Executor * ``[link boost_asio.reference.execution__any_executor.target.overload2 target]``() const;
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__any_executor.target.overload2 more...]]``
+
+
+[section:overload1 execution::any_executor::target (1 of 2 overloads)]
+
+
+Get a pointer to the target executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  Executor * target();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::any_executor::target (2 of 2 overloads)]
+
+
+Get a pointer to the target executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 Executor]``>
+  const Executor * target() const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:target_type execution::any_executor::target_type]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor.target_type..target_type..execution::any_executor] 
+Get the type of the target executor. 
+
+
+  const type_info & target_type() const;
+
+
+
+[endsect]
+
+
+
+[section:_any_executor execution::any_executor::~any_executor]
+
+[indexterm2 boost_asio.indexterm.execution__any_executor._any_executor..~any_executor..execution::any_executor] 
+Destructor. 
+
+
+  ~any_executor();
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__bad_executor execution::bad_executor]
+
+
+Exception thrown when trying to access an empty polymorphic executor. 
+
+
+  class bad_executor :
+    public std::exception
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bad_executor.bad_executor [*bad_executor]]]
+    [Constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__bad_executor.what [*what]]]
+    [Obtain message associated with exception. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bad_executor.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:bad_executor execution::bad_executor::bad_executor]
+
+[indexterm2 boost_asio.indexterm.execution__bad_executor.bad_executor..bad_executor..execution::bad_executor] 
+Constructor. 
+
+
+  bad_executor();
+
+
+
+[endsect]
+
+
+
+[section:what execution::bad_executor::what]
+
+[indexterm2 boost_asio.indexterm.execution__bad_executor.what..what..execution::bad_executor] 
+Obtain message associated with exception. 
+
+
+  virtual const char * what() const;
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:execution__blocking execution::blocking]
+
+[indexterm1 boost_asio.indexterm.execution__blocking..execution::blocking] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_t `execution::blocking_t`] property. 
+
+
+  constexpr blocking_t blocking;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:execution__blocking_adaptation execution::blocking_adaptation]
+
+[indexterm1 boost_asio.indexterm.execution__blocking_adaptation..execution::blocking_adaptation] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_adaptation_t `execution::blocking_adaptation_t`] property. 
+
+
+  constexpr blocking_adaptation_t blocking_adaptation;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__blocking_adaptation_t execution::blocking_adaptation_t]
+
+
+A property to describe whether automatic adaptation of an executor is allowed in order to apply the [link boost_asio.reference.execution__blocking_adaptation_t__allowed_t `execution::blocking_adaptation_t::allowed_t`] property. 
+
+
+  struct blocking_adaptation_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t [*allowed_t]]]
+    [A sub-property that indicates that automatic adaptation is allowed. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t [*disallowed_t]]]
+    [A sub-property that indicates that automatic adaptation is not allowed. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_adaptation_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t [*blocking_adaptation_t]]]
+    [Default constructor. 
+     [hr]
+     Construct from a sub-property value. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.allowed [*allowed]]]
+    [A special value used for accessing the blocking_adaptation_t::allowed_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.disallowed [*disallowed]]]
+    [A special value used for accessing the blocking_adaptation_t::disallowed_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_adaptation_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.is_preferable [*is_preferable]]]
+    [The top-level blocking_adaptation_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.is_requirable [*is_requirable]]]
+    [The top-level blocking_adaptation_t property cannot be required. ]
+  ]
+
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.operator_not__eq_ [*operator!=]]]
+    [Compare property values for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t.operator_eq__eq_ [*operator==]]]
+    [Compare property values for equality. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:allowed execution::blocking_adaptation_t::allowed]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.allowed..allowed..execution::blocking_adaptation_t] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_adaptation_t__allowed_t `execution::blocking_adaptation_t::allowed_t`] property. 
+
+
+  static constexpr allowed_t allowed;
+
+
+
+[endsect]
+
+
+[section:blocking_adaptation_t execution::blocking_adaptation_t::blocking_adaptation_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.blocking_adaptation_t..blocking_adaptation_t..execution::blocking_adaptation_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t.overload1 blocking_adaptation_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t.overload1 more...]]``
+
+
+Construct from a sub-property value. 
+
+
+  constexpr ``[link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t.overload2 blocking_adaptation_t]``(
+      disallowed_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t.overload2 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t.overload3 blocking_adaptation_t]``(
+      allowed_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_adaptation_t.blocking_adaptation_t.overload3 more...]]``
+
+
+[section:overload1 execution::blocking_adaptation_t::blocking_adaptation_t (1 of 3 overloads)]
+
+
+Default constructor. 
+
+
+  constexpr blocking_adaptation_t();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::blocking_adaptation_t::blocking_adaptation_t (2 of 3 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr blocking_adaptation_t(
+      disallowed_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::blocking_adaptation_t::blocking_adaptation_t (3 of 3 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr blocking_adaptation_t(
+      allowed_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:disallowed execution::blocking_adaptation_t::disallowed]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.disallowed..disallowed..execution::blocking_adaptation_t] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t `execution::blocking_adaptation_t::disallowed_t`] property. 
+
+
+  static constexpr disallowed_t disallowed;
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::blocking_adaptation_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_adaptation_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t `execution::blocking_adaptation_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_adaptation_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.is_preferable..is_preferable..execution::blocking_adaptation_t] 
+The top-level [link boost_asio.reference.execution__blocking_adaptation_t `execution::blocking_adaptation_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_adaptation_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.is_requirable..is_requirable..execution::blocking_adaptation_t] 
+The top-level [link boost_asio.reference.execution__blocking_adaptation_t `execution::blocking_adaptation_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::blocking_adaptation_t::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.operator_not__eq_..operator!=..execution::blocking_adaptation_t] 
+Compare property values for inequality. 
+
+
+  friend constexpr bool operator!=(
+      const blocking_adaptation_t & a,
+      const blocking_adaptation_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ execution::blocking_adaptation_t::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.operator_eq__eq_..operator==..execution::blocking_adaptation_t] 
+Compare property values for equality. 
+
+
+  friend constexpr bool operator==(
+      const blocking_adaptation_t & a,
+      const blocking_adaptation_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_adaptation_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_adaptation_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_adaptation_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__blocking_adaptation_t__allowed_t execution::blocking_adaptation_t::allowed_t]
+
+
+A sub-property that indicates that automatic adaptation is allowed. 
+
+
+  struct allowed_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t.allowed_t [*allowed_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_adaptation_t::allowed_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t.is_preferable [*is_preferable]]]
+    [The blocking_adaptation_t::allowed_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__allowed_t.is_requirable [*is_requirable]]]
+    [The blocking_adaptation_t::allowed_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:allowed_t execution::blocking_adaptation_t::allowed_t::allowed_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__allowed_t.allowed_t..allowed_t..execution::blocking_adaptation_t::allowed_t] 
+Default constructor. 
+
+
+  constexpr allowed_t();
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::blocking_adaptation_t::allowed_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__allowed_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_adaptation_t::allowed_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t__allowed_t `execution::blocking_adaptation_t::allowed_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_adaptation_t::allowed_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__allowed_t.is_preferable..is_preferable..execution::blocking_adaptation_t::allowed_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t__allowed_t `execution::blocking_adaptation_t::allowed_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_adaptation_t::allowed_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__allowed_t.is_requirable..is_requirable..execution::blocking_adaptation_t::allowed_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t__allowed_t `execution::blocking_adaptation_t::allowed_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_adaptation_t::allowed_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__allowed_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_adaptation_t::allowed_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_adaptation_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::blocking_adaptation_t::allowed_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__allowed_t.value..value..execution::blocking_adaptation_t::allowed_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr blocking_adaptation_t value();
+
+
+
+[heading Return Value]
+      
+`allowed_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__blocking_adaptation_t__disallowed_t execution::blocking_adaptation_t::disallowed_t]
+
+
+A sub-property that indicates that automatic adaptation is not allowed. 
+
+
+  struct disallowed_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t.disallowed_t [*disallowed_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_adaptation_t::disallowed_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t.is_preferable [*is_preferable]]]
+    [The blocking_adaptation_t::disallowed_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t.is_requirable [*is_requirable]]]
+    [The blocking_adaptation_t::disallowed_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:disallowed_t execution::blocking_adaptation_t::disallowed_t::disallowed_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__disallowed_t.disallowed_t..disallowed_t..execution::blocking_adaptation_t::disallowed_t] 
+Default constructor. 
+
+
+  constexpr disallowed_t();
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::blocking_adaptation_t::disallowed_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__disallowed_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_adaptation_t::disallowed_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t `execution::blocking_adaptation_t::disallowed_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_adaptation_t::disallowed_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__disallowed_t.is_preferable..is_preferable..execution::blocking_adaptation_t::disallowed_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t `execution::blocking_adaptation_t::disallowed_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_adaptation_t::disallowed_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__disallowed_t.is_requirable..is_requirable..execution::blocking_adaptation_t::disallowed_t] 
+The [link boost_asio.reference.execution__blocking_adaptation_t__disallowed_t `execution::blocking_adaptation_t::disallowed_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_adaptation_t::disallowed_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__disallowed_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_adaptation_t::disallowed_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_adaptation_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking_adaptation.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::blocking_adaptation_t::disallowed_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_adaptation_t__disallowed_t.value..value..execution::blocking_adaptation_t::disallowed_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr blocking_adaptation_t value();
+
+
+
+[heading Return Value]
+      
+`disallowed_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__blocking_t execution::blocking_t]
+
+
+A property to describe what guarantees an executor makes about the blocking behaviour of their execution functions. 
+
+
+  struct blocking_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t__always_t [*always_t]]]
+    [A sub-property that indicates that invocation of an executor's execution function shall block until completion of all invocations of the submitted function object. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t__never_t [*never_t]]]
+    [A sub-property that indicates that invocation of an executor's execution function shall not block pending completion of the invocations of the submitted function object. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t__possibly_t [*possibly_t]]]
+    [A sub-property that indicates that invocation of an executor's execution function may block pending completion of one or more invocations of the submitted function object. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.blocking_t [*blocking_t]]]
+    [Default constructor. 
+     [hr]
+     Construct from a sub-property value. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.always [*always]]]
+    [A special value used for accessing the blocking_t::always_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.is_preferable [*is_preferable]]]
+    [The top-level blocking_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.is_requirable [*is_requirable]]]
+    [The top-level blocking_t property cannot be required. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.never [*never]]]
+    [A special value used for accessing the blocking_t::never_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.possibly [*possibly]]]
+    [A special value used for accessing the blocking_t::possibly_t property. ]
+  ]
+
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t.operator_not__eq_ [*operator!=]]]
+    [Compare property values for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_t.operator_eq__eq_ [*operator==]]]
+    [Compare property values for equality. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:always execution::blocking_t::always]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.always..always..execution::blocking_t] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_t__always_t `execution::blocking_t::always_t`] property. 
+
+
+  static constexpr always_t always;
+
+
+
+[endsect]
+
+
+[section:blocking_t execution::blocking_t::blocking_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.blocking_t..blocking_t..execution::blocking_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.execution__blocking_t.blocking_t.overload1 blocking_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_t.blocking_t.overload1 more...]]``
+
+
+Construct from a sub-property value. 
+
+
+  constexpr ``[link boost_asio.reference.execution__blocking_t.blocking_t.overload2 blocking_t]``(
+      possibly_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_t.blocking_t.overload2 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__blocking_t.blocking_t.overload3 blocking_t]``(
+      always_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_t.blocking_t.overload3 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__blocking_t.blocking_t.overload4 blocking_t]``(
+      never_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__blocking_t.blocking_t.overload4 more...]]``
+
+
+[section:overload1 execution::blocking_t::blocking_t (1 of 4 overloads)]
+
+
+Default constructor. 
+
+
+  constexpr blocking_t();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::blocking_t::blocking_t (2 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr blocking_t(
+      possibly_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::blocking_t::blocking_t (3 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr blocking_t(
+      always_t );
+
+
+
+[endsect]
+
+
+
+[section:overload4 execution::blocking_t::blocking_t (4 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr blocking_t(
+      never_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:is_applicable_property_v execution::blocking_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_t] 
+The [link boost_asio.reference.execution__blocking_t `execution::blocking_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.is_preferable..is_preferable..execution::blocking_t] 
+The top-level [link boost_asio.reference.execution__blocking_t `execution::blocking_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.is_requirable..is_requirable..execution::blocking_t] 
+The top-level [link boost_asio.reference.execution__blocking_t `execution::blocking_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:never execution::blocking_t::never]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.never..never..execution::blocking_t] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_t__never_t `execution::blocking_t::never_t`] property. 
+
+
+  static constexpr never_t never;
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::blocking_t::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.operator_not__eq_..operator!=..execution::blocking_t] 
+Compare property values for inequality. 
+
+
+  friend constexpr bool operator!=(
+      const blocking_t & a,
+      const blocking_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ execution::blocking_t::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.operator_eq__eq_..operator==..execution::blocking_t] 
+Compare property values for equality. 
+
+
+  friend constexpr bool operator==(
+      const blocking_t & a,
+      const blocking_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:possibly execution::blocking_t::possibly]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t.possibly..possibly..execution::blocking_t] 
+A special value used for accessing the [link boost_asio.reference.execution__blocking_t__possibly_t `execution::blocking_t::possibly_t`] property. 
+
+
+  static constexpr possibly_t possibly;
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__blocking_t__always_t execution::blocking_t::always_t]
+
+
+A sub-property that indicates that invocation of an executor's execution function shall block until completion of all invocations of the submitted function object. 
+
+
+  struct always_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t__always_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__always_t.always_t [*always_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_t__always_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__always_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_t::always_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__always_t.is_preferable [*is_preferable]]]
+    [The blocking_t::always_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__always_t.is_requirable [*is_requirable]]]
+    [The blocking_t::always_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:always_t execution::blocking_t::always_t::always_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__always_t.always_t..always_t..execution::blocking_t::always_t] 
+Default constructor. 
+
+
+  constexpr always_t();
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::blocking_t::always_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__always_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_t::always_t] 
+The [link boost_asio.reference.execution__blocking_t__always_t `execution::blocking_t::always_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_t::always_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__always_t.is_preferable..is_preferable..execution::blocking_t::always_t] 
+The [link boost_asio.reference.execution__blocking_t__always_t `execution::blocking_t::always_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_t::always_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__always_t.is_requirable..is_requirable..execution::blocking_t::always_t] 
+The [link boost_asio.reference.execution__blocking_t__always_t `execution::blocking_t::always_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_t::always_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__always_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_t::always_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::blocking_t::always_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__always_t.value..value..execution::blocking_t::always_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr blocking_t value();
+
+
+
+[heading Return Value]
+      
+`always_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__blocking_t__never_t execution::blocking_t::never_t]
+
+
+A sub-property that indicates that invocation of an executor's execution function shall not block pending completion of the invocations of the submitted function object. 
+
+
+  struct never_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t__never_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__never_t.never_t [*never_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_t__never_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__never_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_t::never_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__never_t.is_preferable [*is_preferable]]]
+    [The blocking_t::never_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__never_t.is_requirable [*is_requirable]]]
+    [The blocking_t::never_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::blocking_t::never_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__never_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_t::never_t] 
+The [link boost_asio.reference.execution__blocking_t__never_t `execution::blocking_t::never_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_t::never_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__never_t.is_preferable..is_preferable..execution::blocking_t::never_t] 
+The [link boost_asio.reference.execution__blocking_t__never_t `execution::blocking_t::never_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_t::never_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__never_t.is_requirable..is_requirable..execution::blocking_t::never_t] 
+The [link boost_asio.reference.execution__blocking_t__never_t `execution::blocking_t::never_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:never_t execution::blocking_t::never_t::never_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__never_t.never_t..never_t..execution::blocking_t::never_t] 
+Default constructor. 
+
+
+  constexpr never_t();
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_t::never_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__never_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_t::never_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::blocking_t::never_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__never_t.value..value..execution::blocking_t::never_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr blocking_t value();
+
+
+
+[heading Return Value]
+      
+`never_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__blocking_t__possibly_t execution::blocking_t::possibly_t]
+
+
+A sub-property that indicates that invocation of an executor's execution function may block pending completion of one or more invocations of the submitted function object. 
+
+
+  struct possibly_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__blocking_t__possibly_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__possibly_t.possibly_t [*possibly_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__blocking_t__possibly_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__possibly_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The blocking_t::possibly_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__possibly_t.is_preferable [*is_preferable]]]
+    [The blocking_t::possibly_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__blocking_t__possibly_t.is_requirable [*is_requirable]]]
+    [The blocking_t::possibly_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::blocking_t::possibly_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__possibly_t.is_applicable_property_v..is_applicable_property_v..execution::blocking_t::possibly_t] 
+The [link boost_asio.reference.execution__blocking_t__possibly_t `execution::blocking_t::possibly_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::blocking_t::possibly_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__possibly_t.is_preferable..is_preferable..execution::blocking_t::possibly_t] 
+The [link boost_asio.reference.execution__blocking_t__possibly_t `execution::blocking_t::possibly_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::blocking_t::possibly_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__possibly_t.is_requirable..is_requirable..execution::blocking_t::possibly_t] 
+The [link boost_asio.reference.execution__blocking_t__possibly_t `execution::blocking_t::possibly_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::blocking_t::possibly_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__possibly_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::blocking_t::possibly_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef blocking_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/blocking.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:possibly_t execution::blocking_t::possibly_t::possibly_t]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__possibly_t.possibly_t..possibly_t..execution::blocking_t::possibly_t] 
+Default constructor. 
+
+
+  constexpr possibly_t();
+
+
+
+[endsect]
+
+
+
+[section:value execution::blocking_t::possibly_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__blocking_t__possibly_t.value..value..execution::blocking_t::possibly_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr blocking_t value();
+
+
+
+[heading Return Value]
+      
+`possibly_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:execution__bulk_guarantee execution::bulk_guarantee]
+
+[indexterm1 boost_asio.indexterm.execution__bulk_guarantee..execution::bulk_guarantee] 
+A special value used for accessing the [link boost_asio.reference.execution__bulk_guarantee_t `execution::bulk_guarantee_t`] property. 
+
+
+  constexpr bulk_guarantee_t bulk_guarantee;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__bulk_guarantee_t execution::bulk_guarantee_t]
+
+
+A property to communicate the forward progress and ordering guarantees of execution agents associated with the bulk execution. 
+
+
+  struct bulk_guarantee_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t [*parallel_t]]]
+    [A sub-property that indicates that execution agents within the same bulk execution may be parallelised. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t [*sequenced_t]]]
+    [A sub-property that indicates that execution agents within the same bulk execution may not be parallelised and vectorised. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t [*unsequenced_t]]]
+    [A sub-property that indicates that execution agents within the same bulk execution may be parallelised and vectorised. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t [*bulk_guarantee_t]]]
+    [Default constructor. 
+     [hr]
+     Construct from a sub-property value. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The bulk_guarantee_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.is_preferable [*is_preferable]]]
+    [The top-level bulk_guarantee_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.is_requirable [*is_requirable]]]
+    [The top-level bulk_guarantee_t property cannot be required. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.parallel [*parallel]]]
+    [A special value used for accessing the bulk_guarantee_t::parallel_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.sequenced [*sequenced]]]
+    [A special value used for accessing the bulk_guarantee_t::sequenced_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.unsequenced [*unsequenced]]]
+    [A special value used for accessing the bulk_guarantee_t::unsequenced_t property. ]
+  ]
+
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.operator_not__eq_ [*operator!=]]]
+    [Compare property values for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t.operator_eq__eq_ [*operator==]]]
+    [Compare property values for equality. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+[section:bulk_guarantee_t execution::bulk_guarantee_t::bulk_guarantee_t]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.bulk_guarantee_t..bulk_guarantee_t..execution::bulk_guarantee_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload1 bulk_guarantee_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload1 more...]]``
+
+
+Construct from a sub-property value. 
+
+
+  constexpr ``[link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload2 bulk_guarantee_t]``(
+      unsequenced_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload2 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload3 bulk_guarantee_t]``(
+      sequenced_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload3 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload4 bulk_guarantee_t]``(
+      parallel_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__bulk_guarantee_t.bulk_guarantee_t.overload4 more...]]``
+
+
+[section:overload1 execution::bulk_guarantee_t::bulk_guarantee_t (1 of 4 overloads)]
+
+
+Default constructor. 
+
+
+  constexpr bulk_guarantee_t();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::bulk_guarantee_t::bulk_guarantee_t (2 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr bulk_guarantee_t(
+      unsequenced_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::bulk_guarantee_t::bulk_guarantee_t (3 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr bulk_guarantee_t(
+      sequenced_t );
+
+
+
+[endsect]
+
+
+
+[section:overload4 execution::bulk_guarantee_t::bulk_guarantee_t (4 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr bulk_guarantee_t(
+      parallel_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:is_applicable_property_v execution::bulk_guarantee_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.is_applicable_property_v..is_applicable_property_v..execution::bulk_guarantee_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t `execution::bulk_guarantee_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::bulk_guarantee_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.is_preferable..is_preferable..execution::bulk_guarantee_t] 
+The top-level [link boost_asio.reference.execution__bulk_guarantee_t `execution::bulk_guarantee_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::bulk_guarantee_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.is_requirable..is_requirable..execution::bulk_guarantee_t] 
+The top-level [link boost_asio.reference.execution__bulk_guarantee_t `execution::bulk_guarantee_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::bulk_guarantee_t::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.operator_not__eq_..operator!=..execution::bulk_guarantee_t] 
+Compare property values for inequality. 
+
+
+  friend constexpr bool operator!=(
+      const bulk_guarantee_t & a,
+      const bulk_guarantee_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ execution::bulk_guarantee_t::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.operator_eq__eq_..operator==..execution::bulk_guarantee_t] 
+Compare property values for equality. 
+
+
+  friend constexpr bool operator==(
+      const bulk_guarantee_t & a,
+      const bulk_guarantee_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:parallel execution::bulk_guarantee_t::parallel]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.parallel..parallel..execution::bulk_guarantee_t] 
+A special value used for accessing the [link boost_asio.reference.execution__bulk_guarantee_t__parallel_t `execution::bulk_guarantee_t::parallel_t`] property. 
+
+
+  static constexpr parallel_t parallel;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::bulk_guarantee_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::bulk_guarantee_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef bulk_guarantee_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:sequenced execution::bulk_guarantee_t::sequenced]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.sequenced..sequenced..execution::bulk_guarantee_t] 
+A special value used for accessing the [link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t `execution::bulk_guarantee_t::sequenced_t`] property. 
+
+
+  static constexpr sequenced_t sequenced;
+
+
+
+[endsect]
+
+
+
+[section:unsequenced execution::bulk_guarantee_t::unsequenced]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t.unsequenced..unsequenced..execution::bulk_guarantee_t] 
+A special value used for accessing the [link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t `execution::bulk_guarantee_t::unsequenced_t`] property. 
+
+
+  static constexpr unsequenced_t unsequenced;
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__bulk_guarantee_t__parallel_t execution::bulk_guarantee_t::parallel_t]
+
+
+A sub-property that indicates that execution agents within the same bulk execution may be parallelised. 
+
+
+  struct parallel_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t.parallel_t [*parallel_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The bulk_guarantee_t::parallel_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t.is_preferable [*is_preferable]]]
+    [The bulk_guarantee_t::parallel_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__parallel_t.is_requirable [*is_requirable]]]
+    [The bulk_guarantee_t::parallel_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::bulk_guarantee_t::parallel_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__parallel_t.is_applicable_property_v..is_applicable_property_v..execution::bulk_guarantee_t::parallel_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__parallel_t `execution::bulk_guarantee_t::parallel_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::bulk_guarantee_t::parallel_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__parallel_t.is_preferable..is_preferable..execution::bulk_guarantee_t::parallel_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__parallel_t `execution::bulk_guarantee_t::parallel_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::bulk_guarantee_t::parallel_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__parallel_t.is_requirable..is_requirable..execution::bulk_guarantee_t::parallel_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__parallel_t `execution::bulk_guarantee_t::parallel_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:parallel_t execution::bulk_guarantee_t::parallel_t::parallel_t]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__parallel_t.parallel_t..parallel_t..execution::bulk_guarantee_t::parallel_t] 
+Default constructor. 
+
+
+  constexpr parallel_t();
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::bulk_guarantee_t::parallel_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__parallel_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::bulk_guarantee_t::parallel_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef bulk_guarantee_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::bulk_guarantee_t::parallel_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__parallel_t.value..value..execution::bulk_guarantee_t::parallel_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr bulk_guarantee_t value();
+
+
+
+[heading Return Value]
+      
+`parallel_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__bulk_guarantee_t__sequenced_t execution::bulk_guarantee_t::sequenced_t]
+
+
+A sub-property that indicates that execution agents within the same bulk execution may not be parallelised and vectorised. 
+
+
+  struct sequenced_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t.sequenced_t [*sequenced_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The bulk_guarantee_t::sequenced_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t.is_preferable [*is_preferable]]]
+    [The bulk_guarantee_t::sequenced_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t.is_requirable [*is_requirable]]]
+    [The bulk_guarantee_t::sequenced_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::bulk_guarantee_t::sequenced_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__sequenced_t.is_applicable_property_v..is_applicable_property_v..execution::bulk_guarantee_t::sequenced_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t `execution::bulk_guarantee_t::sequenced_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::bulk_guarantee_t::sequenced_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__sequenced_t.is_preferable..is_preferable..execution::bulk_guarantee_t::sequenced_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t `execution::bulk_guarantee_t::sequenced_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::bulk_guarantee_t::sequenced_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__sequenced_t.is_requirable..is_requirable..execution::bulk_guarantee_t::sequenced_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__sequenced_t `execution::bulk_guarantee_t::sequenced_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::bulk_guarantee_t::sequenced_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__sequenced_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::bulk_guarantee_t::sequenced_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef bulk_guarantee_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:sequenced_t execution::bulk_guarantee_t::sequenced_t::sequenced_t]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__sequenced_t.sequenced_t..sequenced_t..execution::bulk_guarantee_t::sequenced_t] 
+Default constructor. 
+
+
+  constexpr sequenced_t();
+
+
+
+[endsect]
+
+
+
+[section:value execution::bulk_guarantee_t::sequenced_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__sequenced_t.value..value..execution::bulk_guarantee_t::sequenced_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr bulk_guarantee_t value();
+
+
+
+[heading Return Value]
+      
+`sequenced_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__bulk_guarantee_t__unsequenced_t execution::bulk_guarantee_t::unsequenced_t]
+
+
+A sub-property that indicates that execution agents within the same bulk execution may be parallelised and vectorised. 
+
+
+  struct unsequenced_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t.unsequenced_t [*unsequenced_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The bulk_guarantee_t::unsequenced_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t.is_preferable [*is_preferable]]]
+    [The bulk_guarantee_t::unsequenced_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t.is_requirable [*is_requirable]]]
+    [The bulk_guarantee_t::unsequenced_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::bulk_guarantee_t::unsequenced_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__unsequenced_t.is_applicable_property_v..is_applicable_property_v..execution::bulk_guarantee_t::unsequenced_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t `execution::bulk_guarantee_t::unsequenced_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::bulk_guarantee_t::unsequenced_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__unsequenced_t.is_preferable..is_preferable..execution::bulk_guarantee_t::unsequenced_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t `execution::bulk_guarantee_t::unsequenced_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::bulk_guarantee_t::unsequenced_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__unsequenced_t.is_requirable..is_requirable..execution::bulk_guarantee_t::unsequenced_t] 
+The [link boost_asio.reference.execution__bulk_guarantee_t__unsequenced_t `execution::bulk_guarantee_t::unsequenced_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::bulk_guarantee_t::unsequenced_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__unsequenced_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::bulk_guarantee_t::unsequenced_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef bulk_guarantee_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/bulk_guarantee.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:unsequenced_t execution::bulk_guarantee_t::unsequenced_t::unsequenced_t]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__unsequenced_t.unsequenced_t..unsequenced_t..execution::bulk_guarantee_t::unsequenced_t] 
+Default constructor. 
+
+
+  constexpr unsequenced_t();
+
+
+
+[endsect]
+
+
+
+[section:value execution::bulk_guarantee_t::unsequenced_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__bulk_guarantee_t__unsequenced_t.value..value..execution::bulk_guarantee_t::unsequenced_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr bulk_guarantee_t value();
+
+
+
+[heading Return Value]
+      
+`unsequenced_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__can_execute execution::can_execute]
+
+
+A type trait that determines whether a `execute` expression is well-formed. 
+
+
+  template<
+      typename T,
+      typename F>
+  struct can_execute
+
+
+Class template `can_execute` is a trait that is derived from `true_type` if the expression `execution::execute(std::declval<T>(), std::declval<F>())` is well formed; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/execute.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__context execution::context]
+
+[indexterm1 boost_asio.indexterm.execution__context..execution::context] 
+A special value used for accessing the [link boost_asio.reference.execution__context_t `execution::context_t`] property. 
+
+
+  constexpr context_t context;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/context.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:execution__context_as execution::context_as]
+
+[indexterm1 boost_asio.indexterm.execution__context_as..execution::context_as] 
+A special value used for accessing the [link boost_asio.reference.execution__context_as_t `execution::context_as_t`] property. 
+
+
+  template <typename U>
+  constexpr context_as_t context_as;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/context_as.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__context_as_t execution::context_as_t]
+
+
+A property that is used to obtain the execution context that is associated with an executor. 
+
+
+  template<
+      typename U>
+  struct context_as_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__context_as_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__context_as_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The context_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__context_as_t.is_preferable [*is_preferable]]]
+    [The context_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__context_as_t.is_requirable [*is_requirable]]]
+    [The context_t property cannot be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/context_as.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::context_as_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__context_as_t.is_applicable_property_v..is_applicable_property_v..execution::context_as_t] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::context_as_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__context_as_t.is_preferable..is_preferable..execution::context_as_t] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::context_as_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__context_as_t.is_requirable..is_requirable..execution::context_as_t] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::context_as_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__context_as_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::context_as_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef T polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/context_as.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__context_t execution::context_t]
+
+
+A property that is used to obtain the execution context that is associated with an executor. 
+
+
+  struct context_t
+
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__context_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The context_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__context_t.is_preferable [*is_preferable]]]
+    [The context_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__context_t.is_requirable [*is_requirable]]]
+    [The context_t property cannot be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/context.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::context_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__context_t.is_applicable_property_v..is_applicable_property_v..execution::context_t] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::context_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__context_t.is_preferable..is_preferable..execution::context_t] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::context_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__context_t.is_requirable..is_requirable..execution::context_t] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:execution__execute execution::execute]
+
+[indexterm1 boost_asio.indexterm.execution__execute..execution::execute] 
+A customisation point that executes a function on an executor. 
+
+
+  constexpr unspecified execute = unspecified;
+
+
+The name `execution::execute` denotes a customization point object.
+
+For some subexpressions `e` and `f`, let `E` be a type such that `decltype((e))` is `E` and let `F` be a type such that `decltype((f))` is `F`. The expression `execution::execute(e, f)` is ill-formed if `F` does not model `invocable`, or if `E` does not model either `executor` or `sender`. Otherwise, it is expression-equivalent to:
+
+
+* `e.execute(f)`, if that expression is valid. If the function selected does not execute the function object `f` on the executor `e`, the program is ill-formed with no diagnostic required.
+
+
+* Otherwise, `execute(e, f)`, if that expression is valid, with overload resolution performed in a context that includes the declaration `void execute();` and that does not include a declaration of `execution::execute`. If the function selected by overload resolution does not execute the function object `f` on the executor `e`, the program is ill-formed with no diagnostic required. 
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/execute.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__invocable_archetype execution::invocable_archetype]
+
+
+An archetypal function object used for determining adherence to the execution::executor concept. 
+
+
+  struct invocable_archetype
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__invocable_archetype.operator_lp__rp_ [*operator()]]]
+    [Function call operator. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/invocable_archetype.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:operator_lp__rp_ execution::invocable_archetype::operator()]
+
+[indexterm2 boost_asio.indexterm.execution__invocable_archetype.operator_lp__rp_..operator()..execution::invocable_archetype] 
+Function call operator. 
+
+
+  template<
+      typename... Args>
+  void operator()(
+      Args && ...);
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__is_executor execution::is_executor]
+
+
+The [link boost_asio.reference.execution__is_executor `execution::is_executor`] trait detects whether a type T satisfies the execution::executor concept. 
+
+
+  template<
+      typename T>
+  struct is_executor
+
+
+Class template `is_executor` is a UnaryTypeTrait that is derived from `true_type` if the type `T` meets the concept definition for an executor, otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/executor.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__mapping execution::mapping]
+
+[indexterm1 boost_asio.indexterm.execution__mapping..execution::mapping] 
+A special value used for accessing the [link boost_asio.reference.execution__mapping_t `execution::mapping_t`] property. 
+
+
+  constexpr mapping_t mapping;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__mapping_t execution::mapping_t]
+
+
+A property to describe what guarantees an executor makes about the mapping of execution agents on to threads of execution. 
+
+
+  struct mapping_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t [*new_thread_t]]]
+    [A sub-property that indicates that execution agents are mapped on to new threads of execution. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t__other_t [*other_t]]]
+    [A sub-property that indicates that the mapping of execution agents is implementation-defined. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t__thread_t [*thread_t]]]
+    [A sub-property that indicates that execution agents are mapped on to threads of execution. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.mapping_t [*mapping_t]]]
+    [Default constructor. 
+     [hr]
+     Construct from a sub-property value. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The mapping_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.is_preferable [*is_preferable]]]
+    [The top-level mapping_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.is_requirable [*is_requirable]]]
+    [The top-level mapping_t property cannot be required. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.new_thread [*new_thread]]]
+    [A special value used for accessing the mapping_t::new_thread_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.other [*other]]]
+    [A special value used for accessing the mapping_t::other_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.thread [*thread]]]
+    [A special value used for accessing the mapping_t::thread_t property. ]
+  ]
+
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t.operator_not__eq_ [*operator!=]]]
+    [Compare property values for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__mapping_t.operator_eq__eq_ [*operator==]]]
+    [Compare property values for equality. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::mapping_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.is_applicable_property_v..is_applicable_property_v..execution::mapping_t] 
+The [link boost_asio.reference.execution__mapping_t `execution::mapping_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::mapping_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.is_preferable..is_preferable..execution::mapping_t] 
+The top-level [link boost_asio.reference.execution__mapping_t `execution::mapping_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::mapping_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.is_requirable..is_requirable..execution::mapping_t] 
+The top-level [link boost_asio.reference.execution__mapping_t `execution::mapping_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+[section:mapping_t execution::mapping_t::mapping_t]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.mapping_t..mapping_t..execution::mapping_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.execution__mapping_t.mapping_t.overload1 mapping_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__mapping_t.mapping_t.overload1 more...]]``
+
+
+Construct from a sub-property value. 
+
+
+  constexpr ``[link boost_asio.reference.execution__mapping_t.mapping_t.overload2 mapping_t]``(
+      thread_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__mapping_t.mapping_t.overload2 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__mapping_t.mapping_t.overload3 mapping_t]``(
+      new_thread_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__mapping_t.mapping_t.overload3 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__mapping_t.mapping_t.overload4 mapping_t]``(
+      other_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__mapping_t.mapping_t.overload4 more...]]``
+
+
+[section:overload1 execution::mapping_t::mapping_t (1 of 4 overloads)]
+
+
+Default constructor. 
+
+
+  constexpr mapping_t();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::mapping_t::mapping_t (2 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr mapping_t(
+      thread_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::mapping_t::mapping_t (3 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr mapping_t(
+      new_thread_t );
+
+
+
+[endsect]
+
+
+
+[section:overload4 execution::mapping_t::mapping_t (4 of 4 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr mapping_t(
+      other_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:new_thread execution::mapping_t::new_thread]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.new_thread..new_thread..execution::mapping_t] 
+A special value used for accessing the [link boost_asio.reference.execution__mapping_t__new_thread_t `execution::mapping_t::new_thread_t`] property. 
+
+
+  static constexpr new_thread_t new_thread;
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::mapping_t::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.operator_not__eq_..operator!=..execution::mapping_t] 
+Compare property values for inequality. 
+
+
+  friend constexpr bool operator!=(
+      const mapping_t & a,
+      const mapping_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ execution::mapping_t::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.operator_eq__eq_..operator==..execution::mapping_t] 
+Compare property values for equality. 
+
+
+  friend constexpr bool operator==(
+      const mapping_t & a,
+      const mapping_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:other execution::mapping_t::other]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.other..other..execution::mapping_t] 
+A special value used for accessing the [link boost_asio.reference.execution__mapping_t__other_t `execution::mapping_t::other_t`] property. 
+
+
+  static constexpr other_t other;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::mapping_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::mapping_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef mapping_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:thread execution::mapping_t::thread]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t.thread..thread..execution::mapping_t] 
+A special value used for accessing the [link boost_asio.reference.execution__mapping_t__thread_t `execution::mapping_t::thread_t`] property. 
+
+
+  static constexpr thread_t thread;
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__mapping_t__new_thread_t execution::mapping_t::new_thread_t]
+
+
+A sub-property that indicates that execution agents are mapped on to new threads of execution. 
+
+
+  struct new_thread_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t.new_thread_t [*new_thread_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The mapping_t::new_thread_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t.is_preferable [*is_preferable]]]
+    [The mapping_t::new_thread_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__new_thread_t.is_requirable [*is_requirable]]]
+    [The mapping_t::new_thread_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::mapping_t::new_thread_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__new_thread_t.is_applicable_property_v..is_applicable_property_v..execution::mapping_t::new_thread_t] 
+The [link boost_asio.reference.execution__mapping_t__new_thread_t `execution::mapping_t::new_thread_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::mapping_t::new_thread_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__new_thread_t.is_preferable..is_preferable..execution::mapping_t::new_thread_t] 
+The [link boost_asio.reference.execution__mapping_t__new_thread_t `execution::mapping_t::new_thread_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::mapping_t::new_thread_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__new_thread_t.is_requirable..is_requirable..execution::mapping_t::new_thread_t] 
+The [link boost_asio.reference.execution__mapping_t__new_thread_t `execution::mapping_t::new_thread_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:new_thread_t execution::mapping_t::new_thread_t::new_thread_t]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__new_thread_t.new_thread_t..new_thread_t..execution::mapping_t::new_thread_t] 
+Default constructor. 
+
+
+  constexpr new_thread_t();
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::mapping_t::new_thread_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__new_thread_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::mapping_t::new_thread_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef mapping_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::mapping_t::new_thread_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__new_thread_t.value..value..execution::mapping_t::new_thread_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr mapping_t value();
+
+
+
+[heading Return Value]
+      
+`new_thread_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__mapping_t__other_t execution::mapping_t::other_t]
+
+
+A sub-property that indicates that the mapping of execution agents is implementation-defined. 
+
+
+  struct other_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t__other_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__other_t.other_t [*other_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__mapping_t__other_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__other_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The mapping_t::other_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__other_t.is_preferable [*is_preferable]]]
+    [The mapping_t::other_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__other_t.is_requirable [*is_requirable]]]
+    [The mapping_t::other_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::mapping_t::other_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__other_t.is_applicable_property_v..is_applicable_property_v..execution::mapping_t::other_t] 
+The [link boost_asio.reference.execution__mapping_t__other_t `execution::mapping_t::other_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::mapping_t::other_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__other_t.is_preferable..is_preferable..execution::mapping_t::other_t] 
+The [link boost_asio.reference.execution__mapping_t__other_t `execution::mapping_t::other_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::mapping_t::other_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__other_t.is_requirable..is_requirable..execution::mapping_t::other_t] 
+The [link boost_asio.reference.execution__mapping_t__other_t `execution::mapping_t::other_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:other_t execution::mapping_t::other_t::other_t]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__other_t.other_t..other_t..execution::mapping_t::other_t] 
+Default constructor. 
+
+
+  constexpr other_t();
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::mapping_t::other_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__other_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::mapping_t::other_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef mapping_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::mapping_t::other_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__other_t.value..value..execution::mapping_t::other_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr mapping_t value();
+
+
+
+[heading Return Value]
+      
+`other_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__mapping_t__thread_t execution::mapping_t::thread_t]
+
+
+A sub-property that indicates that execution agents are mapped on to threads of execution. 
+
+
+  struct thread_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__mapping_t__thread_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__thread_t.thread_t [*thread_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__mapping_t__thread_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__thread_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The mapping_t::thread_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__thread_t.is_preferable [*is_preferable]]]
+    [The mapping_t::thread_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__mapping_t__thread_t.is_requirable [*is_requirable]]]
+    [The mapping_t::thread_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::mapping_t::thread_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__thread_t.is_applicable_property_v..is_applicable_property_v..execution::mapping_t::thread_t] 
+The [link boost_asio.reference.execution__mapping_t__thread_t `execution::mapping_t::thread_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::mapping_t::thread_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__thread_t.is_preferable..is_preferable..execution::mapping_t::thread_t] 
+The [link boost_asio.reference.execution__mapping_t__thread_t `execution::mapping_t::thread_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::mapping_t::thread_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__thread_t.is_requirable..is_requirable..execution::mapping_t::thread_t] 
+The [link boost_asio.reference.execution__mapping_t__thread_t `execution::mapping_t::thread_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::mapping_t::thread_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__thread_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::mapping_t::thread_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef mapping_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/mapping.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:thread_t execution::mapping_t::thread_t::thread_t]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__thread_t.thread_t..thread_t..execution::mapping_t::thread_t] 
+Default constructor. 
+
+
+  constexpr thread_t();
+
+
+
+[endsect]
+
+
+
+[section:value execution::mapping_t::thread_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__mapping_t__thread_t.value..value..execution::mapping_t::thread_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr mapping_t value();
+
+
+
+[heading Return Value]
+      
+`thread_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:execution__occupancy execution::occupancy]
+
+[indexterm1 boost_asio.indexterm.execution__occupancy..execution::occupancy] 
+A special value used for accessing the [link boost_asio.reference.execution__occupancy_t `execution::occupancy_t`] property. 
+
+
+  constexpr occupancy_t occupancy;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/occupancy.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__occupancy_t execution::occupancy_t]
+
+
+A property that gives an estimate of the number of execution agents that should occupy the associated execution context. 
+
+
+  struct occupancy_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__occupancy_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__occupancy_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The occupancy_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__occupancy_t.is_preferable [*is_preferable]]]
+    [The occupancy_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__occupancy_t.is_requirable [*is_requirable]]]
+    [The occupancy_t property cannot be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/occupancy.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::occupancy_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__occupancy_t.is_applicable_property_v..is_applicable_property_v..execution::occupancy_t] 
+The [link boost_asio.reference.execution__occupancy_t `execution::occupancy_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::occupancy_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__occupancy_t.is_preferable..is_preferable..execution::occupancy_t] 
+The [link boost_asio.reference.execution__occupancy_t `execution::occupancy_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::occupancy_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__occupancy_t.is_requirable..is_requirable..execution::occupancy_t] 
+The [link boost_asio.reference.execution__occupancy_t `execution::occupancy_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::occupancy_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__occupancy_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::occupancy_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef std::size_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/occupancy.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:execution__outstanding_work execution::outstanding_work]
+
+[indexterm1 boost_asio.indexterm.execution__outstanding_work..execution::outstanding_work] 
+A special value used for accessing the [link boost_asio.reference.execution__outstanding_work_t `execution::outstanding_work_t`] property. 
+
+
+  constexpr outstanding_work_t outstanding_work;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__outstanding_work_t execution::outstanding_work_t]
+
+
+A property to describe whether task submission is likely in the future. 
+
+
+  struct outstanding_work_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t [*tracked_t]]]
+    [A sub-property that indicates that the executor represents likely future submission of a function object. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t [*untracked_t]]]
+    [A sub-property that indicates that the executor does not represent likely future submission of a function object. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__outstanding_work_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t [*outstanding_work_t]]]
+    [Default constructor. 
+     [hr]
+     Construct from a sub-property value. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The outstanding_work_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.is_preferable [*is_preferable]]]
+    [The top-level outstanding_work_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.is_requirable [*is_requirable]]]
+    [The top-level outstanding_work_t property cannot be required. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.tracked [*tracked]]]
+    [A special value used for accessing the outstanding_work_t::tracked_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.untracked [*untracked]]]
+    [A special value used for accessing the outstanding_work_t::untracked_t property. ]
+  ]
+
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.operator_not__eq_ [*operator!=]]]
+    [Compare property values for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t.operator_eq__eq_ [*operator==]]]
+    [Compare property values for equality. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::outstanding_work_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.is_applicable_property_v..is_applicable_property_v..execution::outstanding_work_t] 
+The [link boost_asio.reference.execution__outstanding_work_t `execution::outstanding_work_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::outstanding_work_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.is_preferable..is_preferable..execution::outstanding_work_t] 
+The top-level [link boost_asio.reference.execution__outstanding_work_t `execution::outstanding_work_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::outstanding_work_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.is_requirable..is_requirable..execution::outstanding_work_t] 
+The top-level [link boost_asio.reference.execution__outstanding_work_t `execution::outstanding_work_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::outstanding_work_t::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.operator_not__eq_..operator!=..execution::outstanding_work_t] 
+Compare property values for inequality. 
+
+
+  friend constexpr bool operator!=(
+      const outstanding_work_t & a,
+      const outstanding_work_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ execution::outstanding_work_t::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.operator_eq__eq_..operator==..execution::outstanding_work_t] 
+Compare property values for equality. 
+
+
+  friend constexpr bool operator==(
+      const outstanding_work_t & a,
+      const outstanding_work_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:outstanding_work_t execution::outstanding_work_t::outstanding_work_t]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.outstanding_work_t..outstanding_work_t..execution::outstanding_work_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t.overload1 outstanding_work_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t.overload1 more...]]``
+
+
+Construct from a sub-property value. 
+
+
+  constexpr ``[link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t.overload2 outstanding_work_t]``(
+      untracked_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t.overload2 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t.overload3 outstanding_work_t]``(
+      tracked_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__outstanding_work_t.outstanding_work_t.overload3 more...]]``
+
+
+[section:overload1 execution::outstanding_work_t::outstanding_work_t (1 of 3 overloads)]
+
+
+Default constructor. 
+
+
+  constexpr outstanding_work_t();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::outstanding_work_t::outstanding_work_t (2 of 3 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr outstanding_work_t(
+      untracked_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::outstanding_work_t::outstanding_work_t (3 of 3 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr outstanding_work_t(
+      tracked_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:polymorphic_query_result_type execution::outstanding_work_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::outstanding_work_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:tracked execution::outstanding_work_t::tracked]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.tracked..tracked..execution::outstanding_work_t] 
+A special value used for accessing the [link boost_asio.reference.execution__outstanding_work_t__tracked_t `execution::outstanding_work_t::tracked_t`] property. 
+
+
+  static constexpr tracked_t tracked;
+
+
+
+[endsect]
+
+
+
+[section:untracked execution::outstanding_work_t::untracked]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t.untracked..untracked..execution::outstanding_work_t] 
+A special value used for accessing the [link boost_asio.reference.execution__outstanding_work_t__untracked_t `execution::outstanding_work_t::untracked_t`] property. 
+
+
+  static constexpr untracked_t untracked;
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__outstanding_work_t__tracked_t execution::outstanding_work_t::tracked_t]
+
+
+A sub-property that indicates that the executor represents likely future submission of a function object. 
+
+
+  struct tracked_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t.tracked_t [*tracked_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The outstanding_work_t::tracked_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t.is_preferable [*is_preferable]]]
+    [The outstanding_work_t::tracked_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__tracked_t.is_requirable [*is_requirable]]]
+    [The outstanding_work_t::tracked_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::outstanding_work_t::tracked_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__tracked_t.is_applicable_property_v..is_applicable_property_v..execution::outstanding_work_t::tracked_t] 
+The [link boost_asio.reference.execution__outstanding_work_t__tracked_t `execution::outstanding_work_t::tracked_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::outstanding_work_t::tracked_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__tracked_t.is_preferable..is_preferable..execution::outstanding_work_t::tracked_t] 
+The [link boost_asio.reference.execution__outstanding_work_t__tracked_t `execution::outstanding_work_t::tracked_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::outstanding_work_t::tracked_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__tracked_t.is_requirable..is_requirable..execution::outstanding_work_t::tracked_t] 
+The [link boost_asio.reference.execution__outstanding_work_t__tracked_t `execution::outstanding_work_t::tracked_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::outstanding_work_t::tracked_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__tracked_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::outstanding_work_t::tracked_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:tracked_t execution::outstanding_work_t::tracked_t::tracked_t]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__tracked_t.tracked_t..tracked_t..execution::outstanding_work_t::tracked_t] 
+Default constructor. 
+
+
+  constexpr tracked_t();
+
+
+
+[endsect]
+
+
+
+[section:value execution::outstanding_work_t::tracked_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__tracked_t.value..value..execution::outstanding_work_t::tracked_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr outstanding_work_t value();
+
+
+
+[heading Return Value]
+      
+`tracked_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__outstanding_work_t__untracked_t execution::outstanding_work_t::untracked_t]
+
+
+A sub-property that indicates that the executor does not represent likely future submission of a function object. 
+
+
+  struct untracked_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t.untracked_t [*untracked_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The outstanding_work_t::untracked_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t.is_preferable [*is_preferable]]]
+    [The outstanding_work_t::untracked_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__outstanding_work_t__untracked_t.is_requirable [*is_requirable]]]
+    [The outstanding_work_t::untracked_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::outstanding_work_t::untracked_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__untracked_t.is_applicable_property_v..is_applicable_property_v..execution::outstanding_work_t::untracked_t] 
+The [link boost_asio.reference.execution__outstanding_work_t__untracked_t `execution::outstanding_work_t::untracked_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::outstanding_work_t::untracked_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__untracked_t.is_preferable..is_preferable..execution::outstanding_work_t::untracked_t] 
+The [link boost_asio.reference.execution__outstanding_work_t__untracked_t `execution::outstanding_work_t::untracked_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::outstanding_work_t::untracked_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__untracked_t.is_requirable..is_requirable..execution::outstanding_work_t::untracked_t] 
+The [link boost_asio.reference.execution__outstanding_work_t__untracked_t `execution::outstanding_work_t::untracked_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::outstanding_work_t::untracked_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__untracked_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::outstanding_work_t::untracked_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/outstanding_work.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:untracked_t execution::outstanding_work_t::untracked_t::untracked_t]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__untracked_t.untracked_t..untracked_t..execution::outstanding_work_t::untracked_t] 
+Default constructor. 
+
+
+  constexpr untracked_t();
+
+
+
+[endsect]
+
+
+
+[section:value execution::outstanding_work_t::untracked_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__outstanding_work_t__untracked_t.value..value..execution::outstanding_work_t::untracked_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr outstanding_work_t value();
+
+
+
+[heading Return Value]
+      
+`untracked_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__prefer_only execution::prefer_only]
+
+
+A property that is used to obtain the execution context that is associated with an executor. 
+
+
+  template<
+      typename Property>
+  struct prefer_only
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__prefer_only.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__prefer_only.is_applicable_property_v [*is_applicable_property_v]]]
+    [The context_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__prefer_only.is_preferable [*is_preferable]]]
+    [The context_t property can be preferred, it the underlying property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__prefer_only.is_requirable [*is_requirable]]]
+    [The context_t property cannot be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/prefer_only.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:is_applicable_property_v execution::prefer_only::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__prefer_only.is_applicable_property_v..is_applicable_property_v..execution::prefer_only] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::prefer_only::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__prefer_only.is_preferable..is_preferable..execution::prefer_only] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property can be preferred, it the underlying property can be preferred. 
+
+
+  static constexpr bool is_preferable = automatically_determined;
+
+
+`true` if `Property::is_preferable` is `true`, otherwise `false`. 
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::prefer_only::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__prefer_only.is_requirable..is_requirable..execution::prefer_only] 
+The [link boost_asio.reference.execution__context_t `execution::context_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::prefer_only::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__prefer_only.polymorphic_query_result_type..polymorphic_query_result_type..execution::prefer_only] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef Property::polymorphic_query_result_type polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/prefer_only.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:execution__relationship execution::relationship]
+
+[indexterm1 boost_asio.indexterm.execution__relationship..execution::relationship] 
+A special value used for accessing the [link boost_asio.reference.execution__relationship_t `execution::relationship_t`] property. 
+
+
+  constexpr relationship_t relationship;
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:execution__relationship_t execution::relationship_t]
+
+
+A property to describe whether submitted tasks represent continuations of the calling context. 
+
+
+  struct relationship_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__relationship_t__continuation_t [*continuation_t]]]
+    [A sub-property that indicates that the executor represents a continuation of the calling context. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__relationship_t__fork_t [*fork_t]]]
+    [A sub-property that indicates that the executor does not represent a continuation of the calling context. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.execution__relationship_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.relationship_t [*relationship_t]]]
+    [Default constructor. 
+     [hr]
+     Construct from a sub-property value. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.continuation [*continuation]]]
+    [A special value used for accessing the relationship_t::continuation_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.fork [*fork]]]
+    [A special value used for accessing the relationship_t::fork_t property. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The relationship_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.is_preferable [*is_preferable]]]
+    [The top-level relationship_t property cannot be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.is_requirable [*is_requirable]]]
+    [The top-level relationship_t property cannot be required. ]
+  ]
+
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t.operator_not__eq_ [*operator!=]]]
+    [Compare property values for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__relationship_t.operator_eq__eq_ [*operator==]]]
+    [Compare property values for equality. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:continuation execution::relationship_t::continuation]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.continuation..continuation..execution::relationship_t] 
+A special value used for accessing the [link boost_asio.reference.execution__relationship_t__continuation_t `execution::relationship_t::continuation_t`] property. 
+
+
+  static constexpr continuation_t continuation;
+
+
+
+[endsect]
+
+
+
+[section:fork execution::relationship_t::fork]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.fork..fork..execution::relationship_t] 
+A special value used for accessing the [link boost_asio.reference.execution__relationship_t__fork_t `execution::relationship_t::fork_t`] property. 
+
+
+  static constexpr fork_t fork;
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::relationship_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.is_applicable_property_v..is_applicable_property_v..execution::relationship_t] 
+The [link boost_asio.reference.execution__relationship_t `execution::relationship_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::relationship_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.is_preferable..is_preferable..execution::relationship_t] 
+The top-level [link boost_asio.reference.execution__relationship_t `execution::relationship_t`] property cannot be preferred. 
+
+
+  static constexpr bool is_preferable = false;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::relationship_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.is_requirable..is_requirable..execution::relationship_t] 
+The top-level [link boost_asio.reference.execution__relationship_t `execution::relationship_t`] property cannot be required. 
+
+
+  static constexpr bool is_requirable = false;
+
+
+
+[endsect]
+
+
+
+[section:operator_not__eq_ execution::relationship_t::operator!=]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.operator_not__eq_..operator!=..execution::relationship_t] 
+Compare property values for inequality. 
+
+
+  friend constexpr bool operator!=(
+      const relationship_t & a,
+      const relationship_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:operator_eq__eq_ execution::relationship_t::operator==]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.operator_eq__eq_..operator==..execution::relationship_t] 
+Compare property values for equality. 
+
+
+  friend constexpr bool operator==(
+      const relationship_t & a,
+      const relationship_t & b);
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::relationship_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::relationship_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef relationship_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+[section:relationship_t execution::relationship_t::relationship_t]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t.relationship_t..relationship_t..execution::relationship_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.execution__relationship_t.relationship_t.overload1 relationship_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__relationship_t.relationship_t.overload1 more...]]``
+
+
+Construct from a sub-property value. 
+
+
+  constexpr ``[link boost_asio.reference.execution__relationship_t.relationship_t.overload2 relationship_t]``(
+      fork_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__relationship_t.relationship_t.overload2 more...]]``
+
+  constexpr ``[link boost_asio.reference.execution__relationship_t.relationship_t.overload3 relationship_t]``(
+      continuation_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.execution__relationship_t.relationship_t.overload3 more...]]``
+
+
+[section:overload1 execution::relationship_t::relationship_t (1 of 3 overloads)]
+
+
+Default constructor. 
+
+
+  constexpr relationship_t();
+
+
+
+[endsect]
+
+
+
+[section:overload2 execution::relationship_t::relationship_t (2 of 3 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr relationship_t(
+      fork_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 execution::relationship_t::relationship_t (3 of 3 overloads)]
+
+
+Construct from a sub-property value. 
+
+
+  constexpr relationship_t(
+      continuation_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[endsect]
+
+[section:execution__relationship_t__continuation_t execution::relationship_t::continuation_t]
+
+
+A sub-property that indicates that the executor represents a continuation of the calling context. 
+
+
+  struct continuation_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__relationship_t__continuation_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__continuation_t.continuation_t [*continuation_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__relationship_t__continuation_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__continuation_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The relationship_t::continuation_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__continuation_t.is_preferable [*is_preferable]]]
+    [The relationship_t::continuation_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__continuation_t.is_requirable [*is_requirable]]]
+    [The relationship_t::continuation_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:continuation_t execution::relationship_t::continuation_t::continuation_t]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__continuation_t.continuation_t..continuation_t..execution::relationship_t::continuation_t] 
+Default constructor. 
+
+
+  constexpr continuation_t();
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::relationship_t::continuation_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__continuation_t.is_applicable_property_v..is_applicable_property_v..execution::relationship_t::continuation_t] 
+The [link boost_asio.reference.execution__relationship_t__continuation_t `execution::relationship_t::continuation_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::relationship_t::continuation_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__continuation_t.is_preferable..is_preferable..execution::relationship_t::continuation_t] 
+The [link boost_asio.reference.execution__relationship_t__continuation_t `execution::relationship_t::continuation_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::relationship_t::continuation_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__continuation_t.is_requirable..is_requirable..execution::relationship_t::continuation_t] 
+The [link boost_asio.reference.execution__relationship_t__continuation_t `execution::relationship_t::continuation_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::relationship_t::continuation_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__continuation_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::relationship_t::continuation_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef relationship_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::relationship_t::continuation_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__continuation_t.value..value..execution::relationship_t::continuation_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr relationship_t value();
+
+
+
+[heading Return Value]
+      
+`continuation_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:execution__relationship_t__fork_t execution::relationship_t::fork_t]
+
+
+A sub-property that indicates that the executor does not represent a continuation of the calling context. 
+
+
+  struct fork_t
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.execution__relationship_t__fork_t.polymorphic_query_result_type [*polymorphic_query_result_type]]]
+    [The type returned by queries against an any_executor. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__fork_t.fork_t [*fork_t]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.execution__relationship_t__fork_t.value [*value]]]
+    [Get the value associated with a property object. ]
+  ]
+  
+]
+
+[heading Data Members]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__fork_t.is_applicable_property_v [*is_applicable_property_v]]]
+    [The relationship_t::fork_t property applies to executors. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__fork_t.is_preferable [*is_preferable]]]
+    [The relationship_t::fork_t property can be preferred. ]
+  ]
+
+  [
+    [[link boost_asio.reference.execution__relationship_t__fork_t.is_requirable [*is_requirable]]]
+    [The relationship_t::fork_t property can be required. ]
+  ]
+
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[section:fork_t execution::relationship_t::fork_t::fork_t]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__fork_t.fork_t..fork_t..execution::relationship_t::fork_t] 
+Default constructor. 
+
+
+  constexpr fork_t();
+
+
+
+[endsect]
+
+
+
+[section:is_applicable_property_v execution::relationship_t::fork_t::is_applicable_property_v]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__fork_t.is_applicable_property_v..is_applicable_property_v..execution::relationship_t::fork_t] 
+The [link boost_asio.reference.execution__relationship_t__fork_t `execution::relationship_t::fork_t`] property applies to executors. 
+
+
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+
+
+[endsect]
+
+
+
+[section:is_preferable execution::relationship_t::fork_t::is_preferable]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__fork_t.is_preferable..is_preferable..execution::relationship_t::fork_t] 
+The [link boost_asio.reference.execution__relationship_t__fork_t `execution::relationship_t::fork_t`] property can be preferred. 
+
+
+  static constexpr bool is_preferable = true;
+
+
+
+[endsect]
+
+
+
+[section:is_requirable execution::relationship_t::fork_t::is_requirable]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__fork_t.is_requirable..is_requirable..execution::relationship_t::fork_t] 
+The [link boost_asio.reference.execution__relationship_t__fork_t `execution::relationship_t::fork_t`] property can be required. 
+
+
+  static constexpr bool is_requirable = true;
+
+
+
+[endsect]
+
+
+
+[section:polymorphic_query_result_type execution::relationship_t::fork_t::polymorphic_query_result_type]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__fork_t.polymorphic_query_result_type..polymorphic_query_result_type..execution::relationship_t::fork_t] 
+The type returned by queries against an `any_executor`. 
+
+
+  typedef relationship_t polymorphic_query_result_type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/execution/relationship.hpp]
+
+['Convenience header: ][^boost/asio/execution.hpp]
+
+
+[endsect]
+
+
+
+[section:value execution::relationship_t::fork_t::value]
+
+[indexterm2 boost_asio.indexterm.execution__relationship_t__fork_t.value..value..execution::relationship_t::fork_t] 
+Get the value associated with a property object. 
+
+
+  static constexpr relationship_t value();
+
+
+
+[heading Return Value]
+      
+`fork_t()`; 
+
+
+
+
+[endsect]
+
+
+
+[endsect]
+
 [section:execution_context execution_context]
 
 
@@ -62650,7 +70330,7 @@ This destruction sequence permits programs to simplify their resource management
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [section:add_service execution_context::add_service]
@@ -62702,7 +70382,7 @@ This function is used to add a service to the [link boost_asio.reference.executi
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [endsect]
@@ -62817,7 +70497,7 @@ A boolean indicating whether the [link boost_asio.reference.execution_context `e
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [endsect]
@@ -62868,7 +70548,7 @@ This function is used to add a service to the [link boost_asio.reference.executi
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [endsect]
@@ -63015,7 +70695,7 @@ The service interface implementing the specified service type. Ownership of the
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [endsect]
@@ -63062,7 +70742,7 @@ This overload is preserved for backwards compatibility with services that inheri
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [endsect]
@@ -63112,7 +70792,7 @@ Class used to uniquely identify a service.
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [section:id execution_context::id::id]
@@ -63188,7 +70868,7 @@ Base class for all [link boost_asio.reference.io_context `io_context`] services.
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [section:context execution_context::service::context]
@@ -69128,7 +76808,7 @@ Helper function to obtain an object's associated executor.
   associated_executor< T, Executor >::type ``[link boost_asio.reference.get_associated_executor.overload2 get_associated_executor]``(
       const T & t,
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.get_associated_executor.overload2 more...]]``
 
   template<
@@ -69183,7 +76863,7 @@ Helper function to obtain an object's associated executor.
   associated_executor< T, Executor >::type get_associated_executor(
       const T & t,
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -69507,7 +77187,7 @@ Exception thrown when trying to add a service object to an [link boost_asio.refe
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [section:invalid_service_owner invalid_service_owner::invalid_service_owner]
@@ -69540,8 +77220,8 @@ Provides core I/O functionality.
 
   [
 
-    [[link boost_asio.reference.io_context__executor_type [*executor_type]]]
-    [Executor used to submit functions to an io_context. ]
+    [[link boost_asio.reference.io_context__basic_executor_type [*basic_executor_type]]]
+    [Executor implementation type used to submit functions to an io_context. ]
   
   ]
 
@@ -69573,6 +77253,13 @@ Provides core I/O functionality.
   
   ]
 
+  [
+
+    [[link boost_asio.reference.io_context.executor_type [*executor_type]]]
+    [Executor used to submit functions to an io_context. ]
+  
+  ]
+
   [
 
     [[link boost_asio.reference.io_context.fork_event [*fork_event]]]
@@ -69835,13 +77522,41 @@ For example:
   
 
 
-Some applications may need to prevent an [link boost_asio.reference.io_context `io_context`] object's `run()` call from returning when there is no more work to do. For example, the [link boost_asio.reference.io_context `io_context`] may be being run in a background thread that is launched prior to the application's asynchronous operations. The `run()` call may be kept running by creating an object of type boost::asio::executor\_work\_guard<io\_context::executor\_type>:
+Some applications may need to prevent an [link boost_asio.reference.io_context `io_context`] object's `run()` call from returning when there is no more work to do. For example, the [link boost_asio.reference.io_context `io_context`] may be being run in a background thread that is launched prior to the application's asynchronous operations. The `run()` call may be kept running by creating an executor that tracks work against the [link boost_asio.reference.io_context `io_context`]:
 
 
 
    boost::asio::io_context io_context;
-   boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
-     = boost::asio::make_work_guard(io_context);
+   auto work = boost::asio::require(io_context.get_executor(),
+       boost::asio::execution::outstanding_work.tracked);
+   ... 
+
+
+
+
+If using C++03, which lacks automatic variable type deduction, you may compute the return type of the require call:
+
+
+
+   boost::asio::io_context io_context;
+   typename boost::asio::require_result_type<
+       boost::asio::io_context::executor_type,
+       boost::asio::exeution::outstanding_work_t::tracked_t>
+     work = boost::asio::require(io_context.get_executor(),
+       boost::asio::execution::outstanding_work.tracked);
+   ... 
+
+
+
+
+or store the result in the type-erasing executor wrapper, any\_io\_executor:
+
+
+
+   boost::asio::io_context io_context;
+   boost::asio::any_io_executor work
+     = boost::asio::require(io_context.get_executor(),
+         boost::asio::execution::outstanding_work.tracked);
    ... 
 
 
@@ -69849,15 +77564,16 @@ Some applications may need to prevent an [link boost_asio.reference.io_context `
 
 To effect a shutdown, the application will then need to call the [link boost_asio.reference.io_context `io_context`] object's `stop()` member function. This will cause the [link boost_asio.reference.io_context `io_context`] `run()` call to return as soon as possible, abandoning unfinished operations and without permitting ready handlers to be dispatched.
 
-Alternatively, if the application requires that all operations and handlers be allowed to finish normally, the work object may be explicitly reset.
+Alternatively, if the application requires that all operations and handlers be allowed to finish normally, store the work-tracking executor in an any\_io\_executor object, so that it may be explicitly reset.
 
 
 
    boost::asio::io_context io_context;
-   boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
-     = boost::asio::make_work_guard(io_context);
+   boost::asio::any_io_executor work
+     = boost::asio::require(io_context.get_executor(),
+         boost::asio::execution::outstanding_work.tracked);
    ...
-   work.reset(); // Allow run() to exit. 
+   work = boost::asio::any_io_executor(); // Allow run() to exit. 
 
 
 
@@ -70021,6 +77737,145 @@ throws an exception.
 
 
 
+[section:executor_type io_context::executor_type]
+
+[indexterm2 boost_asio.indexterm.io_context.executor_type..executor_type..io_context] 
+Executor used to submit functions to an [link boost_asio.reference.io_context `io_context`]. 
+
+
+  typedef basic_executor_type< std::allocator< void >, 0 > executor_type;
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.basic_executor_type [*basic_executor_type]]]
+    [Copy construtor. 
+     [hr]
+     Move construtor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.context [*context]]]
+    [Obtain the underlying execution context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.defer [*defer]]]
+    [Request the io_context to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.dispatch [*dispatch]]]
+    [Request the io_context to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.execute [*execute]]]
+    [Execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.on_work_finished [*on_work_finished]]]
+    [Inform the io_context that some work is no longer outstanding. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.on_work_started [*on_work_started]]]
+    [Inform the io_context that it has some outstanding work to do. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.operator_eq_ [*operator=]]]
+    [Assignment operator. 
+     [hr]
+     Move assignment operator. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.post [*post]]]
+    [Request the io_context to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.query [*query]]]
+    [Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. 
+     [hr]
+     Query the current value of the allocator property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.query__static [*query]]]
+    [Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the outstanding_work property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the outstanding_work.tracked property. 
+     [hr]
+     Obtain an executor with the outstanding_work.untracked property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.running_in_this_thread [*running_in_this_thread]]]
+    [Determine whether the io_context is running in the current thread. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type._basic_executor_type [*~basic_executor_type]]]
+    [Destructor. ]
+  ]
+  
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.operator_not__eq_ [*operator!=]]]
+    [Compare two executors for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.operator_eq__eq_ [*operator==]]]
+    [Compare two executors for equality. ]
+  ]
+  
+]
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/io_context.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
 [section:fork_event io_context::fork_event]
 
 
@@ -71109,13 +78964,16 @@ The destruction sequence described above permits programs to simplify their reso
 
 [endsect]
 
-[section:io_context__executor_type io_context::executor_type]
+[section:io_context__basic_executor_type io_context::basic_executor_type]
 
 
-Executor used to submit functions to an [link boost_asio.reference.io_context `io_context`]. 
+Executor implementation type used to submit functions to an [link boost_asio.reference.io_context `io_context`]. 
 
 
-  class executor_type
+  template<
+      typename Allocator,
+      unsigned int Bits>
+  class basic_executor_type
 
 
 [heading Member Functions]
@@ -71123,40 +78981,101 @@ Executor used to submit functions to an [link boost_asio.reference.io_context `i
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.io_context__executor_type.context [*context]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.basic_executor_type [*basic_executor_type]]]
+    [Copy construtor. 
+     [hr]
+     Move construtor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.context [*context]]]
     [Obtain the underlying execution context. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.defer [*defer]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.defer [*defer]]]
     [Request the io_context to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.dispatch [*dispatch]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.dispatch [*dispatch]]]
     [Request the io_context to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.on_work_finished [*on_work_finished]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.execute [*execute]]]
+    [Execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.on_work_finished [*on_work_finished]]]
     [Inform the io_context that some work is no longer outstanding. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.on_work_started [*on_work_started]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.on_work_started [*on_work_started]]]
     [Inform the io_context that it has some outstanding work to do. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.post [*post]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.operator_eq_ [*operator=]]]
+    [Assignment operator. 
+     [hr]
+     Move assignment operator. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.post [*post]]]
     [Request the io_context to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.running_in_this_thread [*running_in_this_thread]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.query [*query]]]
+    [Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. 
+     [hr]
+     Query the current value of the allocator property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.query__static [*query]]]
+    [Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the outstanding_work property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the outstanding_work.tracked property. 
+     [hr]
+     Obtain an executor with the outstanding_work.untracked property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type.running_in_this_thread [*running_in_this_thread]]]
     [Determine whether the io_context is running in the current thread. ]
   ]
   
+  [
+    [[link boost_asio.reference.io_context__basic_executor_type._basic_executor_type [*~basic_executor_type]]]
+    [Destructor. ]
+  ]
+  
 ]
 
 [heading Friends]
@@ -71164,12 +79083,12 @@ Executor used to submit functions to an [link boost_asio.reference.io_context `i
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.io_context__executor_type.operator_not__eq_ [*operator!=]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.operator_not__eq_ [*operator!=]]]
     [Compare two executors for inequality. ]
   ]
   
   [
-    [[link boost_asio.reference.io_context__executor_type.operator_eq__eq_ [*operator==]]]
+    [[link boost_asio.reference.io_context__basic_executor_type.operator_eq__eq_ [*operator==]]]
     [Compare two executors for equality. ]
   ]
   
@@ -71181,10 +79100,60 @@ Executor used to submit functions to an [link boost_asio.reference.io_context `i
 
 ['Convenience header: ][^boost/asio.hpp]
 
+[section:basic_executor_type io_context::basic_executor_type::basic_executor_type]
 
-[section:context io_context::executor_type::context]
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.basic_executor_type..basic_executor_type..io_context::basic_executor_type] 
+Copy construtor. 
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.context..context..io_context::executor_type] 
+
+  ``[link boost_asio.reference.io_context__basic_executor_type.basic_executor_type.overload1 basic_executor_type]``(
+      const basic_executor_type & other);
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.basic_executor_type.overload1 more...]]``
+
+
+Move construtor. 
+
+
+  ``[link boost_asio.reference.io_context__basic_executor_type.basic_executor_type.overload2 basic_executor_type]``(
+      basic_executor_type && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.basic_executor_type.overload2 more...]]``
+
+
+[section:overload1 io_context::basic_executor_type::basic_executor_type (1 of 2 overloads)]
+
+
+Copy construtor. 
+
+
+  basic_executor_type(
+      const basic_executor_type & other);
+
+
+
+[endsect]
+
+
+
+[section:overload2 io_context::basic_executor_type::basic_executor_type (2 of 2 overloads)]
+
+
+Move construtor. 
+
+
+  basic_executor_type(
+      basic_executor_type && other);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:context io_context::basic_executor_type::context]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.context..context..io_context::basic_executor_type] 
 Obtain the underlying execution context. 
 
 
@@ -71196,18 +79165,18 @@ Obtain the underlying execution context.
 
 
 
-[section:defer io_context::executor_type::defer]
+[section:defer io_context::basic_executor_type::defer]
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.defer..defer..io_context::executor_type] 
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.defer..defer..io_context::basic_executor_type] 
 Request the [link boost_asio.reference.io_context `io_context`] to invoke the given function object. 
 
 
   template<
       typename Function,
-      typename Allocator>
+      typename OtherAllocator>
   void defer(
       Function && f,
-      const Allocator & a) const;
+      const OtherAllocator & a) const;
 
 
 This function is used to ask the [link boost_asio.reference.io_context `io_context`] to execute the given function object. The function object will never be executed inside `defer()`. Instead, it will be scheduled to run on the [link boost_asio.reference.io_context `io_context`].
@@ -71237,18 +79206,18 @@ If the current thread belongs to the [link boost_asio.reference.io_context `io_c
 
 
 
-[section:dispatch io_context::executor_type::dispatch]
+[section:dispatch io_context::basic_executor_type::dispatch]
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.dispatch..dispatch..io_context::executor_type] 
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.dispatch..dispatch..io_context::basic_executor_type] 
 Request the [link boost_asio.reference.io_context `io_context`] to invoke the given function object. 
 
 
   template<
       typename Function,
-      typename Allocator>
+      typename OtherAllocator>
   void dispatch(
       Function && f,
-      const Allocator & a) const;
+      const OtherAllocator & a) const;
 
 
 This function is used to ask the [link boost_asio.reference.io_context `io_context`] to execute the given function object. If the current thread is running the [link boost_asio.reference.io_context `io_context`], `dispatch()` executes the function before returning. Otherwise, the function will be scheduled to run on the [link boost_asio.reference.io_context `io_context`].
@@ -71276,9 +79245,26 @@ This function is used to ask the [link boost_asio.reference.io_context `io_conte
 
 
 
-[section:on_work_finished io_context::executor_type::on_work_finished]
+[section:execute io_context::basic_executor_type::execute]
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.on_work_finished..on_work_finished..io_context::executor_type] 
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.execute..execute..io_context::basic_executor_type] 
+Execution function. 
+
+
+  template<
+      typename Function>
+  void execute(
+      Function && f) const;
+
+
+
+[endsect]
+
+
+
+[section:on_work_finished io_context::basic_executor_type::on_work_finished]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.on_work_finished..on_work_finished..io_context::basic_executor_type] 
 Inform the [link boost_asio.reference.io_context `io_context`] that some work is no longer outstanding. 
 
 
@@ -71292,9 +79278,9 @@ This function is used to inform the [link boost_asio.reference.io_context `io_co
 
 
 
-[section:on_work_started io_context::executor_type::on_work_started]
+[section:on_work_started io_context::basic_executor_type::on_work_started]
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.on_work_started..on_work_started..io_context::executor_type] 
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.on_work_started..on_work_started..io_context::basic_executor_type] 
 Inform the [link boost_asio.reference.io_context `io_context`] that it has some outstanding work to do. 
 
 
@@ -71308,15 +79294,15 @@ This function is used to inform the [link boost_asio.reference.io_context `io_co
 
 
 
-[section:operator_not__eq_ io_context::executor_type::operator!=]
+[section:operator_not__eq_ io_context::basic_executor_type::operator!=]
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.operator_not__eq_..operator!=..io_context::executor_type] 
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.operator_not__eq_..operator!=..io_context::basic_executor_type] 
 Compare two executors for inequality. 
 
 
   friend bool operator!=(
-      const executor_type & a,
-      const executor_type & b);
+      const basic_executor_type & a,
+      const basic_executor_type & b);
 
 
 Two executors are equal if they refer to the same underlying [link boost_asio.reference.io_context `io_context`]. 
@@ -71331,16 +79317,66 @@ Two executors are equal if they refer to the same underlying [link boost_asio.re
 [endsect]
 
 
+[section:operator_eq_ io_context::basic_executor_type::operator=]
 
-[section:operator_eq__eq_ io_context::executor_type::operator==]
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.operator_eq_..operator=..io_context::basic_executor_type] 
+Assignment operator. 
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.operator_eq__eq_..operator==..io_context::executor_type] 
+
+  basic_executor_type & ``[link boost_asio.reference.io_context__basic_executor_type.operator_eq_.overload1 operator=]``(
+      const basic_executor_type & other);
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.operator_eq_.overload1 more...]]``
+
+
+Move assignment operator. 
+
+
+  basic_executor_type & ``[link boost_asio.reference.io_context__basic_executor_type.operator_eq_.overload2 operator=]``(
+      basic_executor_type && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.operator_eq_.overload2 more...]]``
+
+
+[section:overload1 io_context::basic_executor_type::operator= (1 of 2 overloads)]
+
+
+Assignment operator. 
+
+
+  basic_executor_type & operator=(
+      const basic_executor_type & other);
+
+
+
+[endsect]
+
+
+
+[section:overload2 io_context::basic_executor_type::operator= (2 of 2 overloads)]
+
+
+Move assignment operator. 
+
+
+  basic_executor_type & operator=(
+      basic_executor_type && other);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:operator_eq__eq_ io_context::basic_executor_type::operator==]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.operator_eq__eq_..operator==..io_context::basic_executor_type] 
 Compare two executors for equality. 
 
 
   friend bool operator==(
-      const executor_type & a,
-      const executor_type & b);
+      const basic_executor_type & a,
+      const basic_executor_type & b);
 
 
 Two executors are equal if they refer to the same underlying [link boost_asio.reference.io_context `io_context`]. 
@@ -71356,18 +79392,18 @@ Two executors are equal if they refer to the same underlying [link boost_asio.re
 
 
 
-[section:post io_context::executor_type::post]
+[section:post io_context::basic_executor_type::post]
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.post..post..io_context::executor_type] 
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.post..post..io_context::basic_executor_type] 
 Request the [link boost_asio.reference.io_context `io_context`] to invoke the given function object. 
 
 
   template<
       typename Function,
-      typename Allocator>
+      typename OtherAllocator>
   void post(
       Function && f,
-      const Allocator & a) const;
+      const OtherAllocator & a) const;
 
 
 This function is used to ask the [link boost_asio.reference.io_context `io_context`] to execute the given function object. The function object will never be executed inside `post()`. Instead, it will be scheduled to run on the [link boost_asio.reference.io_context `io_context`].
@@ -71394,10 +79430,371 @@ This function is used to ask the [link boost_asio.reference.io_context `io_conte
 [endsect]
 
 
+[section:query io_context::basic_executor_type::query]
 
-[section:running_in_this_thread io_context::executor_type::running_in_this_thread]
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.query..query..io_context::basic_executor_type] 
+Query the current value of the `context` property. 
 
-[indexterm2 boost_asio.indexterm.io_context__executor_type.running_in_this_thread..running_in_this_thread..io_context::executor_type] 
+
+  io_context & ``[link boost_asio.reference.io_context__basic_executor_type.query.overload1 query]``(
+      execution::context_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query.overload1 more...]]``
+
+
+Query the current value of the `blocking` property. 
+
+
+  constexpr execution::blocking_t ``[link boost_asio.reference.io_context__basic_executor_type.query.overload2 query]``(
+      execution::blocking_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query.overload2 more...]]``
+
+
+Query the current value of the `relationship` property. 
+
+
+  constexpr execution::relationship_t ``[link boost_asio.reference.io_context__basic_executor_type.query.overload3 query]``(
+      execution::relationship_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query.overload3 more...]]``
+
+
+Query the current value of the `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr Allocator ``[link boost_asio.reference.io_context__basic_executor_type.query.overload4 query]``(
+      execution::allocator_t< OtherAllocator > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query.overload4 more...]]``
+
+  constexpr Allocator ``[link boost_asio.reference.io_context__basic_executor_type.query.overload5 query]``(
+      execution::allocator_t< void > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query.overload5 more...]]``
+
+
+[section:overload1 io_context::basic_executor_type::query (1 of 5 overloads)]
+
+
+Query the current value of the `context` property. 
+
+
+  io_context & query(
+      execution::context_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload2 io_context::basic_executor_type::query (2 of 5 overloads)]
+
+
+Query the current value of the `blocking` property. 
+
+
+  constexpr execution::blocking_t query(
+      execution::blocking_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload3 io_context::basic_executor_type::query (3 of 5 overloads)]
+
+
+Query the current value of the `relationship` property. 
+
+
+  constexpr execution::relationship_t query(
+      execution::relationship_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload4 io_context::basic_executor_type::query (4 of 5 overloads)]
+
+
+Query the current value of the `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr Allocator query(
+      execution::allocator_t< OtherAllocator > ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload5 io_context::basic_executor_type::query (5 of 5 overloads)]
+
+
+Query the current value of the `allocator` property. 
+
+
+  constexpr Allocator query(
+      execution::allocator_t< void > ) const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+[section:query__static io_context::basic_executor_type::query]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.query__static..query..io_context::basic_executor_type] 
+Query the current value of the `mapping` property. 
+
+
+  static constexpr execution::mapping_t ``[link boost_asio.reference.io_context__basic_executor_type.query__static.overload1 query]``(
+      execution::mapping_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query__static.overload1 more...]]``
+
+
+Query the current value of the `outstanding_work` property. 
+
+
+  static constexpr execution::outstanding_work_t ``[link boost_asio.reference.io_context__basic_executor_type.query__static.overload2 query]``(
+      execution::outstanding_work_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.query__static.overload2 more...]]``
+
+
+[section:overload1 io_context::basic_executor_type::query (1 of 2 overloads)]
+
+
+Query the current value of the `mapping` property. 
+
+
+  static constexpr execution::mapping_t query(
+      execution::mapping_t );
+
+
+
+[endsect]
+
+
+
+[section:overload2 io_context::basic_executor_type::query (2 of 2 overloads)]
+
+
+Query the current value of the `outstanding_work` property. 
+
+
+  static constexpr execution::outstanding_work_t query(
+      execution::outstanding_work_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+[section:require io_context::basic_executor_type::require]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.require..require..io_context::basic_executor_type] 
+Obtain an executor with the `blocking.possibly` property. 
+
+
+  constexpr basic_executor_type ``[link boost_asio.reference.io_context__basic_executor_type.require.overload1 require]``(
+      execution::blocking_t::possibly_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload1 more...]]``
+
+
+Obtain an executor with the `blocking.never` property. 
+
+
+  constexpr basic_executor_type ``[link boost_asio.reference.io_context__basic_executor_type.require.overload2 require]``(
+      execution::blocking_t::never_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload2 more...]]``
+
+
+Obtain an executor with the `relationship.fork` property. 
+
+
+  constexpr basic_executor_type ``[link boost_asio.reference.io_context__basic_executor_type.require.overload3 require]``(
+      execution::relationship_t::fork_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload3 more...]]``
+
+
+Obtain an executor with the `relationship.continuation` property. 
+
+
+  constexpr basic_executor_type ``[link boost_asio.reference.io_context__basic_executor_type.require.overload4 require]``(
+      execution::relationship_t::continuation_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload4 more...]]``
+
+
+Obtain an executor with the `outstanding_work.tracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.io_context__basic_executor_type.require.overload5 require]``(
+      execution::outstanding_work_t::tracked_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload5 more...]]``
+
+
+Obtain an executor with the `outstanding_work.untracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.io_context__basic_executor_type.require.overload6 require]``(
+      execution::outstanding_work_t::untracked_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload6 more...]]``
+
+
+Obtain an executor with the specified `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr basic_executor_type< OtherAllocator, Bits > ``[link boost_asio.reference.io_context__basic_executor_type.require.overload7 require]``(
+      execution::allocator_t< OtherAllocator > a) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload7 more...]]``
+
+
+Obtain an executor with the default `allocator` property. 
+
+
+  constexpr basic_executor_type< std::allocator< void >, Bits > ``[link boost_asio.reference.io_context__basic_executor_type.require.overload8 require]``(
+      execution::allocator_t< void > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.io_context__basic_executor_type.require.overload8 more...]]``
+
+
+[section:overload1 io_context::basic_executor_type::require (1 of 8 overloads)]
+
+
+Obtain an executor with the `blocking.possibly` property. 
+
+
+  constexpr basic_executor_type require(
+      execution::blocking_t::possibly_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload2 io_context::basic_executor_type::require (2 of 8 overloads)]
+
+
+Obtain an executor with the `blocking.never` property. 
+
+
+  constexpr basic_executor_type require(
+      execution::blocking_t::never_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload3 io_context::basic_executor_type::require (3 of 8 overloads)]
+
+
+Obtain an executor with the `relationship.fork` property. 
+
+
+  constexpr basic_executor_type require(
+      execution::relationship_t::fork_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload4 io_context::basic_executor_type::require (4 of 8 overloads)]
+
+
+Obtain an executor with the `relationship.continuation` property. 
+
+
+  constexpr basic_executor_type require(
+      execution::relationship_t::continuation_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload5 io_context::basic_executor_type::require (5 of 8 overloads)]
+
+
+Obtain an executor with the `outstanding_work.tracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::outstanding_work_t::tracked_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload6 io_context::basic_executor_type::require (6 of 8 overloads)]
+
+
+Obtain an executor with the `outstanding_work.untracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::outstanding_work_t::untracked_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload7 io_context::basic_executor_type::require (7 of 8 overloads)]
+
+
+Obtain an executor with the specified `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr basic_executor_type< OtherAllocator, Bits > require(
+      execution::allocator_t< OtherAllocator > a) const;
+
+
+
+[endsect]
+
+
+
+[section:overload8 io_context::basic_executor_type::require (8 of 8 overloads)]
+
+
+Obtain an executor with the default `allocator` property. 
+
+
+  constexpr basic_executor_type< std::allocator< void >, Bits > require(
+      execution::allocator_t< void > ) const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:running_in_this_thread io_context::basic_executor_type::running_in_this_thread]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type.running_in_this_thread..running_in_this_thread..io_context::basic_executor_type] 
 Determine whether the [link boost_asio.reference.io_context `io_context`] is running in the current thread. 
 
 
@@ -71412,6 +79809,20 @@ Determine whether the [link boost_asio.reference.io_context `io_context`] is run
 
 
 
+[endsect]
+
+
+
+[section:_basic_executor_type io_context::basic_executor_type::~basic_executor_type]
+
+[indexterm2 boost_asio.indexterm.io_context__basic_executor_type._basic_executor_type..~basic_executor_type..io_context::basic_executor_type] 
+Destructor. 
+
+
+  ~basic_executor_type();
+
+
+
 [endsect]
 
 
@@ -72285,8 +80696,8 @@ Typedef for backwards compatibility.
 
   [
 
-    [[link boost_asio.reference.io_context__executor_type [*executor_type]]]
-    [Executor used to submit functions to an io_context. ]
+    [[link boost_asio.reference.io_context__basic_executor_type [*basic_executor_type]]]
+    [Executor implementation type used to submit functions to an io_context. ]
   
   ]
 
@@ -72318,6 +80729,13 @@ Typedef for backwards compatibility.
   
   ]
 
+  [
+
+    [[link boost_asio.reference.io_context.executor_type [*executor_type]]]
+    [Executor used to submit functions to an io_context. ]
+  
+  ]
+
   [
 
     [[link boost_asio.reference.io_context.fork_event [*fork_event]]]
@@ -72580,13 +80998,41 @@ For example:
   
 
 
-Some applications may need to prevent an [link boost_asio.reference.io_context `io_context`] object's `run()` call from returning when there is no more work to do. For example, the [link boost_asio.reference.io_context `io_context`] may be being run in a background thread that is launched prior to the application's asynchronous operations. The `run()` call may be kept running by creating an object of type boost::asio::executor\_work\_guard<io\_context::executor\_type>:
+Some applications may need to prevent an [link boost_asio.reference.io_context `io_context`] object's `run()` call from returning when there is no more work to do. For example, the [link boost_asio.reference.io_context `io_context`] may be being run in a background thread that is launched prior to the application's asynchronous operations. The `run()` call may be kept running by creating an executor that tracks work against the [link boost_asio.reference.io_context `io_context`]:
 
 
 
    boost::asio::io_context io_context;
-   boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
-     = boost::asio::make_work_guard(io_context);
+   auto work = boost::asio::require(io_context.get_executor(),
+       boost::asio::execution::outstanding_work.tracked);
+   ... 
+
+
+
+
+If using C++03, which lacks automatic variable type deduction, you may compute the return type of the require call:
+
+
+
+   boost::asio::io_context io_context;
+   typename boost::asio::require_result_type<
+       boost::asio::io_context::executor_type,
+       boost::asio::exeution::outstanding_work_t::tracked_t>
+     work = boost::asio::require(io_context.get_executor(),
+       boost::asio::execution::outstanding_work.tracked);
+   ... 
+
+
+
+
+or store the result in the type-erasing executor wrapper, any\_io\_executor:
+
+
+
+   boost::asio::io_context io_context;
+   boost::asio::any_io_executor work
+     = boost::asio::require(io_context.get_executor(),
+         boost::asio::execution::outstanding_work.tracked);
    ... 
 
 
@@ -72594,15 +81040,16 @@ Some applications may need to prevent an [link boost_asio.reference.io_context `
 
 To effect a shutdown, the application will then need to call the [link boost_asio.reference.io_context `io_context`] object's `stop()` member function. This will cause the [link boost_asio.reference.io_context `io_context`] `run()` call to return as soon as possible, abandoning unfinished operations and without permitting ready handlers to be dispatched.
 
-Alternatively, if the application requires that all operations and handlers be allowed to finish normally, the work object may be explicitly reset.
+Alternatively, if the application requires that all operations and handlers be allowed to finish normally, store the work-tracking executor in an any\_io\_executor object, so that it may be explicitly reset.
 
 
 
    boost::asio::io_context io_context;
-   boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
-     = boost::asio::make_work_guard(io_context);
+   boost::asio::any_io_executor work
+     = boost::asio::require(io_context.get_executor(),
+         boost::asio::execution::outstanding_work.tracked);
    ...
-   work.reset(); // Allow run() to exit. 
+   work = boost::asio::any_io_executor(); // Allow run() to exit. 
 
 
 
@@ -90177,6 +98624,26 @@ Getting the current option value:
 [endsect]
 
 
+[section:is_applicable_property is_applicable_property]
+
+
+
+  template<
+      typename T,
+      typename Property,
+      typename  = void>
+  struct is_applicable_property
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/is_applicable_property.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
 [section:is_const_buffer_sequence is_const_buffer_sequence]
 
 
@@ -90389,6 +98856,98 @@ Trait to determine whether a type satisfies the MutableBufferSequence requiremen
 ['Convenience header: ][^boost/asio.hpp]
 
 
+[endsect]
+
+[section:is_nothrow_prefer is_nothrow_prefer]
+
+
+A type trait that determines whether a `prefer` expression will not throw. 
+
+
+  template<
+      typename T,
+      typename... Properties>
+  struct is_nothrow_prefer
+
+
+Class template `is_nothrow_prefer` is a trait that is derived from `true_type` if the expression `boost::asio::prefer(std::declval<T>(), std::declval<Properties>()...)` is `noexcept`; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/prefer.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+[section:is_nothrow_query is_nothrow_query]
+
+
+A type trait that determines whether a `query` expression will not throw. 
+
+
+  template<
+      typename T,
+      typename Property>
+  struct is_nothrow_query
+
+
+Class template `is_nothrow_query` is a trait that is derived from `true_type` if the expression `boost::asio::query(std::declval<T>(), std::declval<Property>())` is `noexcept`; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/query.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+[section:is_nothrow_require is_nothrow_require]
+
+
+A type trait that determines whether a `require` expression will not throw. 
+
+
+  template<
+      typename T,
+      typename... Properties>
+  struct is_nothrow_require
+
+
+Class template `is_nothrow_require` is a trait that is derived from `true_type` if the expression `boost::asio::require(std::declval<T>(), std::declval<Properties>()...)` is `noexcept`; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+[section:is_nothrow_require_concept is_nothrow_require_concept]
+
+
+A type trait that determines whether a `require_concept` expression will not throw. 
+
+
+  template<
+      typename T,
+      typename Property>
+  struct is_nothrow_require_concept
+
+
+Class template `is_nothrow_require_concept` is a trait that is derived from `true_type` if the expression `boost::asio::require_concept(std::declval<T>(), std::declval<Property>())` is `noexcept`; otherwise `false_type`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require_concept.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
 [endsect]
 
 [section:is_read_buffered is_read_buffered]
@@ -93144,7 +101703,7 @@ Create a [link boost_asio.reference.strand `strand`]  object for an executor.
       typename ``[link boost_asio.reference.Executor1 Executor]``>
   strand< Executor > ``[link boost_asio.reference.make_strand.overload1 make_strand]``(
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.make_strand.overload1 more...]]``
 
 Create a [link boost_asio.reference.strand `strand`]  object for an execution context. 
@@ -93173,7 +101732,7 @@ Create a [link boost_asio.reference.strand `strand`]  object for an executor.
       typename ``[link boost_asio.reference.Executor1 Executor]``>
   strand< Executor > make_strand(
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -93209,7 +101768,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
       typename ``[link boost_asio.reference.Executor1 Executor]``>
   executor_work_guard< Executor > ``[link boost_asio.reference.make_work_guard.overload1 make_work_guard]``(
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.make_work_guard.overload1 more...]]``
 
   template<
@@ -93223,7 +101782,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
       typename T>
   executor_work_guard< typename associated_executor< T >::type > ``[link boost_asio.reference.make_work_guard.overload3 make_work_guard]``(
       const T & t,
-      typename enable_if<!is_executor< T >::value &&!is_convertible< T &, execution_context & >::value >::type *  = 0);
+      typename enable_if< !is_executor< T >::value &&!execution::is_executor< T >::value &&!is_convertible< T &, execution_context & >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.make_work_guard.overload3 more...]]``
 
   template<
@@ -93232,7 +101791,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
   executor_work_guard< typename associated_executor< T, Executor >::type > ``[link boost_asio.reference.make_work_guard.overload4 make_work_guard]``(
       const T & t,
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.make_work_guard.overload4 more...]]``
 
   template<
@@ -93241,7 +101800,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
   executor_work_guard< typename associated_executor< T, typename ExecutionContext::executor_type >::type > ``[link boost_asio.reference.make_work_guard.overload5 make_work_guard]``(
       const T & t,
       ExecutionContext & ctx,
-      typename enable_if<!is_executor< T >::value &&!is_convertible< T &, execution_context & >::value &&is_convertible< ExecutionContext &, execution_context & >::value >::type *  = 0);
+      typename enable_if< !is_executor< T >::value &&!execution::is_executor< T >::value &&!is_convertible< T &, execution_context & >::value &&is_convertible< ExecutionContext &, execution_context & >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.make_work_guard.overload5 more...]]``
 
 [heading Requirements]
@@ -93261,7 +101820,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
       typename ``[link boost_asio.reference.Executor1 Executor]``>
   executor_work_guard< Executor > make_work_guard(
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -93297,7 +101856,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
       typename T>
   executor_work_guard< typename associated_executor< T >::type > make_work_guard(
       const T & t,
-      typename enable_if<!is_executor< T >::value &&!is_convertible< T &, execution_context & >::value >::type *  = 0);
+      typename enable_if< !is_executor< T >::value &&!execution::is_executor< T >::value &&!is_convertible< T &, execution_context & >::value >::type *  = 0);
 
 
 
@@ -93317,7 +101876,7 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
   executor_work_guard< typename associated_executor< T, Executor >::type > make_work_guard(
       const T & t,
       const Executor & ex,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -93337,13 +101896,96 @@ Create an [link boost_asio.reference.executor_work_guard `executor_work_guard`]
   executor_work_guard< typename associated_executor< T, typename ExecutionContext::executor_type >::type > make_work_guard(
       const T & t,
       ExecutionContext & ctx,
-      typename enable_if<!is_executor< T >::value &&!is_convertible< T &, execution_context & >::value &&is_convertible< ExecutionContext &, execution_context & >::value >::type *  = 0);
+      typename enable_if< !is_executor< T >::value &&!execution::is_executor< T >::value &&!is_convertible< T &, execution_context & >::value &&is_convertible< ExecutionContext &, execution_context & >::value >::type *  = 0);
 
 
 
 [endsect]
 
 
+[endsect]
+
+[section:multiple_exceptions multiple_exceptions]
+
+
+Exception thrown when there are multiple pending exceptions to rethrow. 
+
+
+  class multiple_exceptions :
+    public std::exception
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.multiple_exceptions.first_exception [*first_exception]]]
+    [Obtain a pointer to the first exception. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.multiple_exceptions.multiple_exceptions [*multiple_exceptions]]]
+    [Constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.multiple_exceptions.what [*what]]]
+    [Obtain message associated with exception. ]
+  ]
+  
+]
+
+[heading Requirements]
+
+['Header: ][^boost/asio/multiple_exceptions.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:first_exception multiple_exceptions::first_exception]
+
+[indexterm2 boost_asio.indexterm.multiple_exceptions.first_exception..first_exception..multiple_exceptions] 
+Obtain a pointer to the first exception. 
+
+
+  std::exception_ptr first_exception() const;
+
+
+
+[endsect]
+
+
+
+[section:multiple_exceptions multiple_exceptions::multiple_exceptions]
+
+[indexterm2 boost_asio.indexterm.multiple_exceptions.multiple_exceptions..multiple_exceptions..multiple_exceptions] 
+Constructor. 
+
+
+  multiple_exceptions(
+      std::exception_ptr first);
+
+
+
+[endsect]
+
+
+
+[section:what multiple_exceptions::what]
+
+[indexterm2 boost_asio.indexterm.multiple_exceptions.what..what..multiple_exceptions] 
+Obtain message associated with exception. 
+
+
+  virtual const char * what() const;
+
+
+
+[endsect]
+
+
+
 [endsect]
 
 [section:mutable_buffer mutable_buffer]
@@ -94253,7 +102895,7 @@ Provides POSIX descriptor functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_descriptor :
     public posix::descriptor_base
 
@@ -96147,7 +104789,7 @@ Provides stream-oriented descriptor functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_stream_descriptor :
     public posix::basic_descriptor< Executor >
 
@@ -99207,7 +107849,7 @@ Submits a completion token or function object for execution.
   ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` ``[link boost_asio.reference.post.overload2 post]``(
       const Executor & ex,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.post.overload2 more...]]``
 
   template<
@@ -99281,7 +107923,7 @@ Submits a completion token or function object for execution.
   ``[link boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type ['DEDUCED]]`` post(
       const Executor & ex,
       CompletionToken && token = ``[link boost_asio.reference.asynchronous_operations.default_completion_tokens ['DEFAULT]]``,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
 
 
 This function submits an object for execution using the specified executor. The function object is queued for execution, and is never called from the current thread prior to returning from `post()`.
@@ -99347,6 +107989,210 @@ Submits a completion token or function object for execution.
 [endsect]
 
 
+[endsect]
+
+
+[section:prefer prefer]
+
+[indexterm1 boost_asio.indexterm.prefer..prefer] 
+A customisation point that attempts to apply a property to an object. 
+
+
+  constexpr unspecified prefer = unspecified;
+
+
+The name `prefer` denotes a customisation point object. The expression `boost::asio::prefer(E, P0, Pn...)` for some subexpressions `E` and `P0`, and where `Pn...` represents `N` subexpressions (where `N` is 0 or more, and with types `T = decay_t<decltype(E)>` and `Prop0 = decay_t<decltype(P0)>`) is expression-equivalent to:
+
+
+* If `is_applicable_property_v<T, Prop0> && Prop0::is_preferable` is not a well-formed constant expression with value `true`, `boost::asio::prefer(E, P0, Pn...)` is ill-formed.
+
+
+* Otherwise, `E` if `N == 0` and the expression `Prop0::template static_query_v<T> == Prop0::value()` is a well-formed constant expression with value `true`.
+
+
+* Otherwise, `(E).require(P0)` if `N == 0` and the expression `(E).require(P0)` is a valid expression.
+
+
+* Otherwise, `require(E, P0)` if `N == 0` and the expression `require(E, P0)` is a valid expression with overload resolution performed in a context that does not include the declaration of the `require` customization point object.
+
+
+* Otherwise, `(E).prefer(P0)` if `N == 0` and the expression `(E).prefer(P0)` is a valid expression.
+
+
+* Otherwise, `prefer(E, P0)` if `N == 0` and the expression `prefer(E, P0)` is a valid expression with overload resolution performed in a context that does not include the declaration of the `prefer` customization point object.
+
+
+* Otherwise, `E` if `N == 0`.
+
+
+* Otherwise, `boost::asio::prefer(boost::asio::prefer(E, P0), Pn...)` if `N > 0` and the expression `boost::asio::prefer(boost::asio::prefer(E, P0), Pn...)` is a valid expression.
+
+
+* Otherwise, `boost::asio::prefer(E, P0, Pn...)` is ill-formed. 
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/prefer.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+[section:prefer_result_type prefer_result_type]
+
+
+A type trait that determines the result type of a `prefer` expression. 
+
+
+  template<
+      typename T,
+      typename... Properties>
+  struct prefer_result_type
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.prefer_result_type.type [*type]]]
+    [The result of the prefer expression. ]
+  
+  ]
+
+]
+
+Class template `prefer_result_type` is a trait that determines the result type of the expression `boost::asio::prefer(std::declval<T>(), std::declval<Properties>()...)`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/prefer.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:type prefer_result_type::type]
+
+[indexterm2 boost_asio.indexterm.prefer_result_type.type..type..prefer_result_type] 
+The result of the `prefer` expression. 
+
+
+  typedef automatically_determined type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/prefer.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
+[endsect]
+
+
+[section:query query]
+
+[indexterm1 boost_asio.indexterm.query..query] 
+A customisation point that queries the value of a property. 
+
+
+  constexpr unspecified query = unspecified;
+
+
+The name `query` denotes a customization point object. The expression `boost::asio::query(E, P)` for some subexpressions `E` and `P` (with types `T = decay_t<decltype(E)>` and `Prop = decay_t<decltype(P)>`) is expression-equivalent to:
+
+
+* If `is_applicable_property_v<T, Prop>` is not a well-formed constant expression with value `true`, `boost::asio::query(E, P)` is ill-formed.
+
+
+* Otherwise, `Prop::template static_query_v<T>` if the expression `Prop::template static_query_v<T>` is a well-formed constant expression.
+
+
+* Otherwise, `(E).query(P)` if the expression `(E).query(P)` is well-formed.
+
+
+* Otherwise, `query(E, P)` if the expression `query(E, P)` is a valid expression with overload resolution performed in a context that does not include the declaration of the `query` customization point object.
+
+
+* Otherwise, `boost::asio::query(E, P)` is ill-formed. 
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/query.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+[section:query_result_type query_result_type]
+
+
+A type trait that determines the result type of a `query` expression. 
+
+
+  template<
+      typename T,
+      typename Property>
+  struct query_result_type
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.query_result_type.type [*type]]]
+    [The result of the query expression. ]
+  
+  ]
+
+]
+
+Class template `query_result_type` is a trait that determines the result type of the expression `boost::asio::query(std::declval<T>(), std::declval<Property>())`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/query.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:type query_result_type::type]
+
+[indexterm2 boost_asio.indexterm.query_result_type.type..type..query_result_type] 
+The result of the `query` expression. 
+
+
+  typedef automatically_determined type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/query.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
 [endsect]
 
 [section:read read]
@@ -101685,7 +110531,7 @@ After a successful read\_until operation, the dynamic buffer sequence may contai
 To read data into a `std::string` until a newline is encountered: 
 
    std::string data;
-   std::string n = boost::asio::read_until(s,
+   std::size_t n = boost::asio::read_until(s,
        boost::asio::dynamic_buffer(data), '\n');
    std::string line = data.substr(0, n);
    data.erase(0, n); 
@@ -101831,7 +110677,7 @@ After a successful read\_until operation, the dynamic buffer sequence may contai
 To read data into a `std::string` until a CR-LF sequence is encountered: 
 
    std::string data;
-   std::string n = boost::asio::read_until(s,
+   std::size_t n = boost::asio::read_until(s,
        boost::asio::dynamic_buffer(data), "\r\n");
    std::string line = data.substr(0, n);
    data.erase(0, n); 
@@ -101987,7 +110833,7 @@ After a successful read\_until operation, the dynamic buffer sequence may contai
 To read data into a `std::string` until a CR-LF sequence is encountered: 
 
    std::string data;
-   std::string n = boost::asio::read_until(s,
+   std::size_t n = boost::asio::read_until(s,
        boost::asio::dynamic_buffer(data), boost::regex("\r\n"));
    std::string line = data.substr(0, n);
    data.erase(0, n); 
@@ -103013,7 +111859,7 @@ After a successful read\_until operation, the dynamic buffer sequence may contai
 To read data into a `std::string` until a newline is encountered: 
 
    std::string data;
-   std::string n = boost::asio::read_until(s,
+   std::size_t n = boost::asio::read_until(s,
        boost::asio::dynamic_buffer(data), '\n');
    std::string line = data.substr(0, n);
    data.erase(0, n); 
@@ -103159,7 +112005,7 @@ After a successful read\_until operation, the dynamic buffer sequence may contai
 To read data into a `std::string` until a CR-LF sequence is encountered: 
 
    std::string data;
-   std::string n = boost::asio::read_until(s,
+   std::size_t n = boost::asio::read_until(s,
        boost::asio::dynamic_buffer(data), "\r\n");
    std::string line = data.substr(0, n);
    data.erase(0, n); 
@@ -103315,7 +112161,7 @@ After a successful read\_until operation, the dynamic buffer sequence may contai
 To read data into a `std::string` until a CR-LF sequence is encountered: 
 
    std::string data;
-   std::string n = boost::asio::read_until(s,
+   std::size_t n = boost::asio::read_until(s,
        boost::asio::dynamic_buffer(data), boost::regex("\r\n"));
    std::string line = data.substr(0, n);
    data.erase(0, n); 
@@ -103723,6 +112569,201 @@ Constructor.
 
 
 
+[endsect]
+
+
+[section:require require]
+
+[indexterm1 boost_asio.indexterm.require..require] 
+A customisation point that applies a concept-preserving property to an object. 
+
+
+  constexpr unspecified require = unspecified;
+
+
+The name `require` denotes a customisation point object. The expression `boost::asio::require(E, P0, Pn...)` for some subexpressions `E` and `P0`, and where `Pn...` represents `N` subexpressions (where `N` is 0 or more, and with types `T = decay_t<decltype(E)>` and `Prop0 = decay_t<decltype(P0)>`) is expression-equivalent to:
+
+
+* If `is_applicable_property_v<T, Prop0> && Prop0::is_requirable` is not a well-formed constant expression with value `true`, `boost::asio::require(E, P0, Pn...)` is ill-formed.
+
+
+* Otherwise, `E` if `N == 0` and the expression `Prop0::template static_query_v<T> == Prop0::value()` is a well-formed constant expression with value `true`.
+
+
+* Otherwise, `(E).require(P0)` if `N == 0` and the expression `(E).require(P0)` is a valid expression.
+
+
+* Otherwise, `require(E, P0)` if `N == 0` and the expression `require(E, P0)` is a valid expression with overload resolution performed in a context that does not include the declaration of the `require` customization point object.
+
+
+* Otherwise, `boost::asio::require(boost::asio::require(E, P0), Pn...)` if `N > 0` and the expression `boost::asio::require(boost::asio::require(E, P0), Pn...)` is a valid expression.
+
+
+* Otherwise, `boost::asio::require(E, P0, Pn...)` is ill-formed. 
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
+[section:require_concept require_concept]
+
+[indexterm1 boost_asio.indexterm.require_concept..require_concept] 
+A customisation point that applies a concept-enforcing property to an object. 
+
+
+  constexpr unspecified require_concept = unspecified;
+
+
+The name `require_concept` denotes a customization point object. The expression `boost::asio::require_concept(E, P)` for some subexpressions `E` and `P` (with types `T = decay_t<decltype(E)>` and `Prop = decay_t<decltype(P)>`) is expression-equivalent to:
+
+
+* If `is_applicable_property_v<T, Prop> && Prop::is_requirable_concept` is not a well-formed constant expression with value `true`, `boost::asio::require_concept(E, P)` is ill-formed.
+
+
+* Otherwise, `E` if the expression `Prop::template static_query_v<T> == Prop::value()` is a well-formed constant expression with value `true`.
+
+
+* Otherwise, `(E).require_concept(P)` if the expression `(E).require_concept(P)` is well-formed.
+
+
+* Otherwise, `require_concept(E, P)` if the expression `require_concept(E, P)` is a valid expression with overload resolution performed in a context that does not include the declaration of the `require_concept` customization point object.
+
+
+* Otherwise, `boost::asio::require_concept(E, P)` is ill-formed. 
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require_concept.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+[section:require_concept_result_type require_concept_result_type]
+
+
+A type trait that determines the result type of a `require_concept` expression. 
+
+
+  template<
+      typename T,
+      typename Property>
+  struct require_concept_result_type
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.require_concept_result_type.type [*type]]]
+    [The result of the require_concept expression. ]
+  
+  ]
+
+]
+
+Class template `require_concept_result_type` is a trait that determines the result type of the expression `boost::asio::require_concept(std::declval<T>(), std::declval<Property>())`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require_concept.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:type require_concept_result_type::type]
+
+[indexterm2 boost_asio.indexterm.require_concept_result_type.type..type..require_concept_result_type] 
+The result of the `require_concept` expression. 
+
+
+  typedef automatically_determined type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require_concept.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
+[endsect]
+
+[section:require_result_type require_result_type]
+
+
+A type trait that determines the result type of a `require` expression. 
+
+
+  template<
+      typename T,
+      typename... Properties>
+  struct require_result_type
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.require_result_type.type [*type]]]
+    [The result of the require expression. ]
+  
+  ]
+
+]
+
+Class template `require_result_type` is a trait that determines the result type of the expression `boost::asio::require(std::declval<T>(), std::declval<Properties>()...)`. 
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[section:type require_result_type::type]
+
+[indexterm2 boost_asio.indexterm.require_result_type.type..type..require_result_type] 
+The result of the `require` expression. 
+
+
+  typedef automatically_determined type;
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/require.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
 [endsect]
 
 
@@ -104663,7 +113704,7 @@ Exception thrown when trying to add a duplicate service to an [link boost_asio.r
 
 ['Header: ][^boost/asio/execution_context.hpp]
 
-['Convenience header: ][^boost/asio.hpp]
+['Convenience header: ][^boost/asio/execution.hpp]
 
 
 [section:service_already_exists service_already_exists::service_already_exists]
@@ -105888,7 +114929,7 @@ Start a new stackful coroutine, calling the specified handler when it completes.
       Handler && handler,
       Function && function,
       const boost::coroutines::attributes & attributes = boost::coroutines::attributes(),
-      typename enable_if<!is_executor< typename decay< Handler >::type >::value &&!is_convertible< Handler &, execution_context & >::value >::type *  = 0);
+      typename enable_if< !is_executor< typename decay< Handler >::type >::value &&!execution::is_executor< typename decay< Handler >::type >::value &&!is_convertible< Handler &, execution_context & >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.spawn.overload2 more...]]``
 
 Start a new stackful coroutine, inheriting the execution context of another. 
@@ -105911,7 +114952,7 @@ Start a new stackful coroutine that executes on a given executor.
       const Executor & ex,
       Function && function,
       const boost::coroutines::attributes & attributes = boost::coroutines::attributes(),
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.spawn.overload4 more...]]``
 
 Start a new stackful coroutine that executes on a given strand. 
@@ -106037,7 +115078,7 @@ Start a new stackful coroutine, calling the specified handler when it completes.
       Handler && handler,
       Function && function,
       const boost::coroutines::attributes & attributes = boost::coroutines::attributes(),
-      typename enable_if<!is_executor< typename decay< Handler >::type >::value &&!is_convertible< Handler &, execution_context & >::value >::type *  = 0);
+      typename enable_if< !is_executor< typename decay< Handler >::type >::value &&!execution::is_executor< typename decay< Handler >::type >::value &&!is_convertible< Handler &, execution_context & >::value >::type *  = 0);
 
 
 This function is used to launch a new coroutine.
@@ -106126,7 +115167,7 @@ Start a new stackful coroutine that executes on a given executor.
       const Executor & ex,
       Function && function,
       const boost::coroutines::attributes & attributes = boost::coroutines::attributes(),
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< is_executor< Executor >::value||execution::is_executor< Executor >::value >::type *  = 0);
 
 
 This function is used to launch a new coroutine.
@@ -110122,7 +119163,9 @@ Provides stream-oriented functionality using SSL.
   
   [
     [[link boost_asio.reference.ssl__stream.stream [*stream]]]
-    [Construct a stream. ]
+    [Construct a stream. 
+     [hr]
+     Move-construct a stream from another. ]
   ]
   
   [
@@ -111392,10 +120435,31 @@ This function is used to shut down SSL on the stream. The function call will blo
 
 [endsect]
 
-
 [section:stream ssl::stream::stream]
 
 [indexterm2 boost_asio.indexterm.ssl__stream.stream..stream..ssl::stream] 
+Construct a stream. 
+
+
+  template<
+      typename Arg>
+  ``[link boost_asio.reference.ssl__stream.stream.overload1 stream]``(
+      Arg && arg,
+      context & ctx);
+  ``  [''''&raquo;''' [link boost_asio.reference.ssl__stream.stream.overload1 more...]]``
+
+
+Move-construct a stream from another. 
+
+
+  ``[link boost_asio.reference.ssl__stream.stream.overload2 stream]``(
+      stream && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.ssl__stream.stream.overload2 more...]]``
+
+
+[section:overload1 ssl::stream::stream (1 of 2 overloads)]
+
+
 Construct a stream. 
 
 
@@ -111426,6 +120490,35 @@ This constructor creates a stream and initialises the underlying stream object.
 [endsect]
 
 
+
+[section:overload2 ssl::stream::stream (2 of 2 overloads)]
+
+
+Move-construct a stream from another. 
+
+
+  stream(
+      stream && other);
+
+
+
+[heading Parameters]
+    
+
+[variablelist
+  
+[[other][The other stream object from which the move will occur. Must have no outstanding asynchronous operations associated with it. Following the move, `other` has a valid but unspecified state where the only safe operation is destruction. ]]
+
+]
+
+
+
+
+[endsect]
+
+
+[endsect]
+
 [section:write_some ssl::stream::write_some]
 
 [indexterm2 boost_asio.indexterm.ssl__stream.write_some..write_some..ssl::stream] 
@@ -111917,6 +121010,186 @@ Verify the peer.
 
 
 
+[section:static_thread_pool static_thread_pool]
+
+[indexterm1 boost_asio.indexterm.static_thread_pool..static_thread_pool] 
+
+  typedef thread_pool static_thread_pool;
+
+
+[heading Types]
+[table
+  [[Name][Description]]
+
+  [
+
+    [[link boost_asio.reference.thread_pool__basic_executor_type [*basic_executor_type]]]
+    [Executor implementation type used to submit functions to a thread pool. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.thread_pool.executor_type [*executor_type]]]
+    [Executor used to submit functions to a thread pool. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.thread_pool.fork_event [*fork_event]]]
+    [Fork-related event notifications. ]
+  
+  ]
+
+]
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.thread_pool.attach [*attach]]]
+    [Attaches the current thread to the pool. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.executor [*executor]]]
+    [Obtains the executor associated with the pool. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.get_executor [*get_executor]]]
+    [Obtains the executor associated with the pool. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.join [*join]]]
+    [Joins the threads. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.notify_fork [*notify_fork]]]
+    [Notify the execution_context of a fork-related event. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.stop [*stop]]]
+    [Stops the threads. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.thread_pool [*thread_pool]]]
+    [Constructs a pool with an automatically determined number of threads. 
+     [hr]
+     Constructs a pool with a specified number of threads. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.wait [*wait]]]
+    [Waits for threads to complete. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool._thread_pool [*~thread_pool]]]
+    [Destructor. ]
+  ]
+  
+]
+
+[heading Protected Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.thread_pool.destroy [*destroy]]]
+    [Destroys all services in the context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.shutdown [*shutdown]]]
+    [Shuts down all services in the context. ]
+  ]
+  
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.thread_pool.add_service [*add_service]]]
+    [(Deprecated: Use make_service().) Add a service object to the execution_context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.has_service [*has_service]]]
+    [Determine if an execution_context contains a specified service type. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.make_service [*make_service]]]
+    [Creates a service object and adds it to the execution_context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.use_service [*use_service]]]
+    [Obtain the service object corresponding to the given type. ]
+  ]
+  
+]
+
+The thread pool class is an execution context where functions are permitted to run on one of a fixed number of threads.
+
+
+[heading Submitting tasks to the pool]
+  
+
+
+To submit functions to the thread pool, use the [link boost_asio.reference.dispatch `dispatch`] , [link boost_asio.reference.post `post`]  or [link boost_asio.reference.defer `defer`]  free functions.
+
+For example:
+
+
+
+   void my_task()
+   {
+     ...
+   }
+
+   ...
+
+   // Launch the pool with four threads.
+   boost::asio::thread_pool pool(4);
+
+   // Submit a function to the pool.
+   boost::asio::post(pool, my_task);
+
+   // Submit a lambda object to the pool.
+   boost::asio::post(pool,
+       []()
+       {
+         ...
+       });
+
+   // Wait for all tasks in the pool to complete.
+   pool.join(); 
+
+
+
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/static_thread_pool.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
 [section:steady_timer steady_timer]
 
 [indexterm1 boost_asio.indexterm.steady_timer..steady_timer] 
@@ -112201,11 +121474,6 @@ Provides serialised function invocation for any executor type.
 [table
   [[Name][Description]]
 
-  [
-    [[link boost_asio.reference.strand.context [*context]]]
-    [Obtain the underlying execution context. ]
-  ]
-  
   [
     [[link boost_asio.reference.strand.defer [*defer]]]
     [Request the strand to invoke the given function object. ]
@@ -112216,21 +121484,16 @@ Provides serialised function invocation for any executor type.
     [Request the strand to invoke the given function object. ]
   ]
   
+  [
+    [[link boost_asio.reference.strand.execute [*execute]]]
+    []
+  ]
+  
   [
     [[link boost_asio.reference.strand.get_inner_executor [*get_inner_executor]]]
     [Obtain the underlying executor. ]
   ]
   
-  [
-    [[link boost_asio.reference.strand.on_work_finished [*on_work_finished]]]
-    [Inform the strand that some work is no longer outstanding. ]
-  ]
-  
-  [
-    [[link boost_asio.reference.strand.on_work_started [*on_work_started]]]
-    [Inform the strand that it has some outstanding work to do. ]
-  ]
-  
   [
     [[link boost_asio.reference.strand.operator_eq_ [*operator=]]]
     [Assignment operator. 
@@ -112247,6 +121510,21 @@ Provides serialised function invocation for any executor type.
     [Request the strand to invoke the given function object. ]
   ]
   
+  [
+    [[link boost_asio.reference.strand.prefer [*prefer]]]
+    []
+  ]
+  
+  [
+    [[link boost_asio.reference.strand.query [*query]]]
+    [Forward a query to the underlying executor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.strand.require [*require]]]
+    []
+  ]
+  
   [
     [[link boost_asio.reference.strand.running_in_this_thread [*running_in_this_thread]]]
     [Determine whether the strand is running in the current thread. ]
@@ -112297,20 +121575,6 @@ Provides serialised function invocation for any executor type.
 ['Convenience header: ][^boost/asio.hpp]
 
 
-[section:context strand::context]
-
-[indexterm2 boost_asio.indexterm.strand.context..context..strand] 
-Obtain the underlying execution context. 
-
-
-  execution_context & context() const;
-
-
-
-[endsect]
-
-
-
 [section:defer strand::defer]
 
 [indexterm2 boost_asio.indexterm.strand.defer..defer..strand] 
@@ -112385,6 +121649,19 @@ This function is used to ask the strand to execute the given function object on
 
 
 
+[endsect]
+
+
+
+[section:execute strand::execute]
+
+[indexterm2 boost_asio.indexterm.strand.execute..execute..strand] 
+
+  Function::value::type execute(
+      Function && f) const;
+
+
+
 [endsect]
 
 
@@ -112424,38 +121701,6 @@ The type of the underlying executor.
 
 
 
-[section:on_work_finished strand::on_work_finished]
-
-[indexterm2 boost_asio.indexterm.strand.on_work_finished..on_work_finished..strand] 
-Inform the strand that some work is no longer outstanding. 
-
-
-  void on_work_finished() const;
-
-
-The strand delegates this call to its underlying executor. 
-
-
-[endsect]
-
-
-
-[section:on_work_started strand::on_work_started]
-
-[indexterm2 boost_asio.indexterm.strand.on_work_started..on_work_started..strand] 
-Inform the strand that it has some outstanding work to do. 
-
-
-  void on_work_started() const;
-
-
-The strand delegates this call to its underlying executor. 
-
-
-[endsect]
-
-
-
 [section:operator_not__eq_ strand::operator!=]
 
 [indexterm2 boost_asio.indexterm.strand.operator_not__eq_..operator!=..strand] 
@@ -112647,6 +121892,49 @@ This function is used to ask the executor to execute the given function object.
 
 
 
+[endsect]
+
+
+
+[section:prefer strand::prefer]
+
+[indexterm2 boost_asio.indexterm.strand.prefer..prefer..strand] 
+
+  Property strand< typename decay< typename prefer_result_type< const Executor &, Property >::type >::type >::type prefer(
+      const Property & p) const;
+
+
+
+[endsect]
+
+
+
+[section:query strand::query]
+
+[indexterm2 boost_asio.indexterm.strand.query..query..strand] 
+Forward a query to the underlying executor. 
+
+
+  template<
+      typename Property>
+  enable_if< can_query< const Executor &, Property >::value, typename query_result_type< const Executor &, Property >::type >::type query(
+      const Property & p) const;
+
+
+
+[endsect]
+
+
+
+[section:require strand::require]
+
+[indexterm2 boost_asio.indexterm.strand.require..require..strand] 
+
+  Property strand< typename decay< typename require_result_type< const Executor &, Property >::type >::type >::type require(
+      const Property & p) const;
+
+
+
 [endsect]
 
 
@@ -113212,7 +122500,7 @@ This function is implemented as follows:
 The executor type associated with the context. 
 
 
-  typedef system_executor executor_type;
+  typedef basic_system_executor< execution::blocking_t::possibly_t, execution::relationship_t::fork_t, std::allocator< void > > executor_type;
 
 
 [heading Member Functions]
@@ -113220,35 +122508,80 @@ The executor type associated with the context.
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.system_executor.context [*context]]]
+    [[link boost_asio.reference.basic_system_executor.basic_system_executor [*basic_system_executor]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.context [*context]]]
     [Obtain the underlying execution context. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.defer [*defer]]]
+    [[link boost_asio.reference.basic_system_executor.defer [*defer]]]
     [Request the system executor to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.dispatch [*dispatch]]]
+    [[link boost_asio.reference.basic_system_executor.dispatch [*dispatch]]]
     [Request the system executor to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.on_work_finished [*on_work_finished]]]
+    [[link boost_asio.reference.basic_system_executor.execute [*execute]]]
+    [Oneway execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.on_work_finished [*on_work_finished]]]
     [Inform the executor that some work is no longer outstanding. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.on_work_started [*on_work_started]]]
+    [[link boost_asio.reference.basic_system_executor.on_work_started [*on_work_started]]]
     [Inform the executor that it has some outstanding work to do. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.post [*post]]]
+    [[link boost_asio.reference.basic_system_executor.post [*post]]]
     [Request the system executor to invoke the given function object. ]
   ]
   
+  [
+    [[link boost_asio.reference.basic_system_executor.query [*query]]]
+    [Query the current value of the allocator property. 
+     [hr]
+     Query the occupancy (recommended number of work items) for the system context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.query__static [*query]]]
+    [Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.always property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
 ]
 
 [heading Friends]
@@ -113256,18 +122589,18 @@ The executor type associated with the context.
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.system_executor.operator_not__eq_ [*operator!=]]]
+    [[link boost_asio.reference.basic_system_executor.operator_not__eq_ [*operator!=]]]
     [Compare two executors for inequality. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.operator_eq__eq_ [*operator==]]]
+    [[link boost_asio.reference.basic_system_executor.operator_eq__eq_ [*operator==]]]
     [Compare two executors for equality. ]
   ]
   
 ]
 
-The system executor represents an execution context where functions are permitted to run on arbitrary threads. The `post()` and `defer()` functions schedule the function to run on an unspecified system thread pool, and `dispatch()` invokes the function immediately. 
+The system executor represents an execution context where functions are permitted to run on arbitrary threads. When the blocking.never property is established, the system executor will schedule the function to run on an unspecified system thread pool. When either blocking.possibly or blocking.always is established, the executor invokes the function immediately. 
 
 
 [heading Requirements]
@@ -113701,13 +123034,14 @@ Destructor shuts down all threads in the system thread pool.
 
 [endsect]
 
+
 [section:system_executor system_executor]
 
-
+[indexterm1 boost_asio.indexterm.system_executor..system_executor] 
 An executor that uses arbitrary threads. 
 
 
-  class system_executor
+  typedef basic_system_executor< execution::blocking_t::possibly_t, execution::relationship_t::fork_t, std::allocator< void > > system_executor;
 
 
 [heading Member Functions]
@@ -113715,35 +123049,80 @@ An executor that uses arbitrary threads.
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.system_executor.context [*context]]]
+    [[link boost_asio.reference.basic_system_executor.basic_system_executor [*basic_system_executor]]]
+    [Default constructor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.context [*context]]]
     [Obtain the underlying execution context. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.defer [*defer]]]
+    [[link boost_asio.reference.basic_system_executor.defer [*defer]]]
     [Request the system executor to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.dispatch [*dispatch]]]
+    [[link boost_asio.reference.basic_system_executor.dispatch [*dispatch]]]
     [Request the system executor to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.on_work_finished [*on_work_finished]]]
+    [[link boost_asio.reference.basic_system_executor.execute [*execute]]]
+    [Oneway execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.on_work_finished [*on_work_finished]]]
     [Inform the executor that some work is no longer outstanding. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.on_work_started [*on_work_started]]]
+    [[link boost_asio.reference.basic_system_executor.on_work_started [*on_work_started]]]
     [Inform the executor that it has some outstanding work to do. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.post [*post]]]
+    [[link boost_asio.reference.basic_system_executor.post [*post]]]
     [Request the system executor to invoke the given function object. ]
   ]
   
+  [
+    [[link boost_asio.reference.basic_system_executor.query [*query]]]
+    [Query the current value of the allocator property. 
+     [hr]
+     Query the occupancy (recommended number of work items) for the system context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.query__static [*query]]]
+    [Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.basic_system_executor.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.always property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
 ]
 
 [heading Friends]
@@ -113751,162 +123130,21 @@ An executor that uses arbitrary threads.
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.system_executor.operator_not__eq_ [*operator!=]]]
+    [[link boost_asio.reference.basic_system_executor.operator_not__eq_ [*operator!=]]]
     [Compare two executors for inequality. ]
   ]
   
   [
-    [[link boost_asio.reference.system_executor.operator_eq__eq_ [*operator==]]]
+    [[link boost_asio.reference.basic_system_executor.operator_eq__eq_ [*operator==]]]
     [Compare two executors for equality. ]
   ]
   
 ]
 
-The system executor represents an execution context where functions are permitted to run on arbitrary threads. The `post()` and `defer()` functions schedule the function to run on an unspecified system thread pool, and `dispatch()` invokes the function immediately. 
+The system executor represents an execution context where functions are permitted to run on arbitrary threads. When the blocking.never property is established, the system executor will schedule the function to run on an unspecified system thread pool. When either blocking.possibly or blocking.always is established, the executor invokes the function immediately. 
 
-[heading Requirements]
 
-['Header: ][^boost/asio/system_executor.hpp]
-
-['Convenience header: ][^boost/asio.hpp]
-
-
-[section:context system_executor::context]
-
-[indexterm2 boost_asio.indexterm.system_executor.context..context..system_executor] 
-Obtain the underlying execution context. 
-
-
-  system_context & context() const;
-
-
-
-[endsect]
-
-
-
-[section:defer system_executor::defer]
-
-[indexterm2 boost_asio.indexterm.system_executor.defer..defer..system_executor] 
-Request the system executor to invoke the given function object. 
-
-
-  template<
-      typename Function,
-      typename Allocator>
-  void defer(
-      Function && f,
-      const Allocator & a) const;
-
-
-This function is used to ask the executor to execute the given function object. The function object will never be executed inside this function. Instead, it will be scheduled to run on an unspecified system thread pool.
-
-
-[heading Parameters]
-    
-
-[variablelist
-  
-[[f][The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
-``
-   void function(); 
-``
-]]
-
-[[a][An allocator that may be used by the executor to allocate the internal storage needed for function invocation. ]]
-
-]
-
-
-
-
-[endsect]
-
-
-
-[section:dispatch system_executor::dispatch]
-
-[indexterm2 boost_asio.indexterm.system_executor.dispatch..dispatch..system_executor] 
-Request the system executor to invoke the given function object. 
-
-
-  template<
-      typename Function,
-      typename Allocator>
-  void dispatch(
-      Function && f,
-      const Allocator & a) const;
-
-
-This function is used to ask the executor to execute the given function object. The function object will always be executed inside this function.
-
-
-[heading Parameters]
-    
-
-[variablelist
-  
-[[f][The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
-``
-   void function(); 
-``
-]]
-
-[[a][An allocator that may be used by the executor to allocate the internal storage needed for function invocation. ]]
-
-]
-
-
-
-
-[endsect]
-
-
-
-[section:on_work_finished system_executor::on_work_finished]
-
-[indexterm2 boost_asio.indexterm.system_executor.on_work_finished..on_work_finished..system_executor] 
-Inform the executor that some work is no longer outstanding. 
-
-
-  void on_work_finished() const;
-
-
-For the system executor, this is a no-op. 
-
-
-[endsect]
-
-
-
-[section:on_work_started system_executor::on_work_started]
-
-[indexterm2 boost_asio.indexterm.system_executor.on_work_started..on_work_started..system_executor] 
-Inform the executor that it has some outstanding work to do. 
-
-
-  void on_work_started() const;
-
-
-For the system executor, this is a no-op. 
-
-
-[endsect]
-
-
-
-[section:operator_not__eq_ system_executor::operator!=]
-
-[indexterm2 boost_asio.indexterm.system_executor.operator_not__eq_..operator!=..system_executor] 
-Compare two executors for inequality. 
-
-
-  friend bool operator!=(
-      const system_executor & ,
-      const system_executor & );
-
-
-System executors always compare equal. 
+The system executor represents an execution context where functions are permitted to run on arbitrary threads. When the blocking.never property is established, the system executor will schedule the function to run on an unspecified system thread pool. When either blocking.possibly or blocking.always is established, the executor invokes the function immediately. 
 
 [heading Requirements]
 
@@ -113919,72 +123157,6 @@ System executors always compare equal.
 
 
 
-[section:operator_eq__eq_ system_executor::operator==]
-
-[indexterm2 boost_asio.indexterm.system_executor.operator_eq__eq_..operator==..system_executor] 
-Compare two executors for equality. 
-
-
-  friend bool operator==(
-      const system_executor & ,
-      const system_executor & );
-
-
-System executors always compare equal. 
-
-[heading Requirements]
-
-['Header: ][^boost/asio/system_executor.hpp]
-
-['Convenience header: ][^boost/asio.hpp]
-
-
-[endsect]
-
-
-
-[section:post system_executor::post]
-
-[indexterm2 boost_asio.indexterm.system_executor.post..post..system_executor] 
-Request the system executor to invoke the given function object. 
-
-
-  template<
-      typename Function,
-      typename Allocator>
-  void post(
-      Function && f,
-      const Allocator & a) const;
-
-
-This function is used to ask the executor to execute the given function object. The function object will never be executed inside this function. Instead, it will be scheduled to run on an unspecified system thread pool.
-
-
-[heading Parameters]
-    
-
-[variablelist
-  
-[[f][The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
-``
-   void function(); 
-``
-]]
-
-[[a][An allocator that may be used by the executor to allocate the internal storage needed for function invocation. ]]
-
-]
-
-
-
-
-[endsect]
-
-
-
-[endsect]
-
-
 [section:system_timer system_timer]
 
 [indexterm1 boost_asio.indexterm.system_timer..system_timer] 
@@ -114318,7 +123490,14 @@ A simple fixed-size thread pool.
 
   [
 
-    [[link boost_asio.reference.thread_pool__executor_type [*executor_type]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type [*basic_executor_type]]]
+    [Executor implementation type used to submit functions to a thread pool. ]
+  
+  ]
+
+  [
+
+    [[link boost_asio.reference.thread_pool.executor_type [*executor_type]]]
     [Executor used to submit functions to a thread pool. ]
   
   ]
@@ -114336,6 +123515,16 @@ A simple fixed-size thread pool.
 [table
   [[Name][Description]]
 
+  [
+    [[link boost_asio.reference.thread_pool.attach [*attach]]]
+    [Attaches the current thread to the pool. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool.executor [*executor]]]
+    [Obtains the executor associated with the pool. ]
+  ]
+  
   [
     [[link boost_asio.reference.thread_pool.get_executor [*get_executor]]]
     [Obtains the executor associated with the pool. ]
@@ -114363,6 +123552,11 @@ A simple fixed-size thread pool.
      Constructs a pool with a specified number of threads. ]
   ]
   
+  [
+    [[link boost_asio.reference.thread_pool.wait [*wait]]]
+    [Waits for threads to complete. ]
+  ]
+  
   [
     [[link boost_asio.reference.thread_pool._thread_pool [*~thread_pool]]]
     [Destructor. ]
@@ -114419,7 +123613,7 @@ The thread pool class is an execution context where functions are permitted to r
   
 
 
-To submit functions to the [link boost_asio.reference.thread_pool `thread_pool`], use the [link boost_asio.reference.dispatch `dispatch`] , [link boost_asio.reference.post `post`]  or [link boost_asio.reference.defer `defer`]  free functions.
+To submit functions to the thread pool, use the [link boost_asio.reference.dispatch `dispatch`] , [link boost_asio.reference.post `post`]  or [link boost_asio.reference.defer `defer`]  free functions.
 
 For example:
 
@@ -114517,6 +123711,22 @@ This function is used to add a service to the [link boost_asio.reference.executi
 
 
 
+[section:attach thread_pool::attach]
+
+[indexterm2 boost_asio.indexterm.thread_pool.attach..attach..thread_pool] 
+Attaches the current thread to the pool. 
+
+
+  void attach();
+
+
+This function attaches the current thread to the pool so that it may be used for executing submitted function objects. Blocks the calling thread until the pool is stopped or joined and has no outstanding work. 
+
+
+[endsect]
+
+
+
 [section:destroy thread_pool::destroy]
 
 
@@ -114541,6 +123751,165 @@ This function is implemented as follows:
 
 
 
+[section:executor thread_pool::executor]
+
+[indexterm2 boost_asio.indexterm.thread_pool.executor..executor..thread_pool] 
+Obtains the executor associated with the pool. 
+
+
+  executor_type executor();
+
+
+
+[endsect]
+
+
+
+[section:executor_type thread_pool::executor_type]
+
+[indexterm2 boost_asio.indexterm.thread_pool.executor_type..executor_type..thread_pool] 
+Executor used to submit functions to a thread pool. 
+
+
+  typedef basic_executor_type< std::allocator< void >, 0 > executor_type;
+
+
+[heading Member Functions]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.basic_executor_type [*basic_executor_type]]]
+    [Copy construtor. 
+     [hr]
+     Move construtor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.context [*context]]]
+    [Obtain the underlying execution context. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.defer [*defer]]]
+    [Request the thread pool to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.dispatch [*dispatch]]]
+    [Request the thread pool to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.execute [*execute]]]
+    [Execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.on_work_finished [*on_work_finished]]]
+    [Inform the thread pool that some work is no longer outstanding. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.on_work_started [*on_work_started]]]
+    [Inform the thread pool that it has some outstanding work to do. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.operator_eq_ [*operator=]]]
+    [Assignment operator. 
+     [hr]
+     Move assignment operator. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.post [*post]]]
+    [Request the thread pool to invoke the given function object. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.query [*query]]]
+    [Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. 
+     [hr]
+     Query the current value of the allocator property. 
+     [hr]
+     Query the occupancy (recommended number of work items) for the pool. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.query__static [*query]]]
+    [Query the current value of the bulk_guarantee property. 
+     [hr]
+     Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the outstanding_work property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.always property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the outstanding_work.tracked property. 
+     [hr]
+     Obtain an executor with the outstanding_work.untracked property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.running_in_this_thread [*running_in_this_thread]]]
+    [Determine whether the thread pool is running in the current thread. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type._basic_executor_type [*~basic_executor_type]]]
+    [Destructor. ]
+  ]
+  
+]
+
+[heading Friends]
+[table
+  [[Name][Description]]
+
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.operator_not__eq_ [*operator!=]]]
+    [Compare two executors for inequality. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.operator_eq__eq_ [*operator==]]]
+    [Compare two executors for equality. ]
+  ]
+  
+]
+
+
+[heading Requirements]
+
+['Header: ][^boost/asio/thread_pool.hpp]
+
+['Convenience header: ][^boost/asio.hpp]
+
+
+[endsect]
+
+
+
 [section:fork_event thread_pool::fork_event]
 
 
@@ -114983,6 +124352,22 @@ This overload is preserved for backwards compatibility with services that inheri
 [endsect]
 
 
+[section:wait thread_pool::wait]
+
+[indexterm2 boost_asio.indexterm.thread_pool.wait..wait..thread_pool] 
+Waits for threads to complete. 
+
+
+  void wait();
+
+
+This function blocks until the threads in the pool have completed. If `stop()` is not called prior to `wait()`, the `wait()` call will wait until the pool has no more outstanding work. 
+
+
+[endsect]
+
+
+
 [section:_thread_pool thread_pool::~thread_pool]
 
 [indexterm2 boost_asio.indexterm.thread_pool._thread_pool..~thread_pool..thread_pool] 
@@ -115001,13 +124386,16 @@ Automatically stops and joins the pool, if not explicitly done beforehand.
 
 [endsect]
 
-[section:thread_pool__executor_type thread_pool::executor_type]
+[section:thread_pool__basic_executor_type thread_pool::basic_executor_type]
 
 
-Executor used to submit functions to a thread pool. 
+Executor implementation type used to submit functions to a thread pool. 
 
 
-  class executor_type
+  template<
+      typename Allocator,
+      unsigned int Bits>
+  class basic_executor_type
 
 
 [heading Member Functions]
@@ -115015,40 +124403,107 @@ Executor used to submit functions to a thread pool.
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.thread_pool__executor_type.context [*context]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.basic_executor_type [*basic_executor_type]]]
+    [Copy construtor. 
+     [hr]
+     Move construtor. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.context [*context]]]
     [Obtain the underlying execution context. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.defer [*defer]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.defer [*defer]]]
     [Request the thread pool to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.dispatch [*dispatch]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.dispatch [*dispatch]]]
     [Request the thread pool to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.on_work_finished [*on_work_finished]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.execute [*execute]]]
+    [Execution function. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.on_work_finished [*on_work_finished]]]
     [Inform the thread pool that some work is no longer outstanding. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.on_work_started [*on_work_started]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.on_work_started [*on_work_started]]]
     [Inform the thread pool that it has some outstanding work to do. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.post [*post]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.operator_eq_ [*operator=]]]
+    [Assignment operator. 
+     [hr]
+     Move assignment operator. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.post [*post]]]
     [Request the thread pool to invoke the given function object. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.running_in_this_thread [*running_in_this_thread]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.query [*query]]]
+    [Query the current value of the context property. 
+     [hr]
+     Query the current value of the blocking property. 
+     [hr]
+     Query the current value of the relationship property. 
+     [hr]
+     Query the current value of the allocator property. 
+     [hr]
+     Query the occupancy (recommended number of work items) for the pool. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.query__static [*query]]]
+    [Query the current value of the bulk_guarantee property. 
+     [hr]
+     Query the current value of the mapping property. 
+     [hr]
+     Query the current value of the outstanding_work property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.require [*require]]]
+    [Obtain an executor with the blocking.possibly property. 
+     [hr]
+     Obtain an executor with the blocking.always property. 
+     [hr]
+     Obtain an executor with the blocking.never property. 
+     [hr]
+     Obtain an executor with the relationship.fork property. 
+     [hr]
+     Obtain an executor with the relationship.continuation property. 
+     [hr]
+     Obtain an executor with the outstanding_work.tracked property. 
+     [hr]
+     Obtain an executor with the outstanding_work.untracked property. 
+     [hr]
+     Obtain an executor with the specified allocator property. 
+     [hr]
+     Obtain an executor with the default allocator property. ]
+  ]
+  
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type.running_in_this_thread [*running_in_this_thread]]]
     [Determine whether the thread pool is running in the current thread. ]
   ]
   
+  [
+    [[link boost_asio.reference.thread_pool__basic_executor_type._basic_executor_type [*~basic_executor_type]]]
+    [Destructor. ]
+  ]
+  
 ]
 
 [heading Friends]
@@ -115056,12 +124511,12 @@ Executor used to submit functions to a thread pool.
   [[Name][Description]]
 
   [
-    [[link boost_asio.reference.thread_pool__executor_type.operator_not__eq_ [*operator!=]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.operator_not__eq_ [*operator!=]]]
     [Compare two executors for inequality. ]
   ]
   
   [
-    [[link boost_asio.reference.thread_pool__executor_type.operator_eq__eq_ [*operator==]]]
+    [[link boost_asio.reference.thread_pool__basic_executor_type.operator_eq__eq_ [*operator==]]]
     [Compare two executors for equality. ]
   ]
   
@@ -115073,10 +124528,60 @@ Executor used to submit functions to a thread pool.
 
 ['Convenience header: ][^boost/asio.hpp]
 
+[section:basic_executor_type thread_pool::basic_executor_type::basic_executor_type]
 
-[section:context thread_pool::executor_type::context]
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.basic_executor_type..basic_executor_type..thread_pool::basic_executor_type] 
+Copy construtor. 
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.context..context..thread_pool::executor_type] 
+
+  ``[link boost_asio.reference.thread_pool__basic_executor_type.basic_executor_type.overload1 basic_executor_type]``(
+      const basic_executor_type & other);
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.basic_executor_type.overload1 more...]]``
+
+
+Move construtor. 
+
+
+  ``[link boost_asio.reference.thread_pool__basic_executor_type.basic_executor_type.overload2 basic_executor_type]``(
+      basic_executor_type && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.basic_executor_type.overload2 more...]]``
+
+
+[section:overload1 thread_pool::basic_executor_type::basic_executor_type (1 of 2 overloads)]
+
+
+Copy construtor. 
+
+
+  basic_executor_type(
+      const basic_executor_type & other);
+
+
+
+[endsect]
+
+
+
+[section:overload2 thread_pool::basic_executor_type::basic_executor_type (2 of 2 overloads)]
+
+
+Move construtor. 
+
+
+  basic_executor_type(
+      basic_executor_type && other);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:context thread_pool::basic_executor_type::context]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.context..context..thread_pool::basic_executor_type] 
 Obtain the underlying execution context. 
 
 
@@ -115088,18 +124593,18 @@ Obtain the underlying execution context.
 
 
 
-[section:defer thread_pool::executor_type::defer]
+[section:defer thread_pool::basic_executor_type::defer]
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.defer..defer..thread_pool::executor_type] 
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.defer..defer..thread_pool::basic_executor_type] 
 Request the thread pool to invoke the given function object. 
 
 
   template<
       typename Function,
-      typename Allocator>
+      typename OtherAllocator>
   void defer(
       Function && f,
-      const Allocator & a) const;
+      const OtherAllocator & a) const;
 
 
 This function is used to ask the thread pool to execute the given function object. The function object will never be executed inside `defer()`. Instead, it will be scheduled to run on the thread pool.
@@ -115129,18 +124634,18 @@ If the current thread belongs to the thread pool, `defer()` will delay schedulin
 
 
 
-[section:dispatch thread_pool::executor_type::dispatch]
+[section:dispatch thread_pool::basic_executor_type::dispatch]
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.dispatch..dispatch..thread_pool::executor_type] 
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.dispatch..dispatch..thread_pool::basic_executor_type] 
 Request the thread pool to invoke the given function object. 
 
 
   template<
       typename Function,
-      typename Allocator>
+      typename OtherAllocator>
   void dispatch(
       Function && f,
-      const Allocator & a) const;
+      const OtherAllocator & a) const;
 
 
 This function is used to ask the thread pool to execute the given function object. If the current thread belongs to the pool, `dispatch()` executes the function before returning. Otherwise, the function will be scheduled to run on the thread pool.
@@ -115168,9 +124673,26 @@ This function is used to ask the thread pool to execute the given function objec
 
 
 
-[section:on_work_finished thread_pool::executor_type::on_work_finished]
+[section:execute thread_pool::basic_executor_type::execute]
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.on_work_finished..on_work_finished..thread_pool::executor_type] 
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.execute..execute..thread_pool::basic_executor_type] 
+Execution function. 
+
+
+  template<
+      typename Function>
+  void execute(
+      Function && f) const;
+
+
+
+[endsect]
+
+
+
+[section:on_work_finished thread_pool::basic_executor_type::on_work_finished]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.on_work_finished..on_work_finished..thread_pool::basic_executor_type] 
 Inform the thread pool that some work is no longer outstanding. 
 
 
@@ -115184,9 +124706,9 @@ This function is used to inform the thread pool that some work has finished. Onc
 
 
 
-[section:on_work_started thread_pool::executor_type::on_work_started]
+[section:on_work_started thread_pool::basic_executor_type::on_work_started]
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.on_work_started..on_work_started..thread_pool::executor_type] 
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.on_work_started..on_work_started..thread_pool::basic_executor_type] 
 Inform the thread pool that it has some outstanding work to do. 
 
 
@@ -115200,15 +124722,15 @@ This function is used to inform the thread pool that some work has begun. This e
 
 
 
-[section:operator_not__eq_ thread_pool::executor_type::operator!=]
+[section:operator_not__eq_ thread_pool::basic_executor_type::operator!=]
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.operator_not__eq_..operator!=..thread_pool::executor_type] 
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.operator_not__eq_..operator!=..thread_pool::basic_executor_type] 
 Compare two executors for inequality. 
 
 
   friend bool operator!=(
-      const executor_type & a,
-      const executor_type & b);
+      const basic_executor_type & a,
+      const basic_executor_type & b);
 
 
 Two executors are equal if they refer to the same underlying thread pool. 
@@ -115223,16 +124745,66 @@ Two executors are equal if they refer to the same underlying thread pool.
 [endsect]
 
 
+[section:operator_eq_ thread_pool::basic_executor_type::operator=]
 
-[section:operator_eq__eq_ thread_pool::executor_type::operator==]
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.operator_eq_..operator=..thread_pool::basic_executor_type] 
+Assignment operator. 
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.operator_eq__eq_..operator==..thread_pool::executor_type] 
+
+  basic_executor_type & ``[link boost_asio.reference.thread_pool__basic_executor_type.operator_eq_.overload1 operator=]``(
+      const basic_executor_type & other);
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.operator_eq_.overload1 more...]]``
+
+
+Move assignment operator. 
+
+
+  basic_executor_type & ``[link boost_asio.reference.thread_pool__basic_executor_type.operator_eq_.overload2 operator=]``(
+      basic_executor_type && other);
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.operator_eq_.overload2 more...]]``
+
+
+[section:overload1 thread_pool::basic_executor_type::operator= (1 of 2 overloads)]
+
+
+Assignment operator. 
+
+
+  basic_executor_type & operator=(
+      const basic_executor_type & other);
+
+
+
+[endsect]
+
+
+
+[section:overload2 thread_pool::basic_executor_type::operator= (2 of 2 overloads)]
+
+
+Move assignment operator. 
+
+
+  basic_executor_type & operator=(
+      basic_executor_type && other);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:operator_eq__eq_ thread_pool::basic_executor_type::operator==]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.operator_eq__eq_..operator==..thread_pool::basic_executor_type] 
 Compare two executors for equality. 
 
 
   friend bool operator==(
-      const executor_type & a,
-      const executor_type & b);
+      const basic_executor_type & a,
+      const basic_executor_type & b);
 
 
 Two executors are equal if they refer to the same underlying thread pool. 
@@ -115248,18 +124820,18 @@ Two executors are equal if they refer to the same underlying thread pool.
 
 
 
-[section:post thread_pool::executor_type::post]
+[section:post thread_pool::basic_executor_type::post]
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.post..post..thread_pool::executor_type] 
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.post..post..thread_pool::basic_executor_type] 
 Request the thread pool to invoke the given function object. 
 
 
   template<
       typename Function,
-      typename Allocator>
+      typename OtherAllocator>
   void post(
       Function && f,
-      const Allocator & a) const;
+      const OtherAllocator & a) const;
 
 
 This function is used to ask the thread pool to execute the given function object. The function object will never be executed inside `post()`. Instead, it will be scheduled to run on the thread pool.
@@ -115286,10 +124858,440 @@ This function is used to ask the thread pool to execute the given function objec
 [endsect]
 
 
+[section:query thread_pool::basic_executor_type::query]
 
-[section:running_in_this_thread thread_pool::executor_type::running_in_this_thread]
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.query..query..thread_pool::basic_executor_type] 
+Query the current value of the `context` property. 
 
-[indexterm2 boost_asio.indexterm.thread_pool__executor_type.running_in_this_thread..running_in_this_thread..thread_pool::executor_type] 
+
+  thread_pool & ``[link boost_asio.reference.thread_pool__basic_executor_type.query.overload1 query]``(
+      execution::context_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query.overload1 more...]]``
+
+
+Query the current value of the `blocking` property. 
+
+
+  constexpr execution::blocking_t ``[link boost_asio.reference.thread_pool__basic_executor_type.query.overload2 query]``(
+      execution::blocking_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query.overload2 more...]]``
+
+
+Query the current value of the `relationship` property. 
+
+
+  constexpr execution::relationship_t ``[link boost_asio.reference.thread_pool__basic_executor_type.query.overload3 query]``(
+      execution::relationship_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query.overload3 more...]]``
+
+
+Query the current value of the `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr Allocator ``[link boost_asio.reference.thread_pool__basic_executor_type.query.overload4 query]``(
+      execution::allocator_t< OtherAllocator > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query.overload4 more...]]``
+
+  constexpr Allocator ``[link boost_asio.reference.thread_pool__basic_executor_type.query.overload5 query]``(
+      execution::allocator_t< void > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query.overload5 more...]]``
+
+
+Query the occupancy (recommended number of work items) for the pool. 
+
+
+  std::size_t ``[link boost_asio.reference.thread_pool__basic_executor_type.query.overload6 query]``(
+      execution::occupancy_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query.overload6 more...]]``
+
+
+[section:overload1 thread_pool::basic_executor_type::query (1 of 6 overloads)]
+
+
+Query the current value of the `context` property. 
+
+
+  thread_pool & query(
+      execution::context_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload2 thread_pool::basic_executor_type::query (2 of 6 overloads)]
+
+
+Query the current value of the `blocking` property. 
+
+
+  constexpr execution::blocking_t query(
+      execution::blocking_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload3 thread_pool::basic_executor_type::query (3 of 6 overloads)]
+
+
+Query the current value of the `relationship` property. 
+
+
+  constexpr execution::relationship_t query(
+      execution::relationship_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload4 thread_pool::basic_executor_type::query (4 of 6 overloads)]
+
+
+Query the current value of the `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr Allocator query(
+      execution::allocator_t< OtherAllocator > ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload5 thread_pool::basic_executor_type::query (5 of 6 overloads)]
+
+
+Query the current value of the `allocator` property. 
+
+
+  constexpr Allocator query(
+      execution::allocator_t< void > ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload6 thread_pool::basic_executor_type::query (6 of 6 overloads)]
+
+
+Query the occupancy (recommended number of work items) for the pool. 
+
+
+  std::size_t query(
+      execution::occupancy_t ) const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+[section:query__static thread_pool::basic_executor_type::query]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.query__static..query..thread_pool::basic_executor_type] 
+Query the current value of the `bulk_guarantee` property. 
+
+
+  static constexpr execution::bulk_guarantee_t ``[link boost_asio.reference.thread_pool__basic_executor_type.query__static.overload1 query]``(
+      execution::bulk_guarantee_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query__static.overload1 more...]]``
+
+
+Query the current value of the `mapping` property. 
+
+
+  static constexpr execution::mapping_t ``[link boost_asio.reference.thread_pool__basic_executor_type.query__static.overload2 query]``(
+      execution::mapping_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query__static.overload2 more...]]``
+
+
+Query the current value of the `outstanding_work` property. 
+
+
+  static constexpr execution::outstanding_work_t ``[link boost_asio.reference.thread_pool__basic_executor_type.query__static.overload3 query]``(
+      execution::outstanding_work_t );
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.query__static.overload3 more...]]``
+
+
+[section:overload1 thread_pool::basic_executor_type::query (1 of 3 overloads)]
+
+
+Query the current value of the `bulk_guarantee` property. 
+
+
+  static constexpr execution::bulk_guarantee_t query(
+      execution::bulk_guarantee_t );
+
+
+
+[endsect]
+
+
+
+[section:overload2 thread_pool::basic_executor_type::query (2 of 3 overloads)]
+
+
+Query the current value of the `mapping` property. 
+
+
+  static constexpr execution::mapping_t query(
+      execution::mapping_t );
+
+
+
+[endsect]
+
+
+
+[section:overload3 thread_pool::basic_executor_type::query (3 of 3 overloads)]
+
+
+Query the current value of the `outstanding_work` property. 
+
+
+  static constexpr execution::outstanding_work_t query(
+      execution::outstanding_work_t );
+
+
+
+[endsect]
+
+
+[endsect]
+
+[section:require thread_pool::basic_executor_type::require]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.require..require..thread_pool::basic_executor_type] 
+Obtain an executor with the `blocking.possibly` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload1 require]``(
+      execution::blocking_t::possibly_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload1 more...]]``
+
+
+Obtain an executor with the `blocking.always` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload2 require]``(
+      execution::blocking_t::always_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload2 more...]]``
+
+
+Obtain an executor with the `blocking.never` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload3 require]``(
+      execution::blocking_t::never_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload3 more...]]``
+
+
+Obtain an executor with the `relationship.fork` property. 
+
+
+  constexpr basic_executor_type ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload4 require]``(
+      execution::relationship_t::fork_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload4 more...]]``
+
+
+Obtain an executor with the `relationship.continuation` property. 
+
+
+  constexpr basic_executor_type ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload5 require]``(
+      execution::relationship_t::continuation_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload5 more...]]``
+
+
+Obtain an executor with the `outstanding_work.tracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload6 require]``(
+      execution::outstanding_work_t::tracked_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload6 more...]]``
+
+
+Obtain an executor with the `outstanding_work.untracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload7 require]``(
+      execution::outstanding_work_t::untracked_t ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload7 more...]]``
+
+
+Obtain an executor with the specified `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr basic_executor_type< OtherAllocator, Bits > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload8 require]``(
+      execution::allocator_t< OtherAllocator > a) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload8 more...]]``
+
+
+Obtain an executor with the default `allocator` property. 
+
+
+  constexpr basic_executor_type< std::allocator< void >, Bits > ``[link boost_asio.reference.thread_pool__basic_executor_type.require.overload9 require]``(
+      execution::allocator_t< void > ) const;
+  ``  [''''&raquo;''' [link boost_asio.reference.thread_pool__basic_executor_type.require.overload9 more...]]``
+
+
+[section:overload1 thread_pool::basic_executor_type::require (1 of 9 overloads)]
+
+
+Obtain an executor with the `blocking.possibly` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::blocking_t::possibly_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload2 thread_pool::basic_executor_type::require (2 of 9 overloads)]
+
+
+Obtain an executor with the `blocking.always` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::blocking_t::always_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload3 thread_pool::basic_executor_type::require (3 of 9 overloads)]
+
+
+Obtain an executor with the `blocking.never` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::blocking_t::never_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload4 thread_pool::basic_executor_type::require (4 of 9 overloads)]
+
+
+Obtain an executor with the `relationship.fork` property. 
+
+
+  constexpr basic_executor_type require(
+      execution::relationship_t::fork_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload5 thread_pool::basic_executor_type::require (5 of 9 overloads)]
+
+
+Obtain an executor with the `relationship.continuation` property. 
+
+
+  constexpr basic_executor_type require(
+      execution::relationship_t::continuation_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload6 thread_pool::basic_executor_type::require (6 of 9 overloads)]
+
+
+Obtain an executor with the `outstanding_work.tracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::outstanding_work_t::tracked_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload7 thread_pool::basic_executor_type::require (7 of 9 overloads)]
+
+
+Obtain an executor with the `outstanding_work.untracked` property. 
+
+
+  constexpr basic_executor_type< Allocator, unspecified > require(
+      execution::outstanding_work_t::untracked_t ) const;
+
+
+
+[endsect]
+
+
+
+[section:overload8 thread_pool::basic_executor_type::require (8 of 9 overloads)]
+
+
+Obtain an executor with the specified `allocator` property. 
+
+
+  template<
+      typename OtherAllocator>
+  constexpr basic_executor_type< OtherAllocator, Bits > require(
+      execution::allocator_t< OtherAllocator > a) const;
+
+
+
+[endsect]
+
+
+
+[section:overload9 thread_pool::basic_executor_type::require (9 of 9 overloads)]
+
+
+Obtain an executor with the default `allocator` property. 
+
+
+  constexpr basic_executor_type< std::allocator< void >, Bits > require(
+      execution::allocator_t< void > ) const;
+
+
+
+[endsect]
+
+
+[endsect]
+
+
+[section:running_in_this_thread thread_pool::basic_executor_type::running_in_this_thread]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type.running_in_this_thread..running_in_this_thread..thread_pool::basic_executor_type] 
 Determine whether the thread pool is running in the current thread. 
 
 
@@ -115299,11 +125301,25 @@ Determine whether the thread pool is running in the current thread.
 
 [heading Return Value]
       
-`true` if the current thread belongs to the pool. Otherwise returns `false`. 
+`true` if the current thread is running the thread pool. Otherwise returns `false`. 
 
 
 
 
+[endsect]
+
+
+
+[section:_basic_executor_type thread_pool::basic_executor_type::~basic_executor_type]
+
+[indexterm2 boost_asio.indexterm.thread_pool__basic_executor_type._basic_executor_type..~basic_executor_type..thread_pool::basic_executor_type] 
+Destructor. 
+
+
+  ~basic_executor_type();
+
+
+
 [endsect]
 
 
@@ -115668,7 +125684,7 @@ A completion token that represents the currently executing coroutine.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   struct use_awaitable_t
 
 
@@ -115696,7 +125712,9 @@ A completion token that represents the currently executing coroutine.
   
   [
     [[link boost_asio.reference.use_awaitable_t.use_awaitable_t [*use_awaitable_t]]]
-    [Default constructor. ]
+    [Default constructor. 
+     [hr]
+     Constructor used to specify file name, line, and function name. ]
   ]
   
 ]
@@ -115739,10 +125757,29 @@ Function helper to adapt an I/O object to use `use_awaitable_t` as its default c
 [endsect]
 
 
-
 [section:use_awaitable_t use_awaitable_t::use_awaitable_t]
 
 [indexterm2 boost_asio.indexterm.use_awaitable_t.use_awaitable_t..use_awaitable_t..use_awaitable_t] 
+Default constructor. 
+
+
+  constexpr ``[link boost_asio.reference.use_awaitable_t.use_awaitable_t.overload1 use_awaitable_t]``();
+  ``  [''''&raquo;''' [link boost_asio.reference.use_awaitable_t.use_awaitable_t.overload1 more...]]``
+
+
+Constructor used to specify file name, line, and function name. 
+
+
+  constexpr ``[link boost_asio.reference.use_awaitable_t.use_awaitable_t.overload2 use_awaitable_t]``(
+      const char * file_name,
+      int line,
+      const char * function_name);
+  ``  [''''&raquo;''' [link boost_asio.reference.use_awaitable_t.use_awaitable_t.overload2 more...]]``
+
+
+[section:overload1 use_awaitable_t::use_awaitable_t (1 of 2 overloads)]
+
+
 Default constructor. 
 
 
@@ -115754,6 +125791,25 @@ Default constructor.
 
 
 
+[section:overload2 use_awaitable_t::use_awaitable_t (2 of 2 overloads)]
+
+
+Constructor used to specify file name, line, and function name. 
+
+
+  constexpr use_awaitable_t(
+      const char * file_name,
+      int line,
+      const char * function_name);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
 [endsect]
 
 [section:use_awaitable_t__executor_with_default use_awaitable_t::executor_with_default]
@@ -115786,7 +125842,9 @@ Adapts an executor to add the `use_awaitable_t` completion token as the default.
 
   [
     [[link boost_asio.reference.use_awaitable_t__executor_with_default.executor_with_default [*executor_with_default]]]
-    [Construct the adapted executor from the inner executor type. ]
+    [Construct the adapted executor from the inner executor type. 
+     [hr]
+     Convert the specified executor to the inner executor type, then use that to construct the adapted executor. ]
   ]
   
 ]
@@ -115831,7 +125889,9 @@ Specify `use_awaitable_t` as the default completion token type.
   
   [
     [[link boost_asio.reference.use_awaitable_t.use_awaitable_t [*use_awaitable_t]]]
-    [Default constructor. ]
+    [Default constructor. 
+     [hr]
+     Constructor used to specify file name, line, and function name. ]
   ]
   
 ]
@@ -115862,10 +125922,31 @@ When used with co\_await, the initiating function (`async_read_some` in the abov
 [endsect]
 
 
-
 [section:executor_with_default use_awaitable_t::executor_with_default::executor_with_default]
 
 [indexterm2 boost_asio.indexterm.use_awaitable_t__executor_with_default.executor_with_default..executor_with_default..use_awaitable_t::executor_with_default] 
+Construct the adapted executor from the inner executor type. 
+
+
+  ``[link boost_asio.reference.use_awaitable_t__executor_with_default.executor_with_default.overload1 executor_with_default]``(
+      const InnerExecutor & ex);
+  ``  [''''&raquo;''' [link boost_asio.reference.use_awaitable_t__executor_with_default.executor_with_default.overload1 more...]]``
+
+
+Convert the specified executor to the inner executor type, then use that to construct the adapted executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 OtherExecutor]``>
+  ``[link boost_asio.reference.use_awaitable_t__executor_with_default.executor_with_default.overload2 executor_with_default]``(
+      const OtherExecutor & ex,
+      typename enable_if< is_convertible< OtherExecutor, InnerExecutor >::value >::type *  = 0);
+  ``  [''''&raquo;''' [link boost_asio.reference.use_awaitable_t__executor_with_default.executor_with_default.overload2 more...]]``
+
+
+[section:overload1 use_awaitable_t::executor_with_default::executor_with_default (1 of 2 overloads)]
+
+
 Construct the adapted executor from the inner executor type. 
 
 
@@ -115878,6 +125959,26 @@ Construct the adapted executor from the inner executor type.
 
 
 
+[section:overload2 use_awaitable_t::executor_with_default::executor_with_default (2 of 2 overloads)]
+
+
+Convert the specified executor to the inner executor type, then use that to construct the adapted executor. 
+
+
+  template<
+      typename ``[link boost_asio.reference.Executor1 OtherExecutor]``>
+  executor_with_default(
+      const OtherExecutor & ex,
+      typename enable_if< is_convertible< OtherExecutor, InnerExecutor >::value >::type *  = 0);
+
+
+
+[endsect]
+
+
+[endsect]
+
+
 [endsect]
 
 
@@ -116144,10 +126245,11 @@ The [link boost_asio.reference.uses_executor `uses_executor`] trait detects whet
   template<
       typename T,
       typename ``[link boost_asio.reference.Executor1 Executor]``>
-  struct uses_executor
+  struct uses_executor :
+    public false_type
 
 
-Meets the BinaryTypeTrait requirements. The Asio library provides a definition that is derived from false\_type. A program may specialize this template to derive from true\_type for a user-defined type T that can be constructed with an executor, where the first argument of a constructor has type [link boost_asio.reference.executor_arg_t `executor_arg_t`] and the second argument is convertible from type Executor. 
+Meets the BinaryTypeTrait requirements. The Asio library provides a definition that is derived from `false_type`. A program may specialize this template to derive from true\_type for a user-defined type T that can be constructed with an executor, where the first argument of a constructor has type [link boost_asio.reference.executor_arg_t `executor_arg_t`] and the second argument is convertible from type Executor. 
 
 [heading Requirements]
 
@@ -116256,7 +126358,7 @@ Provides object-oriented handle functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_object_handle
 
 
@@ -117398,7 +127500,7 @@ Provides Windows handle functionality for objects that support overlapped I/O.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_overlapped_handle
 
 
@@ -118495,7 +128597,7 @@ Provides random-access handle functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_random_access_handle :
     public windows::basic_overlapped_handle< Executor >
 
@@ -120022,7 +130124,7 @@ Provides stream-oriented handle functionality.
 
 
   template<
-      typename ``[link boost_asio.reference.Executor1 Executor]`` = executor>
+      typename ``[link boost_asio.reference.Executor1 Executor]`` = any_io_executor>
   class basic_stream_handle :
     public windows::basic_overlapped_handle< Executor >
 
@@ -121953,7 +132055,7 @@ Construct an [link boost_asio.reference.windows__overlapped_ptr `windows::overla
   explicit ``[link boost_asio.reference.windows__overlapped_ptr.overlapped_ptr.overload3 overlapped_ptr]``(
       const Executor & ex,
       Handler && handler,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.windows__overlapped_ptr.overlapped_ptr.overload3 more...]]``
 
 
@@ -122003,7 +132105,7 @@ Construct an [link boost_asio.reference.windows__overlapped_ptr `windows::overla
   overlapped_ptr(
       const Executor & ex,
       Handler && handler,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -122054,7 +132156,7 @@ Reset to contain the specified handler, freeing any current OVERLAPPED object.
   void ``[link boost_asio.reference.windows__overlapped_ptr.reset.overload3 reset]``(
       const Executor & ex,
       Handler && handler,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
   ``  [''''&raquo;''' [link boost_asio.reference.windows__overlapped_ptr.reset.overload3 more...]]``
 
 
@@ -122104,7 +132206,7 @@ Reset to contain the specified handler, freeing any current OVERLAPPED object.
   void reset(
       const Executor & ex,
       Handler && handler,
-      typename enable_if< is_executor< Executor >::value >::type *  = 0);
+      typename enable_if< execution::is_executor< Executor >::value||is_executor< Executor >::value >::type *  = 0);
 
 
 
@@ -124774,4 +134876,4 @@ The initiating function (async\_read\_some in the above example) suspends the cu
 
 [endsect]
 
-[endsect]
\ No newline at end of file
+[endsect]
diff --git a/doc/reference.xsl b/doc/reference.xsl
index 055f7183..8e8a7ca6 100644
--- a/doc/reference.xsl
+++ b/doc/reference.xsl
@@ -110,7 +110,8 @@
             not(contains(compoundname, 'std_allocator_void')) and
             not(contains(compoundname, 'thread_function')) and
             not(contains(compoundname, 'context_impl')) and
-            not(contains(compoundname, 'initiate_'))">
+            not(contains(compoundname, 'initiate_')) and
+            not(contains(compoundname, '_is_deprecated'))">
           <xsl:call-template name="class"/>
         </xsl:if>
       </xsl:when>
@@ -124,7 +125,8 @@
             not(contains(name, 'std_allocator_void')) and
             not(contains(name, 'thread_function')) and
             not(contains(name, 'io_context_impl')) and
-            not(contains(name, 'initiate_'))">
+            not(contains(name, 'initiate_')) and
+            not(contains(name, '_is_deprecated'))">
           <xsl:call-template name="namespace-memberdef"/>
         </xsl:if>
       </xsl:otherwise>
@@ -133,6 +135,7 @@
 
   <xsl:value-of select="$newline"/>
   <xsl:text>[endsect]</xsl:text>
+  <xsl:value-of select="$newline"/>
 
 </xsl:template>
 
@@ -214,7 +217,11 @@
 
 <xsl:template name="make-id">
   <xsl:param name="name"/>
+  <xsl:param name="static"/>
   <xsl:choose>
+    <xsl:when test="$name='query' and $static='yes'">
+      <xsl:text>query__static</xsl:text>
+    </xsl:when>
     <xsl:when test="contains($name, 'boost::system::')">
       <xsl:call-template name="make-id">
         <xsl:with-param name="name"
@@ -263,6 +270,12 @@
          select="concat(substring-before($name, '&gt;'), '_gt_', substring-after($name, '&gt;'))"/>
       </xsl:call-template>
     </xsl:when>
+    <xsl:when test="contains($name, '&amp;')">
+      <xsl:call-template name="make-id">
+        <xsl:with-param name="name"
+         select="concat(substring-before($name, '&amp;'), '_amp_', substring-after($name, '&amp;'))"/>
+      </xsl:call-template>
+    </xsl:when>
     <xsl:when test="contains($name, '[')">
       <xsl:call-template name="make-id">
         <xsl:with-param name="name"
@@ -774,6 +787,9 @@
   <xsl:value-of select="$newline"/>
   <xsl:text>['Convenience header: ]</xsl:text>
   <xsl:choose>
+    <xsl:when test="contains($file, 'boost/asio/execution')">
+      <xsl:text>[^boost/asio/execution.hpp]</xsl:text>
+    </xsl:when>
     <xsl:when test="contains($file, 'boost/asio/ssl')">
       <xsl:text>[^boost/asio/ssl.hpp]</xsl:text>
     </xsl:when>
@@ -909,6 +925,7 @@
   <xsl:variable name="id">
     <xsl:call-template name="make-id">
       <xsl:with-param name="name" select="$name"/>
+      <xsl:with-param name="static" select="@static"/>
     </xsl:call-template>
   </xsl:variable>
   <xsl:variable name="doxygen-id">
@@ -958,6 +975,7 @@
   <xsl:variable name="id">
     <xsl:call-template name="make-id">
       <xsl:with-param name="name" select="$name"/>
+      <xsl:with-param name="static" select="@static"/>
     </xsl:call-template>
   </xsl:variable>
   <xsl:variable name="doxygen-id">
@@ -1008,6 +1026,7 @@
   <xsl:variable name="id">
     <xsl:call-template name="make-id">
       <xsl:with-param name="name" select="$name"/>
+      <xsl:with-param name="static" select="@static"/>
     </xsl:call-template>
   </xsl:variable>
   <xsl:variable name="doxygen-id">
@@ -1219,6 +1238,7 @@
   <xsl:variable name="id">
     <xsl:call-template name="make-id">
       <xsl:with-param name="name" select="$name"/>
+      <xsl:with-param name="static" select="@static"/>
     </xsl:call-template>
   </xsl:variable>
   <xsl:variable name="doxygen-id">
@@ -1362,7 +1382,7 @@
   </xsl:text>typedef <xsl:value-of select="type"/><xsl:text> </xsl:text><xsl:value-of select="name"/>;<xsl:text>
 
 </xsl:text>
-<xsl:if test="count(type/ref) &gt; 0 and not(contains(type, '*'))">
+<xsl:if test="count(type/ref) &gt; 0 and not(contains(type, '*')) and not(contains(name, 'polymorphic_query_result_type'))">
   <xsl:variable name="class-refid">
     <xsl:choose>
       <xsl:when test="type='basic_address_iterator&lt; address_v4 &gt;'">
@@ -1407,6 +1427,14 @@
 
 
 <xsl:template name="variable">
+<xsl:if test="contains(name, 'is_applicable_property_v')">
+<xsl:text>
+  template &lt;typename T&gt;</xsl:text>
+</xsl:if>
+<xsl:if test="contains(name, 'context_as')">
+<xsl:text>
+  template &lt;typename U&gt;</xsl:text>
+</xsl:if>
 <xsl:text>
   </xsl:text><xsl:if test="@static='yes'">static </xsl:if><xsl:value-of
  select="type"/><xsl:text> </xsl:text><xsl:value-of select="name"/>
@@ -1492,6 +1520,15 @@
         <xsl:when test="declname = 'Args'">
           <xsl:value-of select="declname"/>
         </xsl:when>
+        <xsl:when test="declname = 'AwaitableExecutor'">
+          <xsl:value-of select="concat('``[link boost_asio.reference.Executor1 ', declname, ']``')"/>
+        </xsl:when>
+        <xsl:when test="declname = 'Bits'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
+        <xsl:when test="declname = 'Blocking'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
         <xsl:when test="declname = 'BufferSequence'">
           <xsl:value-of select="declname"/>
         </xsl:when>
@@ -1579,6 +1616,12 @@
         <xsl:when test="declname = 'OtherHandler'">
           <xsl:value-of select="declname"/>
         </xsl:when>
+        <xsl:when test="declname = 'OtherSupportableProperties'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
+        <xsl:when test="declname = 'OutstandingWork'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
         <xsl:when test="declname = 'PasswordCallback'">
           <xsl:value-of select="declname"/>
         </xsl:when>
@@ -1591,6 +1634,12 @@
         <xsl:when test="declname = 'PointerToPodType'">
           <xsl:value-of select="declname"/>
         </xsl:when>
+        <xsl:when test="declname = 'Properties'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
+        <xsl:when test="declname = 'Property'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
         <xsl:when test="declname = 'Protocol1'">
           <xsl:value-of select="concat('``[link boost_asio.reference.Protocol ', declname, ']``')"/>
         </xsl:when>
@@ -1600,6 +1649,9 @@
         <xsl:when test="declname = 'RawSocketService1'">
           <xsl:value-of select="concat('``[link boost_asio.reference.RawSocketService ', declname, ']``')"/>
         </xsl:when>
+        <xsl:when test="declname = 'Relationship'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
         <xsl:when test="declname = 'Rep'">
           <xsl:value-of select="declname"/>
         </xsl:when>
@@ -1624,6 +1676,9 @@
         <xsl:when test="declname = 'StreamSocketService1'">
           <xsl:value-of select="concat('``[link boost_asio.reference.StreamSocketService ', declname, ']``')"/>
         </xsl:when>
+        <xsl:when test="declname = 'SupportableProperties'">
+          <xsl:value-of select="declname"/>
+        </xsl:when>
         <xsl:when test="declname = 'T'">
           <xsl:value-of select="declname"/>
         </xsl:when>
diff --git a/doc/requirements/Executor.qbk b/doc/requirements/Executor.qbk
index d2bf64c0..e1ff1214 100644
--- a/doc/requirements/Executor.qbk
+++ b/doc/requirements/Executor.qbk
@@ -7,6 +7,78 @@
 
 [section:Executor1 Executor requirements]
 
+[heading Standard executors]
+
+An executor is defined by the following concept:
+
+    template<class E>
+      concept executor =
+        invocable<remove_cvref_t<F>&>
+          && constructible_from<remove_cvref_t<F>, F>
+          && move_constructible<remove_cvref_t<F>>
+          && copy_constructible<E>
+          && is_nothrow_copy_constructible_v<E>
+          && equality_comparable<E>
+          &&
+          requires(const E& e, invocable_archetype f)
+          {
+            execution::execute(e, static_cast<invocable_archetype&&>(f));
+          };
+
+Neither an executor's equality comparison nor `swap` operation shall exit via
+an exception.
+
+None of an executor type's copy constructor, destructor, equality comparison,
+`swap` function, `execute` function, or associated `query` functions shall
+introduce data races as a result of concurrent invocations of those functions
+from different threads.
+
+For any two (possibly const) values `x1` and `x2` of some executor type `X`,
+`x1 == x2` shall return `true` only if `boost::asio::query(x1,p) == boost::asio::query(x2,p)`
+for every property `p` where both `boost::asio::query(x1,p)` and `boost::asio::query(x2,p)`
+are well-formed and result in a non-void type that is `equality_comparable`
+(C++Std [equalitycomparable]). [inline_note The above requirements imply that `x1
+== x2` returns `true` if `x1` and `x2` can be interchanged with identical
+effects. An executor may conceptually contain additional properties which are
+not exposed by a named property type that can be observed via `boost::asio::query`; in
+this case, it is up to the concrete executor implementation to decide if these
+properties affect equality. Returning `false` does not necessarily imply that
+the effects are not identical.]
+
+An executor type's destructor shall not block pending completion of the
+submitted function objects. [inline_note The ability to wait for completion of
+submitted function objects may be provided by the associated execution
+context.]
+
+In addition to the above requirements, types `E` and `F` model `executor_of`
+only if they satisfy the requirements of the Table below.
+
+Let:
+
+* `e` denotes a (possibly const) executor object of type `E`,
+
+* `cf` denotes the function object `DECAY_COPY(std::forward<F>(f))`
+
+* `f` denotes a function of type `F&&` invocable as `cf()` and where
+  `decay_t<F>` models `move_constructible`.
+
+The expression `execution::execute(e, f)`:
+
+* Evaluates `DECAY_COPY(std::forward<F>(f))` on the calling thread to create
+  `cf` that will be invoked at most once by an execution agent.
+
+* May block pending completion of this invocation. Synchronizes with
+  [intro.multithread] the invocation of `f`.
+
+* Shall not propagate any exception thrown by the function object or any other
+  function submitted to the executor.
+
+[inline_note The treatment of exceptions thrown by one-way submitted functions
+is implementation-defined. The forward progress guarantee of the associated
+execution agent(s) is implementation-defined.]
+
+[heading Networking TS-style executors]
+
 The library describes a standard set of requirements for ['executors]. A type
 meeting the `Executor` requirements embodies a set of rules for determining how
 submitted function objects are to be executed.
diff --git a/doc/tutorial.qbk b/doc/tutorial.qbk
index f814b2c4..ec74c662 100644
--- a/doc/tutorial.qbk
+++ b/doc/tutorial.qbk
@@ -1536,6 +1536,8 @@ We use an [link boost_asio.reference.ip__udp.resolver ip::udp::resolver] object
 
 The [link boost_asio.reference.ip__basic_resolver.resolve ip::udp::resolver::resolve()] function is guaranteed to return at least one endpoint in the list if it does not fail. This means it is safe to dereference the return value directly.
 
+Since UDP is datagram-oriented, we will not be using a stream socket. Create an [link boost_asio.reference.ip__udp.socket ip::udp::socket] and initiate contact with the remote endpoint.
+
 
 
   ``''''''``    udp::socket socket(io_context);
@@ -1544,26 +1546,32 @@ The [link boost_asio.reference.ip__basic_resolver.resolve ip::udp::resolver::res
   ``''''''``    boost::array<char, 1> send_buf  = {{ 0 }};
   ``''''''``    socket.send_to(boost::asio::buffer(send_buf), receiver_endpoint);
 
-  ``''''''``    boost::array<char, 128> recv_buf;
-  ``''''''``    udp::endpoint sender_endpoint;
-
-
-
-Since UDP is datagram-oriented, we will not be using a stream socket. Create an [link boost_asio.reference.ip__udp.socket ip::udp::socket] and initiate contact with the remote endpoint.
-
-
-
 
 
 Now we need to be ready to accept whatever the server sends back to us. The endpoint on our side that receives the server's response will be initialised by [link boost_asio.reference.basic_datagram_socket.receive_from ip::udp::socket::receive_from()].
 
 
 
+  ``''''''``    boost::array<char, 128> recv_buf;
+  ``''''''``    udp::endpoint sender_endpoint;
+  ``''''''``    size_t len = socket.receive_from(
+  ``''''''``        boost::asio::buffer(recv_buf), sender_endpoint);
+
+  ``''''''``    std::cout.write(recv_buf.data(), len);
+  ``''''''``  }
+
 
 
 Finally, handle any exceptions that may have been thrown.
 
 
+  ``''''''``  catch (std::exception& e)
+  ``''''''``  {
+  ``''''''``    std::cerr << e.what() << std::endl;
+  ``''''''``  }
+
+  ``''''''``  return 0;
+  ``''''''``}
 
 See the [link boost_asio.tutorial.tutdaytime4.src full source listing]
 
@@ -2378,4 +2386,4 @@ Return to [link boost_asio.tutorial.tutdaytime7 Daytime.7 - A combined TCP/UDP a
 [endsect]
 
 
-[endsect]
\ No newline at end of file
+[endsect]
diff --git a/doc/tutorial.xsl b/doc/tutorial.xsl
index 232de794..6dd9a745 100644
--- a/doc/tutorial.xsl
+++ b/doc/tutorial.xsl
@@ -66,6 +66,7 @@
 
   <xsl:value-of select="$newline"/>
   <xsl:text>[endsect]</xsl:text>
+  <xsl:value-of select="$newline"/>
 
 </xsl:template>
 
@@ -121,6 +122,12 @@
          select="concat(substring-before($name, '&gt;'), '_gt_', substring-after($name, '&gt;'))"/>
       </xsl:call-template>
     </xsl:when>
+    <xsl:when test="contains($name, '&amp;')">
+      <xsl:call-template name="make-id">
+        <xsl:with-param name="name"
+         select="concat(substring-before($name, '&amp;'), '_amp_', substring-after($name, '&amp;'))"/>
+      </xsl:call-template>
+    </xsl:when>
     <xsl:when test="contains($name, '+')">
       <xsl:call-template name="make-id">
         <xsl:with-param name="name"
diff --git a/example/cpp03/http/server2/io_context_pool.cpp b/example/cpp03/http/server2/io_context_pool.cpp
index 427c2260..ef63bcc6 100644
--- a/example/cpp03/http/server2/io_context_pool.cpp
+++ b/example/cpp03/http/server2/io_context_pool.cpp
@@ -29,7 +29,8 @@ io_context_pool::io_context_pool(std::size_t pool_size)
   {
     io_context_ptr io_context(new boost::asio::io_context);
     io_contexts_.push_back(io_context);
-    work_.push_back(boost::asio::make_work_guard(*io_context));
+    work_.push_back(boost::asio::require(io_context->get_executor(),
+          boost::asio::execution::outstanding_work.tracked));
   }
 }
 
diff --git a/example/cpp03/http/server2/io_context_pool.hpp b/example/cpp03/http/server2/io_context_pool.hpp
index 86bd5b45..6a046730 100644
--- a/example/cpp03/http/server2/io_context_pool.hpp
+++ b/example/cpp03/http/server2/io_context_pool.hpp
@@ -39,14 +39,12 @@ public:
 
 private:
   typedef boost::shared_ptr<boost::asio::io_context> io_context_ptr;
-  typedef boost::asio::executor_work_guard<
-    boost::asio::io_context::executor_type> io_context_work;
 
   /// The pool of io_contexts.
   std::vector<io_context_ptr> io_contexts_;
 
-  /// The work that keeps the io_contexts running.
-  std::list<io_context_work> work_;
+  /// The work-tracking executors that keep the io_contexts running.
+  std::list<boost::asio::any_io_executor> work_;
 
   /// The next io_context to use for a connection.
   std::size_t next_io_context_;
diff --git a/example/cpp03/nonblocking/third_party_lib.cpp b/example/cpp03/nonblocking/third_party_lib.cpp
index 86b11c6d..30de7dbc 100644
--- a/example/cpp03/nonblocking/third_party_lib.cpp
+++ b/example/cpp03/nonblocking/third_party_lib.cpp
@@ -83,7 +83,7 @@ class connection
 public:
   typedef boost::shared_ptr<connection> pointer;
 
-  static pointer create(const boost::asio::executor& ex)
+  static pointer create(const boost::asio::any_io_executor& ex)
   {
     return pointer(new connection(ex));
   }
@@ -102,7 +102,7 @@ public:
   }
 
 private:
-  connection(const boost::asio::executor& ex)
+  connection(const boost::asio::any_io_executor& ex)
     : socket_(ex),
       session_impl_(socket_),
       read_in_progress_(false),
diff --git a/example/cpp03/services/basic_logger.hpp b/example/cpp03/services/basic_logger.hpp
index d7cc4257..bf865f2e 100644
--- a/example/cpp03/services/basic_logger.hpp
+++ b/example/cpp03/services/basic_logger.hpp
@@ -52,12 +52,6 @@ public:
     service_.destroy(impl_);
   }
 
-  /// Get the io_context associated with the object.
-  boost::asio::io_context& get_io_context()
-  {
-    return service_.get_io_context();
-  }
-
   /// Set the output file for all logger instances.
   void use_file(const std::string& file)
   {
diff --git a/example/cpp03/services/daytime_client.cpp b/example/cpp03/services/daytime_client.cpp
index 59a0a626..f792d57c 100644
--- a/example/cpp03/services/daytime_client.cpp
+++ b/example/cpp03/services/daytime_client.cpp
@@ -30,7 +30,9 @@ void read_handler(const boost::system::error_code& e,
   }
   else
   {
-    services::logger logger(s->get_executor().context(), "read_handler");
+    boost::asio::execution_context& context = boost::asio::query(
+        s->get_executor(), boost::asio::execution::context);
+    services::logger logger(context, "read_handler");
 
     std::string msg = "Read error: ";
     msg += e.message();
@@ -40,7 +42,9 @@ void read_handler(const boost::system::error_code& e,
 
 void connect_handler(const boost::system::error_code& e, tcp::socket* s)
 {
-  services::logger logger(s->get_executor().context(), "connect_handler");
+  boost::asio::execution_context& context = boost::asio::query(
+      s->get_executor(), boost::asio::execution::context);
+  services::logger logger(context, "connect_handler");
 
   if (!e)
   {
diff --git a/example/cpp03/services/logger_service.hpp b/example/cpp03/services/logger_service.hpp
index 4f439c5e..4db34efc 100644
--- a/example/cpp03/services/logger_service.hpp
+++ b/example/cpp03/services/logger_service.hpp
@@ -45,7 +45,8 @@ public:
   logger_service(boost::asio::execution_context& context)
     : boost::asio::execution_context::service(context),
       work_io_context_(),
-      work_(boost::asio::make_work_guard(work_io_context_)),
+      work_(boost::asio::require(work_io_context_.get_executor(),
+            boost::asio::execution::outstanding_work.tracked)),
       work_thread_(new boost::thread(
             boost::bind(&boost::asio::io_context::run, &work_io_context_)))
   {
@@ -56,7 +57,7 @@ public:
   {
     /// Indicate that we have finished with the private io_context. Its
     /// io_context::run() function will exit once all other work has completed.
-    work_.reset();
+    work_ = boost::asio::any_io_executor();
     if (work_thread_)
       work_thread_->join();
   }
@@ -128,11 +129,10 @@ private:
   /// Private io_context used for performing logging operations.
   boost::asio::io_context work_io_context_;
 
-  /// Work for the private io_context to perform. If we do not give the
-  /// io_context some work to do then the io_context::run() function will exit
-  /// immediately.
-  boost::asio::executor_work_guard<
-      boost::asio::io_context::executor_type> work_;
+  /// A work-tracking executor giving work for the private io_context to
+  /// perform. If we do not give the io_context some work to do then the
+  /// io_context::run() function will exit immediately.
+  boost::asio::any_io_executor work_;
 
   /// Thread used for running the work io_context's run loop.
   boost::scoped_ptr<boost::thread> work_thread_;
diff --git a/example/cpp03/timeouts/blocking_token_tcp_client.cpp b/example/cpp03/timeouts/blocking_token_tcp_client.cpp
index effb491c..d415bbfa 100644
--- a/example/cpp03/timeouts/blocking_token_tcp_client.cpp
+++ b/example/cpp03/timeouts/blocking_token_tcp_client.cpp
@@ -98,7 +98,8 @@ public:
   // use this function to run the io_context until the operation is complete.
   return_type get()
   {
-    boost::asio::io_context& io_context = socket_.get_executor().context();
+    boost::asio::io_context& io_context = boost::asio::query(
+        socket_.get_executor(), boost::asio::execution::context);
 
     // Restart the io_context, as it may have been left in the "stopped" state
     // by a previous operation.
diff --git a/example/cpp03/tutorial/daytime_dox.txt b/example/cpp03/tutorial/daytime_dox.txt
index 5ec49c67..ea2d8ca2 100644
--- a/example/cpp03/tutorial/daytime_dox.txt
+++ b/example/cpp03/tutorial/daytime_dox.txt
@@ -277,8 +277,6 @@ The boost::asio::ip::udp::resolver::resolve() function is guaranteed to return a
 least one endpoint in the list if it does not fail. This means it is safe to
 dereference the return value directly.
 
-\until udp::endpoint
-
 Since UDP is datagram-oriented, we will not be using a stream socket. Create an
 boost::asio::ip::udp::socket and initiate contact with the remote endpoint.
 
diff --git a/example/cpp11/executors/actor.cpp b/example/cpp11/executors/actor.cpp
index 2e3311d4..81dc0584 100644
--- a/example/cpp11/executors/actor.cpp
+++ b/example/cpp11/executors/actor.cpp
@@ -1,5 +1,5 @@
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/defer.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/asio/system_executor.hpp>
@@ -10,8 +10,8 @@
 #include <typeinfo>
 #include <vector>
 
+using boost::asio::any_io_executor;
 using boost::asio::defer;
-using boost::asio::executor;
 using boost::asio::post;
 using boost::asio::strand;
 using boost::asio::system_executor;
@@ -106,7 +106,7 @@ public:
 
 protected:
   // Construct the actor to use the specified executor for all message handlers.
-  actor(executor e)
+  actor(any_io_executor e)
     : executor_(std::move(e))
   {
   }
@@ -124,7 +124,7 @@ protected:
   template <class Actor, class Message>
   void deregister_handler(void (Actor::* mf)(Message, actor_address))
   {
-    const std::type_info& id = typeid(message_handler<Message>);
+    const std::type_info& id = typeid(Message);
     for (auto iter = handlers_.begin(); iter != handlers_.end(); ++iter)
     {
       if ((*iter)->message_id() == id)
@@ -171,7 +171,7 @@ private:
   // All messages associated with a single actor object should be processed
   // non-concurrently. We use a strand to ensure non-concurrent execution even
   // if the underlying executor may use multiple threads.
-  strand<executor> executor_;
+  strand<any_io_executor> executor_;
 
   std::vector<std::shared_ptr<message_handler_base>> handlers_;
 };
@@ -221,7 +221,7 @@ using boost::asio::thread_pool;
 class member : public actor
 {
 public:
-  explicit member(executor e)
+  explicit member(any_io_executor e)
     : actor(std::move(e))
   {
     register_handler(&member::init_handler);
diff --git a/example/cpp11/executors/bank_account_1.cpp b/example/cpp11/executors/bank_account_1.cpp
index 35b659be..1e5d7304 100644
--- a/example/cpp11/executors/bank_account_1.cpp
+++ b/example/cpp11/executors/bank_account_1.cpp
@@ -1,9 +1,9 @@
-#include <boost/asio/post.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 
-using boost::asio::post;
-using boost::asio::thread_pool;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // Traditional active object pattern.
 // Member functions do not block.
@@ -11,37 +11,43 @@ using boost::asio::thread_pool;
 class bank_account
 {
   int balance_ = 0;
-  mutable thread_pool pool_{1};
+  mutable static_thread_pool pool_{1};
 
 public:
   void deposit(int amount)
   {
-    post(pool_, [=]
-      {
-        balance_ += amount;
-      });
+    execution::execute(
+        pool_.executor(),
+        [this, amount]
+        {
+          balance_ += amount;
+        });
   }
 
   void withdraw(int amount)
   {
-    post(pool_, [=]
-      {
-        if (balance_ >= amount)
-          balance_ -= amount;
-      });
+    execution::execute(
+        pool_.executor(),
+        [this, amount]
+        {
+          if (balance_ >= amount)
+            balance_ -= amount;
+        });
   }
 
   void print_balance() const
   {
-    post(pool_, [=]
-      {
-        std::cout << "balance = " << balance_ << "\n";
-      });
+    execution::execute(
+        pool_.executor(),
+        [this]
+        {
+          std::cout << "balance = " << balance_ << "\n";
+        });
   }
 
   ~bank_account()
   {
-    pool_.join();
+    pool_.wait();
   }
 };
 
diff --git a/example/cpp11/executors/bank_account_2.cpp b/example/cpp11/executors/bank_account_2.cpp
index aebff764..b012d2fb 100644
--- a/example/cpp11/executors/bank_account_2.cpp
+++ b/example/cpp11/executors/bank_account_2.cpp
@@ -1,11 +1,9 @@
-#include <boost/asio/post.hpp>
-#include <boost/asio/thread_pool.hpp>
-#include <boost/asio/use_future.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 
-using boost::asio::post;
-using boost::asio::thread_pool;
-using boost::asio::use_future;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // Traditional active object pattern.
 // Member functions block until operation is finished.
@@ -13,35 +11,43 @@ using boost::asio::use_future;
 class bank_account
 {
   int balance_ = 0;
-  mutable thread_pool pool_{1};
+  mutable static_thread_pool pool_{1};
 
 public:
   void deposit(int amount)
   {
-    post(pool_,
-      use_future([=]
+    execution::execute(
+        boost::asio::require(pool_.executor(),
+          execution::blocking.always),
+        [this, amount]
         {
           balance_ += amount;
-        })).get();
+        });
   }
 
   void withdraw(int amount)
   {
-    post(pool_,
-      use_future([=]
+    execution::execute(
+        boost::asio::require(pool_.executor(),
+          execution::blocking.always),
+        [this, amount]
         {
           if (balance_ >= amount)
             balance_ -= amount;
-        })).get();
+        });
   }
 
   int balance() const
   {
-    return post(pool_,
-      use_future([=]
+    int result = 0;
+    execution::execute(
+        boost::asio::require(pool_.executor(),
+          execution::blocking.always),
+        [this, &result]
         {
-          return balance_;
-        })).get();
+          result = balance_;
+        });
+    return result;
   }
 };
 
diff --git a/example/cpp11/executors/fork_join.cpp b/example/cpp11/executors/fork_join.cpp
index 98926d53..24a338e8 100644
--- a/example/cpp11/executors/fork_join.cpp
+++ b/example/cpp11/executors/fork_join.cpp
@@ -1,6 +1,6 @@
-#include <boost/asio/dispatch.hpp>
-#include <boost/asio/execution_context.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
+#include <algorithm>
 #include <condition_variable>
 #include <memory>
 #include <mutex>
@@ -8,14 +8,13 @@
 #include <thread>
 #include <numeric>
 
-using boost::asio::dispatch;
-using boost::asio::execution_context;
-using boost::asio::thread_pool;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // A fixed-size thread pool used to implement fork/join semantics. Functions
 // are scheduled using a simple FIFO queue. Implementing work stealing, or
 // using a queue based on atomic operations, are left as tasks for the reader.
-class fork_join_pool : public execution_context
+class fork_join_pool
 {
 public:
   // The constructor starts a thread pool with the specified number of threads.
@@ -23,7 +22,7 @@ public:
   // Additional threads may temporarily be added to the pool if they join a
   // fork_executor.
   explicit fork_join_pool(
-      std::size_t thread_count = std::thread::hardware_concurrency() * 2)
+      std::size_t thread_count = std::max(std::thread::hardware_concurrency(), 1u) * 2)
     : use_count_(1),
       threads_(thread_count)
   {
@@ -33,7 +32,9 @@ public:
       // it is time to shut down, i.e. the use count is zero.
       for (thread_count_ = 0; thread_count_ < thread_count; ++thread_count_)
       {
-        dispatch(threads_, [&]
+        execution::execute(
+            threads_.executor(),
+            [this]
             {
               std::unique_lock<std::mutex> lock(mutex_);
               while (use_count_ > 0)
@@ -45,7 +46,7 @@ public:
     catch (...)
     {
       stop_threads();
-      threads_.join();
+      threads_.wait();
       throw;
     }
   }
@@ -54,7 +55,7 @@ public:
   ~fork_join_pool()
   {
     stop_threads();
-    threads_.join();
+    threads_.wait();
   }
 
 private:
@@ -118,7 +119,7 @@ private:
 
   // Dispatch a function, executing it immediately if the queue is already
   // loaded. Otherwise adds the function to the queue and wakes a thread.
-  void do_dispatch(std::shared_ptr<function_base> p,
+  void do_execute(std::shared_ptr<function_base> p,
       const std::shared_ptr<std::size_t>& work_count)
   {
     std::unique_lock<std::mutex> lock(mutex_);
@@ -136,16 +137,6 @@ private:
     }
   }
 
-  // Add a function to the queue and wake a thread.
-  void do_post(std::shared_ptr<function_base> p,
-      const std::shared_ptr<std::size_t>& work_count)
-  {
-    std::lock_guard<std::mutex> lock(mutex_);
-    queue_.push(p);
-    do_work_started(work_count);
-    condition_.notify_one();
-  }
-
   // Ask all threads to shut down.
   void stop_threads()
   {
@@ -159,7 +150,7 @@ private:
   std::queue<std::shared_ptr<function_base>> queue_;
   std::size_t use_count_;
   std::size_t thread_count_;
-  thread_pool threads_;
+  static_thread_pool threads_;
 };
 
 // A class that satisfies the Executor requirements. Every function or piece of
@@ -173,45 +164,16 @@ public:
   {
   }
 
-  fork_join_pool& context() const noexcept
+  fork_join_pool& query(execution::context_t) const noexcept
   {
     return context_;
   }
 
-  void on_work_started() const noexcept
+  template <class Func>
+  void execute(Func f) const
   {
-    std::lock_guard<std::mutex> lock(context_.mutex_);
-    context_.do_work_started(work_count_);
-  }
-
-  void on_work_finished() const noexcept
-  {
-    std::lock_guard<std::mutex> lock(context_.mutex_);
-    context_.do_work_finished(work_count_);
-  }
-
-  template <class Func, class Alloc>
-  void dispatch(Func&& f, const Alloc& a) const
-  {
-    auto p(std::allocate_shared<function<Func>>(
-          typename std::allocator_traits<Alloc>::template rebind_alloc<char>(a),
-          std::move(f), work_count_));
-    context_.do_dispatch(p, work_count_);
-  }
-
-  template <class Func, class Alloc>
-  void post(Func f, const Alloc& a) const
-  {
-    auto p(std::allocate_shared<function<Func>>(
-          typename std::allocator_traits<Alloc>::template rebind_alloc<char>(a),
-          std::move(f), work_count_));
-    context_.do_post(p, work_count_);
-  }
-
-  template <class Func, class Alloc>
-  void defer(Func&& f, const Alloc& a) const
-  {
-    post(std::forward<Func>(f), a);
+    auto p(std::make_shared<function<Func>>(std::move(f), work_count_));
+    context_.do_execute(p, work_count_);
   }
 
   friend bool operator==(const fork_executor& a,
@@ -290,8 +252,8 @@ void fork_join_sort(Iterator begin, Iterator end)
     {
       fork_executor fork(pool);
       join_guard join(fork);
-      dispatch(fork, [=]{ fork_join_sort(begin, begin + n / 2); });
-      dispatch(fork, [=]{ fork_join_sort(begin + n / 2, end); });
+      execution::execute(fork, [=]{ fork_join_sort(begin, begin + n / 2); });
+      execution::execute(fork, [=]{ fork_join_sort(begin + n / 2, end); });
     }
     std::inplace_merge(begin, begin + n / 2, end);
   }
diff --git a/example/cpp11/executors/pipeline.cpp b/example/cpp11/executors/pipeline.cpp
index 9c2a778f..2c23dec7 100644
--- a/example/cpp11/executors/pipeline.cpp
+++ b/example/cpp11/executors/pipeline.cpp
@@ -20,9 +20,10 @@ using boost::asio::post;
 using boost::asio::system_executor;
 using boost::asio::use_future;
 using boost::asio::use_service;
+namespace execution = boost::asio::execution;
 
 // An executor that launches a new thread for each function submitted to it.
-// This class satisfies the Executor requirements.
+// This class satisfies the executor requirements.
 class thread_executor
 {
 private:
@@ -55,40 +56,28 @@ private:
   };
 
 public:
-  execution_context& context() const noexcept
+  execution_context& query(execution::context_t) const
   {
-    return system_executor().context();
+    return boost::asio::query(system_executor(), execution::context);
   }
 
-  void on_work_started() const noexcept
+  execution::blocking_t query(execution::blocking_t) const
   {
-    // This executor doesn't count work.
+    return execution::blocking.never;
   }
 
-  void on_work_finished() const noexcept
+  thread_executor require(execution::blocking_t::never_t) const
   {
-    // This executor doesn't count work.
+    return *this;
   }
 
-  template <class Func, class Alloc>
-  void dispatch(Func&& f, const Alloc& a) const
+  template <class Func>
+  void execute(Func f) const
   {
-    post(std::forward<Func>(f), a);
-  }
-
-  template <class Func, class Alloc>
-  void post(Func f, const Alloc&) const
-  {
-    thread_bag& bag = use_service<thread_bag>(context());
+    thread_bag& bag = use_service<thread_bag>(query(execution::context));
     bag.add_thread(std::thread(std::move(f)));
   }
 
-  template <class Func, class Alloc>
-  void defer(Func&& f, const Alloc& a) const
-  {
-    post(std::forward<Func>(f), a);
-  }
-
   friend bool operator==(const thread_executor&,
       const thread_executor&) noexcept
   {
@@ -292,7 +281,7 @@ void writer(queue_back<std::string> in)
 
 int main()
 {
-  thread_pool pool;
+  thread_pool pool(1);
 
   auto f = pipeline(reader, filter, bind_executor(pool, upper), writer);
   f.wait();
diff --git a/example/cpp11/executors/priority_scheduler.cpp b/example/cpp11/executors/priority_scheduler.cpp
index 7c9bc80d..c73861bf 100644
--- a/example/cpp11/executors/priority_scheduler.cpp
+++ b/example/cpp11/executors/priority_scheduler.cpp
@@ -8,6 +8,7 @@
 
 using boost::asio::dispatch;
 using boost::asio::execution_context;
+namespace execution = boost::asio::execution;
 
 class priority_scheduler : public execution_context
 {
@@ -21,47 +22,20 @@ public:
     {
     }
 
-    priority_scheduler& context() const noexcept
+    priority_scheduler& query(execution::context_t) const noexcept
     {
       return context_;
     }
 
-    void on_work_started() const noexcept
+    template <class Func>
+    void execute(Func f) const
     {
-      // This executor doesn't count work. Instead, the scheduler simply runs
-      // until explicitly stopped.
-    }
-
-    void on_work_finished() const noexcept
-    {
-      // This executor doesn't count work. Instead, the scheduler simply runs
-      // until explicitly stopped.
-    }
-
-    template <class Func, class Alloc>
-    void dispatch(Func&& f, const Alloc& a) const
-    {
-      post(std::forward<Func>(f), a);
-    }
-
-    template <class Func, class Alloc>
-    void post(Func f, const Alloc& a) const
-    {
-      auto p(std::allocate_shared<item<Func>>(
-            typename std::allocator_traits<
-              Alloc>::template rebind_alloc<char>(a),
-            priority_, std::move(f)));
+      auto p(std::make_shared<item<Func>>(priority_, std::move(f)));
       std::lock_guard<std::mutex> lock(context_.mutex_);
       context_.queue_.push(p);
       context_.condition_.notify_one();
     }
 
-    template <class Func, class Alloc>
-    void defer(Func&& f, const Alloc& a) const
-    {
-      post(std::forward<Func>(f), a);
-    }
-
     friend bool operator==(const executor_type& a,
         const executor_type& b) noexcept
     {
diff --git a/example/cpp11/futures/daytime_client.cpp b/example/cpp11/futures/daytime_client.cpp
index 7f787ed0..282993e6 100644
--- a/example/cpp11/futures/daytime_client.cpp
+++ b/example/cpp11/futures/daytime_client.cpp
@@ -77,7 +77,8 @@ int main(int argc, char* argv[])
     // We run the io_context off in its own thread so that it operates
     // completely asynchronously with respect to the rest of the program.
     boost::asio::io_context io_context;
-    auto work = boost::asio::make_work_guard(io_context);
+    auto work = boost::asio::require(io_context.get_executor(),
+        boost::asio::execution::outstanding_work.tracked);
     std::thread thread([&io_context](){ io_context.run(); });
 
     get_daytime(io_context, argv[1]);
diff --git a/example/cpp11/handler_tracking/async_tcp_echo_server.cpp b/example/cpp11/handler_tracking/async_tcp_echo_server.cpp
index f0c674e1..57f1ca6f 100644
--- a/example/cpp11/handler_tracking/async_tcp_echo_server.cpp
+++ b/example/cpp11/handler_tracking/async_tcp_echo_server.cpp
@@ -16,6 +16,13 @@
 
 using boost::asio::ip::tcp;
 
+// Define a helper macro to invoke BOOST_ASIO_HANDLER_LOCATION with the current
+// file name, line number, and function name. For the function name, you might
+// also consider using __PRETTY_FUNCTION__, BOOST_CURRENT_FUNCTION, or a hand-
+// crafted name. For C++20 or later, you may also use std::source_location.
+#define HANDLER_LOCATION \
+  BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, __func__))
+
 class session
   : public std::enable_shared_from_this<session>
 {
@@ -27,16 +34,22 @@ public:
 
   void start()
   {
+    HANDLER_LOCATION;
+
     do_read();
   }
 
 private:
   void do_read()
   {
+    HANDLER_LOCATION;
+
     auto self(shared_from_this());
     socket_.async_read_some(boost::asio::buffer(data_, max_length),
         [this, self](boost::system::error_code ec, std::size_t length)
         {
+          HANDLER_LOCATION;
+
           if (!ec)
           {
             do_write(length);
@@ -46,10 +59,14 @@ private:
 
   void do_write(std::size_t length)
   {
+    HANDLER_LOCATION;
+
     auto self(shared_from_this());
     boost::asio::async_write(socket_, boost::asio::buffer(data_, length),
         [this, self](boost::system::error_code ec, std::size_t /*length*/)
         {
+          HANDLER_LOCATION;
+
           if (!ec)
           {
             do_read();
@@ -74,9 +91,13 @@ public:
 private:
   void do_accept()
   {
+    HANDLER_LOCATION;
+
     acceptor_.async_accept(
         [this](boost::system::error_code ec, tcp::socket socket)
         {
+          HANDLER_LOCATION;
+
           if (!ec)
           {
             std::make_shared<session>(std::move(socket))->start();
diff --git a/example/cpp11/handler_tracking/custom_tracking.hpp b/example/cpp11/handler_tracking/custom_tracking.hpp
index 1bb5b6ad..7a5d4712 100644
--- a/example/cpp11/handler_tracking/custom_tracking.hpp
+++ b/example/cpp11/handler_tracking/custom_tracking.hpp
@@ -24,6 +24,9 @@
 # define BOOST_ASIO_HANDLER_TRACKING_INIT \
   ::custom_tracking::init()
 
+# define BOOST_ASIO_HANDLER_LOCATION(args) \
+  ::custom_tracking::location args
+
 # define BOOST_ASIO_HANDLER_CREATION(args) \
   ::custom_tracking::creation args
 
@@ -71,6 +74,13 @@ struct custom_tracking
   {
   }
 
+  // Record a source location.
+  static void location(const char* file_name,
+      int line, const char* function_name)
+  {
+    std::printf("At location %s:%d in %s\n", file_name, line, function_name);
+  }
+
   // Record the creation of a tracked handler.
   static void creation(boost::asio::execution_context& /*ctx*/,
       tracked_handler& h, const char* object_type, void* /*object*/,
diff --git a/example/cpp11/operations/composed_6.cpp b/example/cpp11/operations/composed_6.cpp
index d3a51fc7..ec126cdf 100644
--- a/example/cpp11/operations/composed_6.cpp
+++ b/example/cpp11/operations/composed_6.cpp
@@ -97,7 +97,9 @@ struct async_write_message_initiation
       // As our composed operation performs multiple underlying I/O operations,
       // we should maintain a work object against the I/O executor. This tells
       // the I/O executor that there is still more work to come in the future.
-      boost::asio::executor_work_guard<tcp::socket::executor_type> io_work_;
+      typename std::decay<decltype(boost::asio::prefer(
+            std::declval<tcp::socket::executor_type>(),
+            boost::asio::execution::outstanding_work.tracked))>::type io_work_;
 
       // The user-supplied completion handler, called once only on completion
       // of the entire composed operation.
@@ -134,9 +136,6 @@ struct async_write_message_initiation
         // This point is reached only on completion of the entire composed
         // operation.
 
-        // We no longer have any future work coming for the I/O executor.
-        io_work_.reset();
-
         // Deallocate the encoded message before calling the user-supplied
         // completion handler.
         encoded_message_.reset();
@@ -187,7 +186,8 @@ struct async_write_message_initiation
           socket, std::move(encoded_message),
           repeat_count, std::move(delay_timer),
           intermediate_completion_handler::starting,
-          boost::asio::make_work_guard(socket.get_executor()),
+          boost::asio::prefer(socket.get_executor(),
+              boost::asio::execution::outstanding_work.tracked),
           std::forward<CompletionHandler>(completion_handler)});
   }
 };
diff --git a/example/cpp11/socks4/sync_client.cpp b/example/cpp11/socks4/sync_client.cpp
index 1e8e6b71..2b2c4421 100644
--- a/example/cpp11/socks4/sync_client.cpp
+++ b/example/cpp11/socks4/sync_client.cpp
@@ -44,7 +44,8 @@ int main(int argc, char* argv[])
 
     // Get an endpoint for the Boost website. This will be passed to the SOCKS
     // 4 server. Explicitly specify IPv4 since SOCKS 4 does not support IPv6.
-    auto http_endpoint = *resolver.resolve(tcp::v4(), "www.boost.org", "http");
+    auto http_endpoint =
+      *resolver.resolve(tcp::v4(), "www.boost.org", "http").begin();
 
     // Send the request to the SOCKS 4 server.
     socks4::request socks_request(
diff --git a/example/cpp11/ssl/server.cpp b/example/cpp11/ssl/server.cpp
index 32936a67..ce7ee9f0 100644
--- a/example/cpp11/ssl/server.cpp
+++ b/example/cpp11/ssl/server.cpp
@@ -19,8 +19,8 @@ using boost::asio::ip::tcp;
 class session : public std::enable_shared_from_this<session>
 {
 public:
-  session(tcp::socket socket, boost::asio::ssl::context& context)
-    : socket_(std::move(socket), context)
+  session(boost::asio::ssl::stream<tcp::socket> socket)
+    : socket_(std::move(socket))
   {
   }
 
@@ -106,7 +106,9 @@ private:
         {
           if (!error)
           {
-            std::make_shared<session>(std::move(socket), context_)->start();
+            std::make_shared<session>(
+                boost::asio::ssl::stream<tcp::socket>(
+                  std::move(socket), context_))->start();
           }
 
           do_accept();
diff --git a/example/cpp11/timeouts/blocking_token_tcp_client.cpp b/example/cpp11/timeouts/blocking_token_tcp_client.cpp
index 031275f7..592d03e8 100644
--- a/example/cpp11/timeouts/blocking_token_tcp_client.cpp
+++ b/example/cpp11/timeouts/blocking_token_tcp_client.cpp
@@ -98,7 +98,8 @@ public:
   // use this function to run the io_context until the operation is complete.
   return_type get()
   {
-    boost::asio::io_context& io_context = socket_.get_executor().context();
+    boost::asio::io_context& io_context = boost::asio::query(
+        socket_.get_executor(), boost::asio::execution::context);
 
     // Restart the io_context, as it may have been left in the "stopped" state
     // by a previous operation.
diff --git a/example/cpp14/executors/actor.cpp b/example/cpp14/executors/actor.cpp
index 7046e7ba..92056996 100644
--- a/example/cpp14/executors/actor.cpp
+++ b/example/cpp14/executors/actor.cpp
@@ -1,4 +1,8 @@
-#include <boost/asio/ts/executor.hpp>
+#include <boost/asio/any_io_executor.hpp>
+#include <boost/asio/defer.hpp>
+#include <boost/asio/post.hpp>
+#include <boost/asio/strand.hpp>
+#include <boost/asio/system_executor.hpp>
 #include <condition_variable>
 #include <deque>
 #include <memory>
@@ -6,8 +10,8 @@
 #include <typeinfo>
 #include <vector>
 
+using boost::asio::any_io_executor;
 using boost::asio::defer;
-using boost::asio::executor;
 using boost::asio::post;
 using boost::asio::strand;
 using boost::asio::system_executor;
@@ -94,7 +98,7 @@ public:
   {
     // Execute the message handler in the context of the target's executor.
     post(to->executor_,
-      [=, msg=std::move(msg)]
+      [=, msg=std::move(msg)]() mutable
       {
         to->call_handler(std::move(msg), from);
       });
@@ -102,7 +106,7 @@ public:
 
 protected:
   // Construct the actor to use the specified executor for all message handlers.
-  actor(executor e)
+  actor(any_io_executor e)
     : executor_(std::move(e))
   {
   }
@@ -166,7 +170,7 @@ private:
   // All messages associated with a single actor object should be processed
   // non-concurrently. We use a strand to ensure non-concurrent execution even
   // if the underlying executor may use multiple threads.
-  strand<executor> executor_;
+  strand<any_io_executor> executor_;
 
   std::vector<std::shared_ptr<message_handler_base>> handlers_;
 };
@@ -216,7 +220,7 @@ using boost::asio::thread_pool;
 class member : public actor
 {
 public:
-  explicit member(executor e)
+  explicit member(any_io_executor e)
     : actor(std::move(e))
   {
     register_handler(&member::init_handler);
diff --git a/example/cpp14/executors/async_1.cpp b/example/cpp14/executors/async_1.cpp
index db72563a..407b8c7f 100644
--- a/example/cpp14/executors/async_1.cpp
+++ b/example/cpp14/executors/async_1.cpp
@@ -1,29 +1,35 @@
-#include <boost/asio/ts/executor.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/associated_executor.hpp>
+#include <boost/asio/bind_executor.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 #include <string>
 
 using boost::asio::bind_executor;
-using boost::asio::dispatch;
-using boost::asio::make_work_guard;
-using boost::asio::post;
-using boost::asio::thread_pool;
+using boost::asio::get_associated_executor;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // A function to asynchronously read a single line from an input stream.
-template <class Handler>
-void async_getline(std::istream& is, Handler handler)
+template <class IoExecutor, class Handler>
+void async_getline(IoExecutor io_ex, std::istream& is, Handler handler)
 {
-  // Create executor_work for the handler's associated executor.
-  auto work = make_work_guard(handler);
+  // Track work for the handler's associated executor.
+  auto work_ex = boost::asio::prefer(
+      get_associated_executor(handler, io_ex),
+      execution::outstanding_work.tracked);
 
   // Post a function object to do the work asynchronously.
-  post([&is, work, handler=std::move(handler)]() mutable
+  execution::execute(
+      boost::asio::require(io_ex, execution::blocking.never),
+      [&is, work_ex, handler=std::move(handler)]() mutable
       {
         std::string line;
         std::getline(is, line);
 
         // Pass the result to the handler, via the associated executor.
-        dispatch(work.get_executor(),
+        execution::execute(
+            boost::asio::prefer(work_ex, execution::blocking.possibly),
             [line=std::move(line), handler=std::move(handler)]() mutable
             {
               handler(std::move(line));
@@ -33,15 +39,18 @@ void async_getline(std::istream& is, Handler handler)
 
 int main()
 {
-  thread_pool pool;
+  static_thread_pool io_pool(1);
+  static_thread_pool completion_pool(1);
 
   std::cout << "Enter a line: ";
 
-  async_getline(std::cin,
-      bind_executor(pool, [](std::string line)
+  async_getline(io_pool.executor(), std::cin,
+      bind_executor(completion_pool.executor(),
+        [](std::string line)
         {
           std::cout << "Line: " << line << "\n";
         }));
 
-  pool.join();
+  io_pool.wait();
+  completion_pool.wait();
 }
diff --git a/example/cpp14/executors/async_2.cpp b/example/cpp14/executors/async_2.cpp
index 6f40a902..1987c3b5 100644
--- a/example/cpp14/executors/async_2.cpp
+++ b/example/cpp14/executors/async_2.cpp
@@ -1,30 +1,35 @@
-#include <boost/asio/ts/executor.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/associated_executor.hpp>
+#include <boost/asio/bind_executor.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 #include <string>
 
 using boost::asio::bind_executor;
-using boost::asio::dispatch;
 using boost::asio::get_associated_executor;
-using boost::asio::make_work_guard;
-using boost::asio::post;
-using boost::asio::thread_pool;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // A function to asynchronously read a single line from an input stream.
-template <class Handler>
-void async_getline(std::istream& is, Handler handler)
+template <class IoExecutor, class Handler>
+void async_getline(IoExecutor io_ex, std::istream& is, Handler handler)
 {
-  // Create executor_work for the handler's associated executor.
-  auto work = make_work_guard(handler);
+  // Track work for the handler's associated executor.
+  auto work_ex = boost::asio::prefer(
+      get_associated_executor(handler, io_ex),
+      execution::outstanding_work.tracked);
 
   // Post a function object to do the work asynchronously.
-  post([&is, work, handler=std::move(handler)]() mutable
+  execution::execute(
+      boost::asio::require(io_ex, execution::blocking.never),
+      [&is, work_ex, handler=std::move(handler)]() mutable
       {
         std::string line;
         std::getline(is, line);
 
         // Pass the result to the handler, via the associated executor.
-        dispatch(work.get_executor(),
+        execution::execute(
+            boost::asio::prefer(work_ex, execution::blocking.possibly),
             [line=std::move(line), handler=std::move(handler)]() mutable
             {
               handler(std::move(line));
@@ -33,36 +38,44 @@ void async_getline(std::istream& is, Handler handler)
 }
 
 // A function to asynchronously read multiple lines from an input stream.
-template <class Handler>
-void async_getlines(std::istream& is, std::string init, Handler handler)
+template <class IoExecutor, class Handler>
+void async_getlines(IoExecutor io_ex, std::istream& is, std::string init, Handler handler)
 {
-  // Get the final handler's associated executor.
-  auto ex = get_associated_executor(handler);
+  // Track work for the I/O executor.
+  auto io_work_ex = boost::asio::prefer(io_ex,
+      execution::outstanding_work.tracked);
+
+  // Track work for the handler's associated executor.
+  auto handler_work_ex = boost::asio::prefer(
+      get_associated_executor(handler, io_ex),
+      execution::outstanding_work.tracked);
 
   // Use the associated executor for each operation in the composition.
-  async_getline(is,
-      bind_executor(ex,
-        [&is, lines=std::move(init), handler=std::move(handler)]
+  async_getline(io_work_ex, is,
+      bind_executor(handler_work_ex,
+        [io_work_ex, &is, lines=std::move(init), handler=std::move(handler)]
         (std::string line) mutable
         {
           if (line.empty())
             handler(lines);
           else
-            async_getlines(is, lines + line + "\n", std::move(handler));
+            async_getlines(io_work_ex, is, lines + line + "\n", std::move(handler));
         }));
 }
 
 int main()
 {
-  thread_pool pool;
+  static_thread_pool io_pool(1);
+  static_thread_pool completion_pool(1);
 
   std::cout << "Enter text, terminating with a blank line:\n";
 
-  async_getlines(std::cin, "",
-      bind_executor(pool, [](std::string lines)
+  async_getlines(io_pool.executor(), std::cin, "",
+      bind_executor(completion_pool.executor(), [](std::string lines)
         {
           std::cout << "Lines:\n" << lines << "\n";
         }));
 
-  pool.join();
+  io_pool.wait();
+  completion_pool.wait();
 }
diff --git a/example/cpp14/executors/bank_account_1.cpp b/example/cpp14/executors/bank_account_1.cpp
index 6464b48d..1e5d7304 100644
--- a/example/cpp14/executors/bank_account_1.cpp
+++ b/example/cpp14/executors/bank_account_1.cpp
@@ -1,9 +1,9 @@
-#include <boost/asio/ts/executor.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 
-using boost::asio::post;
-using boost::asio::thread_pool;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // Traditional active object pattern.
 // Member functions do not block.
@@ -11,37 +11,43 @@ using boost::asio::thread_pool;
 class bank_account
 {
   int balance_ = 0;
-  mutable thread_pool pool_{1};
+  mutable static_thread_pool pool_{1};
 
 public:
   void deposit(int amount)
   {
-    post(pool_, [=]
-      {
-        balance_ += amount;
-      });
+    execution::execute(
+        pool_.executor(),
+        [this, amount]
+        {
+          balance_ += amount;
+        });
   }
 
   void withdraw(int amount)
   {
-    post(pool_, [=]
-      {
-        if (balance_ >= amount)
-          balance_ -= amount;
-      });
+    execution::execute(
+        pool_.executor(),
+        [this, amount]
+        {
+          if (balance_ >= amount)
+            balance_ -= amount;
+        });
   }
 
   void print_balance() const
   {
-    post(pool_, [=]
-      {
-        std::cout << "balance = " << balance_ << "\n";
-      });
+    execution::execute(
+        pool_.executor(),
+        [this]
+        {
+          std::cout << "balance = " << balance_ << "\n";
+        });
   }
 
   ~bank_account()
   {
-    pool_.join();
+    pool_.wait();
   }
 };
 
diff --git a/example/cpp14/executors/bank_account_2.cpp b/example/cpp14/executors/bank_account_2.cpp
index 8de9a3cc..b012d2fb 100644
--- a/example/cpp14/executors/bank_account_2.cpp
+++ b/example/cpp14/executors/bank_account_2.cpp
@@ -1,10 +1,9 @@
-#include <boost/asio/ts/executor.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 
-using boost::asio::post;
-using boost::asio::thread_pool;
-using boost::asio::use_future;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // Traditional active object pattern.
 // Member functions block until operation is finished.
@@ -12,35 +11,43 @@ using boost::asio::use_future;
 class bank_account
 {
   int balance_ = 0;
-  mutable thread_pool pool_{1};
+  mutable static_thread_pool pool_{1};
 
 public:
   void deposit(int amount)
   {
-    post(pool_,
-      use_future([=]
+    execution::execute(
+        boost::asio::require(pool_.executor(),
+          execution::blocking.always),
+        [this, amount]
         {
           balance_ += amount;
-        })).get();
+        });
   }
 
   void withdraw(int amount)
   {
-    post(pool_,
-      use_future([=]
+    execution::execute(
+        boost::asio::require(pool_.executor(),
+          execution::blocking.always),
+        [this, amount]
         {
           if (balance_ >= amount)
             balance_ -= amount;
-        })).get();
+        });
   }
 
   int balance() const
   {
-    return post(pool_,
-      use_future([=]
+    int result = 0;
+    execution::execute(
+        boost::asio::require(pool_.executor(),
+          execution::blocking.always),
+        [this, &result]
         {
-          return balance_;
-        })).get();
+          result = balance_;
+        });
+    return result;
   }
 };
 
diff --git a/example/cpp14/executors/fork_join.cpp b/example/cpp14/executors/fork_join.cpp
index 2d9b4f7b..24a338e8 100644
--- a/example/cpp14/executors/fork_join.cpp
+++ b/example/cpp14/executors/fork_join.cpp
@@ -1,5 +1,6 @@
-#include <boost/asio/ts/executor.hpp>
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/static_thread_pool.hpp>
+#include <algorithm>
 #include <condition_variable>
 #include <memory>
 #include <mutex>
@@ -7,14 +8,13 @@
 #include <thread>
 #include <numeric>
 
-using boost::asio::dispatch;
-using boost::asio::execution_context;
-using boost::asio::thread_pool;
+using boost::asio::static_thread_pool;
+namespace execution = boost::asio::execution;
 
 // A fixed-size thread pool used to implement fork/join semantics. Functions
 // are scheduled using a simple FIFO queue. Implementing work stealing, or
 // using a queue based on atomic operations, are left as tasks for the reader.
-class fork_join_pool : public execution_context
+class fork_join_pool
 {
 public:
   // The constructor starts a thread pool with the specified number of threads.
@@ -22,7 +22,7 @@ public:
   // Additional threads may temporarily be added to the pool if they join a
   // fork_executor.
   explicit fork_join_pool(
-      std::size_t thread_count = std::thread::hardware_concurrency() * 2)
+      std::size_t thread_count = std::max(std::thread::hardware_concurrency(), 1u) * 2)
     : use_count_(1),
       threads_(thread_count)
   {
@@ -32,7 +32,9 @@ public:
       // it is time to shut down, i.e. the use count is zero.
       for (thread_count_ = 0; thread_count_ < thread_count; ++thread_count_)
       {
-        dispatch(threads_, [&]
+        execution::execute(
+            threads_.executor(),
+            [this]
             {
               std::unique_lock<std::mutex> lock(mutex_);
               while (use_count_ > 0)
@@ -44,7 +46,7 @@ public:
     catch (...)
     {
       stop_threads();
-      threads_.join();
+      threads_.wait();
       throw;
     }
   }
@@ -53,7 +55,7 @@ public:
   ~fork_join_pool()
   {
     stop_threads();
-    threads_.join();
+    threads_.wait();
   }
 
 private:
@@ -117,7 +119,7 @@ private:
 
   // Dispatch a function, executing it immediately if the queue is already
   // loaded. Otherwise adds the function to the queue and wakes a thread.
-  void do_dispatch(std::shared_ptr<function_base> p,
+  void do_execute(std::shared_ptr<function_base> p,
       const std::shared_ptr<std::size_t>& work_count)
   {
     std::unique_lock<std::mutex> lock(mutex_);
@@ -135,16 +137,6 @@ private:
     }
   }
 
-  // Add a function to the queue and wake a thread.
-  void do_post(std::shared_ptr<function_base> p,
-      const std::shared_ptr<std::size_t>& work_count)
-  {
-    std::lock_guard<std::mutex> lock(mutex_);
-    queue_.push(p);
-    do_work_started(work_count);
-    condition_.notify_one();
-  }
-
   // Ask all threads to shut down.
   void stop_threads()
   {
@@ -158,7 +150,7 @@ private:
   std::queue<std::shared_ptr<function_base>> queue_;
   std::size_t use_count_;
   std::size_t thread_count_;
-  thread_pool threads_;
+  static_thread_pool threads_;
 };
 
 // A class that satisfies the Executor requirements. Every function or piece of
@@ -172,45 +164,16 @@ public:
   {
   }
 
-  fork_join_pool& context() const noexcept
+  fork_join_pool& query(execution::context_t) const noexcept
   {
     return context_;
   }
 
-  void on_work_started() const noexcept
+  template <class Func>
+  void execute(Func f) const
   {
-    std::lock_guard<std::mutex> lock(context_.mutex_);
-    context_.do_work_started(work_count_);
-  }
-
-  void on_work_finished() const noexcept
-  {
-    std::lock_guard<std::mutex> lock(context_.mutex_);
-    context_.do_work_finished(work_count_);
-  }
-
-  template <class Func, class Alloc>
-  void dispatch(Func&& f, const Alloc& a) const
-  {
-    auto p(std::allocate_shared<function<Func>>(
-          typename std::allocator_traits<Alloc>::template rebind_alloc<char>(a),
-          std::move(f), work_count_));
-    context_.do_dispatch(p, work_count_);
-  }
-
-  template <class Func, class Alloc>
-  void post(Func f, const Alloc& a) const
-  {
-    auto p(std::allocate_shared<function<Func>>(
-          typename std::allocator_traits<Alloc>::template rebind_alloc<char>(a),
-          std::move(f), work_count_));
-    context_.do_post(p, work_count_);
-  }
-
-  template <class Func, class Alloc>
-  void defer(Func&& f, const Alloc& a) const
-  {
-    post(std::forward<Func>(f), a);
+    auto p(std::make_shared<function<Func>>(std::move(f), work_count_));
+    context_.do_execute(p, work_count_);
   }
 
   friend bool operator==(const fork_executor& a,
@@ -289,8 +252,8 @@ void fork_join_sort(Iterator begin, Iterator end)
     {
       fork_executor fork(pool);
       join_guard join(fork);
-      dispatch(fork, [=]{ fork_join_sort(begin, begin + n / 2); });
-      dispatch(fork, [=]{ fork_join_sort(begin + n / 2, end); });
+      execution::execute(fork, [=]{ fork_join_sort(begin, begin + n / 2); });
+      execution::execute(fork, [=]{ fork_join_sort(begin + n / 2, end); });
     }
     std::inplace_merge(begin, begin + n / 2, end);
   }
diff --git a/example/cpp14/executors/pipeline.cpp b/example/cpp14/executors/pipeline.cpp
index bd837083..83e1ee49 100644
--- a/example/cpp14/executors/pipeline.cpp
+++ b/example/cpp14/executors/pipeline.cpp
@@ -1,4 +1,6 @@
-#include <boost/asio/ts/executor.hpp>
+#include <boost/asio/associated_executor.hpp>
+#include <boost/asio/bind_executor.hpp>
+#include <boost/asio/execution.hpp>
 #include <condition_variable>
 #include <future>
 #include <memory>
@@ -8,29 +10,19 @@
 #include <vector>
 #include <cctype>
 
-using boost::asio::execution_context;
 using boost::asio::executor_binder;
 using boost::asio::get_associated_executor;
-using boost::asio::post;
-using boost::asio::system_executor;
-using boost::asio::use_future;
-using boost::asio::use_service;
+namespace execution = boost::asio::execution;
 
 // An executor that launches a new thread for each function submitted to it.
-// This class satisfies the Executor requirements.
+// This class satisfies the executor requirements.
 class thread_executor
 {
 private:
-  // Service to track all threads started through a thread_executor.
-  class thread_bag : public execution_context::service
+  // Singleton execution context that manages threads launched by the new_thread_executor.
+  class thread_bag
   {
-  public:
-    typedef thread_bag key_type;
-
-    explicit thread_bag(execution_context& ctx)
-      : execution_context::service(ctx)
-    {
-    }
+    friend class thread_executor;
 
     void add_thread(std::thread&& t)
     {
@@ -38,8 +30,9 @@ private:
       threads_.push_back(std::move(t));
     }
 
-  private:
-    virtual void shutdown()
+    thread_bag() = default;
+
+    ~thread_bag()
     {
       for (auto& t : threads_)
         t.join();
@@ -50,40 +43,24 @@ private:
   };
 
 public:
-  execution_context& context() const noexcept
+  static thread_bag& query(execution::context_t)
   {
-    return system_executor().context();
+    static thread_bag threads;
+    return threads;
   }
 
-  void on_work_started() const noexcept
+  static constexpr auto query(execution::blocking_t)
   {
-    // This executor doesn't count work.
+    return execution::blocking.never;
   }
 
-  void on_work_finished() const noexcept
+  template <class Func>
+  void execute(Func f) const
   {
-    // This executor doesn't count work.
-  }
-
-  template <class Func, class Alloc>
-  void dispatch(Func&& f, const Alloc& a) const
-  {
-    post(std::forward<Func>(f), a);
-  }
-
-  template <class Func, class Alloc>
-  void post(Func f, const Alloc&) const
-  {
-    thread_bag& bag = use_service<thread_bag>(context());
+    thread_bag& bag = query(execution::context);
     bag.add_thread(std::thread(std::move(f)));
   }
 
-  template <class Func, class Alloc>
-  void defer(Func&& f, const Alloc& a) const
-  {
-    post(std::forward<Func>(f), a);
-  }
-
   friend bool operator==(const thread_executor&,
       const thread_executor&) noexcept
   {
@@ -186,7 +163,16 @@ std::future<void> pipeline(queue_back<T> in, F f)
 
   // Run the function, and as we're the last stage return a future so that the
   // caller can wait for the pipeline to finish.
-  return post(ex, use_future([in, f = std::move(f)]() mutable { f(in); }));
+  std::packaged_task<void()> task(
+      [in, f = std::move(f)]() mutable
+      {
+        f(in);
+      });
+  std::future<void> fut = task.get_future();
+  execution::execute(
+      boost::asio::require(ex, execution::blocking.never),
+      std::move(task));
+  return fut;
 }
 
 // Launch an intermediate stage in a pipeline.
@@ -205,7 +191,9 @@ std::future<void> pipeline(queue_back<T> in, F f, Tail... t)
   auto ex = get_associated_executor(f, thread_executor());
 
   // Run the function.
-  post(ex, [in, out, f = std::move(f)]() mutable
+  execution::execute(
+      boost::asio::require(ex, execution::blocking.never),
+      [in, out, f = std::move(f)]() mutable
       {
         f(in, out);
         out.stop();
@@ -231,7 +219,9 @@ std::future<void> pipeline(F f, Tail... t)
   auto ex = get_associated_executor(f, thread_executor());
 
   // Run the function.
-  post(ex, [out, f = std::move(f)]() mutable
+  execution::execute(
+      boost::asio::require(ex, execution::blocking.never),
+      [out, f = std::move(f)]() mutable
       {
         f(out);
         out.stop();
@@ -243,12 +233,12 @@ std::future<void> pipeline(F f, Tail... t)
 
 //------------------------------------------------------------------------------
 
-#include <boost/asio/thread_pool.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <iostream>
 #include <string>
 
 using boost::asio::bind_executor;
-using boost::asio::thread_pool;
+using boost::asio::static_thread_pool;
 
 void reader(queue_front<std::string> out)
 {
@@ -287,8 +277,8 @@ void writer(queue_back<std::string> in)
 
 int main()
 {
-  thread_pool pool;
+  static_thread_pool pool(1);
 
-  auto f = pipeline(reader, filter, bind_executor(pool, upper), writer);
+  auto f = pipeline(reader, filter, bind_executor(pool.executor(), upper), writer);
   f.wait();
 }
diff --git a/example/cpp14/executors/priority_scheduler.cpp b/example/cpp14/executors/priority_scheduler.cpp
index f1185319..b0c890e4 100644
--- a/example/cpp14/executors/priority_scheduler.cpp
+++ b/example/cpp14/executors/priority_scheduler.cpp
@@ -1,66 +1,74 @@
-#include <boost/asio/ts/executor.hpp>
+#include <boost/asio/execution.hpp>
 #include <condition_variable>
 #include <iostream>
 #include <memory>
 #include <mutex>
 #include <queue>
 
-using boost::asio::dispatch;
-using boost::asio::execution_context;
+namespace execution = boost::asio::execution;
 
-class priority_scheduler : public execution_context
+namespace custom_props {
+
+  struct priority
+  {
+    template <typename T>
+    static constexpr bool is_applicable_property_v =
+      execution::is_executor<T>::value;
+
+    static constexpr bool is_requirable = true;
+    static constexpr bool is_preferable = true;
+
+    using polymorphic_query_result_type = int;
+
+    int value() const { return value_; }
+
+    int value_ = 1;
+  };
+
+  constexpr priority low_priority{0};
+  constexpr priority normal_priority{1};
+  constexpr priority high_priority{2};
+
+} // namespace custom_props
+
+class priority_scheduler
 {
 public:
   // A class that satisfies the Executor requirements.
   class executor_type
   {
   public:
-    executor_type(priority_scheduler& ctx, int pri) noexcept
-      : context_(ctx), priority_(pri)
+    executor_type(priority_scheduler& ctx) noexcept
+      : context_(ctx), priority_(custom_props::normal_priority.value())
     {
     }
 
-    priority_scheduler& context() const noexcept
+    priority_scheduler& query(execution::context_t) const noexcept
     {
       return context_;
     }
 
-    void on_work_started() const noexcept
+    int query(custom_props::priority) const noexcept
     {
-      // This executor doesn't count work. Instead, the scheduler simply runs
-      // until explicitly stopped.
+      return priority_;
     }
 
-    void on_work_finished() const noexcept
+    executor_type require(custom_props::priority pri) const
     {
-      // This executor doesn't count work. Instead, the scheduler simply runs
-      // until explicitly stopped.
+      executor_type new_ex(*this);
+      new_ex.priority_ = pri.value();
+      return new_ex;
     }
 
-    template <class Func, class Alloc>
-    void dispatch(Func&& f, const Alloc& a) const
+    template <class Func>
+    void execute(Func f) const
     {
-      post(std::forward<Func>(f), a);
-    }
-
-    template <class Func, class Alloc>
-    void post(Func f, const Alloc& a) const
-    {
-      auto p(std::allocate_shared<item<Func>>(
-            typename std::allocator_traits<
-              Alloc>::template rebind_alloc<char>(a),
-            priority_, std::move(f)));
+      auto p(std::make_shared<item<Func>>(priority_, std::move(f)));
       std::lock_guard<std::mutex> lock(context_.mutex_);
       context_.queue_.push(p);
       context_.condition_.notify_one();
     }
 
-    template <class Func, class Alloc>
-    void defer(Func&& f, const Alloc& a) const
-    {
-      post(std::forward<Func>(f), a);
-    }
-
     friend bool operator==(const executor_type& a,
         const executor_type& b) noexcept
     {
@@ -78,15 +86,9 @@ public:
     int priority_;
   };
 
-  ~priority_scheduler() noexcept
+  executor_type executor() noexcept
   {
-    shutdown();
-    destroy();
-  }
-
-  executor_type get_executor(int pri = 0) noexcept
-  {
-    return executor_type(*const_cast<priority_scheduler*>(this), pri);
+    return executor_type(*const_cast<priority_scheduler*>(this));
   }
 
   void run()
@@ -158,16 +160,22 @@ private:
 int main()
 {
   priority_scheduler sched;
-  auto low = sched.get_executor(0);
-  auto med = sched.get_executor(1);
-  auto high = sched.get_executor(2);
-  dispatch(low, []{ std::cout << "1\n"; });
-  dispatch(low, []{ std::cout << "11\n"; });
-  dispatch(med, []{ std::cout << "2\n"; });
-  dispatch(med, []{ std::cout << "22\n"; });
-  dispatch(high, []{ std::cout << "3\n"; });
-  dispatch(high, []{ std::cout << "33\n"; });
-  dispatch(high, []{ std::cout << "333\n"; });
-  dispatch(sched.get_executor(-1), [&]{ sched.stop(); });
+  auto ex = sched.executor();
+  auto prefer_low = boost::asio::prefer(ex, custom_props::low_priority);
+  auto low = boost::asio::require(ex, custom_props::low_priority);
+  auto med = boost::asio::require(ex, custom_props::normal_priority);
+  auto high = boost::asio::require(ex, custom_props::high_priority);
+  execution::any_executor<custom_props::priority> poly_high(high);
+  execution::execute(prefer_low, []{ std::cout << "1\n"; });
+  execution::execute(low, []{ std::cout << "11\n"; });
+  execution::execute(low, []{ std::cout << "111\n"; });
+  execution::execute(med, []{ std::cout << "2\n"; });
+  execution::execute(med, []{ std::cout << "22\n"; });
+  execution::execute(high, []{ std::cout << "3\n"; });
+  execution::execute(high, []{ std::cout << "33\n"; });
+  execution::execute(high, []{ std::cout << "333\n"; });
+  execution::execute(poly_high, []{ std::cout << "3333\n"; });
+  execution::execute(boost::asio::require(ex, custom_props::priority{-1}), [&]{ sched.stop(); });
   sched.run();
+  std::cout << "polymorphic query result = " << boost::asio::query(poly_high, custom_props::priority{}) << "\n";
 }
diff --git a/example/cpp14/operations/composed_6.cpp b/example/cpp14/operations/composed_6.cpp
index 8b6d0119..cdfb71a8 100644
--- a/example/cpp14/operations/composed_6.cpp
+++ b/example/cpp14/operations/composed_6.cpp
@@ -108,7 +108,9 @@ auto async_write_messages(tcp::socket& socket,
       // As our composed operation performs multiple underlying I/O operations,
       // we should maintain a work object against the I/O executor. This tells
       // the I/O executor that there is still more work to come in the future.
-      boost::asio::executor_work_guard<tcp::socket::executor_type> io_work_;
+      typename std::decay<decltype(boost::asio::prefer(
+            std::declval<tcp::socket::executor_type>(),
+            boost::asio::execution::outstanding_work.tracked))>::type io_work_;
 
       // The user-supplied completion handler, called once only on completion
       // of the entire composed operation.
@@ -145,9 +147,6 @@ auto async_write_messages(tcp::socket& socket,
         // This point is reached only on completion of the entire composed
         // operation.
 
-        // We no longer have any future work coming for the I/O executor.
-        io_work_.reset();
-
         // Deallocate the encoded message before calling the user-supplied
         // completion handler.
         encoded_message_.reset();
@@ -198,7 +197,8 @@ auto async_write_messages(tcp::socket& socket,
           socket, std::move(encoded_message),
           repeat_count, std::move(delay_timer),
           intermediate_completion_handler::starting,
-          boost::asio::make_work_guard(socket.get_executor()),
+          boost::asio::prefer(socket.get_executor(),
+              boost::asio::execution::outstanding_work.tracked),
           std::forward<decltype(completion_handler)>(completion_handler)});
   };
 
diff --git a/example/cpp17/coroutines_ts/chat_server.cpp b/example/cpp17/coroutines_ts/chat_server.cpp
index e233e9d6..8803be57 100644
--- a/example/cpp17/coroutines_ts/chat_server.cpp
+++ b/example/cpp17/coroutines_ts/chat_server.cpp
@@ -204,10 +204,7 @@ int main(int argc, char* argv[])
     {
       unsigned short port = std::atoi(argv[i]);
       co_spawn(io_context,
-          [&io_context, port]
-          {
-            return listener(tcp::acceptor(io_context, {tcp::v4(), port}));
-          },
+          listener(tcp::acceptor(io_context, {tcp::v4(), port})),
           detached);
     }
 
diff --git a/example/cpp17/coroutines_ts/echo_server.cpp b/example/cpp17/coroutines_ts/echo_server.cpp
index 7ca12c69..ed42fa57 100644
--- a/example/cpp17/coroutines_ts/echo_server.cpp
+++ b/example/cpp17/coroutines_ts/echo_server.cpp
@@ -23,6 +23,11 @@ using boost::asio::detached;
 using boost::asio::use_awaitable;
 namespace this_coro = boost::asio::this_coro;
 
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+# define use_awaitable \
+  boost::asio::use_awaitable_t(__FILE__, __LINE__, __PRETTY_FUNCTION__)
+#endif
+
 awaitable<void> echo(tcp::socket socket)
 {
   try
@@ -47,12 +52,7 @@ awaitable<void> listener()
   for (;;)
   {
     tcp::socket socket = co_await acceptor.async_accept(use_awaitable);
-    co_spawn(executor,
-        [socket = std::move(socket)]() mutable
-        {
-          return echo(std::move(socket));
-        },
-        detached);
+    co_spawn(executor, echo(std::move(socket)), detached);
   }
 }
 
@@ -65,7 +65,7 @@ int main()
     boost::asio::signal_set signals(io_context, SIGINT, SIGTERM);
     signals.async_wait([&](auto, auto){ io_context.stop(); });
 
-    co_spawn(io_context, listener, detached);
+    co_spawn(io_context, listener(), detached);
 
     io_context.run();
   }
diff --git a/example/cpp17/coroutines_ts/echo_server_with_default.cpp b/example/cpp17/coroutines_ts/echo_server_with_default.cpp
index a34f8bf5..9ded4846 100644
--- a/example/cpp17/coroutines_ts/echo_server_with_default.cpp
+++ b/example/cpp17/coroutines_ts/echo_server_with_default.cpp
@@ -49,12 +49,7 @@ awaitable<void> listener()
   for (;;)
   {
     auto socket = co_await acceptor.async_accept();
-    co_spawn(executor,
-        [socket = std::move(socket)]() mutable
-        {
-          return echo(std::move(socket));
-        },
-        detached);
+    co_spawn(executor, echo(std::move(socket)), detached);
   }
 }
 
@@ -67,7 +62,7 @@ int main()
     boost::asio::signal_set signals(io_context, SIGINT, SIGTERM);
     signals.async_wait([&](auto, auto){ io_context.stop(); });
 
-    co_spawn(io_context, listener, detached);
+    co_spawn(io_context, listener(), detached);
 
     io_context.run();
   }
diff --git a/example/cpp17/coroutines_ts/range_based_for.cpp b/example/cpp17/coroutines_ts/range_based_for.cpp
index 477349ae..210e0525 100644
--- a/example/cpp17/coroutines_ts/range_based_for.cpp
+++ b/example/cpp17/coroutines_ts/range_based_for.cpp
@@ -91,12 +91,7 @@ int main()
     signals.async_wait([&](auto, auto){ io_context.stop(); });
 
     tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
-    co_spawn(io_context,
-        [acceptor = std::move(acceptor)]() mutable
-        {
-          return listener(std::move(acceptor));
-        },
-        detached);
+    co_spawn(io_context, listener(std::move(acceptor)), detached);
 
     io_context.run();
   }
diff --git a/example/cpp17/coroutines_ts/refactored_echo_server.cpp b/example/cpp17/coroutines_ts/refactored_echo_server.cpp
index 062efc16..8ef0a274 100644
--- a/example/cpp17/coroutines_ts/refactored_echo_server.cpp
+++ b/example/cpp17/coroutines_ts/refactored_echo_server.cpp
@@ -56,12 +56,7 @@ awaitable<void> listener()
   for (;;)
   {
     tcp::socket socket = co_await acceptor.async_accept(use_awaitable);
-    co_spawn(executor,
-        [socket = std::move(socket)]() mutable
-        {
-          return echo(std::move(socket));
-        },
-        detached);
+    co_spawn(executor, echo(std::move(socket)), detached);
   }
 }
 
@@ -74,7 +69,7 @@ int main()
     boost::asio::signal_set signals(io_context, SIGINT, SIGTERM);
     signals.async_wait([&](auto, auto){ io_context.stop(); });
 
-    co_spawn(io_context, listener, detached);
+    co_spawn(io_context, listener(), detached);
 
     io_context.run();
   }
diff --git a/include/boost/asio.hpp b/include/boost/asio.hpp
index 01b44555..8e460363 100644
--- a/include/boost/asio.hpp
+++ b/include/boost/asio.hpp
@@ -54,6 +54,22 @@
 #include <boost/asio/detached.hpp>
 #include <boost/asio/dispatch.hpp>
 #include <boost/asio/error.hpp>
+#include <boost/asio/execution.hpp>
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/any_executor.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/blocking_adaptation.hpp>
+#include <boost/asio/execution/bulk_guarantee.hpp>
+#include <boost/asio/execution/context.hpp>
+#include <boost/asio/execution/context_as.hpp>
+#include <boost/asio/execution/execute.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/execution/invocable_archetype.hpp>
+#include <boost/asio/execution/mapping.hpp>
+#include <boost/asio/execution/occupancy.hpp>
+#include <boost/asio/execution/outstanding_work.hpp>
+#include <boost/asio/execution/prefer_only.hpp>
+#include <boost/asio/execution/relationship.hpp>
 #include <boost/asio/execution_context.hpp>
 #include <boost/asio/executor.hpp>
 #include <boost/asio/executor_work_guard.hpp>
@@ -94,6 +110,7 @@
 #include <boost/asio/ip/udp.hpp>
 #include <boost/asio/ip/unicast.hpp>
 #include <boost/asio/ip/v6_only.hpp>
+#include <boost/asio/is_applicable_property.hpp>
 #include <boost/asio/is_executor.hpp>
 #include <boost/asio/is_read_buffered.hpp>
 #include <boost/asio/is_write_buffered.hpp>
@@ -101,6 +118,7 @@
 #include <boost/asio/local/connect_pair.hpp>
 #include <boost/asio/local/datagram_protocol.hpp>
 #include <boost/asio/local/stream_protocol.hpp>
+#include <boost/asio/multiple_exceptions.hpp>
 #include <boost/asio/packaged_task.hpp>
 #include <boost/asio/placeholders.hpp>
 #include <boost/asio/posix/basic_descriptor.hpp>
@@ -109,14 +127,19 @@
 #include <boost/asio/posix/descriptor_base.hpp>
 #include <boost/asio/posix/stream_descriptor.hpp>
 #include <boost/asio/post.hpp>
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
 #include <boost/asio/read.hpp>
 #include <boost/asio/read_at.hpp>
 #include <boost/asio/read_until.hpp>
 #include <boost/asio/redirect_error.hpp>
+#include <boost/asio/require.hpp>
+#include <boost/asio/require_concept.hpp>
 #include <boost/asio/serial_port.hpp>
 #include <boost/asio/serial_port_base.hpp>
 #include <boost/asio/signal_set.hpp>
 #include <boost/asio/socket_base.hpp>
+#include <boost/asio/static_thread_pool.hpp>
 #include <boost/asio/steady_timer.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/asio/streambuf.hpp>
diff --git a/include/boost/asio/any_io_executor.hpp b/include/boost/asio/any_io_executor.hpp
new file mode 100644
index 00000000..1be8fb6c
--- /dev/null
+++ b/include/boost/asio/any_io_executor.hpp
@@ -0,0 +1,73 @@
+//
+// any_io_executor.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_ANY_IO_EXECUTOR_HPP
+#define BOOST_ASIO_ANY_IO_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#if defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+# include <boost/asio/executor.hpp>
+#else // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+# include <boost/asio/execution.hpp>
+# include <boost/asio/execution_context.hpp>
+#endif // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+typedef executor any_io_executor;
+
+#else // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+/// Polymorphic executor type for use with I/O objects.
+/**
+ * The @c any_io_executor type is a polymorphic executor that supports the set
+ * of properties required by I/O objects. It is defined as the
+ * execution::any_executor class template parameterised as follows:
+ * @code execution::any_executor<
+ *   execution::context_as_t<execution_context&>,
+ *   execution::blocking_t::never_t,
+ *   execution::prefer_only<execution::blocking_t::possibly_t>,
+ *   execution::prefer_only<execution::outstanding_work_t::tracked_t>,
+ *   execution::prefer_only<execution::outstanding_work_t::untracked_t>,
+ *   execution::prefer_only<execution::relationship_t::fork_t>,
+ *   execution::prefer_only<execution::relationship_t::continuation_t>
+ * > @endcode
+ */
+#if defined(GENERATING_DOCUMENTATION)
+typedef execution::any_executor<...> any_io_executor;
+#else // defined(GENERATING_DOCUMENTATION)
+typedef execution::any_executor<
+    execution::context_as_t<execution_context&>,
+    execution::blocking_t::never_t,
+    execution::prefer_only<execution::blocking_t::possibly_t>,
+    execution::prefer_only<execution::outstanding_work_t::tracked_t>,
+    execution::prefer_only<execution::outstanding_work_t::untracked_t>,
+    execution::prefer_only<execution::relationship_t::fork_t>,
+    execution::prefer_only<execution::relationship_t::continuation_t>
+  > any_io_executor;
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#endif // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_ANY_IO_EXECUTOR_HPP
diff --git a/include/boost/asio/associated_executor.hpp b/include/boost/asio/associated_executor.hpp
index 18544969..6c9d2c1a 100644
--- a/include/boost/asio/associated_executor.hpp
+++ b/include/boost/asio/associated_executor.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
 #include <boost/asio/is_executor.hpp>
 #include <boost/asio/system_executor.hpp>
 
@@ -114,8 +115,9 @@ get_associated_executor(const T& t) BOOST_ASIO_NOEXCEPT
 template <typename T, typename Executor>
 inline typename associated_executor<T, Executor>::type
 get_associated_executor(const T& t, const Executor& ex,
-    typename enable_if<is_executor<
-      Executor>::value>::type* = 0) BOOST_ASIO_NOEXCEPT
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type* = 0) BOOST_ASIO_NOEXCEPT
 {
   return associated_executor<T, Executor>::get(t, ex);
 }
diff --git a/include/boost/asio/awaitable.hpp b/include/boost/asio/awaitable.hpp
index 6bf14569..55fbe4cb 100644
--- a/include/boost/asio/awaitable.hpp
+++ b/include/boost/asio/awaitable.hpp
@@ -19,8 +19,13 @@
 
 #if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
 
-#include <experimental/coroutine>
-#include <boost/asio/executor.hpp>
+#if defined(BOOST_ASIO_HAS_STD_COROUTINE)
+# include <coroutine>
+#else // defined(BOOST_ASIO_HAS_STD_COROUTINE)
+# include <experimental/coroutine>
+#endif // defined(BOOST_ASIO_HAS_STD_COROUTINE)
+
+#include <boost/asio/any_io_executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -28,8 +33,13 @@ namespace boost {
 namespace asio {
 namespace detail {
 
+#if defined(BOOST_ASIO_HAS_STD_COROUTINE)
+using std::coroutine_handle;
+using std::suspend_always;
+#else // defined(BOOST_ASIO_HAS_STD_COROUTINE)
 using std::experimental::coroutine_handle;
 using std::experimental::suspend_always;
+#endif // defined(BOOST_ASIO_HAS_STD_COROUTINE)
 
 template <typename> class awaitable_thread;
 template <typename, typename> class awaitable_frame;
@@ -37,7 +47,7 @@ template <typename, typename> class awaitable_frame;
 } // namespace detail
 
 /// The return type of a coroutine or asynchronous operation.
-template <typename T, typename Executor = executor>
+template <typename T, typename Executor = any_io_executor>
 class awaitable
 {
 public:
diff --git a/include/boost/asio/basic_datagram_socket.hpp b/include/boost/asio/basic_datagram_socket.hpp
index cdcae844..98a6dd63 100644
--- a/include/boost/asio/basic_datagram_socket.hpp
+++ b/include/boost/asio/basic_datagram_socket.hpp
@@ -33,7 +33,7 @@ namespace asio {
 #define BOOST_ASIO_BASIC_DATAGRAM_SOCKET_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename Protocol, typename Executor = executor>
+template <typename Protocol, typename Executor = any_io_executor>
 class basic_datagram_socket;
 
 #endif // !defined(BOOST_ASIO_BASIC_DATAGRAM_SOCKET_FWD_DECL)
@@ -1094,7 +1094,7 @@ private:
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_send(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1127,8 +1127,8 @@ private:
 
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_send_to(
-          self_->impl_.get_implementation(), buffers, destination, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers, destination,
+          flags, handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1162,7 +1162,7 @@ private:
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_receive(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1195,8 +1195,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_receive_from(
-          self_->impl_.get_implementation(), buffers, *sender_endpoint, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers, *sender_endpoint,
+          flags, handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_deadline_timer.hpp b/include/boost/asio/basic_deadline_timer.hpp
index 181c7d1d..33730364 100644
--- a/include/boost/asio/basic_deadline_timer.hpp
+++ b/include/boost/asio/basic_deadline_timer.hpp
@@ -21,6 +21,7 @@
   || defined(GENERATING_DOCUMENTATION)
 
 #include <cstddef>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/detail/deadline_timer_service.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
@@ -28,7 +29,6 @@
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/time_traits.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -126,7 +126,7 @@ namespace asio {
  */
 template <typename Time,
     typename TimeTraits = boost::asio::time_traits<Time>,
-    typename Executor = executor>
+    typename Executor = any_io_executor>
 class basic_deadline_timer
 {
 public:
@@ -672,8 +672,8 @@ private:
 
       detail::non_const_lvalue<WaitHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(),
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_raw_socket.hpp b/include/boost/asio/basic_raw_socket.hpp
index 3b47b9e9..7f620620 100644
--- a/include/boost/asio/basic_raw_socket.hpp
+++ b/include/boost/asio/basic_raw_socket.hpp
@@ -33,7 +33,7 @@ namespace asio {
 #define BOOST_ASIO_BASIC_RAW_SOCKET_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename Protocol, typename Executor = executor>
+template <typename Protocol, typename Executor = any_io_executor>
 class basic_raw_socket;
 
 #endif // !defined(BOOST_ASIO_BASIC_RAW_SOCKET_FWD_DECL)
@@ -1086,7 +1086,7 @@ private:
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_send(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1119,8 +1119,8 @@ private:
 
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_send_to(
-          self_->impl_.get_implementation(), buffers, destination, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers, destination,
+          flags, handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1154,7 +1154,7 @@ private:
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_receive(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1187,8 +1187,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_receive_from(
-          self_->impl_.get_implementation(), buffers, *sender_endpoint, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers, *sender_endpoint,
+          flags, handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_seq_packet_socket.hpp b/include/boost/asio/basic_seq_packet_socket.hpp
index 6ceca2e6..97fb5617 100644
--- a/include/boost/asio/basic_seq_packet_socket.hpp
+++ b/include/boost/asio/basic_seq_packet_socket.hpp
@@ -31,7 +31,7 @@ namespace asio {
 #define BOOST_ASIO_BASIC_SEQ_PACKET_SOCKET_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename Protocol, typename Executor = executor>
+template <typename Protocol, typename Executor = any_io_executor>
 class basic_seq_packet_socket;
 
 #endif // !defined(BOOST_ASIO_BASIC_SEQ_PACKET_SOCKET_FWD_DECL)
@@ -707,7 +707,7 @@ private:
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_send(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -741,8 +741,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_receive_with_flags(
-          self_->impl_.get_implementation(), buffers, in_flags, *out_flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers, in_flags,
+          *out_flags, handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_serial_port.hpp b/include/boost/asio/basic_serial_port.hpp
index 883f191e..3fd33706 100644
--- a/include/boost/asio/basic_serial_port.hpp
+++ b/include/boost/asio/basic_serial_port.hpp
@@ -22,6 +22,7 @@
   || defined(GENERATING_DOCUMENTATION)
 
 #include <string>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
@@ -30,7 +31,6 @@
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/serial_port_base.hpp>
 #if defined(BOOST_ASIO_HAS_IOCP)
 # include <boost/asio/detail/win_iocp_serial_port_service.hpp>
@@ -56,7 +56,7 @@ namespace asio {
  * @e Distinct @e objects: Safe.@n
  * @e Shared @e objects: Unsafe.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_serial_port
   : public serial_port_base
 {
@@ -850,8 +850,8 @@ private:
 
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_write_some(
-          self_->impl_.get_implementation(), buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -883,8 +883,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_read_some(
-          self_->impl_.get_implementation(), buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_signal_set.hpp b/include/boost/asio/basic_signal_set.hpp
index 5ea391c0..194d29a9 100644
--- a/include/boost/asio/basic_signal_set.hpp
+++ b/include/boost/asio/basic_signal_set.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
@@ -26,7 +27,6 @@
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 
 namespace boost {
 namespace asio {
@@ -91,7 +91,7 @@ namespace asio {
  * that any signals registered using signal_set objects are unblocked in at
  * least one thread.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_signal_set
 {
 public:
@@ -553,8 +553,8 @@ private:
 
       detail::non_const_lvalue<SignalHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(),
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_socket.hpp b/include/boost/asio/basic_socket.hpp
index 33565b93..1a349e49 100644
--- a/include/boost/asio/basic_socket.hpp
+++ b/include/boost/asio/basic_socket.hpp
@@ -15,6 +15,7 @@
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
@@ -24,7 +25,6 @@
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/asio/socket_base.hpp>
 
@@ -49,7 +49,7 @@ namespace asio {
 #define BOOST_ASIO_BASIC_SOCKET_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename Protocol, typename Executor = executor>
+template <typename Protocol, typename Executor = any_io_executor>
 class basic_socket;
 
 #endif // !defined(BOOST_ASIO_BASIC_SOCKET_FWD_DECL)
@@ -1847,7 +1847,7 @@ private:
         detail::non_const_lvalue<ConnectHandler> handler2(handler);
         self_->impl_.get_service().async_connect(
             self_->impl_.get_implementation(), peer_endpoint,
-            handler2.value, self_->impl_.get_implementation_executor());
+            handler2.value, self_->impl_.get_executor());
       }
     }
 
@@ -1879,8 +1879,8 @@ private:
 
       detail::non_const_lvalue<WaitHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), w, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), w,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_socket_acceptor.hpp b/include/boost/asio/basic_socket_acceptor.hpp
index 7897853d..e3894aaf 100644
--- a/include/boost/asio/basic_socket_acceptor.hpp
+++ b/include/boost/asio/basic_socket_acceptor.hpp
@@ -16,6 +16,7 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/basic_socket.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
@@ -24,7 +25,6 @@
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/socket_base.hpp>
 
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
@@ -48,7 +48,7 @@ namespace asio {
 #define BOOST_ASIO_BASIC_SOCKET_ACCEPTOR_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename Protocol, typename Executor = executor>
+template <typename Protocol, typename Executor = any_io_executor>
 class basic_socket_acceptor;
 
 #endif // !defined(BOOST_ASIO_BASIC_SOCKET_ACCEPTOR_FWD_DECL)
@@ -2401,8 +2401,8 @@ private:
 
       detail::non_const_lvalue<WaitHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), w, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), w,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -2436,7 +2436,7 @@ private:
       detail::non_const_lvalue<AcceptHandler> handler2(handler);
       self_->impl_.get_service().async_accept(
           self_->impl_.get_implementation(), *peer, peer_endpoint,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -2470,7 +2470,7 @@ private:
       detail::non_const_lvalue<MoveAcceptHandler> handler2(handler);
       self_->impl_.get_service().async_move_accept(
           self_->impl_.get_implementation(), peer_ex, peer_endpoint,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_stream_socket.hpp b/include/boost/asio/basic_stream_socket.hpp
index ee9c0ee5..91934e16 100644
--- a/include/boost/asio/basic_stream_socket.hpp
+++ b/include/boost/asio/basic_stream_socket.hpp
@@ -33,7 +33,7 @@ namespace asio {
 #define BOOST_ASIO_BASIC_STREAM_SOCKET_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename Protocol, typename Executor = executor>
+template <typename Protocol, typename Executor = any_io_executor>
 class basic_stream_socket;
 
 #endif // !defined(BOOST_ASIO_BASIC_STREAM_SOCKET_FWD_DECL)
@@ -1001,7 +1001,7 @@ private:
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_send(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -1035,7 +1035,7 @@ private:
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_receive(
           self_->impl_.get_implementation(), buffers, flags,
-          handler2.value, self_->impl_.get_implementation_executor());
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/basic_waitable_timer.hpp b/include/boost/asio/basic_waitable_timer.hpp
index cd84f88c..2bab2192 100644
--- a/include/boost/asio/basic_waitable_timer.hpp
+++ b/include/boost/asio/basic_waitable_timer.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <cstddef>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/detail/chrono_time_traits.hpp>
 #include <boost/asio/detail/deadline_timer_service.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
@@ -24,7 +25,6 @@
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/error.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/wait_traits.hpp>
 
 #if defined(BOOST_ASIO_HAS_MOVE)
@@ -42,7 +42,7 @@ namespace asio {
 // Forward declaration with defaulted arguments.
 template <typename Clock,
     typename WaitTraits = boost::asio::wait_traits<Clock>,
-    typename Executor = executor>
+    typename Executor = any_io_executor>
 class basic_waitable_timer;
 
 #endif // !defined(BOOST_ASIO_BASIC_WAITABLE_TIMER_FWD_DECL)
@@ -319,6 +319,54 @@ public:
     impl_ = std::move(other.impl_);
     return *this;
   }
+
+  // All timers have access to each other's implementations.
+  template <typename Clock1, typename WaitTraits1, typename Executor1>
+  friend class basic_waitable_timer;
+
+  /// Move-construct a basic_waitable_timer from another.
+  /**
+   * This constructor moves a timer from one object to another.
+   *
+   * @param other The other basic_waitable_timer object from which the move will
+   * occur.
+   *
+   * @note Following the move, the moved-from object is in the same state as if
+   * constructed using the @c basic_waitable_timer(const executor_type&)
+   * constructor.
+   */
+  template <typename Executor1>
+  basic_waitable_timer(
+      basic_waitable_timer<Clock, WaitTraits, Executor1>&& other,
+      typename enable_if<
+          is_convertible<Executor1, Executor>::value
+      >::type* = 0)
+    : impl_(std::move(other.impl_))
+  {
+  }
+
+  /// Move-assign a basic_waitable_timer from another.
+  /**
+   * This assignment operator moves a timer from one object to another. Cancels
+   * any outstanding asynchronous operations associated with the target object.
+   *
+   * @param other The other basic_waitable_timer object from which the move will
+   * occur.
+   *
+   * @note Following the move, the moved-from object is in the same state as if
+   * constructed using the @c basic_waitable_timer(const executor_type&)
+   * constructor.
+   */
+  template <typename Executor1>
+  typename enable_if<
+    is_convertible<Executor1, Executor>::value,
+    basic_waitable_timer&
+  >::type operator=(basic_waitable_timer<Clock, WaitTraits, Executor1>&& other)
+  {
+    basic_waitable_timer tmp(std::move(other));
+    impl_ = std::move(tmp.impl_);
+    return *this;
+  }
 #endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
 
   /// Destroys the timer.
@@ -743,8 +791,8 @@ private:
 
       detail::non_const_lvalue<WaitHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(),
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/bind_executor.hpp b/include/boost/asio/bind_executor.hpp
index 69683a93..89662438 100644
--- a/include/boost/asio/bind_executor.hpp
+++ b/include/boost/asio/bind_executor.hpp
@@ -21,6 +21,7 @@
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/associated_allocator.hpp>
 #include <boost/asio/async_result.hpp>
+#include <boost/asio/execution/executor.hpp>
 #include <boost/asio/execution_context.hpp>
 #include <boost/asio/is_executor.hpp>
 #include <boost/asio/uses_executor.hpp>
@@ -155,16 +156,14 @@ struct executor_binder_argument_type<R(&)(A1, A2)>
   typedef A2 second_argument_type;
 };
 
-// Helper to:
-// - Apply the empty base optimisation to the executor.
-// - Perform uses_executor construction of the target type, if required.
+// Helper to perform uses_executor construction of the target type, if
+// required.
 
 template <typename T, typename Executor, bool UsesExecutor>
 class executor_binder_base;
 
 template <typename T, typename Executor>
 class executor_binder_base<T, Executor, true>
-  : protected Executor
 {
 protected:
   template <typename E, typename U>
@@ -496,7 +495,9 @@ private:
 template <typename Executor, typename T>
 inline executor_binder<typename decay<T>::type, Executor>
 bind_executor(const Executor& ex, BOOST_ASIO_MOVE_ARG(T) t,
-    typename enable_if<is_executor<Executor>::value>::type* = 0)
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type* = 0)
 {
   return executor_binder<typename decay<T>::type, Executor>(
       executor_arg_t(), ex, BOOST_ASIO_MOVE_CAST(T)(t));
diff --git a/include/boost/asio/buffer.hpp b/include/boost/asio/buffer.hpp
index 90e10ed0..59418f26 100644
--- a/include/boost/asio/buffer.hpp
+++ b/include/boost/asio/buffer.hpp
@@ -50,11 +50,13 @@
 
 #if defined(BOOST_ASIO_HAS_BOOST_WORKAROUND)
 # include <boost/detail/workaround.hpp>
-# if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x582)) \
-    || BOOST_WORKAROUND(__SUNPRO_CC, BOOST_TESTED_AT(0x590))
+# if !defined(__clang__)
+#  if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x582))
+#   define BOOST_ASIO_ENABLE_ARRAY_BUFFER_WORKAROUND
+#  endif // BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x582))
+# elif BOOST_WORKAROUND(__SUNPRO_CC, BOOST_TESTED_AT(0x590))
 #  define BOOST_ASIO_ENABLE_ARRAY_BUFFER_WORKAROUND
-# endif // BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x582))
-        // || BOOST_WORKAROUND(__SUNPRO_CC, BOOST_TESTED_AT(0x590))
+# endif // BOOST_WORKAROUND(__SUNPRO_CC, BOOST_TESTED_AT(0x590))
 #endif // defined(BOOST_ASIO_HAS_BOOST_WORKAROUND)
 
 #if defined(BOOST_ASIO_ENABLE_ARRAY_BUFFER_WORKAROUND)
diff --git a/include/boost/asio/co_spawn.hpp b/include/boost/asio/co_spawn.hpp
index 991fe252..a0553421 100644
--- a/include/boost/asio/co_spawn.hpp
+++ b/include/boost/asio/co_spawn.hpp
@@ -20,6 +20,7 @@
 #if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
 
 #include <boost/asio/awaitable.hpp>
+#include <boost/asio/execution/executor.hpp>
 #include <boost/asio/execution_context.hpp>
 #include <boost/asio/is_executor.hpp>
 
@@ -46,13 +47,321 @@ struct awaitable_signature<awaitable<void, Executor>>
 
 } // namespace detail
 
-/// Spawn a new thread of execution.
+/// Spawn a new coroutined-based thread of execution.
 /**
- * The entry point function object @c f must have the signature:
+ * @param ex The executor that will be used to schedule the new thread of
+ * execution.
  *
- * @code awaitable<void, E> f(); @endcode
+ * @param a The boost::asio::awaitable object that is the result of calling the
+ * coroutine's entry point function.
  *
- * where @c E is convertible from @c Executor.
+ * @param token The completion token that will handle the notification that
+ * the thread of execution has completed. The function signature of the
+ * completion handler must be:
+ * @code void handler(std::exception_ptr, T); @endcode
+ *
+ * @par Example
+ * @code
+ * boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+ * {
+ *   std::size_t bytes_transferred = 0;
+ *
+ *   try
+ *   {
+ *     char data[1024];
+ *     for (;;)
+ *     {
+ *       std::size_t n = co_await socket.async_read_some(
+ *           boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *       co_await boost::asio::async_write(socket,
+ *           boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *
+ *       bytes_transferred += n;
+ *     }
+ *   }
+ *   catch (const std::exception&)
+ *   {
+ *   }
+ *
+ *   co_return bytes_transferred;
+ * }
+ *
+ * // ...
+ *
+ * boost::asio::co_spawn(my_executor,
+ *   echo(std::move(my_tcp_socket)),
+ *   [](std::exception_ptr e, std::size_t n)
+ *   {
+ *     std::cout << "transferred " << n << "\n";
+ *   });
+ * @endcode
+ */
+template <typename Executor, typename T, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr, T)) CompletionToken
+        BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(Executor)>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr, T))
+co_spawn(const Executor& ex, awaitable<T, AwaitableExecutor> a,
+    CompletionToken&& token
+      BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
+    typename enable_if<
+      (is_executor<Executor>::value || execution::is_executor<Executor>::value)
+        && is_convertible<Executor, AwaitableExecutor>::value
+    >::type* = 0);
+
+/// Spawn a new coroutined-based thread of execution.
+/**
+ * @param ex The executor that will be used to schedule the new thread of
+ * execution.
+ *
+ * @param a The boost::asio::awaitable object that is the result of calling the
+ * coroutine's entry point function.
+ *
+ * @param token The completion token that will handle the notification that
+ * the thread of execution has completed. The function signature of the
+ * completion handler must be:
+ * @code void handler(std::exception_ptr); @endcode
+ *
+ * @par Example
+ * @code
+ * boost::asio::awaitable<void> echo(tcp::socket socket)
+ * {
+ *   try
+ *   {
+ *     char data[1024];
+ *     for (;;)
+ *     {
+ *       std::size_t n = co_await socket.async_read_some(
+ *           boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *       co_await boost::asio::async_write(socket,
+ *           boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *     }
+ *   }
+ *   catch (const std::exception& e)
+ *   {
+ *     std::cerr << "Exception: " << e.what() << "\n";
+ *   }
+ * }
+ *
+ * // ...
+ *
+ * boost::asio::co_spawn(my_executor,
+ *   echo(std::move(my_tcp_socket)),
+ *   boost::asio::detached);
+ * @endcode
+ */
+template <typename Executor, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr)) CompletionToken
+        BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(Executor)>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr))
+co_spawn(const Executor& ex, awaitable<void, AwaitableExecutor> a,
+    CompletionToken&& token
+      BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
+    typename enable_if<
+      (is_executor<Executor>::value || execution::is_executor<Executor>::value)
+        && is_convertible<Executor, AwaitableExecutor>::value
+    >::type* = 0);
+
+/// Spawn a new coroutined-based thread of execution.
+/**
+ * @param ctx An execution context that will provide the executor to be used to
+ * schedule the new thread of execution.
+ *
+ * @param a The boost::asio::awaitable object that is the result of calling the
+ * coroutine's entry point function.
+ *
+ * @param token The completion token that will handle the notification that
+ * the thread of execution has completed. The function signature of the
+ * completion handler must be:
+ * @code void handler(std::exception_ptr); @endcode
+ *
+ * @par Example
+ * @code
+ * boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+ * {
+ *   std::size_t bytes_transferred = 0;
+ *
+ *   try
+ *   {
+ *     char data[1024];
+ *     for (;;)
+ *     {
+ *       std::size_t n = co_await socket.async_read_some(
+ *           boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *       co_await boost::asio::async_write(socket,
+ *           boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *
+ *       bytes_transferred += n;
+ *     }
+ *   }
+ *   catch (const std::exception&)
+ *   {
+ *   }
+ *
+ *   co_return bytes_transferred;
+ * }
+ *
+ * // ...
+ *
+ * boost::asio::co_spawn(my_io_context,
+ *   echo(std::move(my_tcp_socket)),
+ *   [](std::exception_ptr e, std::size_t n)
+ *   {
+ *     std::cout << "transferred " << n << "\n";
+ *   });
+ * @endcode
+ */
+template <typename ExecutionContext, typename T, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr, T)) CompletionToken
+        BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(
+          typename ExecutionContext::executor_type)>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr, T))
+co_spawn(ExecutionContext& ctx, awaitable<T, AwaitableExecutor> a,
+    CompletionToken&& token
+      BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(
+        typename ExecutionContext::executor_type),
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value
+        && is_convertible<typename ExecutionContext::executor_type,
+          AwaitableExecutor>::value
+    >::type* = 0);
+
+/// Spawn a new coroutined-based thread of execution.
+/**
+ * @param ctx An execution context that will provide the executor to be used to
+ * schedule the new thread of execution.
+ *
+ * @param a The boost::asio::awaitable object that is the result of calling the
+ * coroutine's entry point function.
+ *
+ * @param token The completion token that will handle the notification that
+ * the thread of execution has completed. The function signature of the
+ * completion handler must be:
+ * @code void handler(std::exception_ptr); @endcode
+ *
+ * @par Example
+ * @code
+ * boost::asio::awaitable<void> echo(tcp::socket socket)
+ * {
+ *   try
+ *   {
+ *     char data[1024];
+ *     for (;;)
+ *     {
+ *       std::size_t n = co_await socket.async_read_some(
+ *           boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *       co_await boost::asio::async_write(socket,
+ *           boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *     }
+ *   }
+ *   catch (const std::exception& e)
+ *   {
+ *     std::cerr << "Exception: " << e.what() << "\n";
+ *   }
+ * }
+ *
+ * // ...
+ *
+ * boost::asio::co_spawn(my_io_context,
+ *   echo(std::move(my_tcp_socket)),
+ *   boost::asio::detached);
+ * @endcode
+ */
+template <typename ExecutionContext, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr)) CompletionToken
+        BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(
+          typename ExecutionContext::executor_type)>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr))
+co_spawn(ExecutionContext& ctx, awaitable<void, AwaitableExecutor> a,
+    CompletionToken&& token
+      BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(
+        typename ExecutionContext::executor_type),
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value
+        && is_convertible<typename ExecutionContext::executor_type,
+          AwaitableExecutor>::value
+    >::type* = 0);
+
+/// Spawn a new coroutined-based thread of execution.
+/**
+ * @param ex The executor that will be used to schedule the new thread of
+ * execution.
+ *
+ * @param f A nullary function object with a return type of the form
+ * @c boost::asio::awaitable<R,E> that will be used as the coroutine's entry
+ * point.
+ *
+ * @param token The completion token that will handle the notification that the
+ * thread of execution has completed. If @c R is @c void, the function
+ * signature of the completion handler must be:
+ *
+ * @code void handler(std::exception_ptr); @endcode
+ * Otherwise, the function signature of the completion handler must be:
+ * @code void handler(std::exception_ptr, R); @endcode
+ *
+ *
+ * @par Example
+ * @code
+ * boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+ * {
+ *   std::size_t bytes_transferred = 0;
+ *
+ *   try
+ *   {
+ *     char data[1024];
+ *     for (;;)
+ *     {
+ *       std::size_t n = co_await socket.async_read_some(
+ *           boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *       co_await boost::asio::async_write(socket,
+ *           boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *
+ *       bytes_transferred += n;
+ *     }
+ *   }
+ *   catch (const std::exception&)
+ *   {
+ *   }
+ *
+ *   co_return bytes_transferred;
+ * }
+ *
+ * // ...
+ *
+ * boost::asio::co_spawn(my_executor,
+ *   [socket = std::move(my_tcp_socket)]() mutable
+ *     -> boost::asio::awaitable<void>
+ *   {
+ *     try
+ *     {
+ *       char data[1024];
+ *       for (;;)
+ *       {
+ *         std::size_t n = co_await socket.async_read_some(
+ *             boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *         co_await boost::asio::async_write(socket,
+ *             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *       }
+ *     }
+ *     catch (const std::exception& e)
+ *     {
+ *       std::cerr << "Exception: " << e.what() << "\n";
+ *     }
+ *   }, boost::asio::detached);
+ * @endcode
  */
 template <typename Executor, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::awaitable_signature<
@@ -64,16 +373,78 @@ co_spawn(const Executor& ex, F&& f,
     CompletionToken&& token
       BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
     typename enable_if<
-      is_executor<Executor>::value
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
     >::type* = 0);
 
-/// Spawn a new thread of execution.
+/// Spawn a new coroutined-based thread of execution.
 /**
- * The entry point function object @c f must have the signature:
+ * @param ctx An execution context that will provide the executor to be used to
+ * schedule the new thread of execution.
  *
- * @code awaitable<void, E> f(); @endcode
+ * @param f A nullary function object with a return type of the form
+ * @c boost::asio::awaitable<R,E> that will be used as the coroutine's entry
+ * point.
  *
- * where @c E is convertible from @c ExecutionContext::executor_type.
+ * @param token The completion token that will handle the notification that the
+ * thread of execution has completed. If @c R is @c void, the function
+ * signature of the completion handler must be:
+ *
+ * @code void handler(std::exception_ptr); @endcode
+ * Otherwise, the function signature of the completion handler must be:
+ * @code void handler(std::exception_ptr, R); @endcode
+ *
+ *
+ * @par Example
+ * @code
+ * boost::asio::awaitable<std::size_t> echo(tcp::socket socket)
+ * {
+ *   std::size_t bytes_transferred = 0;
+ *
+ *   try
+ *   {
+ *     char data[1024];
+ *     for (;;)
+ *     {
+ *       std::size_t n = co_await socket.async_read_some(
+ *           boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *       co_await boost::asio::async_write(socket,
+ *           boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *
+ *       bytes_transferred += n;
+ *     }
+ *   }
+ *   catch (const std::exception&)
+ *   {
+ *   }
+ *
+ *   co_return bytes_transferred;
+ * }
+ *
+ * // ...
+ *
+ * boost::asio::co_spawn(my_io_context,
+ *   [socket = std::move(my_tcp_socket)]() mutable
+ *     -> boost::asio::awaitable<void>
+ *   {
+ *     try
+ *     {
+ *       char data[1024];
+ *       for (;;)
+ *       {
+ *         std::size_t n = co_await socket.async_read_some(
+ *             boost::asio::buffer(data), boost::asio::use_awaitable);
+ *
+ *         co_await boost::asio::async_write(socket,
+ *             boost::asio::buffer(data, n), boost::asio::use_awaitable);
+ *       }
+ *     }
+ *     catch (const std::exception& e)
+ *     {
+ *       std::cerr << "Exception: " << e.what() << "\n";
+ *     }
+ *   }, boost::asio::detached);
+ * @endcode
  */
 template <typename ExecutionContext, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::awaitable_signature<
diff --git a/include/boost/asio/defer.hpp b/include/boost/asio/defer.hpp
index a21aeb92..7967f9dc 100644
--- a/include/boost/asio/defer.hpp
+++ b/include/boost/asio/defer.hpp
@@ -19,6 +19,7 @@
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/execution_context.hpp>
+#include <boost/asio/execution/executor.hpp>
 #include <boost/asio/is_executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -101,7 +102,9 @@ BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) defer(
     const Executor& ex,
     BOOST_ASIO_MOVE_ARG(CompletionToken) token
       BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
-    typename enable_if<is_executor<Executor>::value>::type* = 0);
+    typename enable_if<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    >::type* = 0);
 
 /// Submits a completion token or function object for execution.
 /**
diff --git a/include/boost/asio/detached.hpp b/include/boost/asio/detached.hpp
index c84d954f..7f384a4e 100644
--- a/include/boost/asio/detached.hpp
+++ b/include/boost/asio/detached.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <memory>
+#include <boost/asio/detail/type_traits.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -42,6 +43,55 @@ public:
   BOOST_ASIO_CONSTEXPR detached_t()
   {
   }
+
+  /// Adapts an executor to add the @c detached_t completion token as the
+  /// default.
+  template <typename InnerExecutor>
+  struct executor_with_default : InnerExecutor
+  {
+    /// Specify @c detached_t as the default completion token type.
+    typedef detached_t default_completion_token_type;
+
+    /// Construct the adapted executor from the inner executor type.
+    executor_with_default(const InnerExecutor& ex) BOOST_ASIO_NOEXCEPT
+      : InnerExecutor(ex)
+    {
+    }
+
+    /// Convert the specified executor to the inner executor type, then use
+    /// that to construct the adapted executor.
+    template <typename OtherExecutor>
+    executor_with_default(const OtherExecutor& ex,
+        typename enable_if<
+          is_convertible<OtherExecutor, InnerExecutor>::value
+        >::type* = 0) BOOST_ASIO_NOEXCEPT
+      : InnerExecutor(ex)
+    {
+    }
+  };
+
+  /// Type alias to adapt an I/O object to use @c detached_t as its
+  /// default completion token type.
+#if defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+  template <typename T>
+  using as_default_on_t = typename T::template rebind_executor<
+      executor_with_default<typename T::executor_type> >::other;
+#endif // defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+  /// Function helper to adapt an I/O object to use @c detached_t as its
+  /// default completion token type.
+  template <typename T>
+  static typename decay<T>::type::template rebind_executor<
+      executor_with_default<typename decay<T>::type::executor_type>
+    >::other
+  as_default_on(BOOST_ASIO_MOVE_ARG(T) object)
+  {
+    return typename decay<T>::type::template rebind_executor<
+        executor_with_default<typename decay<T>::type::executor_type>
+      >::other(BOOST_ASIO_MOVE_CAST(T)(object));
+  }
 };
 
 /// A special value, similar to std::nothrow.
diff --git a/include/boost/asio/detail/assert.hpp b/include/boost/asio/detail/assert.hpp
index 1c935754..8634176a 100644
--- a/include/boost/asio/detail/assert.hpp
+++ b/include/boost/asio/detail/assert.hpp
@@ -29,4 +29,12 @@
 # define BOOST_ASIO_ASSERT(expr) assert(expr)
 #endif // defined(BOOST_ASIO_HAS_BOOST_ASSERT)
 
+#if defined(BOOST_ASIO_HAS_STATIC_ASSERT)
+# define BOOST_ASIO_STATIC_ASSERT(c, n, m) static_assert((c), m)
+#else // defined(BOOST_ASIO_HAS_STATIC_ASSERT)
+# define BOOST_ASIO_STATIC_ASSERT(c, n, m) \
+  typedef char static_assert_ ## n \
+    [(c) ? 1 : -1] BOOST_ASIO_UNUSED_TYPEDEF
+#endif // defined(BOOST_ASIO_HAS_STATIC_ASSERT)
+
 #endif // BOOST_ASIO_DETAIL_ASSERT_HPP
diff --git a/include/boost/asio/detail/atomic_count.hpp b/include/boost/asio/detail/atomic_count.hpp
index d12443dd..bd6643b5 100644
--- a/include/boost/asio/detail/atomic_count.hpp
+++ b/include/boost/asio/detail/atomic_count.hpp
@@ -32,12 +32,31 @@ namespace detail {
 #if !defined(BOOST_ASIO_HAS_THREADS)
 typedef long atomic_count;
 inline void increment(atomic_count& a, long b) { a += b; }
+inline void ref_count_up(atomic_count& a) { ++a; }
+inline bool ref_count_down(atomic_count& a) { return --a == 0; }
 #elif defined(BOOST_ASIO_HAS_STD_ATOMIC)
 typedef std::atomic<long> atomic_count;
 inline void increment(atomic_count& a, long b) { a += b; }
+
+inline void ref_count_up(atomic_count& a)
+{
+  a.fetch_add(1, std::memory_order_relaxed);
+}
+
+inline bool ref_count_down(atomic_count& a)
+{
+  if (a.fetch_sub(1, std::memory_order_release) == 1)
+  {
+    std::atomic_thread_fence(std::memory_order_acquire);
+    return true;
+  }
+  return false;
+}
 #else // defined(BOOST_ASIO_HAS_STD_ATOMIC)
 typedef boost::detail::atomic_count atomic_count;
 inline void increment(atomic_count& a, long b) { while (b > 0) ++a, --b; }
+inline void ref_count_up(atomic_count& a) { ++a; }
+inline bool ref_count_down(atomic_count& a) { return --a == 0; }
 #endif // defined(BOOST_ASIO_HAS_STD_ATOMIC)
 
 } // namespace detail
diff --git a/include/boost/asio/detail/bind_handler.hpp b/include/boost/asio/detail/bind_handler.hpp
index 3b610336..bc28d7b9 100644
--- a/include/boost/asio/detail/bind_handler.hpp
+++ b/include/boost/asio/detail/bind_handler.hpp
@@ -76,19 +76,29 @@ public:
 };
 
 template <typename Handler, typename Arg1>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     binder1<Handler, Arg1>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     binder1<Handler, Arg1>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1>
@@ -100,19 +110,27 @@ inline bool asio_handler_is_continuation(
 }
 
 template <typename Function, typename Handler, typename Arg1>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     binder1<Handler, Arg1>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler, typename Arg1>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     binder1<Handler, Arg1>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1>
@@ -177,19 +195,29 @@ public:
 };
 
 template <typename Handler, typename Arg1, typename Arg2>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     binder2<Handler, Arg1, Arg2>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     binder2<Handler, Arg1, Arg2>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2>
@@ -201,19 +229,27 @@ inline bool asio_handler_is_continuation(
 }
 
 template <typename Function, typename Handler, typename Arg1, typename Arg2>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     binder2<Handler, Arg1, Arg2>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler, typename Arg1, typename Arg2>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     binder2<Handler, Arg1, Arg2>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2>
@@ -284,19 +320,29 @@ public:
 };
 
 template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
@@ -309,20 +355,28 @@ inline bool asio_handler_is_continuation(
 
 template <typename Function, typename Handler,
     typename Arg1, typename Arg2, typename Arg3>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler,
     typename Arg1, typename Arg2, typename Arg3>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
@@ -402,20 +456,30 @@ public:
 
 template <typename Handler, typename Arg1,
     typename Arg2, typename Arg3, typename Arg4>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1,
     typename Arg2, typename Arg3, typename Arg4>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1,
@@ -429,20 +493,28 @@ inline bool asio_handler_is_continuation(
 
 template <typename Function, typename Handler, typename Arg1,
     typename Arg2, typename Arg3, typename Arg4>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler, typename Arg1,
     typename Arg2, typename Arg3, typename Arg4>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1,
@@ -528,20 +600,30 @@ public:
 
 template <typename Handler, typename Arg1, typename Arg2,
     typename Arg3, typename Arg4, typename Arg5>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2,
     typename Arg3, typename Arg4, typename Arg5>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2,
@@ -555,20 +637,28 @@ inline bool asio_handler_is_continuation(
 
 template <typename Function, typename Handler, typename Arg1,
     typename Arg2, typename Arg3, typename Arg4, typename Arg5>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler, typename Arg1,
     typename Arg2, typename Arg3, typename Arg4, typename Arg5>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2,
@@ -611,19 +701,29 @@ public:
 };
 
 template <typename Handler, typename Arg1>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     move_binder1<Handler, Arg1>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     move_binder1<Handler, Arg1>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1>
@@ -635,11 +735,15 @@ inline bool asio_handler_is_continuation(
 }
 
 template <typename Function, typename Handler, typename Arg1>
-inline void asio_handler_invoke(BOOST_ASIO_MOVE_ARG(Function) function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(BOOST_ASIO_MOVE_ARG(Function) function,
     move_binder1<Handler, Arg1>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       BOOST_ASIO_MOVE_CAST(Function)(function), this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2>
@@ -674,19 +778,29 @@ public:
 };
 
 template <typename Handler, typename Arg1, typename Arg2>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     move_binder2<Handler, Arg1, Arg2>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     move_binder2<Handler, Arg1, Arg2>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Arg1, typename Arg2>
@@ -698,11 +812,15 @@ inline bool asio_handler_is_continuation(
 }
 
 template <typename Function, typename Handler, typename Arg1, typename Arg2>
-inline void asio_handler_invoke(BOOST_ASIO_MOVE_ARG(Function) function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(BOOST_ASIO_MOVE_ARG(Function) function,
     move_binder2<Handler, Arg1, Arg2>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       BOOST_ASIO_MOVE_CAST(Function)(function), this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 #endif // defined(BOOST_ASIO_HAS_MOVE)
diff --git a/include/boost/asio/detail/blocking_executor_op.hpp b/include/boost/asio/detail/blocking_executor_op.hpp
new file mode 100644
index 00000000..7ca1cfff
--- /dev/null
+++ b/include/boost/asio/detail/blocking_executor_op.hpp
@@ -0,0 +1,109 @@
+//
+// detail/blocking_executor_op.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_DETAIL_BLOCKING_EXECUTOR_OP_HPP
+#define BOOST_ASIO_DETAIL_BLOCKING_EXECUTOR_OP_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/event.hpp>
+#include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/mutex.hpp>
+#include <boost/asio/detail/scheduler_operation.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace detail {
+
+template <typename Operation = scheduler_operation>
+class blocking_executor_op_base : public Operation
+{
+public:
+  blocking_executor_op_base(typename Operation::func_type complete_func)
+    : Operation(complete_func),
+      is_complete_(false)
+  {
+  }
+
+  void wait()
+  {
+    boost::asio::detail::mutex::scoped_lock lock(mutex_);
+    while (!is_complete_)
+      event_.wait(lock);
+  }
+
+protected:
+  struct do_complete_cleanup
+  {
+    ~do_complete_cleanup()
+    {
+      boost::asio::detail::mutex::scoped_lock lock(op_->mutex_);
+      op_->is_complete_ = true;
+      op_->event_.unlock_and_signal_one_for_destruction(lock);
+    }
+
+    blocking_executor_op_base* op_;
+  };
+
+private:
+  boost::asio::detail::mutex mutex_;
+  boost::asio::detail::event event_;
+  bool is_complete_;
+};
+
+template <typename Handler, typename Operation = scheduler_operation>
+class blocking_executor_op : public blocking_executor_op_base<Operation>
+{
+public:
+  blocking_executor_op(Handler& h)
+    : blocking_executor_op_base<Operation>(&blocking_executor_op::do_complete),
+      handler_(h)
+  {
+  }
+
+  static void do_complete(void* owner, Operation* base,
+      const boost::system::error_code& /*ec*/,
+      std::size_t /*bytes_transferred*/)
+  {
+    blocking_executor_op* o(static_cast<blocking_executor_op*>(base));
+
+    typename blocking_executor_op_base<Operation>::do_complete_cleanup
+      on_exit = { o };
+    (void)on_exit;
+
+    BOOST_ASIO_HANDLER_COMPLETION((*o));
+
+    // Make the upcall if required.
+    if (owner)
+    {
+      fenced_block b(fenced_block::half);
+      BOOST_ASIO_HANDLER_INVOCATION_BEGIN(());
+      boost_asio_handler_invoke_helpers::invoke(o->handler_, o->handler_);
+      BOOST_ASIO_HANDLER_INVOCATION_END;
+    }
+  }
+
+private:
+  Handler& handler_;
+};
+
+} // namespace detail
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_DETAIL_BLOCKING_EXECUTOR_OP_HPP
diff --git a/include/boost/asio/detail/buffer_sequence_adapter.hpp b/include/boost/asio/detail/buffer_sequence_adapter.hpp
index f0aa0013..38276c05 100644
--- a/include/boost/asio/detail/buffer_sequence_adapter.hpp
+++ b/include/boost/asio/detail/buffer_sequence_adapter.hpp
@@ -105,6 +105,8 @@ class buffer_sequence_adapter
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = false };
+
   explicit buffer_sequence_adapter(const Buffers& buffer_sequence)
     : count_(0), total_buffer_size_(0)
   {
@@ -154,6 +156,16 @@ public:
         boost::asio::buffer_sequence_end(buffer_sequence));
   }
 
+  enum { linearisation_storage_size = 8192 };
+
+  static Buffer linearise(const Buffers& buffer_sequence,
+      const boost::asio::mutable_buffer& storage)
+  {
+    return buffer_sequence_adapter::linearise(
+        boost::asio::buffer_sequence_begin(buffer_sequence),
+        boost::asio::buffer_sequence_end(buffer_sequence), storage);
+  }
+
 private:
   template <typename Iterator>
   void init(Iterator begin, Iterator end)
@@ -202,6 +214,30 @@ private:
     return Buffer();
   }
 
+  template <typename Iterator>
+  static Buffer linearise(Iterator begin, Iterator end,
+      const boost::asio::mutable_buffer& storage)
+  {
+    boost::asio::mutable_buffer unused_storage = storage;
+    Iterator iter = begin;
+    while (iter != end && unused_storage.size() != 0)
+    {
+      Buffer buffer(*iter);
+      ++iter;
+      if (buffer.size() == 0)
+        continue;
+      if (unused_storage.size() == storage.size())
+      {
+        if (iter == end)
+          return buffer;
+        if (buffer.size() >= unused_storage.size())
+          return buffer;
+      }
+      unused_storage += boost::asio::buffer_copy(unused_storage, buffer);
+    }
+    return Buffer(storage.data(), storage.size() - unused_storage.size());
+  }
+
   native_buffer_type buffers_[max_buffers];
   std::size_t count_;
   std::size_t total_buffer_size_;
@@ -212,6 +248,8 @@ class buffer_sequence_adapter<Buffer, boost::asio::mutable_buffer>
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = true };
+
   explicit buffer_sequence_adapter(
       const boost::asio::mutable_buffer& buffer_sequence)
   {
@@ -254,6 +292,14 @@ public:
     return Buffer(buffer_sequence);
   }
 
+  enum { linearisation_storage_size = 1 };
+
+  static Buffer linearise(const boost::asio::mutable_buffer& buffer_sequence,
+      const Buffer&)
+  {
+    return Buffer(buffer_sequence);
+  }
+
 private:
   native_buffer_type buffer_;
   std::size_t total_buffer_size_;
@@ -264,6 +310,8 @@ class buffer_sequence_adapter<Buffer, boost::asio::const_buffer>
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = true };
+
   explicit buffer_sequence_adapter(
       const boost::asio::const_buffer& buffer_sequence)
   {
@@ -306,6 +354,14 @@ public:
     return Buffer(buffer_sequence);
   }
 
+  enum { linearisation_storage_size = 1 };
+
+  static Buffer linearise(const boost::asio::const_buffer& buffer_sequence,
+      const Buffer&)
+  {
+    return Buffer(buffer_sequence);
+  }
+
 private:
   native_buffer_type buffer_;
   std::size_t total_buffer_size_;
@@ -318,6 +374,8 @@ class buffer_sequence_adapter<Buffer, boost::asio::mutable_buffers_1>
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = true };
+
   explicit buffer_sequence_adapter(
       const boost::asio::mutable_buffers_1& buffer_sequence)
   {
@@ -360,6 +418,14 @@ public:
     return Buffer(buffer_sequence);
   }
 
+  enum { linearisation_storage_size = 1 };
+
+  static Buffer linearise(const boost::asio::mutable_buffers_1& buffer_sequence,
+      const Buffer&)
+  {
+    return Buffer(buffer_sequence);
+  }
+
 private:
   native_buffer_type buffer_;
   std::size_t total_buffer_size_;
@@ -370,6 +436,8 @@ class buffer_sequence_adapter<Buffer, boost::asio::const_buffers_1>
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = true };
+
   explicit buffer_sequence_adapter(
       const boost::asio::const_buffers_1& buffer_sequence)
   {
@@ -412,6 +480,14 @@ public:
     return Buffer(buffer_sequence);
   }
 
+  enum { linearisation_storage_size = 1 };
+
+  static Buffer linearise(const boost::asio::const_buffers_1& buffer_sequence,
+      const Buffer&)
+  {
+    return Buffer(buffer_sequence);
+  }
+
 private:
   native_buffer_type buffer_;
   std::size_t total_buffer_size_;
@@ -424,6 +500,8 @@ class buffer_sequence_adapter<Buffer, boost::array<Elem, 2> >
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = false };
+
   explicit buffer_sequence_adapter(
       const boost::array<Elem, 2>& buffer_sequence)
   {
@@ -469,6 +547,19 @@ public:
         ? buffer_sequence[0] : buffer_sequence[1]);
   }
 
+  enum { linearisation_storage_size = 8192 };
+
+  static Buffer linearise(const boost::array<Elem, 2>& buffer_sequence,
+      const boost::asio::mutable_buffer& storage)
+  {
+    if (buffer_sequence[0].size() == 0)
+      return Buffer(buffer_sequence[1]);
+    if (buffer_sequence[1].size() == 0)
+      return Buffer(buffer_sequence[0]);
+    return Buffer(storage.data(),
+        boost::asio::buffer_copy(storage, buffer_sequence));
+  }
+
 private:
   native_buffer_type buffers_[2];
   std::size_t total_buffer_size_;
@@ -481,6 +572,8 @@ class buffer_sequence_adapter<Buffer, std::array<Elem, 2> >
   : buffer_sequence_adapter_base
 {
 public:
+  enum { is_single_buffer = false };
+
   explicit buffer_sequence_adapter(
       const std::array<Elem, 2>& buffer_sequence)
   {
@@ -526,6 +619,19 @@ public:
         ? buffer_sequence[0] : buffer_sequence[1]);
   }
 
+  enum { linearisation_storage_size = 8192 };
+
+  static Buffer linearise(const std::array<Elem, 2>& buffer_sequence,
+      const boost::asio::mutable_buffer& storage)
+  {
+    if (buffer_sequence[0].size() == 0)
+      return Buffer(buffer_sequence[1]);
+    if (buffer_sequence[1].size() == 0)
+      return Buffer(buffer_sequence[0]);
+    return Buffer(storage.data(),
+        boost::asio::buffer_copy(storage, buffer_sequence));
+  }
+
 private:
   native_buffer_type buffers_[2];
   std::size_t total_buffer_size_;
diff --git a/include/boost/asio/detail/completion_handler.hpp b/include/boost/asio/detail/completion_handler.hpp
index 7ad8e36b..4d7ac23a 100644
--- a/include/boost/asio/detail/completion_handler.hpp
+++ b/include/boost/asio/detail/completion_handler.hpp
@@ -28,17 +28,17 @@ namespace boost {
 namespace asio {
 namespace detail {
 
-template <typename Handler>
+template <typename Handler, typename IoExecutor>
 class completion_handler : public operation
 {
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(completion_handler);
 
-  completion_handler(Handler& h)
+  completion_handler(Handler& h, const IoExecutor& io_ex)
     : operation(&completion_handler::do_complete),
-      handler_(BOOST_ASIO_MOVE_CAST(Handler)(h))
+      handler_(BOOST_ASIO_MOVE_CAST(Handler)(h)),
+      work_(handler_, io_ex)
   {
-    handler_work<Handler>::start(handler_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -48,10 +48,14 @@ public:
     // Take ownership of the handler object.
     completion_handler* h(static_cast<completion_handler*>(base));
     ptr p = { boost::asio::detail::addressof(h->handler_), h, h };
-    handler_work<Handler> w(h->handler_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*h));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          h->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -74,6 +78,7 @@ public:
 
 private:
   Handler handler_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/conditionally_enabled_event.hpp b/include/boost/asio/detail/conditionally_enabled_event.hpp
index 18100546..4fb3071e 100644
--- a/include/boost/asio/detail/conditionally_enabled_event.hpp
+++ b/include/boost/asio/detail/conditionally_enabled_event.hpp
@@ -65,6 +65,14 @@ public:
       event_.unlock_and_signal_one(lock);
   }
 
+  // Unlock the mutex and signal one waiter who may destroy us.
+  void unlock_and_signal_one_for_destruction(
+      conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      event_.unlock_and_signal_one(lock);
+  }
+
   // If there's a waiter, unlock the mutex and signal it.
   bool maybe_unlock_and_signal_one(
       conditionally_enabled_mutex::scoped_lock& lock)
diff --git a/include/boost/asio/detail/config.hpp b/include/boost/asio/detail/config.hpp
index d48528a4..66c78bd8 100644
--- a/include/boost/asio/detail/config.hpp
+++ b/include/boost/asio/detail/config.hpp
@@ -61,6 +61,9 @@
 # define BOOST_ASIO_DECL
 #endif // !defined(BOOST_ASIO_DECL)
 
+// Helper macro for documentation.
+#define BOOST_ASIO_UNSPECIFIED(e) e
+
 // Microsoft Visual C++ detection.
 #if !defined(BOOST_ASIO_MSVC)
 # if defined(BOOST_ASIO_HAS_BOOST_CONFIG) && defined(BOOST_MSVC)
@@ -180,6 +183,13 @@
 #  endif // defined(BOOST_ASIO_MSVC)
 # endif // !defined(BOOST_ASIO_DISABLE_VARIADIC_TEMPLATES)
 #endif // !defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#if !defined(BOOST_ASIO_ELLIPSIS)
+# if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#  define BOOST_ASIO_ELLIPSIS ...
+# else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#  define BOOST_ASIO_ELLIPSIS
+# endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#endif // !defined(BOOST_ASIO_ELLIPSIS)
 
 // Support deleted functions on compilers known to allow it.
 #if !defined(BOOST_ASIO_DELETED)
@@ -234,39 +244,87 @@
 #  define BOOST_ASIO_CONSTEXPR
 # endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
 #endif // !defined(BOOST_ASIO_CONSTEXPR)
+#if !defined(BOOST_ASIO_STATIC_CONSTEXPR)
+# if defined(BOOST_ASIO_HAS_CONSTEXPR)
+#  define BOOST_ASIO_STATIC_CONSTEXPR(type, assignment) \
+    static constexpr type assignment
+# else // defined(BOOST_ASIO_HAS_CONSTEXPR)
+#  define BOOST_ASIO_STATIC_CONSTEXPR(type, assignment) \
+    static const type assignment
+# endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+#endif // !defined(BOOST_ASIO_STATIC_CONSTEXPR)
+#if !defined(BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT)
+# if defined(BOOST_ASIO_HAS_CONSTEXPR)
+#  if defined(__GNUC__)
+#   if (__GNUC__ >= 8)
+#    define BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(type, name) \
+      static constexpr const type name{}
+#   else // (__GNUC__ >= 8)
+#    define BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(type, name) \
+      static const type name
+#   endif // (__GNUC__ >= 8)
+#  else // defined(__GNUC__)
+#   define BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(type, name) \
+     static constexpr const type name{}
+#  endif // defined(__GNUC__)
+# else // defined(BOOST_ASIO_HAS_CONSTEXPR)
+#  define BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(type, name) \
+    static const type name
+# endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+#endif // !defined(BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT)
 
 // Support noexcept on compilers known to allow it.
-#if !defined(BOOST_ASIO_NOEXCEPT)
+#if !defined(BOOST_ASIO_HAS_NOEXCEPT)
 # if !defined(BOOST_ASIO_DISABLE_NOEXCEPT)
 #  if defined(BOOST_ASIO_HAS_BOOST_CONFIG) && (BOOST_VERSION >= 105300)
+#   if !defined(BOOST_NO_NOEXCEPT)
+#    define BOOST_ASIO_HAS_NOEXCEPT 1
+#   endif // !defined(BOOST_NO_NOEXCEPT)
 #   define BOOST_ASIO_NOEXCEPT BOOST_NOEXCEPT
 #   define BOOST_ASIO_NOEXCEPT_OR_NOTHROW BOOST_NOEXCEPT_OR_NOTHROW
+#   define BOOST_ASIO_NOEXCEPT_IF(c) BOOST_NOEXCEPT_IF(c)
 #  elif defined(__clang__)
 #   if __has_feature(__cxx_noexcept__)
-#    define BOOST_ASIO_NOEXCEPT noexcept(true)
-#    define BOOST_ASIO_NOEXCEPT_OR_NOTHROW noexcept(true)
+#    define BOOST_ASIO_HAS_NOEXCEPT 1
 #   endif // __has_feature(__cxx_noexcept__)
 #  elif defined(__GNUC__)
 #   if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4)
 #    if (__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)
-#      define BOOST_ASIO_NOEXCEPT noexcept(true)
-#      define BOOST_ASIO_NOEXCEPT_OR_NOTHROW noexcept(true)
+#      define BOOST_ASIO_HAS_NOEXCEPT 1
 #    endif // (__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)
 #   endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4)
 #  elif defined(BOOST_ASIO_MSVC)
 #   if (_MSC_VER >= 1900)
-#    define BOOST_ASIO_NOEXCEPT noexcept(true)
-#    define BOOST_ASIO_NOEXCEPT_OR_NOTHROW noexcept(true)
+#    define BOOST_ASIO_HAS_NOEXCEPT 1
 #   endif // (_MSC_VER >= 1900)
 #  endif // defined(BOOST_ASIO_MSVC)
 # endif // !defined(BOOST_ASIO_DISABLE_NOEXCEPT)
 # if !defined(BOOST_ASIO_NOEXCEPT)
-#  define BOOST_ASIO_NOEXCEPT
 # endif // !defined(BOOST_ASIO_NOEXCEPT)
 # if !defined(BOOST_ASIO_NOEXCEPT_OR_NOTHROW)
-#  define BOOST_ASIO_NOEXCEPT_OR_NOTHROW throw()
 # endif // !defined(BOOST_ASIO_NOEXCEPT_OR_NOTHROW)
+#endif // !defined(BOOST_ASIO_HAS_NOEXCEPT)
+#if !defined(BOOST_ASIO_NOEXCEPT)
+# if defined(BOOST_ASIO_HAS_NOEXCEPT)
+#  define BOOST_ASIO_NOEXCEPT noexcept(true)
+# else // defined(BOOST_ASIO_HAS_NOEXCEPT)
+#  define BOOST_ASIO_NOEXCEPT
+# endif // defined(BOOST_ASIO_HAS_NOEXCEPT)
 #endif // !defined(BOOST_ASIO_NOEXCEPT)
+#if !defined(BOOST_ASIO_NOEXCEPT_OR_NOTHROW)
+# if defined(BOOST_ASIO_HAS_NOEXCEPT)
+#  define BOOST_ASIO_NOEXCEPT_OR_NOTHROW noexcept(true)
+# else // defined(BOOST_ASIO_HAS_NOEXCEPT)
+#  define BOOST_ASIO_NOEXCEPT_OR_NOTHROW throw()
+# endif // defined(BOOST_ASIO_HAS_NOEXCEPT)
+#endif // !defined(BOOST_ASIO_NOEXCEPT_OR_NOTHROW)
+#if !defined(BOOST_ASIO_NOEXCEPT_IF)
+# if defined(BOOST_ASIO_HAS_NOEXCEPT)
+#  define BOOST_ASIO_NOEXCEPT_IF(c) noexcept(c)
+# else // defined(BOOST_ASIO_HAS_NOEXCEPT)
+#  define BOOST_ASIO_NOEXCEPT_IF(c)
+# endif // defined(BOOST_ASIO_HAS_NOEXCEPT)
+#endif // !defined(BOOST_ASIO_NOEXCEPT_IF)
 
 // Support automatic type deduction on compilers known to support it.
 #if !defined(BOOST_ASIO_HAS_DECLTYPE)
@@ -354,6 +412,113 @@
 # endif // !defined(BOOST_ASIO_DISABLE_CONCEPTS)
 #endif // !defined(BOOST_ASIO_HAS_CONCEPTS)
 
+// Support template variables on compilers known to allow it.
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+# if !defined(BOOST_ASIO_DISABLE_VARIABLE_TEMPLATES)
+#  if defined(__clang__)
+#   if (__cplusplus >= 201402)
+#    if __has_feature(__cxx_variable_templates__)
+#     define BOOST_ASIO_HAS_VARIABLE_TEMPLATES 1
+#    endif // __has_feature(__cxx_variable_templates__)
+#   endif // (__cplusplus >= 201703)
+#  endif // defined(__clang__)
+#  if defined(__GNUC__)
+#   if (__GNUC__ >= 5)
+#    if (__cplusplus >= 201402)
+#     define BOOST_ASIO_HAS_VARIABLE_TEMPLATES 1
+#    endif // (__cplusplus >= 201402)
+#   endif // (__GNUC__ >= 5)
+#  endif // defined(__GNUC__)
+#  if defined(BOOST_ASIO_MSVC)
+#   if (_MSC_VER >= 1901)
+#    define BOOST_ASIO_HAS_VARIABLE_TEMPLATES 1
+#   endif // (_MSC_VER >= 1901)
+#  endif // defined(BOOST_ASIO_MSVC)
+# endif // !defined(BOOST_ASIO_DISABLE_VARIABLE_TEMPLATES)
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+// Support SFINAEd template variables on compilers known to allow it.
+#if !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+# if !defined(BOOST_ASIO_DISABLE_SFINAE_VARIABLE_TEMPLATES)
+#  if defined(__clang__)
+#   if (__cplusplus >= 201703)
+#    if __has_feature(__cxx_variable_templates__)
+#     define BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES 1
+#    endif // __has_feature(__cxx_variable_templates__)
+#   endif // (__cplusplus >= 201703)
+#  endif // defined(__clang__)
+#  if defined(__GNUC__)
+#   if (__GNUC__ >= 7)
+#    if (__cplusplus >= 201402)
+#     define BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES 1
+#    endif // (__cplusplus >= 201402)
+#   endif // (__GNUC__ >= 7)
+#  endif // defined(__GNUC__)
+#  if defined(BOOST_ASIO_MSVC)
+#   if (_MSC_VER >= 1901)
+#    define BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES 1
+#   endif // (_MSC_VER >= 1901)
+#  endif // defined(BOOST_ASIO_MSVC)
+# endif // !defined(BOOST_ASIO_DISABLE_SFINAE_VARIABLE_TEMPLATES)
+#endif // !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+// Support SFINAE use of constant expressions on compilers known to allow it.
+#if !defined(BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE)
+# if !defined(BOOST_ASIO_DISABLE_CONSTANT_EXPRESSION_SFINAE)
+#  if defined(__clang__)
+#   if (__cplusplus >= 201402)
+#    define BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE 1
+#   endif // (__cplusplus >= 201703)
+#  endif // defined(__clang__)
+#  if defined(__GNUC__)
+#   if (__GNUC__ >= 7)
+#    if (__cplusplus >= 201402)
+#     define BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE 1
+#    endif // (__cplusplus >= 201402)
+#   endif // (__GNUC__ >= 7)
+#  endif // defined(__GNUC__)
+#  if defined(BOOST_ASIO_MSVC)
+#   if (_MSC_VER >= 1901)
+#    define BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE 1
+#   endif // (_MSC_VER >= 1901)
+#  endif // defined(BOOST_ASIO_MSVC)
+# endif // !defined(BOOST_ASIO_DISABLE_CONSTANT_EXPRESSION_SFINAE)
+#endif // !defined(BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE)
+
+// Enable workarounds for lack of working expression SFINAE.
+#if !defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# if !defined(BOOST_ASIO_DISABLE_WORKING_EXPRESSION_SFINAE)
+#  if !defined(BOOST_ASIO_MSVC)
+#   if (__cplusplus >= 201103)
+#    define BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE 1
+#   endif // (__cplusplus >= 201103)
+#  endif // defined(BOOST_ASIO_MSVC)
+# endif // !defined(BOOST_ASIO_DISABLE_WORKING_EXPRESSION_SFINAE)
+#endif // !defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+// Support static_assert on compilers known to allow it.
+#if !defined(BOOST_ASIO_HAS_STATIC_ASSERT)
+# if !defined(BOOST_ASIO_DISABLE_STATIC_ASSERT)
+#  if defined(__clang__)
+#   if __has_feature(__cxx_static_assert__)
+#    define BOOST_ASIO_HAS_STATIC_ASSERT 1
+#   endif // __has_feature(__cxx_static_assert__)
+#  endif // defined(__clang__)
+#  if defined(__GNUC__)
+#   if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ > 4)
+#    if (__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)
+#     define BOOST_ASIO_HAS_STATIC_ASSERT 1
+#    endif // (__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)
+#   endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ > 4)
+#  endif // defined(__GNUC__)
+#  if defined(BOOST_ASIO_MSVC)
+#   if (_MSC_VER >= 1900)
+#    define BOOST_ASIO_HAS_STATIC_ASSERT 1
+#   endif // (_MSC_VER >= 1900)
+#  endif // defined(BOOST_ASIO_MSVC)
+# endif // !defined(BOOST_ASIO_DISABLE_STATIC_ASSERT)
+#endif // !defined(BOOST_ASIO_HAS_STATIC_ASSERT)
+
 // Standard library support for system errors.
 # if !defined(BOOST_ASIO_DISABLE_STD_SYSTEM_ERROR)
 #  if defined(__clang__)
@@ -927,6 +1092,61 @@
 # endif // !defined(BOOST_ASIO_DISABLE_STD_INVOKE_RESULT)
 #endif // !defined(BOOST_ASIO_HAS_STD_INVOKE_RESULT)
 
+// Standard library support for std::exception_ptr and std::current_exception.
+#if !defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+# if !defined(BOOST_ASIO_DISABLE_STD_EXCEPTION_PTR)
+#  if defined(__clang__)
+#   if defined(BOOST_ASIO_HAS_CLANG_LIBCXX)
+#    define BOOST_ASIO_HAS_STD_EXCEPTION_PTR 1
+#   elif (__cplusplus >= 201103)
+#    define BOOST_ASIO_HAS_STD_EXCEPTION_PTR 1
+#   endif // (__cplusplus >= 201103)
+#  elif defined(__GNUC__)
+#   if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4)
+#    if (__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)
+#     define BOOST_ASIO_HAS_STD_EXCEPTION_PTR 1
+#    endif // (__cplusplus >= 201103) || defined(__GXX_EXPERIMENTAL_CXX0X__)
+#   endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4)
+#  endif // defined(__GNUC__)
+#  if defined(BOOST_ASIO_MSVC)
+#   if (_MSC_VER >= 1800)
+#    define BOOST_ASIO_HAS_STD_EXCEPTION_PTR 1
+#   endif // (_MSC_VER >= 1800)
+#  endif // defined(BOOST_ASIO_MSVC)
+# endif // !defined(BOOST_ASIO_DISABLE_STD_EXCEPTION_PTR)
+#endif // !defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+
+// Standard library support for std::source_location.
+#if !defined(BOOST_ASIO_HAS_STD_SOURCE_LOCATION)
+# if !defined(BOOST_ASIO_DISABLE_STD_SOURCE_LOCATION)
+// ...
+# endif // !defined(BOOST_ASIO_DISABLE_STD_SOURCE_LOCATION)
+#endif // !defined(BOOST_ASIO_HAS_STD_SOURCE_LOCATION)
+
+// Standard library support for std::experimental::source_location.
+#if !defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+# if !defined(BOOST_ASIO_DISABLE_STD_EXPERIMENTAL_SOURCE_LOCATION)
+#  if defined(__GNUC__)
+#   if (__cplusplus >= 201709)
+#    if __has_include(<experimental/source_location>)
+#     define BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION 1
+#    endif // __has_include(<experimental/source_location>)
+#   endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 9)) || (__GNUC__ > 4)
+#  endif // defined(__GNUC__)
+# endif // !defined(BOOST_ASIO_DISABLE_STD_EXPERIMENTAL_SOURCE_LOCATION)
+#endif // !defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+
+// Standard library has a source_location that we can use.
+#if !defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+# if !defined(BOOST_ASIO_DISABLE_SOURCE_LOCATION)
+#  if defined(BOOST_ASIO_HAS_STD_SOURCE_LOCATION)
+#   define BOOST_ASIO_HAS_SOURCE_LOCATION 1
+#  elif defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+#   define BOOST_ASIO_HAS_SOURCE_LOCATION 1
+#  endif // defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+# endif // !defined(BOOST_ASIO_DISABLE_SOURCE_LOCATION)
+#endif // !defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+
 // Windows App target. Windows but with a limited API.
 #if !defined(BOOST_ASIO_WINDOWS_APP)
 # if defined(_WIN32_WINNT) && (_WIN32_WINNT >= 0x0603)
@@ -970,17 +1190,17 @@
 // Windows: target OS version.
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 # if !defined(_WIN32_WINNT) && !defined(_WIN32_WINDOWS)
-#  if defined(_MSC_VER) || defined(__BORLANDC__)
+#  if defined(_MSC_VER) || (defined(__BORLANDC__) && !defined(__clang__))
 #   pragma message( \
   "Please define _WIN32_WINNT or _WIN32_WINDOWS appropriately. For example:\n"\
   "- add -D_WIN32_WINNT=0x0601 to the compiler command line; or\n"\
   "- add _WIN32_WINNT=0x0601 to your project's Preprocessor Definitions.\n"\
   "Assuming _WIN32_WINNT=0x0601 (i.e. Windows 7 target).")
-#  else // defined(_MSC_VER) || defined(__BORLANDC__)
+#  else // defined(_MSC_VER) || (defined(__BORLANDC__) && !defined(__clang__))
 #   warning Please define _WIN32_WINNT or _WIN32_WINDOWS appropriately.
 #   warning For example, add -D_WIN32_WINNT=0x0601 to the compiler command line.
 #   warning Assuming _WIN32_WINNT=0x0601 (i.e. Windows 7 target).
-#  endif // defined(_MSC_VER) || defined(__BORLANDC__)
+#  endif // defined(_MSC_VER) || (defined(__BORLANDC__) && !defined(__clang__))
 #  define _WIN32_WINNT 0x0601
 # endif // !defined(_WIN32_WINNT) && !defined(_WIN32_WINDOWS)
 # if defined(_MSC_VER)
@@ -1379,9 +1599,9 @@
 #   if (__GNUC__ >= 3)
 #    define BOOST_ASIO_HAS_HANDLER_HOOKS 1
 #   endif // (__GNUC__ >= 3)
-#  elif !defined(__BORLANDC__)
+#  elif !defined(__BORLANDC__) || defined(__clang__)
 #   define BOOST_ASIO_HAS_HANDLER_HOOKS 1
-#  endif // !defined(__BORLANDC__)
+#  endif // !defined(__BORLANDC__) || defined(__clang__)
 # endif // !defined(BOOST_ASIO_DISABLE_HANDLER_HOOKS)
 #endif // !defined(BOOST_ASIO_HAS_HANDLER_HOOKS)
 
@@ -1460,7 +1680,7 @@
 # define BOOST_ASIO_UNUSED_VARIABLE
 #endif // !defined(BOOST_ASIO_UNUSED_VARIABLE)
 
-// Support co_await on compilers known to allow it.
+// Support the co_await keyword on compilers known to allow it.
 #if !defined(BOOST_ASIO_HAS_CO_AWAIT)
 # if !defined(BOOST_ASIO_DISABLE_CO_AWAIT)
 #  if defined(BOOST_ASIO_MSVC)
@@ -1470,14 +1690,33 @@
 #    endif // defined(_RESUMABLE_FUNCTIONS_SUPPORTED)
 #   endif // (_MSC_FULL_VER >= 190023506)
 #  endif // defined(BOOST_ASIO_MSVC)
+#  if defined(__clang__)
+#   if (__cplusplus >= 201703) && (__cpp_coroutines >= 201703)
+#    if __has_include(<experimental/coroutine>)
+#     define BOOST_ASIO_HAS_CO_AWAIT 1
+#    endif // __has_include(<experimental/coroutine>)
+#   endif // (__cplusplus >= 201703) && (__cpp_coroutines >= 201703)
+#  elif defined(__GNUC__)
+#   if (__cplusplus >= 201709) && (__cpp_impl_coroutine >= 201902)
+#    if __has_include(<coroutine>)
+#     define BOOST_ASIO_HAS_CO_AWAIT 1
+#    endif // __has_include(<coroutine>)
+#   endif // (__cplusplus >= 201709) && (__cpp_impl_coroutine >= 201902)
+#  endif // defined(__GNUC__)
 # endif // !defined(BOOST_ASIO_DISABLE_CO_AWAIT)
-# if defined(__clang__)
-#  if (__cplusplus >= 201703) && (__cpp_coroutines >= 201703)
-#   if __has_include(<experimental/coroutine>)
-#    define BOOST_ASIO_HAS_CO_AWAIT 1
-#   endif // __has_include(<experimental/coroutine>)
-#  endif // (__cplusplus >= 201703) && (__cpp_coroutines >= 201703)
-# endif // defined(__clang__)
 #endif // !defined(BOOST_ASIO_HAS_CO_AWAIT)
 
+// Standard library support for coroutines.
+#if !defined(BOOST_ASIO_HAS_STD_COROUTINE)
+# if !defined(BOOST_ASIO_DISABLE_STD_COROUTINE)
+#  if defined(__GNUC__)
+#   if (__cplusplus >= 201709) && (__cpp_impl_coroutine >= 201902)
+#    if __has_include(<coroutine>)
+#     define BOOST_ASIO_HAS_STD_COROUTINE 1
+#    endif // __has_include(<coroutine>)
+#   endif // (__cplusplus >= 201709) && (__cpp_impl_coroutine >= 201902)
+#  endif // defined(__GNUC__)
+# endif // !defined(BOOST_ASIO_DISABLE_STD_COROUTINE)
+#endif // !defined(BOOST_ASIO_HAS_STD_COROUTINE)
+
 #endif // BOOST_ASIO_DETAIL_CONFIG_HPP
diff --git a/include/boost/asio/detail/deadline_timer_service.hpp b/include/boost/asio/detail/deadline_timer_service.hpp
index 0fe58c8b..02bf13ac 100644
--- a/include/boost/asio/detail/deadline_timer_service.hpp
+++ b/include/boost/asio/detail/deadline_timer_service.hpp
@@ -98,7 +98,7 @@ public:
     cancel(impl, ec);
   }
 
-  // Move-construct a new serial port implementation.
+  // Move-construct a new timer implementation.
   void move_construct(implementation_type& impl,
       implementation_type& other_impl)
   {
@@ -111,7 +111,7 @@ public:
     other_impl.might_have_pending_waits = false;
   }
 
-  // Move-assign from another serial port implementation.
+  // Move-assign from another timer implementation.
   void move_assign(implementation_type& impl,
       deadline_timer_service& other_service,
       implementation_type& other_impl)
@@ -130,6 +130,21 @@ public:
     other_impl.might_have_pending_waits = false;
   }
 
+  // Move-construct a new timer implementation.
+  void converting_move_construct(implementation_type& impl,
+      deadline_timer_service&, implementation_type& other_impl)
+  {
+    move_construct(impl, other_impl);
+  }
+
+  // Move-assign from another timer implementation.
+  void converting_move_assign(implementation_type& impl,
+      deadline_timer_service& other_service,
+      implementation_type& other_impl)
+  {
+    move_assign(impl, other_service, other_impl);
+  }
+
   // Cancel any asynchronous wait operations associated with the timer.
   std::size_t cancel(implementation_type& impl, boost::system::error_code& ec)
   {
diff --git a/include/boost/asio/detail/descriptor_ops.hpp b/include/boost/asio/detail/descriptor_ops.hpp
index 55690acf..7efbf822 100644
--- a/include/boost/asio/detail/descriptor_ops.hpp
+++ b/include/boost/asio/detail/descriptor_ops.hpp
@@ -51,13 +51,18 @@ enum
 
 typedef unsigned char state_type;
 
-template <typename ReturnType>
-inline ReturnType error_wrapper(ReturnType return_value,
-    boost::system::error_code& ec)
+inline void get_last_error(
+    boost::system::error_code& ec, bool is_error_condition)
 {
-  ec = boost::system::error_code(errno,
-      boost::asio::error::get_system_category());
-  return return_value;
+  if (!is_error_condition)
+  {
+    ec.assign(0, ec.category());
+  }
+  else
+  {
+    ec = boost::system::error_code(errno,
+        boost::asio::error::get_system_category());
+  }
 }
 
 BOOST_ASIO_DECL int open(const char* path, int flags,
@@ -77,17 +82,30 @@ typedef iovec buf;
 BOOST_ASIO_DECL std::size_t sync_read(int d, state_type state, buf* bufs,
     std::size_t count, bool all_empty, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL std::size_t sync_read1(int d, state_type state, void* data,
+    std::size_t size, boost::system::error_code& ec);
+
 BOOST_ASIO_DECL bool non_blocking_read(int d, buf* bufs, std::size_t count,
     boost::system::error_code& ec, std::size_t& bytes_transferred);
 
+BOOST_ASIO_DECL bool non_blocking_read1(int d, void* data, std::size_t size,
+    boost::system::error_code& ec, std::size_t& bytes_transferred);
+
 BOOST_ASIO_DECL std::size_t sync_write(int d, state_type state,
     const buf* bufs, std::size_t count, bool all_empty,
     boost::system::error_code& ec);
 
+BOOST_ASIO_DECL std::size_t sync_write1(int d, state_type state,
+    const void* data, std::size_t size, boost::system::error_code& ec);
+
 BOOST_ASIO_DECL bool non_blocking_write(int d,
     const buf* bufs, std::size_t count,
     boost::system::error_code& ec, std::size_t& bytes_transferred);
 
+BOOST_ASIO_DECL bool non_blocking_write1(int d,
+    const void* data, std::size_t size,
+    boost::system::error_code& ec, std::size_t& bytes_transferred);
+
 BOOST_ASIO_DECL int ioctl(int d, state_type& state, long cmd,
     ioctl_arg_type* arg, boost::system::error_code& ec);
 
diff --git a/include/boost/asio/detail/descriptor_read_op.hpp b/include/boost/asio/detail/descriptor_read_op.hpp
index f0b6be7b..f3bfe952 100644
--- a/include/boost/asio/detail/descriptor_read_op.hpp
+++ b/include/boost/asio/detail/descriptor_read_op.hpp
@@ -37,9 +37,11 @@ template <typename MutableBufferSequence>
 class descriptor_read_op_base : public reactor_op
 {
 public:
-  descriptor_read_op_base(int descriptor,
-      const MutableBufferSequence& buffers, func_type complete_func)
-    : reactor_op(&descriptor_read_op_base::do_perform, complete_func),
+  descriptor_read_op_base(const boost::system::error_code& success_ec,
+      int descriptor, const MutableBufferSequence& buffers,
+      func_type complete_func)
+    : reactor_op(success_ec,
+        &descriptor_read_op_base::do_perform, complete_func),
       descriptor_(descriptor),
       buffers_(buffers)
   {
@@ -49,12 +51,24 @@ public:
   {
     descriptor_read_op_base* o(static_cast<descriptor_read_op_base*>(base));
 
-    buffer_sequence_adapter<boost::asio::mutable_buffer,
-        MutableBufferSequence> bufs(o->buffers_);
+    typedef buffer_sequence_adapter<boost::asio::mutable_buffer,
+        MutableBufferSequence> bufs_type;
 
-    status result = descriptor_ops::non_blocking_read(o->descriptor_,
-        bufs.buffers(), bufs.count(), o->ec_, o->bytes_transferred_)
-      ? done : not_done;
+    status result;
+    if (bufs_type::is_single_buffer)
+    {
+      result = descriptor_ops::non_blocking_read1(o->descriptor_,
+          bufs_type::first(o->buffers_).data(),
+          bufs_type::first(o->buffers_).size(),
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
+    else
+    {
+      bufs_type bufs(o->buffers_);
+      result = descriptor_ops::non_blocking_read(o->descriptor_,
+          bufs.buffers(), bufs.count(), o->ec_, o->bytes_transferred_)
+        ? done : not_done;
+    }
 
     BOOST_ASIO_HANDLER_REACTOR_OPERATION((*o, "non_blocking_read",
           o->ec_, o->bytes_transferred_));
@@ -74,14 +88,14 @@ class descriptor_read_op
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(descriptor_read_op);
 
-  descriptor_read_op(int descriptor, const MutableBufferSequence& buffers,
+  descriptor_read_op(const boost::system::error_code& success_ec,
+      int descriptor, const MutableBufferSequence& buffers,
       Handler& handler, const IoExecutor& io_ex)
-    : descriptor_read_op_base<MutableBufferSequence>(
+    : descriptor_read_op_base<MutableBufferSequence>(success_ec,
         descriptor, buffers, &descriptor_read_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -91,10 +105,14 @@ public:
     // Take ownership of the handler object.
     descriptor_read_op* o(static_cast<descriptor_read_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -118,7 +136,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/descriptor_write_op.hpp b/include/boost/asio/detail/descriptor_write_op.hpp
index abc36a5b..77646649 100644
--- a/include/boost/asio/detail/descriptor_write_op.hpp
+++ b/include/boost/asio/detail/descriptor_write_op.hpp
@@ -37,9 +37,11 @@ template <typename ConstBufferSequence>
 class descriptor_write_op_base : public reactor_op
 {
 public:
-  descriptor_write_op_base(int descriptor,
-      const ConstBufferSequence& buffers, func_type complete_func)
-    : reactor_op(&descriptor_write_op_base::do_perform, complete_func),
+  descriptor_write_op_base(const boost::system::error_code& success_ec,
+      int descriptor, const ConstBufferSequence& buffers,
+      func_type complete_func)
+    : reactor_op(success_ec,
+        &descriptor_write_op_base::do_perform, complete_func),
       descriptor_(descriptor),
       buffers_(buffers)
   {
@@ -49,12 +51,24 @@ public:
   {
     descriptor_write_op_base* o(static_cast<descriptor_write_op_base*>(base));
 
-    buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence> bufs(o->buffers_);
+    typedef buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence> bufs_type;
 
-    status result = descriptor_ops::non_blocking_write(o->descriptor_,
-        bufs.buffers(), bufs.count(), o->ec_, o->bytes_transferred_)
-      ? done : not_done;
+    status result;
+    if (bufs_type::is_single_buffer)
+    {
+      result = descriptor_ops::non_blocking_write1(o->descriptor_,
+          bufs_type::first(o->buffers_).data(),
+          bufs_type::first(o->buffers_).size(),
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
+    else
+    {
+      bufs_type bufs(o->buffers_);
+      result = descriptor_ops::non_blocking_write(o->descriptor_,
+          bufs.buffers(), bufs.count(), o->ec_, o->bytes_transferred_)
+        ? done : not_done;
+    }
 
     BOOST_ASIO_HANDLER_REACTOR_OPERATION((*o, "non_blocking_write",
           o->ec_, o->bytes_transferred_));
@@ -74,14 +88,14 @@ class descriptor_write_op
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(descriptor_write_op);
 
-  descriptor_write_op(int descriptor, const ConstBufferSequence& buffers,
+  descriptor_write_op(const boost::system::error_code& success_ec,
+      int descriptor, const ConstBufferSequence& buffers,
       Handler& handler, const IoExecutor& io_ex)
-    : descriptor_write_op_base<ConstBufferSequence>(
+    : descriptor_write_op_base<ConstBufferSequence>(success_ec,
         descriptor, buffers, &descriptor_write_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -91,10 +105,14 @@ public:
     // Take ownership of the handler object.
     descriptor_write_op* o(static_cast<descriptor_write_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -118,7 +136,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/executor_function.hpp b/include/boost/asio/detail/executor_function.hpp
index d13a2ca2..14e0440e 100644
--- a/include/boost/asio/detail/executor_function.hpp
+++ b/include/boost/asio/detail/executor_function.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/memory.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -24,57 +25,80 @@ namespace boost {
 namespace asio {
 namespace detail {
 
-class executor_function_base
+#if defined(BOOST_ASIO_HAS_MOVE)
+
+// Lightweight, move-only function object wrapper.
+class executor_function
 {
 public:
-  void complete()
+  template <typename F, typename Alloc>
+  explicit executor_function(F f, const Alloc& a)
   {
-    func_(this, true);
+    // Allocate and construct an object to wrap the function.
+    typedef impl<F, Alloc> impl_type;
+    typename impl_type::ptr p = {
+      detail::addressof(a), impl_type::ptr::allocate(a), 0 };
+    impl_ = new (p.v) impl_type(BOOST_ASIO_MOVE_CAST(F)(f), a);
+    p.v = 0;
   }
 
-  void destroy()
+  executor_function(executor_function&& other) BOOST_ASIO_NOEXCEPT
+    : impl_(other.impl_)
   {
-    func_(this, false);
+    other.impl_ = 0;
   }
 
-protected:
-  typedef void (*func_type)(executor_function_base*, bool);
-
-  executor_function_base(func_type func)
-    : func_(func)
+  ~executor_function()
   {
+    if (impl_)
+      impl_->complete_(impl_, false);
   }
 
-  // Prevents deletion through this type.
-  ~executor_function_base()
+  void operator()()
   {
+    if (impl_)
+    {
+      impl_base* i = impl_;
+      impl_ = 0;
+      i->complete_(i, true);
+    }
   }
 
 private:
-  func_type func_;
-};
-
-template <typename Function, typename Alloc>
-class executor_function : public executor_function_base
-{
-public:
-  BOOST_ASIO_DEFINE_TAGGED_HANDLER_ALLOCATOR_PTR(
-      thread_info_base::executor_function_tag, executor_function);
-
-  template <typename F>
-  executor_function(BOOST_ASIO_MOVE_ARG(F) f, const Alloc& allocator)
-    : executor_function_base(&executor_function::do_complete),
-      function_(BOOST_ASIO_MOVE_CAST(F)(f)),
-      allocator_(allocator)
+  // Base class for polymorphic function implementations.
+  struct impl_base
   {
-  }
+    void (*complete_)(impl_base*, bool);
+  };
 
-  static void do_complete(executor_function_base* base, bool call)
+  // Polymorphic function implementation.
+  template <typename Function, typename Alloc>
+  struct impl : impl_base
+  {
+    BOOST_ASIO_DEFINE_TAGGED_HANDLER_ALLOCATOR_PTR(
+        thread_info_base::executor_function_tag, impl);
+
+    template <typename F>
+    impl(BOOST_ASIO_MOVE_ARG(F) f, const Alloc& a)
+      : function_(BOOST_ASIO_MOVE_CAST(F)(f)),
+        allocator_(a)
+    {
+      complete_ = &executor_function::complete<Function, Alloc>;
+    }
+
+    Function function_;
+    Alloc allocator_;
+  };
+
+  // Helper to complete function invocation.
+  template <typename Function, typename Alloc>
+  static void complete(impl_base* base, bool call)
   {
     // Take ownership of the function object.
-    executor_function* o(static_cast<executor_function*>(base));
-    Alloc allocator(o->allocator_);
-    ptr p = { detail::addressof(allocator), o, o };
+    impl<Function, Alloc>* i(static_cast<impl<Function, Alloc>*>(base));
+    Alloc allocator(i->allocator_);
+    typename impl<Function, Alloc>::ptr p = {
+      detail::addressof(allocator), i, i };
 
     // Make a copy of the function so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
@@ -82,7 +106,7 @@ public:
     // associated with the function. Consequently, a local copy of the function
     // is required to ensure that any owning sub-object remains valid until
     // after we have deallocated the memory here.
-    Function function(BOOST_ASIO_MOVE_CAST(Function)(o->function_));
+    Function function(BOOST_ASIO_MOVE_CAST(Function)(i->function_));
     p.reset();
 
     // Make the upcall if required.
@@ -92,9 +116,84 @@ public:
     }
   }
 
+  impl_base* impl_;
+};
+
+#else // defined(BOOST_ASIO_HAS_MOVE)
+
+// Not so lightweight, copyable function object wrapper.
+class executor_function
+{
+public:
+  template <typename F, typename Alloc>
+  explicit executor_function(const F& f, const Alloc&)
+    : impl_(new impl<typename decay<F>::type>(f))
+  {
+  }
+
+  void operator()()
+  {
+    impl_->complete_(impl_.get());
+  }
+
 private:
-  Function function_;
-  Alloc allocator_;
+  // Base class for polymorphic function implementations.
+  struct impl_base
+  {
+    void (*complete_)(impl_base*);
+  };
+
+  // Polymorphic function implementation.
+  template <typename F>
+  struct impl : impl_base
+  {
+    impl(const F& f)
+      : function_(f)
+    {
+      complete_ = &executor_function::complete<F>;
+    }
+
+    F function_;
+  };
+
+  // Helper to complete function invocation.
+  template <typename F>
+  static void complete(impl_base* i)
+  {
+    static_cast<impl<F>*>(i)->function_();
+  }
+
+  shared_ptr<impl_base> impl_;
+};
+
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+// Lightweight, non-owning, copyable function object wrapper.
+class executor_function_view
+{
+public:
+  template <typename F>
+  explicit executor_function_view(F& f) BOOST_ASIO_NOEXCEPT
+    : complete_(&executor_function_view::complete<F>),
+      function_(&f)
+  {
+  }
+
+  void operator()()
+  {
+    complete_(function_);
+  }
+
+private:
+  // Helper to complete function invocation.
+  template <typename F>
+  static void complete(void* f)
+  {
+    (*static_cast<F*>(f))();
+  }
+
+  void (*complete_)(void*);
+  void* function_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/handler_alloc_helpers.hpp b/include/boost/asio/detail/handler_alloc_helpers.hpp
index 41319d17..4d713940 100644
--- a/include/boost/asio/detail/handler_alloc_helpers.hpp
+++ b/include/boost/asio/detail/handler_alloc_helpers.hpp
@@ -19,6 +19,7 @@
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/noncopyable.hpp>
 #include <boost/asio/detail/recycling_allocator.hpp>
+#include <boost/asio/detail/thread_info_base.hpp>
 #include <boost/asio/associated_allocator.hpp>
 #include <boost/asio/handler_alloc_hook.hpp>
 
@@ -29,11 +30,41 @@
 // boost_asio_handler_alloc_helpers namespace is defined here for that purpose.
 namespace boost_asio_handler_alloc_helpers {
 
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+template <typename Handler>
+inline void error_if_hooks_are_defined(Handler& h)
+{
+  using boost::asio::asio_handler_allocate;
+  // If you get an error here it is because some of your handlers still
+  // overload asio_handler_allocate, but this hook is no longer used.
+  (void)static_cast<boost::asio::asio_handler_allocate_is_no_longer_used>(
+    asio_handler_allocate(static_cast<std::size_t>(0),
+      boost::asio::detail::addressof(h)));
+
+  using boost::asio::asio_handler_deallocate;
+  // If you get an error here it is because some of your handlers still
+  // overload asio_handler_deallocate, but this hook is no longer used.
+  (void)static_cast<boost::asio::asio_handler_deallocate_is_no_longer_used>(
+    asio_handler_deallocate(static_cast<void*>(0),
+      static_cast<std::size_t>(0), boost::asio::detail::addressof(h)));
+}
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
+
 template <typename Handler>
 inline void* allocate(std::size_t s, Handler& h)
 {
 #if !defined(BOOST_ASIO_HAS_HANDLER_HOOKS)
   return ::operator new(s);
+#elif defined(BOOST_ASIO_NO_DEPRECATED)
+  // The asio_handler_allocate hook is no longer used to obtain memory.
+  (void)&error_if_hooks_are_defined<Handler>;
+  (void)h;
+#if !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
+  return boost::asio::detail::thread_info_base::allocate(
+      boost::asio::detail::thread_context::thread_call_stack::top(), s);
+#else // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
+  return ::operator new(size);
+#endif // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
 #else
   using boost::asio::asio_handler_allocate;
   return asio_handler_allocate(s, boost::asio::detail::addressof(h));
@@ -45,6 +76,17 @@ inline void deallocate(void* p, std::size_t s, Handler& h)
 {
 #if !defined(BOOST_ASIO_HAS_HANDLER_HOOKS)
   ::operator delete(p);
+#elif defined(BOOST_ASIO_NO_DEPRECATED)
+  // The asio_handler_allocate hook is no longer used to obtain memory.
+  (void)&error_if_hooks_are_defined<Handler>;
+  (void)h;
+#if !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
+  boost::asio::detail::thread_info_base::deallocate(
+      boost::asio::detail::thread_context::thread_call_stack::top(), p, s);
+#else // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
+  (void)s;
+  ::operator delete(p);
+#endif // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
 #else
   using boost::asio::asio_handler_deallocate;
   asio_handler_deallocate(p, s, boost::asio::detail::addressof(h));
diff --git a/include/boost/asio/detail/handler_invoke_helpers.hpp b/include/boost/asio/detail/handler_invoke_helpers.hpp
index 79fc7674..35007e45 100644
--- a/include/boost/asio/detail/handler_invoke_helpers.hpp
+++ b/include/boost/asio/detail/handler_invoke_helpers.hpp
@@ -26,12 +26,29 @@
 // namespace is defined here for that purpose.
 namespace boost_asio_handler_invoke_helpers {
 
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+template <typename Function, typename Context>
+inline void error_if_hook_is_defined(Function& function, Context& context)
+{
+  using boost::asio::asio_handler_invoke;
+  // If you get an error here it is because some of your handlers still
+  // overload asio_handler_invoke, but this hook is no longer used.
+  (void)static_cast<boost::asio::asio_handler_invoke_is_no_longer_used>(
+    asio_handler_invoke(function, boost::asio::detail::addressof(context)));
+}
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
+
 template <typename Function, typename Context>
 inline void invoke(Function& function, Context& context)
 {
 #if !defined(BOOST_ASIO_HAS_HANDLER_HOOKS)
   Function tmp(function);
   tmp();
+#elif defined(BOOST_ASIO_NO_DEPRECATED)
+  // The asio_handler_invoke hook is no longer used to invoke the function.
+  (void)&error_if_hook_is_defined<Function, Context>;
+  (void)context;
+  function();
 #else
   using boost::asio::asio_handler_invoke;
   asio_handler_invoke(function, boost::asio::detail::addressof(context));
@@ -44,6 +61,12 @@ inline void invoke(const Function& function, Context& context)
 #if !defined(BOOST_ASIO_HAS_HANDLER_HOOKS)
   Function tmp(function);
   tmp();
+#elif defined(BOOST_ASIO_NO_DEPRECATED)
+  // The asio_handler_invoke hook is no longer used to invoke the function.
+  (void)&error_if_hook_is_defined<const Function, Context>;
+  (void)context;
+  Function tmp(function);
+  tmp();
 #else
   using boost::asio::asio_handler_invoke;
   asio_handler_invoke(function, boost::asio::detail::addressof(context));
diff --git a/include/boost/asio/detail/handler_tracking.hpp b/include/boost/asio/detail/handler_tracking.hpp
index 3eeb2046..78730412 100644
--- a/include/boost/asio/detail/handler_tracking.hpp
+++ b/include/boost/asio/detail/handler_tracking.hpp
@@ -90,6 +90,28 @@ public:
   // Initialise the tracking system.
   BOOST_ASIO_DECL static void init();
 
+  class location
+  {
+  public:
+    // Constructor adds a location to the stack.
+    BOOST_ASIO_DECL explicit location(const char* file,
+        int line, const char* func);
+
+    // Destructor removes a location from the stack.
+    BOOST_ASIO_DECL ~location();
+
+  private:
+    // Disallow copying and assignment.
+    location(const location&) BOOST_ASIO_DELETED;
+    location& operator=(const location&) BOOST_ASIO_DELETED;
+
+    friend class handler_tracking;
+    const char* file_;
+    int line_;
+    const char* func_;
+    location* next_;
+  };
+
   // Record the creation of a tracked handler.
   BOOST_ASIO_DECL static void creation(
       execution_context& context, tracked_handler& h,
@@ -178,6 +200,9 @@ private:
 # define BOOST_ASIO_HANDLER_TRACKING_INIT \
   boost::asio::detail::handler_tracking::init()
 
+# define BOOST_ASIO_HANDLER_LOCATION(args) \
+  boost::asio::detail::handler_tracking::location tracked_location args
+
 # define BOOST_ASIO_HANDLER_CREATION(args) \
   boost::asio::detail::handler_tracking::creation args
 
@@ -214,6 +239,7 @@ private:
 # define BOOST_ASIO_INHERIT_TRACKED_HANDLER
 # define BOOST_ASIO_ALSO_INHERIT_TRACKED_HANDLER
 # define BOOST_ASIO_HANDLER_TRACKING_INIT (void)0
+# define BOOST_ASIO_HANDLER_LOCATION(loc) (void)0
 # define BOOST_ASIO_HANDLER_CREATION(args) (void)0
 # define BOOST_ASIO_HANDLER_COMPLETION(args) (void)0
 # define BOOST_ASIO_HANDLER_INVOCATION_BEGIN(args) (void)0
diff --git a/include/boost/asio/detail/handler_work.hpp b/include/boost/asio/detail/handler_work.hpp
index e2c860fc..a20a2e0b 100644
--- a/include/boost/asio/detail/handler_work.hpp
+++ b/include/boost/asio/detail/handler_work.hpp
@@ -18,92 +18,277 @@
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/execute.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/execution/outstanding_work.hpp>
+#include <boost/asio/executor_work_guard.hpp>
+#include <boost/asio/prefer.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
+
+class executor;
+class io_context;
+
 namespace detail {
 
-// A helper class template to allow completion handlers to be dispatched
-// through either the new executors framework or the old invocaton hook. The
-// primary template uses the new executors framework.
-template <typename Handler,
-    typename IoExecutor = system_executor, typename HandlerExecutor
-      = typename associated_executor<Handler, IoExecutor>::type>
-class handler_work
+template <typename Executor, typename CandidateExecutor = void,
+    typename IoContext = io_context,
+    typename PolymorphicExecutor = executor, typename = void>
+class handler_work_base
 {
 public:
-  explicit handler_work(Handler& handler) BOOST_ASIO_NOEXCEPT
-    : io_executor_(),
-      executor_(boost::asio::get_associated_executor(handler, io_executor_))
+  explicit handler_work_base(const Executor& ex) BOOST_ASIO_NOEXCEPT
+    : executor_(boost::asio::prefer(ex, execution::outstanding_work.tracked))
   {
   }
 
-  handler_work(Handler& handler, const IoExecutor& io_ex) BOOST_ASIO_NOEXCEPT
-    : io_executor_(io_ex),
-      executor_(boost::asio::get_associated_executor(handler, io_executor_))
+  template <typename OtherExecutor>
+  handler_work_base(const Executor& ex,
+      const OtherExecutor&) BOOST_ASIO_NOEXCEPT
+    : executor_(boost::asio::prefer(ex, execution::outstanding_work.tracked))
   {
   }
 
-  static void start(Handler& handler) BOOST_ASIO_NOEXCEPT
+  handler_work_base(const handler_work_base& other) BOOST_ASIO_NOEXCEPT
+    : executor_(other.executor_)
   {
-    HandlerExecutor ex(boost::asio::get_associated_executor(handler));
-    ex.on_work_started();
   }
 
-  static void start(Handler& handler,
-      const IoExecutor& io_ex) BOOST_ASIO_NOEXCEPT
+#if defined(BOOST_ASIO_HAS_MOVE)
+  handler_work_base(handler_work_base&& other) BOOST_ASIO_NOEXCEPT
+    : executor_(BOOST_ASIO_MOVE_CAST(executor_type)(other.executor_))
   {
-    HandlerExecutor ex(boost::asio::get_associated_executor(handler, io_ex));
-    ex.on_work_started();
-    io_ex.on_work_started();
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  bool owns_work() const BOOST_ASIO_NOEXCEPT
+  {
+    return true;
   }
 
-  ~handler_work()
+  template <typename Function, typename Handler>
+  void dispatch(Function& function, Handler& handler)
   {
-    io_executor_.on_work_finished();
-    executor_.on_work_finished();
+    execution::execute(
+        boost::asio::prefer(executor_,
+          execution::blocking.possibly,
+          execution::allocator((get_associated_allocator)(handler))),
+        BOOST_ASIO_MOVE_CAST(Function)(function));
   }
 
-  template <typename Function>
-  void complete(Function& function, Handler& handler)
+private:
+  typedef typename decay<
+      typename prefer_result_type<Executor,
+        execution::outstanding_work_t::tracked_t
+      >::type
+    >::type executor_type;
+
+  executor_type executor_;
+};
+
+template <typename Executor, typename CandidateExecutor,
+    typename IoContext, typename PolymorphicExecutor>
+class handler_work_base<Executor, CandidateExecutor,
+    IoContext, PolymorphicExecutor,
+    typename enable_if<
+      !execution::is_executor<Executor>::value
+        && (!is_same<Executor, PolymorphicExecutor>::value
+          || !is_same<CandidateExecutor, void>::value)
+    >::type>
+{
+public:
+  explicit handler_work_base(const Executor& ex) BOOST_ASIO_NOEXCEPT
+    : executor_(ex),
+      owns_work_(true)
+  {
+    executor_.on_work_started();
+  }
+
+  handler_work_base(const Executor& ex,
+      const Executor& candidate) BOOST_ASIO_NOEXCEPT
+    : executor_(ex),
+      owns_work_(ex != candidate)
+  {
+    if (owns_work_)
+      executor_.on_work_started();
+  }
+
+  template <typename OtherExecutor>
+  handler_work_base(const Executor& ex,
+      const OtherExecutor&) BOOST_ASIO_NOEXCEPT
+    : executor_(ex),
+      owns_work_(true)
+  {
+    executor_.on_work_started();
+  }
+
+  handler_work_base(const handler_work_base& other) BOOST_ASIO_NOEXCEPT
+    : executor_(other.executor_),
+      owns_work_(other.owns_work_)
+  {
+    if (owns_work_)
+      executor_.on_work_started();
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  handler_work_base(handler_work_base&& other) BOOST_ASIO_NOEXCEPT
+    : executor_(BOOST_ASIO_MOVE_CAST(Executor)(other.executor_)),
+      owns_work_(other.owns_work_)
+  {
+    other.owns_work_ = false;
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  ~handler_work_base()
+  {
+    if (owns_work_)
+      executor_.on_work_finished();
+  }
+
+  bool owns_work() const BOOST_ASIO_NOEXCEPT
+  {
+    return owns_work_;
+  }
+
+  template <typename Function, typename Handler>
+  void dispatch(Function& function, Handler& handler)
   {
     executor_.dispatch(BOOST_ASIO_MOVE_CAST(Function)(function),
         boost::asio::get_associated_allocator(handler));
   }
 
 private:
-  // Disallow copying and assignment.
-  handler_work(const handler_work&);
-  handler_work& operator=(const handler_work&);
-
-  IoExecutor io_executor_;
-  HandlerExecutor executor_;
+  Executor executor_;
+  bool owns_work_;
 };
 
-// This specialisation dispatches a handler through the old invocation hook.
-// The specialisation is not strictly required for correctness, as the
-// system_executor will dispatch through the hook anyway. However, by doing
-// this we avoid an extra copy of the handler.
-template <typename Handler>
-class handler_work<Handler, system_executor, system_executor>
+template <typename Executor, typename IoContext, typename PolymorphicExecutor>
+class handler_work_base<Executor, void, IoContext, PolymorphicExecutor,
+    typename enable_if<
+      is_same<
+        Executor,
+        typename IoContext::executor_type
+      >::value
+    >::type>
 {
 public:
-  explicit handler_work(Handler&) BOOST_ASIO_NOEXCEPT {}
-  static void start(Handler&) BOOST_ASIO_NOEXCEPT {}
-  ~handler_work() {}
+  explicit handler_work_base(const Executor&)
+  {
+  }
+
+  bool owns_work() const BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename Executor, typename IoContext>
+class handler_work_base<Executor, void, IoContext, Executor>
+{
+public:
+  explicit handler_work_base(const Executor& ex) BOOST_ASIO_NOEXCEPT
+#if !defined(BOOST_ASIO_NO_TYPEID)
+    : executor_(
+        ex.target_type() == typeid(typename IoContext::executor_type)
+          ? Executor() : ex)
+#else // !defined(BOOST_ASIO_NO_TYPEID)
+    : executor_(ex)
+#endif // !defined(BOOST_ASIO_NO_TYPEID)
+  {
+    if (executor_)
+      executor_.on_work_started();
+  }
+
+  handler_work_base(const Executor& ex,
+      const Executor& candidate) BOOST_ASIO_NOEXCEPT
+    : executor_(ex != candidate ? ex : Executor())
+  {
+    if (executor_)
+      executor_.on_work_started();
+  }
+
+  template <typename OtherExecutor>
+  handler_work_base(const Executor& ex,
+      const OtherExecutor&) BOOST_ASIO_NOEXCEPT
+    : executor_(ex)
+  {
+    executor_.on_work_started();
+  }
+
+  handler_work_base(const handler_work_base& other) BOOST_ASIO_NOEXCEPT
+    : executor_(other.executor_)
+  {
+    if (executor_)
+      executor_.on_work_started();
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  handler_work_base(handler_work_base&& other) BOOST_ASIO_NOEXCEPT
+    : executor_(BOOST_ASIO_MOVE_CAST(Executor)(other.executor_))
+  {
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  ~handler_work_base()
+  {
+    if (executor_)
+      executor_.on_work_finished();
+  }
+
+  bool owns_work() const BOOST_ASIO_NOEXCEPT
+  {
+    return !!executor_;
+  }
+
+  template <typename Function, typename Handler>
+  void dispatch(Function& function, Handler& handler)
+  {
+    executor_.dispatch(BOOST_ASIO_MOVE_CAST(Function)(function),
+        boost::asio::get_associated_allocator(handler));
+  }
+
+private:
+  Executor executor_;
+};
+
+template <typename Handler, typename IoExecutor,
+    typename HandlerExecutor =
+      typename associated_executor<Handler, IoExecutor>::type>
+class handler_work :
+  handler_work_base<IoExecutor>,
+  handler_work_base<HandlerExecutor, IoExecutor>
+{
+public:
+  handler_work(Handler& handler, const IoExecutor& io_ex) BOOST_ASIO_NOEXCEPT
+    : handler_work_base<IoExecutor>(io_ex),
+      handler_work_base<HandlerExecutor, IoExecutor>(
+          boost::asio::get_associated_executor(handler, io_ex), io_ex)
+  {
+  }
 
   template <typename Function>
   void complete(Function& function, Handler& handler)
   {
-    boost_asio_handler_invoke_helpers::invoke(function, handler);
+    if (!handler_work_base<IoExecutor>::owns_work()
+        && !handler_work_base<HandlerExecutor, IoExecutor>::owns_work())
+    {
+      // When using a native implementation, I/O completion handlers are
+      // already dispatched according to the execution context's executor's
+      // rules. We can call the function directly.
+      boost_asio_handler_invoke_helpers::invoke(function, handler);
+    }
+    else
+    {
+      handler_work_base<HandlerExecutor,
+          IoExecutor>::dispatch(function, handler);
+    }
   }
-
-private:
-  // Disallow copying and assignment.
-  handler_work(const handler_work&);
-  handler_work& operator=(const handler_work&);
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/impl/descriptor_ops.ipp b/include/boost/asio/detail/impl/descriptor_ops.ipp
index f4c21d55..16c04f3e 100644
--- a/include/boost/asio/detail/impl/descriptor_ops.ipp
+++ b/include/boost/asio/detail/impl/descriptor_ops.ipp
@@ -33,10 +33,8 @@ namespace descriptor_ops {
 
 int open(const char* path, int flags, boost::system::error_code& ec)
 {
-  errno = 0;
-  int result = error_wrapper(::open(path, flags), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
+  int result = ::open(path, flags);
+  get_last_error(ec, result < 0);
   return result;
 }
 
@@ -45,8 +43,8 @@ int close(int d, state_type& state, boost::system::error_code& ec)
   int result = 0;
   if (d != -1)
   {
-    errno = 0;
-    result = error_wrapper(::close(d), ec);
+    result = ::close(d);
+    get_last_error(ec, result < 0);
 
     if (result != 0
         && (ec == boost::asio::error::would_block
@@ -68,13 +66,11 @@ int close(int d, state_type& state, boost::system::error_code& ec)
 #endif // defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
       state &= ~non_blocking;
 
-      errno = 0;
-      result = error_wrapper(::close(d), ec);
+      result = ::close(d);
+      get_last_error(ec, result < 0);
     }
   }
 
-  if (result == 0)
-    ec = boost::system::error_code();
   return result;
 }
 
@@ -87,23 +83,23 @@ bool set_user_non_blocking(int d, state_type& state,
     return false;
   }
 
-  errno = 0;
 #if defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
-  int result = error_wrapper(::fcntl(d, F_GETFL, 0), ec);
+  int result = ::fcntl(d, F_GETFL, 0);
+  get_last_error(ec, result < 0);
   if (result >= 0)
   {
-    errno = 0;
     int flag = (value ? (result | O_NONBLOCK) : (result & ~O_NONBLOCK));
-    result = error_wrapper(::fcntl(d, F_SETFL, flag), ec);
+    result = ::fcntl(d, F_SETFL, flag);
+    get_last_error(ec, result < 0);
   }
 #else // defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
   ioctl_arg_type arg = (value ? 1 : 0);
-  int result = error_wrapper(::ioctl(d, FIONBIO, &arg), ec);
+  int result = ::ioctl(d, FIONBIO, &arg);
+  get_last_error(ec, result < 0);
 #endif // defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
 
   if (result >= 0)
   {
-    ec = boost::system::error_code();
     if (value)
       state |= user_set_non_blocking;
     else
@@ -137,23 +133,23 @@ bool set_internal_non_blocking(int d, state_type& state,
     return false;
   }
 
-  errno = 0;
 #if defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
-  int result = error_wrapper(::fcntl(d, F_GETFL, 0), ec);
+  int result = ::fcntl(d, F_GETFL, 0);
+  get_last_error(ec, result < 0);
   if (result >= 0)
   {
-    errno = 0;
     int flag = (value ? (result | O_NONBLOCK) : (result & ~O_NONBLOCK));
-    result = error_wrapper(::fcntl(d, F_SETFL, flag), ec);
+    result = ::fcntl(d, F_SETFL, flag);
+    get_last_error(ec, result < 0);
   }
 #else // defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
   ioctl_arg_type arg = (value ? 1 : 0);
-  int result = error_wrapper(::ioctl(d, FIONBIO, &arg), ec);
+  int result = ::ioctl(d, FIONBIO, &arg);
+  get_last_error(ec, result < 0);
 #endif // defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
 
   if (result >= 0)
   {
-    ec = boost::system::error_code();
     if (value)
       state |= internal_non_blocking;
     else
@@ -176,7 +172,7 @@ std::size_t sync_read(int d, state_type state, buf* bufs,
   // A request to read 0 bytes on a stream is a no-op.
   if (all_empty)
   {
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -184,9 +180,54 @@ std::size_t sync_read(int d, state_type state, buf* bufs,
   for (;;)
   {
     // Try to complete the operation without blocking.
-    errno = 0;
-    signed_size_type bytes = error_wrapper(::readv(
-          d, bufs, static_cast<int>(count)), ec);
+    signed_size_type bytes = ::readv(d, bufs, static_cast<int>(count));
+    get_last_error(ec, bytes < 0);
+
+    // Check if operation succeeded.
+    if (bytes > 0)
+      return bytes;
+
+    // Check for EOF.
+    if (bytes == 0)
+    {
+      ec = boost::asio::error::eof;
+      return 0;
+    }
+
+    // Operation failed.
+    if ((state & user_set_non_blocking)
+        || (ec != boost::asio::error::would_block
+          && ec != boost::asio::error::try_again))
+      return 0;
+
+    // Wait for descriptor to become ready.
+    if (descriptor_ops::poll_read(d, 0, ec) < 0)
+      return 0;
+  }
+}
+
+std::size_t sync_read1(int d, state_type state, void* data,
+    std::size_t size, boost::system::error_code& ec)
+{
+  if (d == -1)
+  {
+    ec = boost::asio::error::bad_descriptor;
+    return 0;
+  }
+
+  // A request to read 0 bytes on a stream is a no-op.
+  if (size == 0)
+  {
+    ec.assign(0, ec.category());
+    return 0;
+  }
+
+  // Read some data.
+  for (;;)
+  {
+    // Try to complete the operation without blocking.
+    signed_size_type bytes = ::read(d, data, size);
+    get_last_error(ec, bytes < 0);
 
     // Check if operation succeeded.
     if (bytes > 0)
@@ -217,9 +258,8 @@ bool non_blocking_read(int d, buf* bufs, std::size_t count,
   for (;;)
   {
     // Read some data.
-    errno = 0;
-    signed_size_type bytes = error_wrapper(::readv(
-          d, bufs, static_cast<int>(count)), ec);
+    signed_size_type bytes = ::readv(d, bufs, static_cast<int>(count));
+    get_last_error(ec, bytes < 0);
 
     // Check for end of stream.
     if (bytes == 0)
@@ -228,6 +268,13 @@ bool non_blocking_read(int d, buf* bufs, std::size_t count,
       return true;
     }
 
+    // Check if operation succeeded.
+    if (bytes > 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
+
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
       continue;
@@ -237,15 +284,46 @@ bool non_blocking_read(int d, buf* bufs, std::size_t count,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
+    // Operation failed.
+    bytes_transferred = 0;
+    return true;
+  }
+}
+
+bool non_blocking_read1(int d, void* data, std::size_t size,
+    boost::system::error_code& ec, std::size_t& bytes_transferred)
+{
+  for (;;)
+  {
+    // Read some data.
+    signed_size_type bytes = ::read(d, data, size);
+    get_last_error(ec, bytes < 0);
+
+    // Check for end of stream.
+    if (bytes == 0)
+    {
+      ec = boost::asio::error::eof;
+      return true;
+    }
+
+    // Check if operation succeeded.
     if (bytes > 0)
     {
-      ec = boost::system::error_code();
       bytes_transferred = bytes;
+      return true;
     }
-    else
-      bytes_transferred = 0;
 
+    // Retry operation if interrupted by signal.
+    if (ec == boost::asio::error::interrupted)
+      continue;
+
+    // Check if we need to run the operation again.
+    if (ec == boost::asio::error::would_block
+        || ec == boost::asio::error::try_again)
+      return false;
+
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -262,7 +340,7 @@ std::size_t sync_write(int d, state_type state, const buf* bufs,
   // A request to write 0 bytes on a stream is a no-op.
   if (all_empty)
   {
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -270,9 +348,47 @@ std::size_t sync_write(int d, state_type state, const buf* bufs,
   for (;;)
   {
     // Try to complete the operation without blocking.
-    errno = 0;
-    signed_size_type bytes = error_wrapper(::writev(
-          d, bufs, static_cast<int>(count)), ec);
+    signed_size_type bytes = ::writev(d, bufs, static_cast<int>(count));
+    get_last_error(ec, bytes < 0);
+
+    // Check if operation succeeded.
+    if (bytes > 0)
+      return bytes;
+
+    // Operation failed.
+    if ((state & user_set_non_blocking)
+        || (ec != boost::asio::error::would_block
+          && ec != boost::asio::error::try_again))
+      return 0;
+
+    // Wait for descriptor to become ready.
+    if (descriptor_ops::poll_write(d, 0, ec) < 0)
+      return 0;
+  }
+}
+
+std::size_t sync_write1(int d, state_type state, const void* data,
+    std::size_t size, boost::system::error_code& ec)
+{
+  if (d == -1)
+  {
+    ec = boost::asio::error::bad_descriptor;
+    return 0;
+  }
+
+  // A request to write 0 bytes on a stream is a no-op.
+  if (size == 0)
+  {
+    ec.assign(0, ec.category());
+    return 0;
+  }
+
+  // Write some data.
+  for (;;)
+  {
+    // Try to complete the operation without blocking.
+    signed_size_type bytes = ::write(d, data, size);
+    get_last_error(ec, bytes < 0);
 
     // Check if operation succeeded.
     if (bytes > 0)
@@ -296,9 +412,15 @@ bool non_blocking_write(int d, const buf* bufs, std::size_t count,
   for (;;)
   {
     // Write some data.
-    errno = 0;
-    signed_size_type bytes = error_wrapper(::writev(
-          d, bufs, static_cast<int>(count)), ec);
+    signed_size_type bytes = ::writev(d, bufs, static_cast<int>(count));
+    get_last_error(ec, bytes < 0);
+
+    // Check if operation succeeded.
+    if (bytes >= 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
 
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
@@ -309,15 +431,39 @@ bool non_blocking_write(int d, const buf* bufs, std::size_t count,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
+    // Operation failed.
+    bytes_transferred = 0;
+    return true;
+  }
+}
+
+bool non_blocking_write1(int d, const void* data, std::size_t size,
+    boost::system::error_code& ec, std::size_t& bytes_transferred)
+{
+  for (;;)
+  {
+    // Write some data.
+    signed_size_type bytes = ::write(d, data, size);
+    get_last_error(ec, bytes < 0);
+
+    // Check if operation succeeded.
     if (bytes >= 0)
     {
-      ec = boost::system::error_code();
       bytes_transferred = bytes;
+      return true;
     }
-    else
-      bytes_transferred = 0;
 
+    // Retry operation if interrupted by signal.
+    if (ec == boost::asio::error::interrupted)
+      continue;
+
+    // Check if we need to run the operation again.
+    if (ec == boost::asio::error::would_block
+        || ec == boost::asio::error::try_again)
+      return false;
+
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -331,13 +477,11 @@ int ioctl(int d, state_type& state, long cmd,
     return -1;
   }
 
-  errno = 0;
-  int result = error_wrapper(::ioctl(d, cmd, arg), ec);
+  int result = ::ioctl(d, cmd, arg);
+  get_last_error(ec, result < 0);
 
   if (result >= 0)
   {
-    ec = boost::system::error_code();
-
     // When updating the non-blocking mode we always perform the ioctl syscall,
     // even if the flags would otherwise indicate that the descriptor is
     // already in the correct state. This ensures that the underlying
@@ -371,10 +515,8 @@ int fcntl(int d, int cmd, boost::system::error_code& ec)
     return -1;
   }
 
-  errno = 0;
-  int result = error_wrapper(::fcntl(d, cmd), ec);
-  if (result != -1)
-    ec = boost::system::error_code();
+  int result = ::fcntl(d, cmd);
+  get_last_error(ec, result < 0);
   return result;
 }
 
@@ -386,10 +528,8 @@ int fcntl(int d, int cmd, long arg, boost::system::error_code& ec)
     return -1;
   }
 
-  errno = 0;
-  int result = error_wrapper(::fcntl(d, cmd, arg), ec);
-  if (result != -1)
-    ec = boost::system::error_code();
+  int result = ::fcntl(d, cmd, arg);
+  get_last_error(ec, result < 0);
   return result;
 }
 
@@ -406,13 +546,11 @@ int poll_read(int d, state_type state, boost::system::error_code& ec)
   fds.events = POLLIN;
   fds.revents = 0;
   int timeout = (state & user_set_non_blocking) ? 0 : -1;
-  errno = 0;
-  int result = error_wrapper(::poll(&fds, 1, timeout), ec);
+  int result = ::poll(&fds, 1, timeout);
+  get_last_error(ec, result < 0);
   if (result == 0)
-    ec = (state & user_set_non_blocking)
-      ? boost::asio::error::would_block : boost::system::error_code();
-  else if (result > 0)
-    ec = boost::system::error_code();
+    if (state & user_set_non_blocking)
+      ec = boost::asio::error::would_block;
   return result;
 }
 
@@ -429,13 +567,11 @@ int poll_write(int d, state_type state, boost::system::error_code& ec)
   fds.events = POLLOUT;
   fds.revents = 0;
   int timeout = (state & user_set_non_blocking) ? 0 : -1;
-  errno = 0;
-  int result = error_wrapper(::poll(&fds, 1, timeout), ec);
+  int result = ::poll(&fds, 1, timeout);
+  get_last_error(ec, result < 0);
   if (result == 0)
-    ec = (state & user_set_non_blocking)
-      ? boost::asio::error::would_block : boost::system::error_code();
-  else if (result > 0)
-    ec = boost::system::error_code();
+    if (state & user_set_non_blocking)
+      ec = boost::asio::error::would_block;
   return result;
 }
 
@@ -452,13 +588,11 @@ int poll_error(int d, state_type state, boost::system::error_code& ec)
   fds.events = POLLPRI | POLLERR | POLLHUP;
   fds.revents = 0;
   int timeout = (state & user_set_non_blocking) ? 0 : -1;
-  errno = 0;
-  int result = error_wrapper(::poll(&fds, 1, timeout), ec);
+  int result = ::poll(&fds, 1, timeout);
+  get_last_error(ec, result < 0);
   if (result == 0)
-    ec = (state & user_set_non_blocking)
-      ? boost::asio::error::would_block : boost::system::error_code();
-  else if (result > 0)
-    ec = boost::system::error_code();
+    if (state & user_set_non_blocking)
+      ec = boost::asio::error::would_block;
   return result;
 }
 
diff --git a/include/boost/asio/detail/impl/handler_tracking.ipp b/include/boost/asio/detail/impl/handler_tracking.ipp
index 6c7fcfc1..f87924c6 100644
--- a/include/boost/asio/detail/impl/handler_tracking.ipp
+++ b/include/boost/asio/detail/impl/handler_tracking.ipp
@@ -74,11 +74,12 @@ struct handler_tracking::tracking_state
   static_mutex mutex_;
   uint64_t next_id_;
   tss_ptr<completion>* current_completion_;
+  tss_ptr<location>* current_location_;
 };
 
 handler_tracking::tracking_state* handler_tracking::get_state()
 {
-  static tracking_state state = { BOOST_ASIO_STATIC_MUTEX_INIT, 1, 0 };
+  static tracking_state state = { BOOST_ASIO_STATIC_MUTEX_INIT, 1, 0, 0 };
   return &state;
 }
 
@@ -91,6 +92,25 @@ void handler_tracking::init()
   static_mutex::scoped_lock lock(state->mutex_);
   if (state->current_completion_ == 0)
     state->current_completion_ = new tss_ptr<completion>;
+  if (state->current_location_ == 0)
+    state->current_location_ = new tss_ptr<location>;
+}
+
+handler_tracking::location::location(
+    const char* file, int line, const char* func)
+  : file_(file),
+    line_(line),
+    func_(func),
+    next_(*get_state()->current_location_)
+{
+  if (file_)
+    *get_state()->current_location_ = this;
+}
+
+handler_tracking::location::~location()
+{
+  if (file_)
+    *get_state()->current_location_ = next_;
 }
 
 void handler_tracking::creation(execution_context&,
@@ -110,6 +130,24 @@ void handler_tracking::creation(execution_context&,
   if (completion* current_completion = *state->current_completion_)
     current_id = current_completion->id_;
 
+  for (location* current_location = *state->current_location_;
+      current_location; current_location = current_location->next_)
+  {
+    write_line(
+#if defined(BOOST_ASIO_WINDOWS)
+        "@asio|%I64u.%06I64u|%I64u^%I64u|%s%s%.80s%s(%.80s:%d)\n",
+#else // defined(BOOST_ASIO_WINDOWS)
+        "@asio|%llu.%06llu|%llu^%llu|%s%s%.80s%s(%.80s:%d)\n",
+#endif // defined(BOOST_ASIO_WINDOWS)
+        timestamp.seconds, timestamp.microseconds,
+        current_id, h.id_,
+        current_location == *state->current_location_ ? "in " : "called from ",
+        current_location->func_ ? "'" : "",
+        current_location->func_ ? current_location->func_ : "",
+        current_location->func_ ? "' " : "",
+        current_location->file_, current_location->line_);
+  }
+
   write_line(
 #if defined(BOOST_ASIO_WINDOWS)
       "@asio|%I64u.%06I64u|%I64u*%I64u|%.20s@%p.%.50s\n",
diff --git a/include/boost/asio/detail/impl/reactive_serial_port_service.ipp b/include/boost/asio/detail/impl/reactive_serial_port_service.ipp
index 10cbc6e3..32f749f3 100644
--- a/include/boost/asio/detail/impl/reactive_serial_port_service.ipp
+++ b/include/boost/asio/detail/impl/reactive_serial_port_service.ipp
@@ -70,8 +70,8 @@ boost::system::error_code reactive_serial_port_service::open(
 
   // Set up default serial port options.
   termios ios;
-  errno = 0;
-  s = descriptor_ops::error_wrapper(::tcgetattr(fd, &ios), ec);
+  s = ::tcgetattr(fd, &ios);
+  descriptor_ops::get_last_error(ec, s < 0);
   if (s >= 0)
   {
 #if defined(_BSD_SOURCE) || defined(_DEFAULT_SOURCE)
@@ -86,8 +86,8 @@ boost::system::error_code reactive_serial_port_service::open(
 #endif
     ios.c_iflag |= IGNPAR;
     ios.c_cflag |= CREAD | CLOCAL;
-    errno = 0;
-    s = descriptor_ops::error_wrapper(::tcsetattr(fd, TCSANOW, &ios), ec);
+    s = ::tcsetattr(fd, TCSANOW, &ios);
+    descriptor_ops::get_last_error(ec, s < 0);
   }
   if (s < 0)
   {
@@ -112,18 +112,16 @@ boost::system::error_code reactive_serial_port_service::do_set_option(
     const void* option, boost::system::error_code& ec)
 {
   termios ios;
-  errno = 0;
-  descriptor_ops::error_wrapper(::tcgetattr(
-        descriptor_service_.native_handle(impl), &ios), ec);
-  if (ec)
+  int s = ::tcgetattr(descriptor_service_.native_handle(impl), &ios);
+  descriptor_ops::get_last_error(ec, s < 0);
+  if (s < 0)
     return ec;
 
   if (store(option, ios, ec))
     return ec;
 
-  errno = 0;
-  descriptor_ops::error_wrapper(::tcsetattr(
-        descriptor_service_.native_handle(impl), TCSANOW, &ios), ec);
+  s = ::tcsetattr(descriptor_service_.native_handle(impl), TCSANOW, &ios);
+  descriptor_ops::get_last_error(ec, s < 0);
   return ec;
 }
 
@@ -133,10 +131,9 @@ boost::system::error_code reactive_serial_port_service::do_get_option(
     void* option, boost::system::error_code& ec) const
 {
   termios ios;
-  errno = 0;
-  descriptor_ops::error_wrapper(::tcgetattr(
-        descriptor_service_.native_handle(impl), &ios), ec);
-  if (ec)
+  int s = ::tcgetattr(descriptor_service_.native_handle(impl), &ios);
+  descriptor_ops::get_last_error(ec, s < 0);
+  if (s < 0)
     return ec;
 
   return load(option, ios, ec);
diff --git a/include/boost/asio/detail/impl/scheduler.ipp b/include/boost/asio/detail/impl/scheduler.ipp
index 8ef69856..effe3e23 100644
--- a/include/boost/asio/detail/impl/scheduler.ipp
+++ b/include/boost/asio/detail/impl/scheduler.ipp
@@ -136,6 +136,10 @@ scheduler::~scheduler()
 {
   if (thread_)
   {
+    mutex::scoped_lock lock(mutex_);
+    shutdown_ = true;
+    stop_all_threads(lock);
+    lock.unlock();
     thread_->join();
     delete thread_;
   }
@@ -321,6 +325,12 @@ void scheduler::compensating_work_started()
   ++static_cast<thread_info*>(this_thread)->private_outstanding_work;
 }
 
+void scheduler::capture_current_exception()
+{
+  if (thread_info_base* this_thread = thread_call_stack::contains(this))
+    this_thread->capture_current_exception();
+}
+
 void scheduler::post_immediate_completion(
     scheduler::operation* op, bool is_continuation)
 {
@@ -445,6 +455,7 @@ std::size_t scheduler::do_run_one(mutex::scoped_lock& lock,
 
         // Complete the operation. May throw an exception. Deletes the object.
         o->complete(this, ec, task_result);
+        this_thread.rethrow_pending_exception();
 
         return 1;
       }
@@ -525,6 +536,7 @@ std::size_t scheduler::do_wait_one(mutex::scoped_lock& lock,
 
   // Complete the operation. May throw an exception. Deletes the object.
   o->complete(this, ec, task_result);
+  this_thread.rethrow_pending_exception();
 
   return 1;
 }
@@ -579,6 +591,7 @@ std::size_t scheduler::do_poll_one(mutex::scoped_lock& lock,
 
   // Complete the operation. May throw an exception. Deletes the object.
   o->complete(this, ec, task_result);
+  this_thread.rethrow_pending_exception();
 
   return 1;
 }
diff --git a/include/boost/asio/detail/impl/signal_set_service.ipp b/include/boost/asio/detail/impl/signal_set_service.ipp
index b4e45686..421f8387 100644
--- a/include/boost/asio/detail/impl/signal_set_service.ipp
+++ b/include/boost/asio/detail/impl/signal_set_service.ipp
@@ -90,7 +90,8 @@ class signal_set_service::pipe_read_op : public reactor_op
 {
 public:
   pipe_read_op()
-    : reactor_op(&pipe_read_op::do_perform, pipe_read_op::do_complete)
+    : reactor_op(boost::system::error_code(),
+        &pipe_read_op::do_perform, pipe_read_op::do_complete)
   {
   }
 
diff --git a/include/boost/asio/detail/impl/socket_ops.ipp b/include/boost/asio/detail/impl/socket_ops.ipp
index 9699b2f5..ef4462e5 100644
--- a/include/boost/asio/detail/impl/socket_ops.ipp
+++ b/include/boost/asio/detail/impl/socket_ops.ipp
@@ -74,18 +74,23 @@ inline void clear_last_error()
 
 #if !defined(BOOST_ASIO_WINDOWS_RUNTIME)
 
-template <typename ReturnType>
-inline ReturnType error_wrapper(ReturnType return_value,
-    boost::system::error_code& ec)
+inline void get_last_error(
+    boost::system::error_code& ec, bool is_error_condition)
 {
+  if (!is_error_condition)
+  {
+    ec.assign(0, ec.category());
+  }
+  else
+  {
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  ec = boost::system::error_code(WSAGetLastError(),
-      boost::asio::error::get_system_category());
+    ec = boost::system::error_code(WSAGetLastError(),
+        boost::asio::error::get_system_category());
 #else
-  ec = boost::system::error_code(errno,
-      boost::asio::error::get_system_category());
+    ec = boost::system::error_code(errno,
+        boost::asio::error::get_system_category());
 #endif
-  return return_value;
+  }
 }
 
 template <typename SockLenType>
@@ -108,17 +113,16 @@ socket_type accept(socket_type s, socket_addr_type* addr,
     return invalid_socket;
   }
 
-  clear_last_error();
-
-  socket_type new_s = error_wrapper(call_accept(
-        &msghdr::msg_namelen, s, addr, addrlen), ec);
+  socket_type new_s = call_accept(&msghdr::msg_namelen, s, addr, addrlen);
+  get_last_error(ec, new_s == invalid_socket);
   if (new_s == invalid_socket)
     return new_s;
 
 #if defined(__MACH__) && defined(__APPLE__) || defined(__FreeBSD__)
   int optval = 1;
-  int result = error_wrapper(::setsockopt(new_s,
-        SOL_SOCKET, SO_NOSIGPIPE, &optval, sizeof(optval)), ec);
+  int result = ::setsockopt(new_s, SOL_SOCKET,
+      SO_NOSIGPIPE, &optval, sizeof(optval));
+  get_last_error(ec, result != 0);
   if (result != 0)
   {
     ::close(new_s);
@@ -126,7 +130,7 @@ socket_type accept(socket_type s, socket_addr_type* addr,
   }
 #endif
 
-  ec = boost::system::error_code();
+  ec.assign(0, ec.category());
   return new_s;
 }
 
@@ -283,11 +287,8 @@ int bind(socket_type s, const socket_addr_type* addr,
     return socket_error_retval;
   }
 
-  clear_last_error();
-  int result = error_wrapper(call_bind(
-        &msghdr::msg_namelen, s, addr, addrlen), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = call_bind(&msghdr::msg_namelen, s, addr, addrlen);
+  get_last_error(ec, result != 0);
   return result;
 }
 
@@ -310,12 +311,12 @@ int close(socket_type s, state_type& state,
           SO_LINGER, &opt, sizeof(opt), ignored_ec);
     }
 
-    clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-    result = error_wrapper(::closesocket(s), ec);
+    result = ::closesocket(s);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-    result = error_wrapper(::close(s), ec);
+    result = ::close(s);
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+    get_last_error(ec, result != 0);
 
     if (result != 0
         && (ec == boost::asio::error::would_block
@@ -342,17 +343,15 @@ int close(socket_type s, state_type& state,
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
       state &= ~non_blocking;
 
-      clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-      result = error_wrapper(::closesocket(s), ec);
+      result = ::closesocket(s);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-      result = error_wrapper(::close(s), ec);
+      result = ::close(s);
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+      get_last_error(ec, result != 0);
     }
   }
 
-  if (result == 0)
-    ec = boost::system::error_code();
   return result;
 }
 
@@ -365,26 +364,27 @@ bool set_user_non_blocking(socket_type s,
     return false;
   }
 
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   ioctl_arg_type arg = (value ? 1 : 0);
-  int result = error_wrapper(::ioctlsocket(s, FIONBIO, &arg), ec);
+  int result = ::ioctlsocket(s, FIONBIO, &arg);
+  get_last_error(ec, result < 0);
 #elif defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
-  int result = error_wrapper(::fcntl(s, F_GETFL, 0), ec);
+  int result = ::fcntl(s, F_GETFL, 0);
+  get_last_error(ec, result < 0);
   if (result >= 0)
   {
-    clear_last_error();
     int flag = (value ? (result | O_NONBLOCK) : (result & ~O_NONBLOCK));
-    result = error_wrapper(::fcntl(s, F_SETFL, flag), ec);
+    result = ::fcntl(s, F_SETFL, flag);
+    get_last_error(ec, result < 0);
   }
 #else
   ioctl_arg_type arg = (value ? 1 : 0);
-  int result = error_wrapper(::ioctl(s, FIONBIO, &arg), ec);
+  int result = ::ioctl(s, FIONBIO, &arg);
+  get_last_error(ec, result < 0);
 #endif
 
   if (result >= 0)
   {
-    ec = boost::system::error_code();
     if (value)
       state |= user_set_non_blocking;
     else
@@ -418,26 +418,27 @@ bool set_internal_non_blocking(socket_type s,
     return false;
   }
 
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   ioctl_arg_type arg = (value ? 1 : 0);
-  int result = error_wrapper(::ioctlsocket(s, FIONBIO, &arg), ec);
+  int result = ::ioctlsocket(s, FIONBIO, &arg);
+  get_last_error(ec, result < 0);
 #elif defined(__SYMBIAN32__) || defined(__EMSCRIPTEN__)
-  int result = error_wrapper(::fcntl(s, F_GETFL, 0), ec);
+  int result = ::fcntl(s, F_GETFL, 0);
+  get_last_error(ec, result < 0);
   if (result >= 0)
   {
-    clear_last_error();
     int flag = (value ? (result | O_NONBLOCK) : (result & ~O_NONBLOCK));
-    result = error_wrapper(::fcntl(s, F_SETFL, flag), ec);
+    result = ::fcntl(s, F_SETFL, flag);
+    get_last_error(ec, result < 0);
   }
 #else
   ioctl_arg_type arg = (value ? 1 : 0);
-  int result = error_wrapper(::ioctl(s, FIONBIO, &arg), ec);
+  int result = ::ioctl(s, FIONBIO, &arg);
+  get_last_error(ec, result < 0);
 #endif
 
   if (result >= 0)
   {
-    ec = boost::system::error_code();
     if (value)
       state |= internal_non_blocking;
     else
@@ -456,10 +457,8 @@ int shutdown(socket_type s, int what, boost::system::error_code& ec)
     return socket_error_retval;
   }
 
-  clear_last_error();
-  int result = error_wrapper(::shutdown(s, what), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = ::shutdown(s, what);
+  get_last_error(ec, result != 0);
   return result;
 }
 
@@ -479,13 +478,10 @@ int connect(socket_type s, const socket_addr_type* addr,
     return socket_error_retval;
   }
 
-  clear_last_error();
-  int result = error_wrapper(call_connect(
-        &msghdr::msg_namelen, s, addr, addrlen), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = call_connect(&msghdr::msg_namelen, s, addr, addrlen);
+  get_last_error(ec, result != 0);
 #if defined(__linux__)
-  else if (ec == boost::asio::error::try_again)
+  if (result != 0 && ec == boost::asio::error::try_again)
     ec = boost::asio::error::no_buffer_space;
 #endif // defined(__linux__)
   return result;
@@ -601,7 +597,7 @@ bool non_blocking_connect(socket_type s, boost::system::error_code& ec)
           boost::asio::error::get_system_category());
     }
     else
-      ec = boost::system::error_code();
+      ec.assign(0, ec.category());
   }
 
   return true;
@@ -618,10 +614,8 @@ int socketpair(int af, int type, int protocol,
   ec = boost::asio::error::operation_not_supported;
   return socket_error_retval;
 #else
-  clear_last_error();
-  int result = error_wrapper(::socketpair(af, type, protocol, sv), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = ::socketpair(af, type, protocol, sv);
+  get_last_error(ec, result != 0);
   return result;
 #endif
 }
@@ -637,20 +631,18 @@ bool sockatmark(socket_type s, boost::system::error_code& ec)
 #if defined(SIOCATMARK)
   ioctl_arg_type value = 0;
 # if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  int result = error_wrapper(::ioctlsocket(s, SIOCATMARK, &value), ec);
+  int result = ::ioctlsocket(s, SIOCATMARK, &value);
 # else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  int result = error_wrapper(::ioctl(s, SIOCATMARK, &value), ec);
+  int result = ::ioctl(s, SIOCATMARK, &value);
 # endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  if (result == 0)
-    ec = boost::system::error_code();
+  get_last_error(ec, result < 0);
 # if defined(ENOTTY)
   if (ec.value() == ENOTTY)
     ec = boost::asio::error::not_socket;
 # endif // defined(ENOTTY)
 #else // defined(SIOCATMARK)
-  int value = error_wrapper(::sockatmark(s), ec);
-  if (value != -1)
-    ec = boost::system::error_code();
+  int value = ::sockatmark(s);
+  get_last_error(ec, result < 0);
 #endif // defined(SIOCATMARK)
 
   return ec ? false : value != 0;
@@ -666,12 +658,11 @@ size_t available(socket_type s, boost::system::error_code& ec)
 
   ioctl_arg_type value = 0;
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  int result = error_wrapper(::ioctlsocket(s, FIONREAD, &value), ec);
+  int result = ::ioctlsocket(s, FIONREAD, &value);
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  int result = error_wrapper(::ioctl(s, FIONREAD, &value), ec);
+  int result = ::ioctl(s, FIONREAD, &value);
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  if (result == 0)
-    ec = boost::system::error_code();
+  get_last_error(ec, result < 0);
 #if defined(ENOTTY)
   if (ec.value() == ENOTTY)
     ec = boost::asio::error::not_socket;
@@ -688,10 +679,8 @@ int listen(socket_type s, int backlog, boost::system::error_code& ec)
     return socket_error_retval;
   }
 
-  clear_last_error();
-  int result = error_wrapper(::listen(s, backlog), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = ::listen(s, backlog);
+  get_last_error(ec, result != 0);
   return result;
 }
 
@@ -759,14 +748,14 @@ inline void init_msghdr_msg_name(T& name, const socket_addr_type* addr)
 signed_size_type recv(socket_type s, buf* bufs, size_t count,
     int flags, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   // Receive some data.
   DWORD recv_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
   DWORD recv_flags = flags;
-  int result = error_wrapper(::WSARecv(s, bufs,
-        recv_buf_count, &bytes_transferred, &recv_flags, 0, 0), ec);
+  int result = ::WSARecv(s, bufs, recv_buf_count,
+      &bytes_transferred, &recv_flags, 0, 0);
+  get_last_error(ec, true);
   if (ec.value() == ERROR_NETNAME_DELETED)
     ec = boost::asio::error::connection_reset;
   else if (ec.value() == ERROR_PORT_UNREACHABLE)
@@ -775,15 +764,44 @@ signed_size_type recv(socket_type s, buf* bufs, size_t count,
     result = 0;
   if (result != 0)
     return socket_error_retval;
-  ec = boost::system::error_code();
+  ec.assign(0, ec.category());
   return bytes_transferred;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   msghdr msg = msghdr();
   msg.msg_iov = bufs;
   msg.msg_iovlen = static_cast<int>(count);
-  signed_size_type result = error_wrapper(::recvmsg(s, &msg, flags), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
+  signed_size_type result = ::recvmsg(s, &msg, flags);
+  get_last_error(ec, result < 0);
+  return result;
+#endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+}
+
+signed_size_type recv1(socket_type s, void* data, size_t size,
+    int flags, boost::system::error_code& ec)
+{
+#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+  // Receive some data.
+  WSABUF buf;
+  buf.buf = const_cast<char*>(static_cast<const char*>(data));
+  buf.len = static_cast<ULONG>(size);
+  DWORD bytes_transferred = 0;
+  DWORD recv_flags = flags;
+  int result = ::WSARecv(s, &buf, 1,
+      &bytes_transferred, &recv_flags, 0, 0);
+  get_last_error(ec, true);
+  if (ec.value() == ERROR_NETNAME_DELETED)
+    ec = boost::asio::error::connection_reset;
+  else if (ec.value() == ERROR_PORT_UNREACHABLE)
+    ec = boost::asio::error::connection_refused;
+  else if (ec.value() == WSAEMSGSIZE || ec.value() == ERROR_MORE_DATA)
+    result = 0;
+  if (result != 0)
+    return socket_error_retval;
+  ec.assign(0, ec.category());
+  return bytes_transferred;
+#else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+  signed_size_type result = ::recv(s, static_cast<char*>(data), size, flags);
+  get_last_error(ec, result < 0);
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 }
@@ -800,7 +818,7 @@ size_t sync_recv(socket_type s, state_type state, buf* bufs,
   // A request to read 0 bytes on a stream is a no-op.
   if (all_empty && (state & stream_oriented))
   {
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -810,10 +828,51 @@ size_t sync_recv(socket_type s, state_type state, buf* bufs,
     // Try to complete the operation without blocking.
     signed_size_type bytes = socket_ops::recv(s, bufs, count, flags, ec);
 
+    // Check for EOF.
+    if ((state & stream_oriented) && bytes == 0)
+    {
+      ec = boost::asio::error::eof;
+      return 0;
+    }
+
     // Check if operation succeeded.
-    if (bytes > 0)
+    if (bytes >= 0)
       return bytes;
 
+    // Operation failed.
+    if ((state & user_set_non_blocking)
+        || (ec != boost::asio::error::would_block
+          && ec != boost::asio::error::try_again))
+      return 0;
+
+    // Wait for socket to become ready.
+    if (socket_ops::poll_read(s, 0, -1, ec) < 0)
+      return 0;
+  }
+}
+
+size_t sync_recv1(socket_type s, state_type state, void* data,
+    size_t size, int flags, boost::system::error_code& ec)
+{
+  if (s == invalid_socket)
+  {
+    ec = boost::asio::error::bad_descriptor;
+    return 0;
+  }
+
+  // A request to read 0 bytes on a stream is a no-op.
+  if (size == 0 && (state & stream_oriented))
+  {
+    ec.assign(0, ec.category());
+    return 0;
+  }
+
+  // Read some data.
+  for (;;)
+  {
+    // Try to complete the operation without blocking.
+    signed_size_type bytes = socket_ops::recv1(s, data, size, flags, ec);
+
     // Check for EOF.
     if ((state & stream_oriented) && bytes == 0)
     {
@@ -821,6 +880,10 @@ size_t sync_recv(socket_type s, state_type state, buf* bufs,
       return 0;
     }
 
+    // Check if operation succeeded.
+    if (bytes >= 0)
+      return bytes;
+
     // Operation failed.
     if ((state & user_set_non_blocking)
         || (ec != boost::asio::error::would_block
@@ -883,6 +946,13 @@ bool non_blocking_recv(socket_type s,
       return true;
     }
 
+    // Check if operation succeeded.
+    if (bytes >= 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
+
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
       continue;
@@ -892,15 +962,46 @@ bool non_blocking_recv(socket_type s,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
+    // Operation failed.
+    bytes_transferred = 0;
+    return true;
+  }
+}
+
+bool non_blocking_recv1(socket_type s,
+    void* data, size_t size, int flags, bool is_stream,
+    boost::system::error_code& ec, size_t& bytes_transferred)
+{
+  for (;;)
+  {
+    // Read some data.
+    signed_size_type bytes = socket_ops::recv1(s, data, size, flags, ec);
+
+    // Check for end of stream.
+    if (is_stream && bytes == 0)
+    {
+      ec = boost::asio::error::eof;
+      return true;
+    }
+
+    // Check if operation succeeded.
     if (bytes >= 0)
     {
-      ec = boost::system::error_code();
       bytes_transferred = bytes;
+      return true;
     }
-    else
-      bytes_transferred = 0;
 
+    // Retry operation if interrupted by signal.
+    if (ec == boost::asio::error::interrupted)
+      continue;
+
+    // Check if we need to run the operation again.
+    if (ec == boost::asio::error::would_block
+        || ec == boost::asio::error::try_again)
+      return false;
+
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -911,15 +1012,15 @@ signed_size_type recvfrom(socket_type s, buf* bufs, size_t count,
     int flags, socket_addr_type* addr, std::size_t* addrlen,
     boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   // Receive some data.
   DWORD recv_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
   DWORD recv_flags = flags;
   int tmp_addrlen = (int)*addrlen;
-  int result = error_wrapper(::WSARecvFrom(s, bufs, recv_buf_count,
-        &bytes_transferred, &recv_flags, addr, &tmp_addrlen, 0, 0), ec);
+  int result = ::WSARecvFrom(s, bufs, recv_buf_count,
+        &bytes_transferred, &recv_flags, addr, &tmp_addrlen, 0, 0);
+  get_last_error(ec, true);
   *addrlen = (std::size_t)tmp_addrlen;
   if (ec.value() == ERROR_NETNAME_DELETED)
     ec = boost::asio::error::connection_reset;
@@ -929,7 +1030,7 @@ signed_size_type recvfrom(socket_type s, buf* bufs, size_t count,
     result = 0;
   if (result != 0)
     return socket_error_retval;
-  ec = boost::system::error_code();
+  ec.assign(0, ec.category());
   return bytes_transferred;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   msghdr msg = msghdr();
@@ -937,10 +1038,56 @@ signed_size_type recvfrom(socket_type s, buf* bufs, size_t count,
   msg.msg_namelen = static_cast<int>(*addrlen);
   msg.msg_iov = bufs;
   msg.msg_iovlen = static_cast<int>(count);
-  signed_size_type result = error_wrapper(::recvmsg(s, &msg, flags), ec);
+  signed_size_type result = ::recvmsg(s, &msg, flags);
+  get_last_error(ec, result < 0);
   *addrlen = msg.msg_namelen;
-  if (result >= 0)
-    ec = boost::system::error_code();
+  return result;
+#endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+}
+
+template <typename SockLenType>
+inline signed_size_type call_recvfrom(SockLenType msghdr::*,
+    socket_type s, void* data, size_t size, int flags,
+    socket_addr_type* addr, std::size_t* addrlen)
+{
+  SockLenType tmp_addrlen = addrlen ? (SockLenType)*addrlen : 0;
+  signed_size_type result = ::recvfrom(s, static_cast<char*>(data),
+      size, flags, addr, addrlen ? &tmp_addrlen : 0);
+  if (addrlen)
+    *addrlen = (std::size_t)tmp_addrlen;
+  return result;
+}
+
+signed_size_type recvfrom1(socket_type s, void* data, size_t size,
+    int flags, socket_addr_type* addr, std::size_t* addrlen,
+    boost::system::error_code& ec)
+{
+#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+  // Receive some data.
+  WSABUF buf;
+  buf.buf = static_cast<char*>(data);
+  buf.len = static_cast<ULONG>(size);
+  DWORD bytes_transferred = 0;
+  DWORD recv_flags = flags;
+  int tmp_addrlen = (int)*addrlen;
+  int result = ::WSARecvFrom(s, &buf, 1, &bytes_transferred,
+      &recv_flags, addr, &tmp_addrlen, 0, 0);
+  get_last_error(ec, true);
+  *addrlen = (std::size_t)tmp_addrlen;
+  if (ec.value() == ERROR_NETNAME_DELETED)
+    ec = boost::asio::error::connection_reset;
+  else if (ec.value() == ERROR_PORT_UNREACHABLE)
+    ec = boost::asio::error::connection_refused;
+  else if (ec.value() == WSAEMSGSIZE || ec.value() == ERROR_MORE_DATA)
+    result = 0;
+  if (result != 0)
+    return socket_error_retval;
+  ec.assign(0, ec.category());
+  return bytes_transferred;
+#else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+  signed_size_type result = call_recvfrom(&msghdr::msg_namelen,
+      s, data, size, flags, addr, addrlen);
+  get_last_error(ec, result < 0);
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 }
@@ -978,6 +1125,39 @@ size_t sync_recvfrom(socket_type s, state_type state, buf* bufs,
   }
 }
 
+size_t sync_recvfrom1(socket_type s, state_type state, void* data,
+    size_t size, int flags, socket_addr_type* addr,
+    std::size_t* addrlen, boost::system::error_code& ec)
+{
+  if (s == invalid_socket)
+  {
+    ec = boost::asio::error::bad_descriptor;
+    return 0;
+  }
+
+  // Read some data.
+  for (;;)
+  {
+    // Try to complete the operation without blocking.
+    signed_size_type bytes = socket_ops::recvfrom1(
+        s, data, size, flags, addr, addrlen, ec);
+
+    // Check if operation succeeded.
+    if (bytes >= 0)
+      return bytes;
+
+    // Operation failed.
+    if ((state & user_set_non_blocking)
+        || (ec != boost::asio::error::would_block
+          && ec != boost::asio::error::try_again))
+      return 0;
+
+    // Wait for socket to become ready.
+    if (socket_ops::poll_read(s, 0, -1, ec) < 0)
+      return 0;
+  }
+}
+
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 void complete_iocp_recvfrom(
@@ -1015,6 +1195,13 @@ bool non_blocking_recvfrom(socket_type s,
     signed_size_type bytes = socket_ops::recvfrom(
         s, bufs, count, flags, addr, addrlen, ec);
 
+    // Check if operation succeeded.
+    if (bytes >= 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
+
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
       continue;
@@ -1024,15 +1211,41 @@ bool non_blocking_recvfrom(socket_type s,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
+    // Operation failed.
+    bytes_transferred = 0;
+    return true;
+  }
+}
+
+bool non_blocking_recvfrom1(socket_type s,
+    void* data, size_t size, int flags,
+    socket_addr_type* addr, std::size_t* addrlen,
+    boost::system::error_code& ec, size_t& bytes_transferred)
+{
+  for (;;)
+  {
+    // Read some data.
+    signed_size_type bytes = socket_ops::recvfrom1(
+        s, data, size, flags, addr, addrlen, ec);
+
+    // Check if operation succeeded.
     if (bytes >= 0)
     {
-      ec = boost::system::error_code();
       bytes_transferred = bytes;
+      return true;
     }
-    else
-      bytes_transferred = 0;
 
+    // Retry operation if interrupted by signal.
+    if (ec == boost::asio::error::interrupted)
+      continue;
+
+    // Check if we need to run the operation again.
+    if (ec == boost::asio::error::would_block
+        || ec == boost::asio::error::try_again)
+      return false;
+
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -1042,7 +1255,6 @@ bool non_blocking_recvfrom(socket_type s,
 signed_size_type recvmsg(socket_type s, buf* bufs, size_t count,
     int in_flags, int& out_flags, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   out_flags = 0;
   return socket_ops::recv(s, bufs, count, in_flags, ec);
@@ -1050,12 +1262,10 @@ signed_size_type recvmsg(socket_type s, buf* bufs, size_t count,
   msghdr msg = msghdr();
   msg.msg_iov = bufs;
   msg.msg_iovlen = static_cast<int>(count);
-  signed_size_type result = error_wrapper(::recvmsg(s, &msg, in_flags), ec);
+  signed_size_type result = ::recvmsg(s, &msg, in_flags);
+  get_last_error(ec, result < 0);
   if (result >= 0)
-  {
-    ec = boost::system::error_code();
     out_flags = msg.msg_flags;
-  }
   else
     out_flags = 0;
   return result;
@@ -1131,6 +1341,13 @@ bool non_blocking_recvmsg(socket_type s,
     signed_size_type bytes = socket_ops::recvmsg(
         s, bufs, count, in_flags, out_flags, ec);
 
+    // Check if operation succeeded.
+    if (bytes >= 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
+
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
       continue;
@@ -1140,15 +1357,8 @@ bool non_blocking_recvmsg(socket_type s,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
-    if (bytes >= 0)
-    {
-      ec = boost::system::error_code();
-      bytes_transferred = bytes;
-    }
-    else
-      bytes_transferred = 0;
-
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -1158,21 +1368,21 @@ bool non_blocking_recvmsg(socket_type s,
 signed_size_type send(socket_type s, const buf* bufs, size_t count,
     int flags, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   // Send the data.
   DWORD send_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
   DWORD send_flags = flags;
-  int result = error_wrapper(::WSASend(s, const_cast<buf*>(bufs),
-        send_buf_count, &bytes_transferred, send_flags, 0, 0), ec);
+  int result = ::WSASend(s, const_cast<buf*>(bufs),
+        send_buf_count, &bytes_transferred, send_flags, 0, 0);
+  get_last_error(ec, true);
   if (ec.value() == ERROR_NETNAME_DELETED)
     ec = boost::asio::error::connection_reset;
   else if (ec.value() == ERROR_PORT_UNREACHABLE)
     ec = boost::asio::error::connection_refused;
   if (result != 0)
     return socket_error_retval;
-  ec = boost::system::error_code();
+  ec.assign(0, ec.category());
   return bytes_transferred;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   msghdr msg = msghdr();
@@ -1181,9 +1391,40 @@ signed_size_type send(socket_type s, const buf* bufs, size_t count,
 #if defined(__linux__)
   flags |= MSG_NOSIGNAL;
 #endif // defined(__linux__)
-  signed_size_type result = error_wrapper(::sendmsg(s, &msg, flags), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
+  signed_size_type result = ::sendmsg(s, &msg, flags);
+  get_last_error(ec, result < 0);
+  return result;
+#endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+}
+
+signed_size_type send1(socket_type s, const void* data, size_t size,
+    int flags, boost::system::error_code& ec)
+{
+#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+  // Send the data.
+  WSABUF buf;
+  buf.buf = const_cast<char*>(static_cast<const char*>(data));
+  buf.len = static_cast<ULONG>(size);
+  DWORD bytes_transferred = 0;
+  DWORD send_flags = flags;
+  int result = ::WSASend(s, &buf, 1,
+        &bytes_transferred, send_flags, 0, 0);
+  get_last_error(ec, true);
+  if (ec.value() == ERROR_NETNAME_DELETED)
+    ec = boost::asio::error::connection_reset;
+  else if (ec.value() == ERROR_PORT_UNREACHABLE)
+    ec = boost::asio::error::connection_refused;
+  if (result != 0)
+    return socket_error_retval;
+  ec.assign(0, ec.category());
+  return bytes_transferred;
+#else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(__linux__)
+  flags |= MSG_NOSIGNAL;
+#endif // defined(__linux__)
+  signed_size_type result = ::send(s,
+      static_cast<const char*>(data), size, flags);
+  get_last_error(ec, result < 0);
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 }
@@ -1200,7 +1441,7 @@ size_t sync_send(socket_type s, state_type state, const buf* bufs,
   // A request to write 0 bytes to a stream is a no-op.
   if (all_empty && (state & stream_oriented))
   {
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -1226,6 +1467,44 @@ size_t sync_send(socket_type s, state_type state, const buf* bufs,
   }
 }
 
+size_t sync_send1(socket_type s, state_type state, const void* data,
+    size_t size, int flags, boost::system::error_code& ec)
+{
+  if (s == invalid_socket)
+  {
+    ec = boost::asio::error::bad_descriptor;
+    return 0;
+  }
+
+  // A request to write 0 bytes to a stream is a no-op.
+  if (size == 0 && (state & stream_oriented))
+  {
+    ec.assign(0, ec.category());
+    return 0;
+  }
+
+  // Read some data.
+  for (;;)
+  {
+    // Try to complete the operation without blocking.
+    signed_size_type bytes = socket_ops::send1(s, data, size, flags, ec);
+
+    // Check if operation succeeded.
+    if (bytes >= 0)
+      return bytes;
+
+    // Operation failed.
+    if ((state & user_set_non_blocking)
+        || (ec != boost::asio::error::would_block
+          && ec != boost::asio::error::try_again))
+      return 0;
+
+    // Wait for socket to become ready.
+    if (socket_ops::poll_write(s, 0, -1, ec) < 0)
+      return 0;
+  }
+}
+
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 void complete_iocp_send(
@@ -1257,6 +1536,13 @@ bool non_blocking_send(socket_type s,
     // Write some data.
     signed_size_type bytes = socket_ops::send(s, bufs, count, flags, ec);
 
+    // Check if operation succeeded.
+    if (bytes >= 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
+
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
       continue;
@@ -1266,15 +1552,39 @@ bool non_blocking_send(socket_type s,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
+    // Operation failed.
+    bytes_transferred = 0;
+    return true;
+  }
+}
+
+bool non_blocking_send1(socket_type s,
+    const void* data, size_t size, int flags,
+    boost::system::error_code& ec, size_t& bytes_transferred)
+{
+  for (;;)
+  {
+    // Write some data.
+    signed_size_type bytes = socket_ops::send1(s, data, size, flags, ec);
+
+    // Check if operation succeeded.
     if (bytes >= 0)
     {
-      ec = boost::system::error_code();
       bytes_transferred = bytes;
+      return true;
     }
-    else
-      bytes_transferred = 0;
 
+    // Retry operation if interrupted by signal.
+    if (ec == boost::asio::error::interrupted)
+      continue;
+
+    // Check if we need to run the operation again.
+    if (ec == boost::asio::error::would_block
+        || ec == boost::asio::error::try_again)
+      return false;
+
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -1285,21 +1595,21 @@ signed_size_type sendto(socket_type s, const buf* bufs, size_t count,
     int flags, const socket_addr_type* addr, std::size_t addrlen,
     boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   // Send the data.
   DWORD send_buf_count = static_cast<DWORD>(count);
   DWORD bytes_transferred = 0;
-  int result = error_wrapper(::WSASendTo(s, const_cast<buf*>(bufs),
+  int result = ::WSASendTo(s, const_cast<buf*>(bufs),
         send_buf_count, &bytes_transferred, flags, addr,
-        static_cast<int>(addrlen), 0, 0), ec);
+        static_cast<int>(addrlen), 0, 0);
+  get_last_error(ec, true);
   if (ec.value() == ERROR_NETNAME_DELETED)
     ec = boost::asio::error::connection_reset;
   else if (ec.value() == ERROR_PORT_UNREACHABLE)
     ec = boost::asio::error::connection_refused;
   if (result != 0)
     return socket_error_retval;
-  ec = boost::system::error_code();
+  ec.assign(0, ec.category());
   return bytes_transferred;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   msghdr msg = msghdr();
@@ -1310,9 +1620,49 @@ signed_size_type sendto(socket_type s, const buf* bufs, size_t count,
 #if defined(__linux__)
   flags |= MSG_NOSIGNAL;
 #endif // defined(__linux__)
-  signed_size_type result = error_wrapper(::sendmsg(s, &msg, flags), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
+  signed_size_type result = ::sendmsg(s, &msg, flags);
+  get_last_error(ec, result < 0);
+  return result;
+#endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+}
+
+template <typename SockLenType>
+inline signed_size_type call_sendto(SockLenType msghdr::*,
+    socket_type s, const void* data, size_t size, int flags,
+    const socket_addr_type* addr, std::size_t addrlen)
+{
+  return ::sendto(s, static_cast<char*>(const_cast<void*>(data)),
+      size, flags, addr, (SockLenType)addrlen);
+}
+
+signed_size_type sendto1(socket_type s, const void* data, size_t size,
+    int flags, const socket_addr_type* addr, std::size_t addrlen,
+    boost::system::error_code& ec)
+{
+#if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+  // Send the data.
+  WSABUF buf;
+  buf.buf = const_cast<char*>(static_cast<const char*>(data));
+  buf.len = static_cast<ULONG>(size);
+  DWORD bytes_transferred = 0;
+  int result = ::WSASendTo(s, &buf, 1, &bytes_transferred,
+      flags, addr, static_cast<int>(addrlen), 0, 0);
+  get_last_error(ec, true);
+  if (ec.value() == ERROR_NETNAME_DELETED)
+    ec = boost::asio::error::connection_reset;
+  else if (ec.value() == ERROR_PORT_UNREACHABLE)
+    ec = boost::asio::error::connection_refused;
+  if (result != 0)
+    return socket_error_retval;
+  ec.assign(0, ec.category());
+  return bytes_transferred;
+#else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
+#if defined(__linux__)
+  flags |= MSG_NOSIGNAL;
+#endif // defined(__linux__)
+  signed_size_type result = call_sendto(&msghdr::msg_namelen,
+      s, data, size, flags, addr, addrlen);
+  get_last_error(ec, result < 0);
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 }
@@ -1350,6 +1700,39 @@ size_t sync_sendto(socket_type s, state_type state, const buf* bufs,
   }
 }
 
+size_t sync_sendto1(socket_type s, state_type state, const void* data,
+    size_t size, int flags, const socket_addr_type* addr,
+    std::size_t addrlen, boost::system::error_code& ec)
+{
+  if (s == invalid_socket)
+  {
+    ec = boost::asio::error::bad_descriptor;
+    return 0;
+  }
+
+  // Write some data.
+  for (;;)
+  {
+    // Try to complete the operation without blocking.
+    signed_size_type bytes = socket_ops::sendto1(
+        s, data, size, flags, addr, addrlen, ec);
+
+    // Check if operation succeeded.
+    if (bytes >= 0)
+      return bytes;
+
+    // Operation failed.
+    if ((state & user_set_non_blocking)
+        || (ec != boost::asio::error::would_block
+          && ec != boost::asio::error::try_again))
+      return 0;
+
+    // Wait for socket to become ready.
+    if (socket_ops::poll_write(s, 0, -1, ec) < 0)
+      return 0;
+  }
+}
+
 #if !defined(BOOST_ASIO_HAS_IOCP)
 
 bool non_blocking_sendto(socket_type s,
@@ -1363,6 +1746,13 @@ bool non_blocking_sendto(socket_type s,
     signed_size_type bytes = socket_ops::sendto(
         s, bufs, count, flags, addr, addrlen, ec);
 
+    // Check if operation succeeded.
+    if (bytes >= 0)
+    {
+      bytes_transferred = bytes;
+      return true;
+    }
+
     // Retry operation if interrupted by signal.
     if (ec == boost::asio::error::interrupted)
       continue;
@@ -1372,15 +1762,41 @@ bool non_blocking_sendto(socket_type s,
         || ec == boost::asio::error::try_again)
       return false;
 
-    // Operation is complete.
+    // Operation failed.
+    bytes_transferred = 0;
+    return true;
+  }
+}
+
+bool non_blocking_sendto1(socket_type s,
+    const void* data, size_t size, int flags,
+    const socket_addr_type* addr, std::size_t addrlen,
+    boost::system::error_code& ec, size_t& bytes_transferred)
+{
+  for (;;)
+  {
+    // Write some data.
+    signed_size_type bytes = socket_ops::sendto1(
+        s, data, size, flags, addr, addrlen, ec);
+
+    // Check if operation succeeded.
     if (bytes >= 0)
     {
-      ec = boost::system::error_code();
       bytes_transferred = bytes;
+      return true;
     }
-    else
-      bytes_transferred = 0;
 
+    // Retry operation if interrupted by signal.
+    if (ec == boost::asio::error::interrupted)
+      continue;
+
+    // Check if we need to run the operation again.
+    if (ec == boost::asio::error::would_block
+        || ec == boost::asio::error::try_again)
+      return false;
+
+    // Operation failed.
+    bytes_transferred = 0;
     return true;
   }
 }
@@ -1390,10 +1806,9 @@ bool non_blocking_sendto(socket_type s,
 socket_type socket(int af, int type, int protocol,
     boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  socket_type s = error_wrapper(::WSASocketW(af, type, protocol, 0, 0,
-        WSA_FLAG_OVERLAPPED), ec);
+  socket_type s = ::WSASocketW(af, type, protocol, 0, 0, WSA_FLAG_OVERLAPPED);
+  get_last_error(ec, s == invalid_socket);
   if (s == invalid_socket)
     return s;
 
@@ -1407,17 +1822,15 @@ socket_type socket(int af, int type, int protocol,
         reinterpret_cast<const char*>(&optval), sizeof(optval));
   }
 
-  ec = boost::system::error_code();
-
   return s;
 #elif defined(__MACH__) && defined(__APPLE__) || defined(__FreeBSD__)
-  socket_type s = error_wrapper(::socket(af, type, protocol), ec);
-  if (s == invalid_socket)
-    return s;
+  socket_type s = ::socket(af, type, protocol);
+  get_last_error(ec, s < 0);
 
   int optval = 1;
-  int result = error_wrapper(::setsockopt(s,
-        SOL_SOCKET, SO_NOSIGPIPE, &optval, sizeof(optval)), ec);
+  int result = ::setsockopt(s, SOL_SOCKET,
+      SO_NOSIGPIPE, &optval, sizeof(optval));
+  get_last_error(ec, result != 0);
   if (result != 0)
   {
     ::close(s);
@@ -1426,9 +1839,8 @@ socket_type socket(int af, int type, int protocol,
 
   return s;
 #else
-  int s = error_wrapper(::socket(af, type, protocol), ec);
-  if (s >= 0)
-    ec = boost::system::error_code();
+  int s = ::socket(af, type, protocol);
+  get_last_error(ec, s < 0);
   return s;
 #endif
 }
@@ -1470,7 +1882,7 @@ int setsockopt(socket_type s, state_type& state, int level, int optname,
       state |= enable_connection_aborted;
     else
       state &= ~enable_connection_aborted;
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -1486,22 +1898,21 @@ int setsockopt(socket_type s, state_type& state, int level, int optname,
     typedef int (WSAAPI *sso_t)(SOCKET, int, int, const char*, int);
     if (sso_t sso = (sso_t)::GetProcAddress(winsock_module, "setsockopt"))
     {
-      clear_last_error();
-      return error_wrapper(sso(s, level, optname,
+      int result = sso(s, level, optname,
             reinterpret_cast<const char*>(optval),
-            static_cast<int>(optlen)), ec);
+            static_cast<int>(optlen));
+      get_last_error(ec, result != 0);
+      return result;
     }
   }
   ec = boost::asio::error::fault;
   return socket_error_retval;
 #else // defined(__BORLANDC__)
-  clear_last_error();
-  int result = error_wrapper(call_setsockopt(&msghdr::msg_namelen,
-        s, level, optname, optval, optlen), ec);
+  int result = call_setsockopt(&msghdr::msg_namelen,
+        s, level, optname, optval, optlen);
+  get_last_error(ec, result != 0);
   if (result == 0)
   {
-    ec = boost::system::error_code();
-
 #if defined(__MACH__) && defined(__APPLE__) \
   || defined(__NetBSD__) || defined(__FreeBSD__) \
   || defined(__OpenBSD__) || defined(__QNX__)
@@ -1556,7 +1967,7 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
     }
 
     *static_cast<int*>(optval) = (state & enable_connection_aborted) ? 1 : 0;
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -1569,10 +1980,10 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
     typedef int (WSAAPI *gso_t)(SOCKET, int, int, char*, int*);
     if (gso_t gso = (gso_t)::GetProcAddress(winsock_module, "getsockopt"))
     {
-      clear_last_error();
       int tmp_optlen = static_cast<int>(*optlen);
-      int result = error_wrapper(gso(s, level, optname,
-            reinterpret_cast<char*>(optval), &tmp_optlen), ec);
+      int result = gso(s, level, optname,
+            reinterpret_cast<char*>(optval), &tmp_optlen);
+      get_last_error(ec, result != 0);
       *optlen = static_cast<size_t>(tmp_optlen);
       if (result != 0 && level == IPPROTO_IPV6 && optname == IPV6_V6ONLY
           && ec.value() == WSAENOPROTOOPT && *optlen == sizeof(DWORD))
@@ -1583,7 +1994,7 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
         // value is non-zero (i.e. true). This corresponds to the behavior of
         // IPv6 sockets on Windows platforms pre-Vista.
         *static_cast<DWORD*>(optval) = 1;
-        ec = boost::system::error_code();
+        ec.assign(0, ec.category());
       }
       return result;
     }
@@ -1591,9 +2002,9 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
   ec = boost::asio::error::fault;
   return socket_error_retval;
 #elif defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  clear_last_error();
-  int result = error_wrapper(call_getsockopt(&msghdr::msg_namelen,
-        s, level, optname, optval, optlen), ec);
+  int result = call_getsockopt(&msghdr::msg_namelen,
+        s, level, optname, optval, optlen);
+  get_last_error(ec, result != 0);
   if (result != 0 && level == IPPROTO_IPV6 && optname == IPV6_V6ONLY
       && ec.value() == WSAENOPROTOOPT && *optlen == sizeof(DWORD))
   {
@@ -1603,15 +2014,13 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
     // non-zero (i.e. true). This corresponds to the behavior of IPv6 sockets
     // on Windows platforms pre-Vista.
     *static_cast<DWORD*>(optval) = 1;
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
   }
-  if (result == 0)
-    ec = boost::system::error_code();
   return result;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  clear_last_error();
-  int result = error_wrapper(call_getsockopt(&msghdr::msg_namelen,
-        s, level, optname, optval, optlen), ec);
+  int result = call_getsockopt(&msghdr::msg_namelen,
+        s, level, optname, optval, optlen);
+  get_last_error(ec, result != 0);
 #if defined(__linux__)
   if (result == 0 && level == SOL_SOCKET && *optlen == sizeof(int)
       && (optname == SO_SNDBUF || optname == SO_RCVBUF))
@@ -1624,8 +2033,6 @@ int getsockopt(socket_type s, state_type state, int level, int optname,
     *static_cast<int*>(optval) /= 2;
   }
 #endif // defined(__linux__)
-  if (result == 0)
-    ec = boost::system::error_code();
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
 }
@@ -1668,7 +2075,7 @@ int getpeername(socket_type s, socket_addr_type* addr,
     }
 
     // The cached value is still valid.
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 #else // defined(BOOST_ASIO_WINDOWS) && !defined(BOOST_ASIO_WINDOWS_APP)
@@ -1677,11 +2084,8 @@ int getpeername(socket_type s, socket_addr_type* addr,
 #endif // defined(BOOST_ASIO_WINDOWS) && !defined(BOOST_ASIO_WINDOWS_APP)
        // || defined(__CYGWIN__)
 
-  clear_last_error();
-  int result = error_wrapper(call_getpeername(
-        &msghdr::msg_namelen, s, addr, addrlen), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = call_getpeername(&msghdr::msg_namelen, s, addr, addrlen);
+  get_last_error(ec, result != 0);
   return result;
 }
 
@@ -1704,11 +2108,8 @@ int getsockname(socket_type s, socket_addr_type* addr,
     return socket_error_retval;
   }
 
-  clear_last_error();
-  int result = error_wrapper(call_getsockname(
-        &msghdr::msg_namelen, s, addr, addrlen), ec);
-  if (result == 0)
-    ec = boost::system::error_code();
+  int result = call_getsockname(&msghdr::msg_namelen, s, addr, addrlen);
+  get_last_error(ec, result != 0);
   return result;
 }
 
@@ -1721,20 +2122,17 @@ int ioctl(socket_type s, state_type& state, int cmd,
     return socket_error_retval;
   }
 
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  int result = error_wrapper(::ioctlsocket(s, cmd, arg), ec);
+  int result = ::ioctlsocket(s, cmd, arg);
 #elif defined(__MACH__) && defined(__APPLE__) \
   || defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
-  int result = error_wrapper(::ioctl(s,
-        static_cast<unsigned int>(cmd), arg), ec);
+  int result = ::ioctl(s, static_cast<unsigned int>(cmd), arg);
 #else
-  int result = error_wrapper(::ioctl(s, cmd, arg), ec);
+  int result = ::ioctl(s, cmd, arg);
 #endif
+  get_last_error(ec, result < 0);
   if (result >= 0)
   {
-    ec = boost::system::error_code();
-
     // When updating the non-blocking mode we always perform the ioctl syscall,
     // even if the flags would otherwise indicate that the socket is already in
     // the correct state. This ensures that the underlying socket is put into
@@ -1762,7 +2160,6 @@ int ioctl(socket_type s, state_type& state, int cmd,
 int select(int nfds, fd_set* readfds, fd_set* writefds,
     fd_set* exceptfds, timeval* timeout, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(__EMSCRIPTEN__)
   exceptfds = 0;
 #endif // defined(__EMSCRIPTEN__)
@@ -1773,7 +2170,7 @@ int select(int nfds, fd_set* readfds, fd_set* writefds,
     if (milliseconds == 0)
       milliseconds = 1; // Force context switch.
     ::Sleep(milliseconds);
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 0;
   }
 
@@ -1792,15 +2189,13 @@ int select(int nfds, fd_set* readfds, fd_set* writefds,
   timespec ts;
   ts.tv_sec = timeout ? timeout->tv_sec : 0;
   ts.tv_nsec = timeout ? timeout->tv_usec * 1000 : 0;
-  return error_wrapper(::pselect(nfds, readfds,
-        writefds, exceptfds, timeout ? &ts : 0, 0), ec);
+  int result = ::pselect(nfds, readfds,
+        writefds, exceptfds, timeout ? &ts : 0, 0);
 #else
-  int result = error_wrapper(::select(nfds, readfds,
-        writefds, exceptfds, timeout), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
-  return result;
+  int result = ::select(nfds, readfds, writefds, exceptfds, timeout);
 #endif
+  get_last_error(ec, result < 0);
+  return result;
 }
 
 int poll_read(socket_type s, state_type state,
@@ -1834,8 +2229,8 @@ int poll_read(socket_type s, state_type state,
   }
   else
     timeout = 0;
-  clear_last_error();
-  int result = error_wrapper(::select(s + 1, &fds, 0, 0, timeout), ec);
+  int result = ::select(s + 1, &fds, 0, 0, timeout);
+  get_last_error(ec, result < 0);
 #else // defined(BOOST_ASIO_WINDOWS)
       // || defined(__CYGWIN__)
       // || defined(__SYMBIAN32__)
@@ -1844,16 +2239,14 @@ int poll_read(socket_type s, state_type state,
   fds.events = POLLIN;
   fds.revents = 0;
   int timeout = (state & user_set_non_blocking) ? 0 : msec;
-  clear_last_error();
-  int result = error_wrapper(::poll(&fds, 1, timeout), ec);
+  int result = ::poll(&fds, 1, timeout);
+  get_last_error(ec, result < 0);
 #endif // defined(BOOST_ASIO_WINDOWS)
        // || defined(__CYGWIN__)
        // || defined(__SYMBIAN32__)
   if (result == 0)
-    ec = (state & user_set_non_blocking)
-      ? boost::asio::error::would_block : boost::system::error_code();
-  else if (result > 0)
-    ec = boost::system::error_code();
+    if (state & user_set_non_blocking)
+      ec = boost::asio::error::would_block;
   return result;
 }
 
@@ -1888,8 +2281,8 @@ int poll_write(socket_type s, state_type state,
   }
   else
     timeout = 0;
-  clear_last_error();
-  int result = error_wrapper(::select(s + 1, 0, &fds, 0, timeout), ec);
+  int result = ::select(s + 1, 0, &fds, 0, timeout);
+  get_last_error(ec, result < 0);
 #else // defined(BOOST_ASIO_WINDOWS)
       // || defined(__CYGWIN__)
       // || defined(__SYMBIAN32__)
@@ -1898,16 +2291,14 @@ int poll_write(socket_type s, state_type state,
   fds.events = POLLOUT;
   fds.revents = 0;
   int timeout = (state & user_set_non_blocking) ? 0 : msec;
-  clear_last_error();
-  int result = error_wrapper(::poll(&fds, 1, timeout), ec);
+  int result = ::poll(&fds, 1, timeout);
+  get_last_error(ec, result < 0);
 #endif // defined(BOOST_ASIO_WINDOWS)
        // || defined(__CYGWIN__)
        // || defined(__SYMBIAN32__)
   if (result == 0)
-    ec = (state & user_set_non_blocking)
-      ? boost::asio::error::would_block : boost::system::error_code();
-  else if (result > 0)
-    ec = boost::system::error_code();
+    if (state & user_set_non_blocking)
+      ec = boost::asio::error::would_block;
   return result;
 }
 
@@ -1942,8 +2333,8 @@ int poll_error(socket_type s, state_type state,
   }
   else
     timeout = 0;
-  clear_last_error();
-  int result = error_wrapper(::select(s + 1, 0, 0, &fds, timeout), ec);
+  int result = ::select(s + 1, 0, 0, &fds, timeout);
+  get_last_error(ec, result < 0);
 #else // defined(BOOST_ASIO_WINDOWS)
       // || defined(__CYGWIN__)
       // || defined(__SYMBIAN32__)
@@ -1952,16 +2343,14 @@ int poll_error(socket_type s, state_type state,
   fds.events = POLLPRI | POLLERR | POLLHUP;
   fds.revents = 0;
   int timeout = (state & user_set_non_blocking) ? 0 : msec;
-  clear_last_error();
-  int result = error_wrapper(::poll(&fds, 1, timeout), ec);
+  int result = ::poll(&fds, 1, timeout);
+  get_last_error(ec, result < 0);
 #endif // defined(BOOST_ASIO_WINDOWS)
        // || defined(__CYGWIN__)
        // || defined(__SYMBIAN32__)
   if (result == 0)
-    ec = (state & user_set_non_blocking)
-      ? boost::asio::error::would_block : boost::system::error_code();
-  else if (result > 0)
-    ec = boost::system::error_code();
+    if (state & user_set_non_blocking)
+      ec = boost::asio::error::would_block;
   return result;
 }
 
@@ -1992,11 +2381,8 @@ int poll_connect(socket_type s, int msec, boost::system::error_code& ec)
   }
   else
     timeout = 0;
-  clear_last_error();
-  int result = error_wrapper(::select(
-        s + 1, 0, &write_fds, &except_fds, timeout), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
+  int result = ::select(s + 1, 0, &write_fds, &except_fds, timeout);
+  get_last_error(ec, result < 0);
   return result;
 #else // defined(BOOST_ASIO_WINDOWS)
       // || defined(__CYGWIN__)
@@ -2005,10 +2391,8 @@ int poll_connect(socket_type s, int msec, boost::system::error_code& ec)
   fds.fd = s;
   fds.events = POLLOUT;
   fds.revents = 0;
-  clear_last_error();
-  int result = error_wrapper(::poll(&fds, 1, msec), ec);
-  if (result >= 0)
-    ec = boost::system::error_code();
+  int result = ::poll(&fds, 1, msec);
+  get_last_error(ec, result < 0);
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS)
        // || defined(__CYGWIN__)
@@ -2093,18 +2477,20 @@ const char* inet_ntop(int af, const void* src, char* dest, size_t length,
   DWORD string_length = static_cast<DWORD>(length);
 #if defined(BOOST_NO_ANSI_APIS) || (defined(_MSC_VER) && (_MSC_VER >= 1800))
   LPWSTR string_buffer = (LPWSTR)_alloca(length * sizeof(WCHAR));
-  int result = error_wrapper(::WSAAddressToStringW(&address.base,
-        address_length, 0, string_buffer, &string_length), ec);
+  int result = ::WSAAddressToStringW(&address.base,
+        address_length, 0, string_buffer, &string_length);
+  get_last_error(ec, true);
   ::WideCharToMultiByte(CP_ACP, 0, string_buffer, -1,
       dest, static_cast<int>(length), 0, 0);
 #else
-  int result = error_wrapper(::WSAAddressToStringA(
-        &address.base, address_length, 0, dest, &string_length), ec);
+  int result = ::WSAAddressToStringA(&address.base,
+      address_length, 0, dest, &string_length);
+  get_last_error(ec, true);
 #endif
 
   // Windows may set error code on success.
   if (result != socket_error_retval)
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
 
   // Windows may not set an error code on failure.
   else if (result == socket_error_retval && !ec)
@@ -2112,8 +2498,8 @@ const char* inet_ntop(int af, const void* src, char* dest, size_t length,
 
   return result == socket_error_retval ? 0 : dest;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
-  const char* result = error_wrapper(::inet_ntop(
-        af, src, dest, static_cast<int>(length)), ec);
+  const char* result = ::inet_ntop(af, src, dest, static_cast<int>(length));
+  get_last_error(ec, true);
   if (result == 0 && !ec)
     ec = boost::asio::error::invalid_argument;
   if (result != 0 && af == BOOST_ASIO_OS_DEF(AF_INET6) && scope_id != 0)
@@ -2158,7 +2544,7 @@ int inet_pton(int af, const char* src, void* dest,
     bytes[1] = static_cast<unsigned char>(b1);
     bytes[2] = static_cast<unsigned char>(b2);
     bytes[3] = static_cast<unsigned char>(b3);
-    ec = boost::system::error_code();
+    ec.assign(), ec.category());
     return 1;
   }
   else if (af == BOOST_ASIO_OS_DEF(AF_INET6))
@@ -2274,7 +2660,7 @@ int inet_pton(int af, const char* src, void* dest,
     for (int i = 0; i < num_back_bytes; ++i)
       bytes[16 - num_back_bytes + i] = back_bytes[i];
 
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
     return 1;
   }
   else
@@ -2303,11 +2689,13 @@ int inet_pton(int af, const char* src, void* dest,
   int num_wide_chars = static_cast<int>(strlen(src)) + 1;
   LPWSTR wide_buffer = (LPWSTR)_alloca(num_wide_chars * sizeof(WCHAR));
   ::MultiByteToWideChar(CP_ACP, 0, src, -1, wide_buffer, num_wide_chars);
-  int result = error_wrapper(::WSAStringToAddressW(
-        wide_buffer, af, 0, &address.base, &address_length), ec);
+  int result = ::WSAStringToAddressW(wide_buffer,
+      af, 0, &address.base, &address_length);
+  get_last_error(ec, true);
 #else
-  int result = error_wrapper(::WSAStringToAddressA(
-        const_cast<char*>(src), af, 0, &address.base, &address_length), ec);
+  int result = ::WSAStringToAddressA(const_cast<char*>(src),
+      af, 0, &address.base, &address_length);
+  get_last_error(ec, true);
 #endif
 
   if (af == BOOST_ASIO_OS_DEF(AF_INET))
@@ -2315,12 +2703,12 @@ int inet_pton(int af, const char* src, void* dest,
     if (result != socket_error_retval)
     {
       memcpy(dest, &address.v4.sin_addr, sizeof(in4_addr_type));
-      ec = boost::system::error_code();
+      ec.assign(0, ec.category());
     }
     else if (strcmp(src, "255.255.255.255") == 0)
     {
       static_cast<in4_addr_type*>(dest)->s_addr = INADDR_NONE;
-      ec = boost::system::error_code();
+      ec.assign(0, ec.category());
     }
   }
   else // AF_INET6
@@ -2330,7 +2718,7 @@ int inet_pton(int af, const char* src, void* dest,
       memcpy(dest, &address.v6.sin6_addr, sizeof(in6_addr_type));
       if (scope_id)
         *scope_id = address.v6.sin6_scope_id;
-      ec = boost::system::error_code();
+      ec.assign(0, ec.category());
     }
   }
 
@@ -2339,7 +2727,7 @@ int inet_pton(int af, const char* src, void* dest,
     ec = boost::asio::error::invalid_argument;
 
   if (result != socket_error_retval)
-    ec = boost::system::error_code();
+    ec.assign(0, ec.category());
 
   return result == socket_error_retval ? -1 : 1;
 #else // defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
@@ -2363,7 +2751,8 @@ int inet_pton(int af, const char* src, void* dest,
     src_ptr = src_buf;
   }
 
-  int result = error_wrapper(::inet_pton(af, src_ptr, dest), ec);
+  int result = ::inet_pton(af, src_ptr, dest);
+  get_last_error(ec, true);
   if (result <= 0 && !ec)
     ec = boost::asio::error::invalid_argument;
   if (result > 0 && is_v6 && scope_id)
@@ -2389,7 +2778,6 @@ int inet_pton(int af, const char* src, void* dest,
 
 int gethostname(char* name, int namelen, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
   try
   {
@@ -2420,11 +2808,8 @@ int gethostname(char* name, int namelen, boost::system::error_code& ec)
     return -1;
   }
 #else // defined(BOOST_ASIO_WINDOWS_RUNTIME)
-  int result = error_wrapper(::gethostname(name, namelen), ec);
-# if defined(BOOST_ASIO_WINDOWS)
-  if (result == 0)
-    ec = boost::system::error_code();
-# endif // defined(BOOST_ASIO_WINDOWS)
+  int result = ::gethostname(name, namelen);
+  get_last_error(ec, result != 0);
   return result;
 #endif // defined(BOOST_ASIO_WINDOWS_RUNTIME)
 }
@@ -2459,20 +2844,20 @@ inline boost::system::error_code translate_netdb_error(int error)
 inline hostent* gethostbyaddr(const char* addr, int length, int af,
     hostent* result, char* buffer, int buflength, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   (void)(buffer);
   (void)(buflength);
-  hostent* retval = error_wrapper(::gethostbyaddr(addr, length, af), ec);
+  hostent* retval = ::gethostbyaddr(addr, length, af);
+  get_last_error(ec, !retval);
   if (!retval)
     return 0;
-  ec = boost::system::error_code();
   *result = *retval;
   return retval;
 #elif defined(__sun) || defined(__QNX__)
   int error = 0;
-  hostent* retval = error_wrapper(::gethostbyaddr_r(addr, length, af, result,
-        buffer, buflength, &error), ec);
+  hostent* retval = ::gethostbyaddr_r(addr, length,
+      af, result, buffer, buflength, &error);
+  get_last_error(ec, !retval);
   if (error)
     ec = translate_netdb_error(error);
   return retval;
@@ -2480,8 +2865,8 @@ inline hostent* gethostbyaddr(const char* addr, int length, int af,
   (void)(buffer);
   (void)(buflength);
   int error = 0;
-  hostent* retval = error_wrapper(::getipnodebyaddr(
-        addr, length, af, &error), ec);
+  hostent* retval = ::getipnodebyaddr(addr, length, af, &error);
+  get_last_error(ec, !retval);
   if (error)
     ec = translate_netdb_error(error);
   if (!retval)
@@ -2491,8 +2876,10 @@ inline hostent* gethostbyaddr(const char* addr, int length, int af,
 #else
   hostent* retval = 0;
   int error = 0;
-  error_wrapper(::gethostbyaddr_r(addr, length, af, result, buffer,
-        buflength, &retval, &error), ec);
+  clear_last_error();
+  ::gethostbyaddr_r(addr, length, af, result,
+      buffer, buflength, &retval, &error);
+  get_last_error(ec, true);
   if (error)
     ec = translate_netdb_error(error);
   return retval;
@@ -2502,7 +2889,6 @@ inline hostent* gethostbyaddr(const char* addr, int length, int af,
 inline hostent* gethostbyname(const char* name, int af, struct hostent* result,
     char* buffer, int buflength, int ai_flags, boost::system::error_code& ec)
 {
-  clear_last_error();
 #if defined(BOOST_ASIO_WINDOWS) || defined(__CYGWIN__)
   (void)(buffer);
   (void)(buflength);
@@ -2512,10 +2898,10 @@ inline hostent* gethostbyname(const char* name, int af, struct hostent* result,
     ec = boost::asio::error::address_family_not_supported;
     return 0;
   }
-  hostent* retval = error_wrapper(::gethostbyname(name), ec);
+  hostent* retval = ::gethostbyname(name);
+  get_last_error(ec, !retval);
   if (!retval)
     return 0;
-  ec = boost::system::error_code();
   *result = *retval;
   return result;
 #elif defined(__sun) || defined(__QNX__)
@@ -2526,8 +2912,8 @@ inline hostent* gethostbyname(const char* name, int af, struct hostent* result,
     return 0;
   }
   int error = 0;
-  hostent* retval = error_wrapper(::gethostbyname_r(name, result, buffer,
-        buflength, &error), ec);
+  hostent* retval = ::gethostbyname_r(name, result, buffer, buflength, &error);
+  get_last_error(ec, !retval);
   if (error)
     ec = translate_netdb_error(error);
   return retval;
@@ -2535,8 +2921,8 @@ inline hostent* gethostbyname(const char* name, int af, struct hostent* result,
   (void)(buffer);
   (void)(buflength);
   int error = 0;
-  hostent* retval = error_wrapper(::getipnodebyname(
-        name, af, ai_flags, &error), ec);
+  hostent* retval = ::getipnodebyname(name, af, ai_flags, &error);
+  get_last_error(ec, !retval);
   if (error)
     ec = translate_netdb_error(error);
   if (!retval)
@@ -2552,8 +2938,9 @@ inline hostent* gethostbyname(const char* name, int af, struct hostent* result,
   }
   hostent* retval = 0;
   int error = 0;
-  error_wrapper(::gethostbyname_r(name, result,
-        buffer, buflength, &retval, &error), ec);
+  clear_last_error();
+  ::gethostbyname_r(name, result, buffer, buflength, &retval, &error);
+  get_last_error(ec, true);
   if (error)
     ec = translate_netdb_error(error);
   return retval;
@@ -3269,7 +3656,7 @@ inline boost::system::error_code getnameinfo_emulation(
     }
   }
 
-  ec = boost::system::error_code();
+  ec.assign(0, ec.category());
   return ec;
 }
 
diff --git a/include/boost/asio/detail/impl/strand_executor_service.hpp b/include/boost/asio/detail/impl/strand_executor_service.hpp
index a3ba5f20..2cf557fc 100644
--- a/include/boost/asio/detail/impl/strand_executor_service.hpp
+++ b/include/boost/asio/detail/impl/strand_executor_service.hpp
@@ -20,6 +20,9 @@
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
 #include <boost/asio/detail/recycling_allocator.hpp>
 #include <boost/asio/executor_work_guard.hpp>
+#include <boost/asio/defer.hpp>
+#include <boost/asio/dispatch.hpp>
+#include <boost/asio/post.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -27,8 +30,137 @@ namespace boost {
 namespace asio {
 namespace detail {
 
+template <typename F, typename Allocator>
+class strand_executor_service::allocator_binder
+{
+public:
+  typedef Allocator allocator_type;
+
+  allocator_binder(BOOST_ASIO_MOVE_ARG(F) f, const Allocator& a)
+    : f_(BOOST_ASIO_MOVE_CAST(F)(f)),
+      allocator_(a)
+  {
+  }
+
+  allocator_binder(const allocator_binder& other)
+    : f_(other.f_),
+      allocator_(other.allocator_)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  allocator_binder(allocator_binder&& other)
+    : f_(BOOST_ASIO_MOVE_CAST(F)(other.f_)),
+      allocator_(BOOST_ASIO_MOVE_CAST(allocator_type)(other.allocator_))
+  {
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  allocator_type get_allocator() const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  void operator()()
+  {
+    f_();
+  }
+
+private:
+  F f_;
+  allocator_type allocator_;
+};
+
 template <typename Executor>
-class strand_executor_service::invoker
+class strand_executor_service::invoker<Executor,
+    typename enable_if<
+      execution::is_executor<Executor>::value
+    >::type>
+{
+public:
+  invoker(const implementation_type& impl, Executor& ex)
+    : impl_(impl),
+      executor_(boost::asio::prefer(ex, execution::outstanding_work.tracked))
+  {
+  }
+
+  invoker(const invoker& other)
+    : impl_(other.impl_),
+      executor_(other.executor_)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  invoker(invoker&& other)
+    : impl_(BOOST_ASIO_MOVE_CAST(implementation_type)(other.impl_)),
+      executor_(BOOST_ASIO_MOVE_CAST(executor_type)(other.executor_))
+  {
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  struct on_invoker_exit
+  {
+    invoker* this_;
+
+    ~on_invoker_exit()
+    {
+      this_->impl_->mutex_->lock();
+      this_->impl_->ready_queue_.push(this_->impl_->waiting_queue_);
+      bool more_handlers = this_->impl_->locked_ =
+        !this_->impl_->ready_queue_.empty();
+      this_->impl_->mutex_->unlock();
+
+      if (more_handlers)
+      {
+        recycling_allocator<void> allocator;
+        execution::execute(
+            boost::asio::prefer(
+              boost::asio::require(this_->executor_,
+                execution::blocking.never),
+            execution::allocator(allocator)),
+            BOOST_ASIO_MOVE_CAST(invoker)(*this_));
+      }
+    }
+  };
+
+  void operator()()
+  {
+    // Indicate that this strand is executing on the current thread.
+    call_stack<strand_impl>::context ctx(impl_.get());
+
+    // Ensure the next handler, if any, is scheduled on block exit.
+    on_invoker_exit on_exit = { this };
+    (void)on_exit;
+
+    // Run all ready handlers. No lock is required since the ready queue is
+    // accessed only within the strand.
+    boost::system::error_code ec;
+    while (scheduler_operation* o = impl_->ready_queue_.front())
+    {
+      impl_->ready_queue_.pop();
+      o->complete(impl_.get(), ec, 0);
+    }
+  }
+
+private:
+  typedef typename decay<
+      typename prefer_result_type<
+        Executor,
+        execution::outstanding_work_t::tracked_t
+      >::type
+    >::type executor_type;
+
+  implementation_type impl_;
+  executor_type executor_;
+};
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+template <typename Executor>
+class strand_executor_service::invoker<Executor,
+    typename enable_if<
+      !execution::is_executor<Executor>::value
+    >::type>
 {
 public:
   invoker(const implementation_type& impl, Executor& ex)
@@ -96,6 +228,68 @@ private:
   executor_work_guard<Executor> work_;
 };
 
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+template <typename Executor, typename Function>
+inline void strand_executor_service::execute(const implementation_type& impl,
+    Executor& ex, BOOST_ASIO_MOVE_ARG(Function) function,
+    typename enable_if<
+      can_query<Executor, execution::allocator_t<void> >::value
+    >::type*)
+{
+  return strand_executor_service::execute(impl, ex,
+      BOOST_ASIO_MOVE_CAST(Function)(function),
+      boost::asio::query(ex, execution::allocator));
+}
+
+template <typename Executor, typename Function>
+inline void strand_executor_service::execute(const implementation_type& impl,
+    Executor& ex, BOOST_ASIO_MOVE_ARG(Function) function,
+    typename enable_if<
+      !can_query<Executor, execution::allocator_t<void> >::value
+    >::type*)
+{
+  return strand_executor_service::execute(impl, ex,
+      BOOST_ASIO_MOVE_CAST(Function)(function),
+      std::allocator<void>());
+}
+
+template <typename Executor, typename Function, typename Allocator>
+void strand_executor_service::execute(const implementation_type& impl,
+    Executor& ex, BOOST_ASIO_MOVE_ARG(Function) function, const Allocator& a)
+{
+  typedef typename decay<Function>::type function_type;
+
+  // If the executor is not never-blocking, and we are already in the strand,
+  // then the function can run immediately.
+  if (boost::asio::query(ex, execution::blocking) != execution::blocking.never
+      && call_stack<strand_impl>::contains(impl.get()))
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(BOOST_ASIO_MOVE_CAST(Function)(function));
+
+    fenced_block b(fenced_block::full);
+    boost_asio_handler_invoke_helpers::invoke(tmp, tmp);
+    return;
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef executor_op<function_type, Allocator> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(function), a);
+
+  BOOST_ASIO_HANDLER_CREATION((impl->service_->context(), *p.p,
+        "strand_executor", impl.get(), 0, "execute"));
+
+  // Add the function to the strand and schedule the strand if required.
+  bool first = enqueue(impl, p.p);
+  p.v = p.p = 0;
+  if (first)
+  {
+    execution::execute(ex, invoker<Executor>(impl, ex));
+  }
+}
+
 template <typename Executor, typename Function, typename Allocator>
 void strand_executor_service::dispatch(const implementation_type& impl,
     Executor& ex, BOOST_ASIO_MOVE_ARG(Function) function, const Allocator& a)
@@ -125,7 +319,11 @@ void strand_executor_service::dispatch(const implementation_type& impl,
   bool first = enqueue(impl, p.p);
   p.v = p.p = 0;
   if (first)
-    ex.dispatch(invoker<Executor>(impl, ex), a);
+  {
+    boost::asio::dispatch(ex,
+        allocator_binder<invoker<Executor>, Allocator>(
+          invoker<Executor>(impl, ex), a));
+  }
 }
 
 // Request invocation of the given function and return immediately.
@@ -147,7 +345,11 @@ void strand_executor_service::post(const implementation_type& impl,
   bool first = enqueue(impl, p.p);
   p.v = p.p = 0;
   if (first)
-    ex.post(invoker<Executor>(impl, ex), a);
+  {
+    boost::asio::post(ex,
+        allocator_binder<invoker<Executor>, Allocator>(
+          invoker<Executor>(impl, ex), a));
+  }
 }
 
 // Request invocation of the given function and return immediately.
@@ -169,7 +371,11 @@ void strand_executor_service::defer(const implementation_type& impl,
   bool first = enqueue(impl, p.p);
   p.v = p.p = 0;
   if (first)
-    ex.defer(invoker<Executor>(impl, ex), a);
+  {
+    boost::asio::defer(ex,
+        allocator_binder<invoker<Executor>, Allocator>(
+          invoker<Executor>(impl, ex), a));
+  }
 }
 
 } // namespace detail
diff --git a/include/boost/asio/detail/impl/strand_service.hpp b/include/boost/asio/detail/impl/strand_service.hpp
index 6ca4673c..fe95d630 100644
--- a/include/boost/asio/detail/impl/strand_service.hpp
+++ b/include/boost/asio/detail/impl/strand_service.hpp
@@ -36,7 +36,7 @@ inline strand_service::strand_impl::strand_impl()
 
 struct strand_service::on_dispatch_exit
 {
-  io_context_impl* io_context_;
+  io_context_impl* io_context_impl_;
   strand_impl* impl_;
 
   ~on_dispatch_exit()
@@ -47,7 +47,7 @@ struct strand_service::on_dispatch_exit
     impl_->mutex_.unlock();
 
     if (more_handlers)
-      io_context_->post_immediate_completion(impl_, false);
+      io_context_impl_->post_immediate_completion(impl_, false);
   }
 };
 
@@ -64,10 +64,10 @@ void strand_service::dispatch(strand_service::implementation_type& impl,
   }
 
   // Allocate and construct an operation to wrap the handler.
-  typedef completion_handler<Handler> op;
+  typedef completion_handler<Handler, io_context::executor_type> op;
   typename op::ptr p = { boost::asio::detail::addressof(handler),
     op::ptr::allocate(handler), 0 };
-  p.p = new (p.v) op(handler);
+  p.p = new (p.v) op(handler, io_context_.get_executor());
 
   BOOST_ASIO_HANDLER_CREATION((this->context(),
         *p.p, "strand", impl, 0, "dispatch"));
@@ -82,11 +82,10 @@ void strand_service::dispatch(strand_service::implementation_type& impl,
     call_stack<strand_impl>::context ctx(impl);
 
     // Ensure the next handler, if any, is scheduled on block exit.
-    on_dispatch_exit on_exit = { &io_context_, impl };
+    on_dispatch_exit on_exit = { &io_context_impl_, impl };
     (void)on_exit;
 
-    completion_handler<Handler>::do_complete(
-        &io_context_, o, boost::system::error_code(), 0);
+    op::do_complete(&io_context_impl_, o, boost::system::error_code(), 0);
   }
 }
 
@@ -99,10 +98,10 @@ void strand_service::post(strand_service::implementation_type& impl,
     boost_asio_handler_cont_helpers::is_continuation(handler);
 
   // Allocate and construct an operation to wrap the handler.
-  typedef completion_handler<Handler> op;
+  typedef completion_handler<Handler, io_context::executor_type> op;
   typename op::ptr p = { boost::asio::detail::addressof(handler),
     op::ptr::allocate(handler), 0 };
-  p.p = new (p.v) op(handler);
+  p.p = new (p.v) op(handler, io_context_.get_executor());
 
   BOOST_ASIO_HANDLER_CREATION((this->context(),
         *p.p, "strand", impl, 0, "post"));
diff --git a/include/boost/asio/detail/impl/strand_service.ipp b/include/boost/asio/detail/impl/strand_service.ipp
index e7f5f1be..885bb0aa 100644
--- a/include/boost/asio/detail/impl/strand_service.ipp
+++ b/include/boost/asio/detail/impl/strand_service.ipp
@@ -44,7 +44,8 @@ struct strand_service::on_do_complete_exit
 
 strand_service::strand_service(boost::asio::io_context& io_context)
   : boost::asio::detail::service_base<strand_service>(io_context),
-    io_context_(boost::asio::use_service<io_context_impl>(io_context)),
+    io_context_(io_context),
+    io_context_impl_(boost::asio::use_service<io_context_impl>(io_context)),
     mutex_(),
     salt_(0)
 {
@@ -95,7 +96,7 @@ bool strand_service::do_dispatch(implementation_type& impl, operation* op)
 {
   // If we are running inside the io_context, and no other handler already
   // holds the strand lock, then the handler can run immediately.
-  bool can_dispatch = io_context_.can_dispatch();
+  bool can_dispatch = io_context_impl_.can_dispatch();
   impl->mutex_.lock();
   if (can_dispatch && !impl->locked_)
   {
@@ -118,7 +119,7 @@ bool strand_service::do_dispatch(implementation_type& impl, operation* op)
     impl->locked_ = true;
     impl->mutex_.unlock();
     impl->ready_queue_.push(op);
-    io_context_.post_immediate_completion(impl, false);
+    io_context_impl_.post_immediate_completion(impl, false);
   }
 
   return false;
@@ -141,7 +142,7 @@ void strand_service::do_post(implementation_type& impl,
     impl->locked_ = true;
     impl->mutex_.unlock();
     impl->ready_queue_.push(op);
-    io_context_.post_immediate_completion(impl, is_continuation);
+    io_context_impl_.post_immediate_completion(impl, is_continuation);
   }
 }
 
diff --git a/include/boost/asio/detail/impl/win_iocp_io_context.ipp b/include/boost/asio/detail/impl/win_iocp_io_context.ipp
index 55f18586..bc9c1d2b 100644
--- a/include/boost/asio/detail/impl/win_iocp_io_context.ipp
+++ b/include/boost/asio/detail/impl/win_iocp_io_context.ipp
@@ -114,6 +114,7 @@ win_iocp_io_context::~win_iocp_io_context()
 {
   if (thread_.get())
   {
+    stop();
     thread_->join();
     thread_.reset();
   }
@@ -200,7 +201,7 @@ size_t win_iocp_io_context::run(boost::system::error_code& ec)
   thread_call_stack::context ctx(this, this_thread);
 
   size_t n = 0;
-  while (do_one(INFINITE, ec))
+  while (do_one(INFINITE, this_thread, ec))
     if (n != (std::numeric_limits<size_t>::max)())
       ++n;
   return n;
@@ -218,7 +219,7 @@ size_t win_iocp_io_context::run_one(boost::system::error_code& ec)
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
-  return do_one(INFINITE, ec);
+  return do_one(INFINITE, this_thread, ec);
 }
 
 size_t win_iocp_io_context::wait_one(long usec, boost::system::error_code& ec)
@@ -233,7 +234,7 @@ size_t win_iocp_io_context::wait_one(long usec, boost::system::error_code& ec)
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
-  return do_one(usec < 0 ? INFINITE : ((usec - 1) / 1000 + 1), ec);
+  return do_one(usec < 0 ? INFINITE : ((usec - 1) / 1000 + 1), this_thread, ec);
 }
 
 size_t win_iocp_io_context::poll(boost::system::error_code& ec)
@@ -249,7 +250,7 @@ size_t win_iocp_io_context::poll(boost::system::error_code& ec)
   thread_call_stack::context ctx(this, this_thread);
 
   size_t n = 0;
-  while (do_one(0, ec))
+  while (do_one(0, this_thread, ec))
     if (n != (std::numeric_limits<size_t>::max)())
       ++n;
   return n;
@@ -267,7 +268,7 @@ size_t win_iocp_io_context::poll_one(boost::system::error_code& ec)
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
-  return do_one(0, ec);
+  return do_one(0, this_thread, ec);
 }
 
 void win_iocp_io_context::stop()
@@ -287,6 +288,12 @@ void win_iocp_io_context::stop()
   }
 }
 
+void win_iocp_io_context::capture_current_exception()
+{
+  if (thread_info_base* this_thread = thread_call_stack::contains(this))
+    this_thread->capture_current_exception();
+}
+
 void win_iocp_io_context::post_deferred_completion(win_iocp_operation* op)
 {
   // Flag the operation as ready.
@@ -396,7 +403,8 @@ void win_iocp_io_context::on_completion(win_iocp_operation* op,
   }
 }
 
-size_t win_iocp_io_context::do_one(DWORD msec, boost::system::error_code& ec)
+size_t win_iocp_io_context::do_one(DWORD msec,
+    win_iocp_thread_info& this_thread, boost::system::error_code& ec)
 {
   for (;;)
   {
@@ -458,6 +466,7 @@ size_t win_iocp_io_context::do_one(DWORD msec, boost::system::error_code& ec)
         (void)on_exit;
 
         op->complete(this, result_ec, bytes_transferred);
+        this_thread.rethrow_pending_exception();
         ec = boost::system::error_code();
         return 1;
       }
diff --git a/include/boost/asio/detail/io_object_executor.hpp b/include/boost/asio/detail/io_object_executor.hpp
deleted file mode 100644
index dd775b45..00000000
--- a/include/boost/asio/detail/io_object_executor.hpp
+++ /dev/null
@@ -1,169 +0,0 @@
-//
-// io_object_executor.hpp
-// ~~~~~~~~~~~~~~~~~~~~~~
-//
-// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-
-#ifndef BOOST_ASIO_DETAIL_IO_OBJECT_EXECUTOR_HPP
-#define BOOST_ASIO_DETAIL_IO_OBJECT_EXECUTOR_HPP
-
-#if defined(_MSC_VER) && (_MSC_VER >= 1200)
-# pragma once
-#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
-
-#include <boost/asio/detail/config.hpp>
-#include <boost/asio/detail/handler_invoke_helpers.hpp>
-#include <boost/asio/detail/type_traits.hpp>
-#include <boost/asio/io_context.hpp>
-
-#include <boost/asio/detail/push_options.hpp>
-
-namespace boost {
-namespace asio {
-namespace detail {
-
-// Wrap the (potentially polymorphic) executor so that we can bypass it when
-// dispatching on a target executor that has a native I/O implementation.
-template <typename Executor>
-class io_object_executor
-{
-public:
-  io_object_executor(const Executor& ex,
-      bool native_implementation) BOOST_ASIO_NOEXCEPT
-    : executor_(ex),
-      has_native_impl_(native_implementation)
-  {
-  }
-
-  io_object_executor(const io_object_executor& other) BOOST_ASIO_NOEXCEPT
-    : executor_(other.executor_),
-      has_native_impl_(other.has_native_impl_)
-  {
-  }
-
-  template <typename Executor1>
-  io_object_executor(
-      const io_object_executor<Executor1>& other) BOOST_ASIO_NOEXCEPT
-    : executor_(other.inner_executor()),
-      has_native_impl_(other.has_native_implementation())
-  {
-  }
-
-#if defined(BOOST_ASIO_HAS_MOVE)
-  io_object_executor(io_object_executor&& other) BOOST_ASIO_NOEXCEPT
-    : executor_(BOOST_ASIO_MOVE_CAST(Executor)(other.executor_)),
-      has_native_impl_(other.has_native_impl_)
-  {
-  }
-#endif // defined(BOOST_ASIO_HAS_MOVE)
-
-  const Executor& inner_executor() const BOOST_ASIO_NOEXCEPT
-  {
-    return executor_;
-  }
-
-  bool has_native_implementation() const BOOST_ASIO_NOEXCEPT
-  {
-    return has_native_impl_;
-  }
-
-  execution_context& context() const BOOST_ASIO_NOEXCEPT
-  {
-    return executor_.context();
-  }
-
-  void on_work_started() const BOOST_ASIO_NOEXCEPT
-  {
-    if (is_same<Executor, io_context::executor_type>::value
-        || has_native_impl_)
-    {
-      // When using a native implementation, work is already counted by the
-      // execution context.
-    }
-    else
-    {
-      executor_.on_work_started();
-    }
-  }
-
-  void on_work_finished() const BOOST_ASIO_NOEXCEPT
-  {
-    if (is_same<Executor, io_context::executor_type>::value
-        || has_native_impl_)
-    {
-      // When using a native implementation, work is already counted by the
-      // execution context.
-    }
-    else
-    {
-      executor_.on_work_finished();
-    }
-  }
-
-  template <typename F, typename A>
-  void dispatch(BOOST_ASIO_MOVE_ARG(F) f, const A& a) const
-  {
-    if (is_same<Executor, io_context::executor_type>::value
-        || has_native_impl_)
-    {
-      // When using a native implementation, I/O completion handlers are
-      // already dispatched according to the execution context's executor's
-      // rules. We can call the function directly.
-#if defined(BOOST_ASIO_HAS_MOVE)
-      if (is_same<F, typename decay<F>::type>::value)
-      {
-        boost_asio_handler_invoke_helpers::invoke(f, f);
-        return;
-      }
-#endif // defined(BOOST_ASIO_HAS_MOVE)
-      typename decay<F>::type function(BOOST_ASIO_MOVE_CAST(F)(f));
-      boost_asio_handler_invoke_helpers::invoke(function, function);
-    }
-    else
-    {
-      executor_.dispatch(BOOST_ASIO_MOVE_CAST(F)(f), a);
-    }
-  }
-
-  template <typename F, typename A>
-  void post(BOOST_ASIO_MOVE_ARG(F) f, const A& a) const
-  {
-    executor_.post(BOOST_ASIO_MOVE_CAST(F)(f), a);
-  }
-
-  template <typename F, typename A>
-  void defer(BOOST_ASIO_MOVE_ARG(F) f, const A& a) const
-  {
-    executor_.defer(BOOST_ASIO_MOVE_CAST(F)(f), a);
-  }
-
-  friend bool operator==(const io_object_executor& a,
-      const io_object_executor& b) BOOST_ASIO_NOEXCEPT
-  {
-    return a.executor_ == b.executor_
-      && a.has_native_impl_ == b.has_native_impl_;
-  }
-
-  friend bool operator!=(const io_object_executor& a,
-      const io_object_executor& b) BOOST_ASIO_NOEXCEPT
-  {
-    return a.executor_ != b.executor_
-      || a.has_native_impl_ != b.has_native_impl_;
-  }
-
-private:
-  Executor executor_;
-  const bool has_native_impl_;
-};
-
-} // namespace detail
-} // namespace asio
-} // namespace boost
-
-#include <boost/asio/detail/pop_options.hpp>
-
-#endif // BOOST_ASIO_DETAIL_IO_OBJECT_EXECUTOR_HPP
diff --git a/include/boost/asio/detail/io_object_impl.hpp b/include/boost/asio/detail/io_object_impl.hpp
index 23b2e8ae..54a622d6 100644
--- a/include/boost/asio/detail/io_object_impl.hpp
+++ b/include/boost/asio/detail/io_object_impl.hpp
@@ -17,42 +17,18 @@
 
 #include <new>
 #include <boost/asio/detail/config.hpp>
-#include <boost/asio/detail/io_object_executor.hpp>
 #include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/execution/context.hpp>
 #include <boost/asio/io_context.hpp>
+#include <boost/asio/query.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
-
-class executor;
-
 namespace detail {
 
-inline bool is_native_io_executor(const io_context::executor_type&)
-{
-  return true;
-}
-
-template <typename Executor>
-inline bool is_native_io_executor(const Executor&,
-    typename enable_if<!is_same<Executor, executor>::value>::type* = 0)
-{
-  return false;
-}
-
-template <typename Executor>
-inline bool is_native_io_executor(const Executor& ex,
-    typename enable_if<is_same<Executor, executor>::value>::type* = 0)
-{
-#if !defined (BOOST_ASIO_NO_TYPEID)
-  return ex.target_type() == typeid(io_context::executor_type);
-#else // !defined (BOOST_ASIO_NO_TYPEID)
-  return false;
-#endif // !defined (BOOST_ASIO_NO_TYPEID)
-}
-
 template <typename IoObjectService,
     typename Executor = io_context::executor_type>
 class io_object_impl
@@ -67,13 +43,11 @@ public:
   // The type of the executor associated with the object.
   typedef Executor executor_type;
 
-  // The type of executor to be used when implementing asynchronous operations.
-  typedef io_object_executor<Executor> implementation_executor_type;
-
   // Construct an I/O object using an executor.
   explicit io_object_impl(const executor_type& ex)
-    : service_(&boost::asio::use_service<IoObjectService>(ex.context())),
-      implementation_executor_(ex, (is_native_io_executor)(ex))
+    : service_(&boost::asio::use_service<IoObjectService>(
+          io_object_impl::get_context(ex))),
+      executor_(ex)
   {
     service_->construct(implementation_);
   }
@@ -84,8 +58,7 @@ public:
       typename enable_if<is_convertible<
         ExecutionContext&, execution_context&>::value>::type* = 0)
     : service_(&boost::asio::use_service<IoObjectService>(context)),
-      implementation_executor_(context.get_executor(),
-        is_same<ExecutionContext, io_context>::value)
+      executor_(context.get_executor())
   {
     service_->construct(implementation_);
   }
@@ -94,7 +67,7 @@ public:
   // Move-construct an I/O object.
   io_object_impl(io_object_impl&& other)
     : service_(&other.get_service()),
-      implementation_executor_(other.get_implementation_executor())
+      executor_(other.get_executor())
   {
     service_->move_construct(implementation_, other.implementation_);
   }
@@ -103,8 +76,8 @@ public:
   template <typename IoObjectService1, typename Executor1>
   io_object_impl(io_object_impl<IoObjectService1, Executor1>&& other)
     : service_(&boost::asio::use_service<IoObjectService>(
-            other.get_implementation_executor().context())),
-      implementation_executor_(other.get_implementation_executor())
+            io_object_impl::get_context(other.get_executor()))),
+      executor_(other.get_executor())
   {
     service_->converting_move_construct(implementation_,
         other.get_service(), other.get_implementation());
@@ -125,9 +98,9 @@ public:
     {
       service_->move_assign(implementation_,
           *other.service_, other.implementation_);
-      implementation_executor_.~implementation_executor_type();
-      new (&implementation_executor_) implementation_executor_type(
-          std::move(other.implementation_executor_));
+      executor_.~executor_type();
+      new (&executor_) executor_type(
+          std::move(other.executor_));
       service_ = other.service_;
     }
     return *this;
@@ -135,16 +108,9 @@ public:
 #endif // defined(BOOST_ASIO_HAS_MOVE)
 
   // Get the executor associated with the object.
-  executor_type get_executor() BOOST_ASIO_NOEXCEPT
+  const executor_type& get_executor() BOOST_ASIO_NOEXCEPT
   {
-    return implementation_executor_.inner_executor();
-  }
-
-  // Get the executor to be used when implementing asynchronous operations.
-  const implementation_executor_type& get_implementation_executor()
-    BOOST_ASIO_NOEXCEPT
-  {
-    return implementation_executor_;
+    return executor_;
   }
 
   // Get the service associated with the I/O object.
@@ -172,6 +138,22 @@ public:
   }
 
 private:
+  // Helper function to get an executor's context.
+  template <typename T>
+  static execution_context& get_context(const T& t,
+      typename enable_if<execution::is_executor<T>::value>::type* = 0)
+  {
+    return boost::asio::query(t, execution::context);
+  }
+
+  // Helper function to get an executor's context.
+  template <typename T>
+  static execution_context& get_context(const T& t,
+      typename enable_if<!execution::is_executor<T>::value>::type* = 0)
+  {
+    return t.context();
+  }
+
   // Disallow copying and copy assignment.
   io_object_impl(const io_object_impl&);
   io_object_impl& operator=(const io_object_impl&);
@@ -183,7 +165,7 @@ private:
   implementation_type implementation_;
 
   // The associated executor.
-  implementation_executor_type implementation_executor_;
+  executor_type executor_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/memory.hpp b/include/boost/asio/detail/memory.hpp
index 0f92263c..438abceb 100644
--- a/include/boost/asio/detail/memory.hpp
+++ b/include/boost/asio/detail/memory.hpp
@@ -19,6 +19,7 @@
 #include <memory>
 
 #if !defined(BOOST_ASIO_HAS_STD_SHARED_PTR)
+# include <boost/make_shared.hpp>
 # include <boost/shared_ptr.hpp>
 # include <boost/weak_ptr.hpp>
 #endif // !defined(BOOST_ASIO_HAS_STD_SHARED_PTR)
@@ -32,9 +33,11 @@ namespace asio {
 namespace detail {
 
 #if defined(BOOST_ASIO_HAS_STD_SHARED_PTR)
+using std::make_shared;
 using std::shared_ptr;
 using std::weak_ptr;
 #else // defined(BOOST_ASIO_HAS_STD_SHARED_PTR)
+using boost::make_shared;
 using boost::shared_ptr;
 using boost::weak_ptr;
 #endif // defined(BOOST_ASIO_HAS_STD_SHARED_PTR)
diff --git a/include/boost/asio/detail/null_event.hpp b/include/boost/asio/detail/null_event.hpp
index bb11cb00..fa52981a 100644
--- a/include/boost/asio/detail/null_event.hpp
+++ b/include/boost/asio/detail/null_event.hpp
@@ -56,6 +56,12 @@ public:
   {
   }
 
+  // Unlock the mutex and signal one waiter who may destroy us.
+  template <typename Lock>
+  void unlock_and_signal_one_for_destruction(Lock&)
+  {
+  }
+
   // If there's a waiter, unlock the mutex and signal it.
   template <typename Lock>
   bool maybe_unlock_and_signal_one(Lock&)
diff --git a/include/boost/asio/detail/pop_options.hpp b/include/boost/asio/detail/pop_options.hpp
index a2475b47..982c42e4 100644
--- a/include/boost/asio/detail/pop_options.hpp
+++ b/include/boost/asio/detail/pop_options.hpp
@@ -93,7 +93,7 @@
 
 // Greenhills C++
 
-#elif defined(__BORLANDC__)
+#elif defined(__BORLANDC__) && !defined(__clang__)
 
 // Borland C++
 
diff --git a/include/boost/asio/detail/posix_event.hpp b/include/boost/asio/detail/posix_event.hpp
index e2052300..b5a34860 100644
--- a/include/boost/asio/detail/posix_event.hpp
+++ b/include/boost/asio/detail/posix_event.hpp
@@ -71,6 +71,18 @@ public:
       ::pthread_cond_signal(&cond_); // Ignore EINVAL.
   }
 
+  // Unlock the mutex and signal one waiter who may destroy us.
+  template <typename Lock>
+  void unlock_and_signal_one_for_destruction(Lock& lock)
+  {
+    BOOST_ASIO_ASSERT(lock.locked());
+    state_ |= 1;
+    bool have_waiters = (state_ > 1);
+    if (have_waiters)
+      ::pthread_cond_signal(&cond_); // Ignore EINVAL.
+    lock.unlock();
+  }
+
   // If there's a waiter, unlock the mutex and signal it.
   template <typename Lock>
   bool maybe_unlock_and_signal_one(Lock& lock)
diff --git a/include/boost/asio/detail/push_options.hpp b/include/boost/asio/detail/push_options.hpp
index 05856fd9..201f18a0 100644
--- a/include/boost/asio/detail/push_options.hpp
+++ b/include/boost/asio/detail/push_options.hpp
@@ -102,7 +102,7 @@
 
 // Greenhills C++
 
-#elif defined(__BORLANDC__)
+#elif defined(__BORLANDC__) && !defined(__clang__)
 
 // Borland C++
 
diff --git a/include/boost/asio/detail/reactive_descriptor_service.hpp b/include/boost/asio/detail/reactive_descriptor_service.hpp
index bdd3a426..4ed42a26 100644
--- a/include/boost/asio/detail/reactive_descriptor_service.hpp
+++ b/include/boost/asio/detail/reactive_descriptor_service.hpp
@@ -202,7 +202,7 @@ public:
     typedef reactive_wait_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "descriptor",
           &impl, impl.descriptor_, "async_wait"));
@@ -235,11 +235,22 @@ public:
   size_t write_some(implementation_type& impl,
       const ConstBufferSequence& buffers, boost::system::error_code& ec)
   {
-    buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence> bufs(buffers);
+    typedef buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence> bufs_type;
 
-    return descriptor_ops::sync_write(impl.descriptor_, impl.state_,
-        bufs.buffers(), bufs.count(), bufs.all_empty(), ec);
+    if (bufs_type::is_single_buffer)
+    {
+      return descriptor_ops::sync_write1(impl.descriptor_,
+          impl.state_, bufs_type::first(buffers).data(),
+          bufs_type::first(buffers).size(), ec);
+    }
+    else
+    {
+      bufs_type bufs(buffers);
+
+      return descriptor_ops::sync_write(impl.descriptor_, impl.state_,
+          bufs.buffers(), bufs.count(), bufs.all_empty(), ec);
+    }
   }
 
   // Wait until data can be written without blocking.
@@ -266,7 +277,7 @@ public:
     typedef descriptor_write_op<ConstBufferSequence, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.descriptor_, buffers, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.descriptor_, buffers, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "descriptor",
           &impl, impl.descriptor_, "async_write_some"));
@@ -289,7 +300,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "descriptor",
           &impl, impl.descriptor_, "async_write_some(null_buffers)"));
@@ -303,11 +314,22 @@ public:
   size_t read_some(implementation_type& impl,
       const MutableBufferSequence& buffers, boost::system::error_code& ec)
   {
-    buffer_sequence_adapter<boost::asio::mutable_buffer,
-        MutableBufferSequence> bufs(buffers);
+    typedef buffer_sequence_adapter<boost::asio::mutable_buffer,
+        MutableBufferSequence> bufs_type;
 
-    return descriptor_ops::sync_read(impl.descriptor_, impl.state_,
-        bufs.buffers(), bufs.count(), bufs.all_empty(), ec);
+    if (bufs_type::is_single_buffer)
+    {
+      return descriptor_ops::sync_read1(impl.descriptor_,
+          impl.state_, bufs_type::first(buffers).data(),
+          bufs_type::first(buffers).size(), ec);
+    }
+    else
+    {
+      bufs_type bufs(buffers);
+
+      return descriptor_ops::sync_read(impl.descriptor_, impl.state_,
+          bufs.buffers(), bufs.count(), bufs.all_empty(), ec);
+    }
   }
 
   // Wait until data can be read without blocking.
@@ -335,7 +357,7 @@ public:
     typedef descriptor_read_op<MutableBufferSequence, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.descriptor_, buffers, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.descriptor_, buffers, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "descriptor",
           &impl, impl.descriptor_, "async_read_some"));
@@ -358,7 +380,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "descriptor",
           &impl, impl.descriptor_, "async_read_some(null_buffers)"));
@@ -374,6 +396,9 @@ private:
 
   // The selector that performs event demultiplexing for the service.
   reactor& reactor_;
+
+  // Cached success value to avoid accessing category singleton.
+  const boost::system::error_code success_ec_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_null_buffers_op.hpp b/include/boost/asio/detail/reactive_null_buffers_op.hpp
index efa91902..87de33bb 100644
--- a/include/boost/asio/detail/reactive_null_buffers_op.hpp
+++ b/include/boost/asio/detail/reactive_null_buffers_op.hpp
@@ -16,9 +16,11 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 
@@ -34,13 +36,13 @@ class reactive_null_buffers_op : public reactor_op
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_null_buffers_op);
 
-  reactive_null_buffers_op(Handler& handler, const IoExecutor& io_ex)
-    : reactor_op(&reactive_null_buffers_op::do_perform,
+  reactive_null_buffers_op(const boost::system::error_code& success_ec,
+      Handler& handler, const IoExecutor& io_ex)
+    : reactor_op(success_ec, &reactive_null_buffers_op::do_perform,
         &reactive_null_buffers_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static status do_perform(reactor_op*)
@@ -55,10 +57,14 @@ public:
     // Take ownership of the handler object.
     reactive_null_buffers_op* o(static_cast<reactive_null_buffers_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -82,7 +88,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_serial_port_service.hpp b/include/boost/asio/detail/reactive_serial_port_service.hpp
index 8f50f5b1..776762fc 100644
--- a/include/boost/asio/detail/reactive_serial_port_service.hpp
+++ b/include/boost/asio/detail/reactive_serial_port_service.hpp
@@ -140,9 +140,8 @@ public:
   boost::system::error_code send_break(implementation_type& impl,
       boost::system::error_code& ec)
   {
-    errno = 0;
-    descriptor_ops::error_wrapper(::tcsendbreak(
-          descriptor_service_.native_handle(impl), 0), ec);
+    int result = ::tcsendbreak(descriptor_service_.native_handle(impl), 0);
+    descriptor_ops::get_last_error(ec, result < 0);
     return ec;
   }
 
diff --git a/include/boost/asio/detail/reactive_socket_accept_op.hpp b/include/boost/asio/detail/reactive_socket_accept_op.hpp
index f182caa7..878ffc7e 100644
--- a/include/boost/asio/detail/reactive_socket_accept_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_accept_op.hpp
@@ -17,8 +17,10 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
-#include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_holder.hpp>
@@ -34,10 +36,12 @@ template <typename Socket, typename Protocol>
 class reactive_socket_accept_op_base : public reactor_op
 {
 public:
-  reactive_socket_accept_op_base(socket_type socket,
-      socket_ops::state_type state, Socket& peer, const Protocol& protocol,
-      typename Protocol::endpoint* peer_endpoint, func_type complete_func)
-    : reactor_op(&reactive_socket_accept_op_base::do_perform, complete_func),
+  reactive_socket_accept_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, socket_ops::state_type state, Socket& peer,
+      const Protocol& protocol, typename Protocol::endpoint* peer_endpoint,
+      func_type complete_func)
+    : reactor_op(success_ec,
+        &reactive_socket_accept_op_base::do_perform, complete_func),
       socket_(socket),
       state_(state),
       peer_(peer),
@@ -94,16 +98,16 @@ class reactive_socket_accept_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_accept_op);
 
-  reactive_socket_accept_op(socket_type socket,
-      socket_ops::state_type state, Socket& peer, const Protocol& protocol,
-      typename Protocol::endpoint* peer_endpoint, Handler& handler,
-      const IoExecutor& io_ex)
-    : reactive_socket_accept_op_base<Socket, Protocol>(socket, state, peer,
-        protocol, peer_endpoint, &reactive_socket_accept_op::do_complete),
+  reactive_socket_accept_op(const boost::system::error_code& success_ec,
+      socket_type socket, socket_ops::state_type state, Socket& peer,
+      const Protocol& protocol, typename Protocol::endpoint* peer_endpoint,
+      Handler& handler, const IoExecutor& io_ex)
+    : reactive_socket_accept_op_base<Socket, Protocol>(
+        success_ec, socket, state, peer, protocol, peer_endpoint,
+        &reactive_socket_accept_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -113,7 +117,6 @@ public:
     // Take ownership of the handler object.
     reactive_socket_accept_op* o(static_cast<reactive_socket_accept_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     // On success, assign new connection to peer socket object.
     if (owner)
@@ -121,6 +124,11 @@ public:
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -144,7 +152,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 #if defined(BOOST_ASIO_HAS_MOVE)
@@ -160,18 +168,18 @@ class reactive_socket_move_accept_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_move_accept_op);
 
-  reactive_socket_move_accept_op(const PeerIoExecutor& peer_io_ex,
-      socket_type socket, socket_ops::state_type state,
-      const Protocol& protocol, typename Protocol::endpoint* peer_endpoint,
-      Handler& handler, const IoExecutor& io_ex)
+  reactive_socket_move_accept_op(const boost::system::error_code& success_ec,
+      const PeerIoExecutor& peer_io_ex, socket_type socket,
+      socket_ops::state_type state, const Protocol& protocol,
+      typename Protocol::endpoint* peer_endpoint, Handler& handler,
+      const IoExecutor& io_ex)
     : peer_socket_type(peer_io_ex),
       reactive_socket_accept_op_base<peer_socket_type, Protocol>(
-        socket, state, *this, protocol, peer_endpoint,
+        success_ec, socket, state, *this, protocol, peer_endpoint,
         &reactive_socket_move_accept_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -182,7 +190,6 @@ public:
     reactive_socket_move_accept_op* o(
         static_cast<reactive_socket_move_accept_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     // On success, assign new connection to peer socket object.
     if (owner)
@@ -190,6 +197,11 @@ public:
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -218,7 +230,7 @@ private:
     rebind_executor<PeerIoExecutor>::other peer_socket_type;
 
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 #endif // defined(BOOST_ASIO_HAS_MOVE)
diff --git a/include/boost/asio/detail/reactive_socket_connect_op.hpp b/include/boost/asio/detail/reactive_socket_connect_op.hpp
index b0a31c08..81091b72 100644
--- a/include/boost/asio/detail/reactive_socket_connect_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_connect_op.hpp
@@ -17,8 +17,10 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
-#include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -32,8 +34,10 @@ namespace detail {
 class reactive_socket_connect_op_base : public reactor_op
 {
 public:
-  reactive_socket_connect_op_base(socket_type socket, func_type complete_func)
-    : reactor_op(&reactive_socket_connect_op_base::do_perform, complete_func),
+  reactive_socket_connect_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, func_type complete_func)
+    : reactor_op(success_ec,
+        &reactive_socket_connect_op_base::do_perform, complete_func),
       socket_(socket)
   {
   }
@@ -61,14 +65,13 @@ class reactive_socket_connect_op : public reactive_socket_connect_op_base
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_connect_op);
 
-  reactive_socket_connect_op(socket_type socket,
-      Handler& handler, const IoExecutor& io_ex)
-    : reactive_socket_connect_op_base(socket,
+  reactive_socket_connect_op(const boost::system::error_code& success_ec,
+      socket_type socket, Handler& handler, const IoExecutor& io_ex)
+    : reactive_socket_connect_op_base(success_ec, socket,
         &reactive_socket_connect_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -79,10 +82,14 @@ public:
     reactive_socket_connect_op* o
       (static_cast<reactive_socket_connect_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -106,7 +113,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_socket_recv_op.hpp b/include/boost/asio/detail/reactive_socket_recv_op.hpp
index 7d33c98b..f58de9ad 100644
--- a/include/boost/asio/detail/reactive_socket_recv_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_recv_op.hpp
@@ -19,6 +19,9 @@
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -33,10 +36,12 @@ template <typename MutableBufferSequence>
 class reactive_socket_recv_op_base : public reactor_op
 {
 public:
-  reactive_socket_recv_op_base(socket_type socket,
-      socket_ops::state_type state, const MutableBufferSequence& buffers,
+  reactive_socket_recv_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, socket_ops::state_type state,
+      const MutableBufferSequence& buffers,
       socket_base::message_flags flags, func_type complete_func)
-    : reactor_op(&reactive_socket_recv_op_base::do_perform, complete_func),
+    : reactor_op(success_ec,
+        &reactive_socket_recv_op_base::do_perform, complete_func),
       socket_(socket),
       state_(state),
       buffers_(buffers),
@@ -49,13 +54,26 @@ public:
     reactive_socket_recv_op_base* o(
         static_cast<reactive_socket_recv_op_base*>(base));
 
-    buffer_sequence_adapter<boost::asio::mutable_buffer,
-        MutableBufferSequence> bufs(o->buffers_);
+    typedef buffer_sequence_adapter<boost::asio::mutable_buffer,
+        MutableBufferSequence> bufs_type;
 
-    status result = socket_ops::non_blocking_recv(o->socket_,
-        bufs.buffers(), bufs.count(), o->flags_,
-        (o->state_ & socket_ops::stream_oriented) != 0,
-        o->ec_, o->bytes_transferred_) ? done : not_done;
+    status result;
+    if (bufs_type::is_single_buffer)
+    {
+      result = socket_ops::non_blocking_recv1(o->socket_,
+          bufs_type::first(o->buffers_).data(),
+          bufs_type::first(o->buffers_).size(), o->flags_,
+          (o->state_ & socket_ops::stream_oriented) != 0,
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
+    else
+    {
+      bufs_type bufs(o->buffers_);
+      result = socket_ops::non_blocking_recv(o->socket_,
+          bufs.buffers(), bufs.count(), o->flags_,
+          (o->state_ & socket_ops::stream_oriented) != 0,
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
 
     if (result == done)
       if ((o->state_ & socket_ops::stream_oriented) != 0)
@@ -82,15 +100,15 @@ class reactive_socket_recv_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_recv_op);
 
-  reactive_socket_recv_op(socket_type socket, socket_ops::state_type state,
+  reactive_socket_recv_op(const boost::system::error_code& success_ec,
+      socket_type socket, socket_ops::state_type state,
       const MutableBufferSequence& buffers, socket_base::message_flags flags,
       Handler& handler, const IoExecutor& io_ex)
-    : reactive_socket_recv_op_base<MutableBufferSequence>(socket, state,
-        buffers, flags, &reactive_socket_recv_op::do_complete),
+    : reactive_socket_recv_op_base<MutableBufferSequence>(success_ec, socket,
+        state, buffers, flags, &reactive_socket_recv_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -100,10 +118,14 @@ public:
     // Take ownership of the handler object.
     reactive_socket_recv_op* o(static_cast<reactive_socket_recv_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -127,7 +149,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_socket_recvfrom_op.hpp b/include/boost/asio/detail/reactive_socket_recvfrom_op.hpp
index 9f641d58..b91dd02a 100644
--- a/include/boost/asio/detail/reactive_socket_recvfrom_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_recvfrom_op.hpp
@@ -19,6 +19,9 @@
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -33,10 +36,12 @@ template <typename MutableBufferSequence, typename Endpoint>
 class reactive_socket_recvfrom_op_base : public reactor_op
 {
 public:
-  reactive_socket_recvfrom_op_base(socket_type socket, int protocol_type,
+  reactive_socket_recvfrom_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, int protocol_type,
       const MutableBufferSequence& buffers, Endpoint& endpoint,
       socket_base::message_flags flags, func_type complete_func)
-    : reactor_op(&reactive_socket_recvfrom_op_base::do_perform, complete_func),
+    : reactor_op(success_ec,
+        &reactive_socket_recvfrom_op_base::do_perform, complete_func),
       socket_(socket),
       protocol_type_(protocol_type),
       buffers_(buffers),
@@ -50,14 +55,27 @@ public:
     reactive_socket_recvfrom_op_base* o(
         static_cast<reactive_socket_recvfrom_op_base*>(base));
 
-    buffer_sequence_adapter<boost::asio::mutable_buffer,
-        MutableBufferSequence> bufs(o->buffers_);
+    typedef buffer_sequence_adapter<boost::asio::mutable_buffer,
+        MutableBufferSequence> bufs_type;
 
     std::size_t addr_len = o->sender_endpoint_.capacity();
-    status result = socket_ops::non_blocking_recvfrom(o->socket_,
-        bufs.buffers(), bufs.count(), o->flags_,
-        o->sender_endpoint_.data(), &addr_len,
-        o->ec_, o->bytes_transferred_) ? done : not_done;
+    status result;
+    if (bufs_type::is_single_buffer)
+    {
+      result = socket_ops::non_blocking_recvfrom1(
+          o->socket_, bufs_type::first(o->buffers_).data(),
+          bufs_type::first(o->buffers_).size(), o->flags_,
+          o->sender_endpoint_.data(), &addr_len,
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
+    else
+    {
+      bufs_type bufs(o->buffers_);
+      result = socket_ops::non_blocking_recvfrom(o->socket_,
+          bufs.buffers(), bufs.count(), o->flags_,
+          o->sender_endpoint_.data(), &addr_len,
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
 
     if (result && !o->ec_)
       o->sender_endpoint_.resize(addr_len);
@@ -84,17 +102,17 @@ class reactive_socket_recvfrom_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_recvfrom_op);
 
-  reactive_socket_recvfrom_op(socket_type socket, int protocol_type,
+  reactive_socket_recvfrom_op(const boost::system::error_code& success_ec,
+      socket_type socket, int protocol_type,
       const MutableBufferSequence& buffers, Endpoint& endpoint,
       socket_base::message_flags flags, Handler& handler,
       const IoExecutor& io_ex)
     : reactive_socket_recvfrom_op_base<MutableBufferSequence, Endpoint>(
-        socket, protocol_type, buffers, endpoint, flags,
+        success_ec, socket, protocol_type, buffers, endpoint, flags,
         &reactive_socket_recvfrom_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -105,10 +123,14 @@ public:
     reactive_socket_recvfrom_op* o(
         static_cast<reactive_socket_recvfrom_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -132,7 +154,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_socket_recvmsg_op.hpp b/include/boost/asio/detail/reactive_socket_recvmsg_op.hpp
index d4472c49..15d5c7ea 100644
--- a/include/boost/asio/detail/reactive_socket_recvmsg_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_recvmsg_op.hpp
@@ -19,6 +19,9 @@
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -34,10 +37,12 @@ template <typename MutableBufferSequence>
 class reactive_socket_recvmsg_op_base : public reactor_op
 {
 public:
-  reactive_socket_recvmsg_op_base(socket_type socket,
-      const MutableBufferSequence& buffers, socket_base::message_flags in_flags,
+  reactive_socket_recvmsg_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, const MutableBufferSequence& buffers,
+      socket_base::message_flags in_flags,
       socket_base::message_flags& out_flags, func_type complete_func)
-    : reactor_op(&reactive_socket_recvmsg_op_base::do_perform, complete_func),
+    : reactor_op(success_ec,
+        &reactive_socket_recvmsg_op_base::do_perform, complete_func),
       socket_(socket),
       buffers_(buffers),
       in_flags_(in_flags),
@@ -78,16 +83,17 @@ class reactive_socket_recvmsg_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_recvmsg_op);
 
-  reactive_socket_recvmsg_op(socket_type socket,
-      const MutableBufferSequence& buffers, socket_base::message_flags in_flags,
+  reactive_socket_recvmsg_op(const boost::system::error_code& success_ec,
+      socket_type socket, const MutableBufferSequence& buffers,
+      socket_base::message_flags in_flags,
       socket_base::message_flags& out_flags, Handler& handler,
       const IoExecutor& io_ex)
-    : reactive_socket_recvmsg_op_base<MutableBufferSequence>(socket, buffers,
-        in_flags, out_flags, &reactive_socket_recvmsg_op::do_complete),
+    : reactive_socket_recvmsg_op_base<MutableBufferSequence>(
+        success_ec, socket, buffers, in_flags, out_flags,
+        &reactive_socket_recvmsg_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -98,10 +104,14 @@ public:
     reactive_socket_recvmsg_op* o(
         static_cast<reactive_socket_recvmsg_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -125,7 +135,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_socket_send_op.hpp b/include/boost/asio/detail/reactive_socket_send_op.hpp
index ca2d4588..9840e4c4 100644
--- a/include/boost/asio/detail/reactive_socket_send_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_send_op.hpp
@@ -19,6 +19,9 @@
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -33,10 +36,12 @@ template <typename ConstBufferSequence>
 class reactive_socket_send_op_base : public reactor_op
 {
 public:
-  reactive_socket_send_op_base(socket_type socket,
-      socket_ops::state_type state, const ConstBufferSequence& buffers,
+  reactive_socket_send_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, socket_ops::state_type state,
+      const ConstBufferSequence& buffers,
       socket_base::message_flags flags, func_type complete_func)
-    : reactor_op(&reactive_socket_send_op_base::do_perform, complete_func),
+    : reactor_op(success_ec,
+        &reactive_socket_send_op_base::do_perform, complete_func),
       socket_(socket),
       state_(state),
       buffers_(buffers),
@@ -49,17 +54,34 @@ public:
     reactive_socket_send_op_base* o(
         static_cast<reactive_socket_send_op_base*>(base));
 
-    buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence> bufs(o->buffers_);
+    typedef buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence> bufs_type;
 
-    status result = socket_ops::non_blocking_send(o->socket_,
-          bufs.buffers(), bufs.count(), o->flags_,
+    status result;
+    if (bufs_type::is_single_buffer)
+    {
+      result = socket_ops::non_blocking_send1(o->socket_,
+          bufs_type::first(o->buffers_).data(),
+          bufs_type::first(o->buffers_).size(), o->flags_,
           o->ec_, o->bytes_transferred_) ? done : not_done;
 
-    if (result == done)
-      if ((o->state_ & socket_ops::stream_oriented) != 0)
-        if (o->bytes_transferred_ < bufs.total_size())
-          result = done_and_exhausted;
+      if (result == done)
+        if ((o->state_ & socket_ops::stream_oriented) != 0)
+          if (o->bytes_transferred_ < bufs_type::first(o->buffers_).size())
+            result = done_and_exhausted;
+    }
+    else
+    {
+      bufs_type bufs(o->buffers_);
+      result = socket_ops::non_blocking_send(o->socket_,
+            bufs.buffers(), bufs.count(), o->flags_,
+            o->ec_, o->bytes_transferred_) ? done : not_done;
+
+      if (result == done)
+        if ((o->state_ & socket_ops::stream_oriented) != 0)
+          if (o->bytes_transferred_ < bufs.total_size())
+            result = done_and_exhausted;
+    }
 
     BOOST_ASIO_HANDLER_REACTOR_OPERATION((*o, "non_blocking_send",
           o->ec_, o->bytes_transferred_));
@@ -81,15 +103,15 @@ class reactive_socket_send_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_send_op);
 
-  reactive_socket_send_op(socket_type socket, socket_ops::state_type state,
+  reactive_socket_send_op(const boost::system::error_code& success_ec,
+      socket_type socket, socket_ops::state_type state,
       const ConstBufferSequence& buffers, socket_base::message_flags flags,
       Handler& handler, const IoExecutor& io_ex)
-    : reactive_socket_send_op_base<ConstBufferSequence>(socket,
+    : reactive_socket_send_op_base<ConstBufferSequence>(success_ec, socket,
         state, buffers, flags, &reactive_socket_send_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -99,10 +121,14 @@ public:
     // Take ownership of the handler object.
     reactive_socket_send_op* o(static_cast<reactive_socket_send_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -126,7 +152,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_socket_sendto_op.hpp b/include/boost/asio/detail/reactive_socket_sendto_op.hpp
index a4366ddd..834fe555 100644
--- a/include/boost/asio/detail/reactive_socket_sendto_op.hpp
+++ b/include/boost/asio/detail/reactive_socket_sendto_op.hpp
@@ -19,6 +19,9 @@
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/handler_alloc_helpers.hpp>
+#include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -33,10 +36,12 @@ template <typename ConstBufferSequence, typename Endpoint>
 class reactive_socket_sendto_op_base : public reactor_op
 {
 public:
-  reactive_socket_sendto_op_base(socket_type socket,
-      const ConstBufferSequence& buffers, const Endpoint& endpoint,
-      socket_base::message_flags flags, func_type complete_func)
-    : reactor_op(&reactive_socket_sendto_op_base::do_perform, complete_func),
+  reactive_socket_sendto_op_base(const boost::system::error_code& success_ec,
+      socket_type socket, const ConstBufferSequence& buffers,
+      const Endpoint& endpoint, socket_base::message_flags flags,
+      func_type complete_func)
+    : reactor_op(success_ec,
+        &reactive_socket_sendto_op_base::do_perform, complete_func),
       socket_(socket),
       buffers_(buffers),
       destination_(endpoint),
@@ -49,13 +54,26 @@ public:
     reactive_socket_sendto_op_base* o(
         static_cast<reactive_socket_sendto_op_base*>(base));
 
-    buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence> bufs(o->buffers_);
+    typedef buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence> bufs_type;
 
-    status result = socket_ops::non_blocking_sendto(o->socket_,
+    status result;
+    if (bufs_type::is_single_buffer)
+    {
+      result = socket_ops::non_blocking_sendto1(o->socket_,
+          bufs_type::first(o->buffers_).data(),
+          bufs_type::first(o->buffers_).size(), o->flags_,
+          o->destination_.data(), o->destination_.size(),
+          o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
+    else
+    {
+      bufs_type bufs(o->buffers_);
+      result = socket_ops::non_blocking_sendto(o->socket_,
           bufs.buffers(), bufs.count(), o->flags_,
           o->destination_.data(), o->destination_.size(),
           o->ec_, o->bytes_transferred_) ? done : not_done;
+    }
 
     BOOST_ASIO_HANDLER_REACTOR_OPERATION((*o, "non_blocking_sendto",
           o->ec_, o->bytes_transferred_));
@@ -78,16 +96,16 @@ class reactive_socket_sendto_op :
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_socket_sendto_op);
 
-  reactive_socket_sendto_op(socket_type socket,
-      const ConstBufferSequence& buffers, const Endpoint& endpoint,
-      socket_base::message_flags flags, Handler& handler,
-      const IoExecutor& io_ex)
-    : reactive_socket_sendto_op_base<ConstBufferSequence, Endpoint>(socket,
-        buffers, endpoint, flags, &reactive_socket_sendto_op::do_complete),
+  reactive_socket_sendto_op(const boost::system::error_code& success_ec,
+      socket_type socket, const ConstBufferSequence& buffers,
+      const Endpoint& endpoint, socket_base::message_flags flags,
+      Handler& handler, const IoExecutor& io_ex)
+    : reactive_socket_sendto_op_base<ConstBufferSequence, Endpoint>(
+        success_ec, socket, buffers, endpoint, flags,
+        &reactive_socket_sendto_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -97,10 +115,14 @@ public:
     // Take ownership of the handler object.
     reactive_socket_sendto_op* o(static_cast<reactive_socket_sendto_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -124,7 +146,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_socket_service.hpp b/include/boost/asio/detail/reactive_socket_service.hpp
index 9cc0db30..74ca8ae0 100644
--- a/include/boost/asio/detail/reactive_socket_service.hpp
+++ b/include/boost/asio/detail/reactive_socket_service.hpp
@@ -220,12 +220,23 @@ public:
       const endpoint_type& destination, socket_base::message_flags flags,
       boost::system::error_code& ec)
   {
-    buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence> bufs(buffers);
+    typedef buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence> bufs_type;
 
-    return socket_ops::sync_sendto(impl.socket_, impl.state_,
-        bufs.buffers(), bufs.count(), flags,
-        destination.data(), destination.size(), ec);
+    if (bufs_type::is_single_buffer)
+    {
+      return socket_ops::sync_sendto1(impl.socket_, impl.state_,
+          bufs_type::first(buffers).data(),
+          bufs_type::first(buffers).size(), flags,
+          destination.data(), destination.size(), ec);
+    }
+    else
+    {
+      bufs_type bufs(buffers);
+      return socket_ops::sync_sendto(impl.socket_, impl.state_,
+          bufs.buffers(), bufs.count(), flags,
+          destination.data(), destination.size(), ec);
+    }
   }
 
   // Wait until data can be sent without blocking.
@@ -255,8 +266,8 @@ public:
         endpoint_type, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.socket_, buffers,
-        destination, flags, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_,
+        buffers, destination, flags, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_send_to"));
@@ -278,7 +289,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_send_to(null_buffers)"));
@@ -295,13 +306,25 @@ public:
       endpoint_type& sender_endpoint, socket_base::message_flags flags,
       boost::system::error_code& ec)
   {
-    buffer_sequence_adapter<boost::asio::mutable_buffer,
-        MutableBufferSequence> bufs(buffers);
+    typedef buffer_sequence_adapter<boost::asio::mutable_buffer,
+        MutableBufferSequence> bufs_type;
 
     std::size_t addr_len = sender_endpoint.capacity();
-    std::size_t bytes_recvd = socket_ops::sync_recvfrom(
-        impl.socket_, impl.state_, bufs.buffers(), bufs.count(),
-        flags, sender_endpoint.data(), &addr_len, ec);
+    std::size_t bytes_recvd;
+    if (bufs_type::is_single_buffer)
+    {
+      bytes_recvd = socket_ops::sync_recvfrom1(impl.socket_,
+          impl.state_, bufs_type::first(buffers).data(),
+          bufs_type::first(buffers).size(), flags,
+          sender_endpoint.data(), &addr_len, ec);
+    }
+    else
+    {
+      bufs_type bufs(buffers);
+      bytes_recvd = socket_ops::sync_recvfrom(
+          impl.socket_, impl.state_, bufs.buffers(), bufs.count(),
+          flags, sender_endpoint.data(), &addr_len, ec);
+    }
 
     if (!ec)
       sender_endpoint.resize(addr_len);
@@ -342,8 +365,8 @@ public:
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
     int protocol = impl.protocol_.type();
-    p.p = new (p.v) op(impl.socket_, protocol, buffers,
-        sender_endpoint, flags, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_, protocol,
+        buffers, sender_endpoint, flags, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_receive_from"));
@@ -368,7 +391,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_receive_from(null_buffers)"));
@@ -426,8 +449,8 @@ public:
     typedef reactive_socket_accept_op<Socket, Protocol, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.socket_, impl.state_, peer,
-        impl.protocol_, peer_endpoint, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_, impl.state_,
+        peer, impl.protocol_, peer_endpoint, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_accept"));
@@ -452,8 +475,8 @@ public:
         PeerIoExecutor, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(peer_io_ex, impl.socket_, impl.state_,
-        impl.protocol_, peer_endpoint, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, peer_io_ex, impl.socket_,
+        impl.state_, impl.protocol_, peer_endpoint, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_accept"));
@@ -485,7 +508,7 @@ public:
     typedef reactive_socket_connect_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.socket_, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_connect"));
diff --git a/include/boost/asio/detail/reactive_socket_service_base.hpp b/include/boost/asio/detail/reactive_socket_service_base.hpp
index a8d04ca8..29b379f0 100644
--- a/include/boost/asio/detail/reactive_socket_service_base.hpp
+++ b/include/boost/asio/detail/reactive_socket_service_base.hpp
@@ -204,7 +204,7 @@ public:
     typedef reactive_wait_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_wait"));
@@ -238,11 +238,21 @@ public:
       const ConstBufferSequence& buffers,
       socket_base::message_flags flags, boost::system::error_code& ec)
   {
-    buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence> bufs(buffers);
+    typedef buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence> bufs_type;
 
-    return socket_ops::sync_send(impl.socket_, impl.state_,
-        bufs.buffers(), bufs.count(), flags, bufs.all_empty(), ec);
+    if (bufs_type::is_single_buffer)
+    {
+      return socket_ops::sync_send1(impl.socket_,
+          impl.state_, bufs_type::first(buffers).data(),
+          bufs_type::first(buffers).size(), flags, ec);
+    }
+    else
+    {
+      bufs_type bufs(buffers);
+      return socket_ops::sync_send(impl.socket_, impl.state_,
+          bufs.buffers(), bufs.count(), flags, bufs.all_empty(), ec);
+    }
   }
 
   // Wait until data can be sent without blocking.
@@ -270,8 +280,8 @@ public:
         ConstBufferSequence, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.socket_, impl.state_,
-        buffers, flags, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_,
+        impl.state_, buffers, flags, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_send"));
@@ -295,7 +305,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_send(null_buffers)"));
@@ -310,11 +320,21 @@ public:
       const MutableBufferSequence& buffers,
       socket_base::message_flags flags, boost::system::error_code& ec)
   {
-    buffer_sequence_adapter<boost::asio::mutable_buffer,
-        MutableBufferSequence> bufs(buffers);
+    typedef buffer_sequence_adapter<boost::asio::mutable_buffer,
+        MutableBufferSequence> bufs_type;
 
-    return socket_ops::sync_recv(impl.socket_, impl.state_,
-        bufs.buffers(), bufs.count(), flags, bufs.all_empty(), ec);
+    if (bufs_type::is_single_buffer)
+    {
+      return socket_ops::sync_recv1(impl.socket_,
+          impl.state_, bufs_type::first(buffers).data(),
+          bufs_type::first(buffers).size(), flags, ec);
+    }
+    else
+    {
+      bufs_type bufs(buffers);
+      return socket_ops::sync_recv(impl.socket_, impl.state_,
+          bufs.buffers(), bufs.count(), flags, bufs.all_empty(), ec);
+    }
   }
 
   // Wait until data can be received without blocking.
@@ -343,8 +363,8 @@ public:
         MutableBufferSequence, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.socket_, impl.state_,
-        buffers, flags, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_,
+        impl.state_, buffers, flags, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_receive"));
@@ -373,7 +393,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_receive(null_buffers)"));
@@ -432,8 +452,8 @@ public:
         MutableBufferSequence, Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(impl.socket_, buffers,
-        in_flags, out_flags, handler, io_ex);
+    p.p = new (p.v) op(success_ec_, impl.socket_,
+        buffers, in_flags, out_flags, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_receive_with_flags"));
@@ -460,7 +480,7 @@ public:
     typedef reactive_null_buffers_op<Handler, IoExecutor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_ex);
+    p.p = new (p.v) op(success_ec_, handler, io_ex);
 
     BOOST_ASIO_HANDLER_CREATION((reactor_.context(), *p.p, "socket",
           &impl, impl.socket_, "async_receive_with_flags(null_buffers)"));
@@ -502,6 +522,9 @@ protected:
 
   // The selector that performs event demultiplexing for the service.
   reactor& reactor_;
+
+  // Cached success value to avoid accessing category singleton.
+  const boost::system::error_code success_ec_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactive_wait_op.hpp b/include/boost/asio/detail/reactive_wait_op.hpp
index f8b1b18d..424c28a1 100644
--- a/include/boost/asio/detail/reactive_wait_op.hpp
+++ b/include/boost/asio/detail/reactive_wait_op.hpp
@@ -16,9 +16,11 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 
@@ -34,13 +36,13 @@ class reactive_wait_op : public reactor_op
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(reactive_wait_op);
 
-  reactive_wait_op(Handler& handler, const IoExecutor& io_ex)
-    : reactor_op(&reactive_wait_op::do_perform,
+  reactive_wait_op(const boost::system::error_code& success_ec,
+      Handler& handler, const IoExecutor& io_ex)
+    : reactor_op(success_ec, &reactive_wait_op::do_perform,
         &reactive_wait_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static status do_perform(reactor_op*)
@@ -55,10 +57,14 @@ public:
     // Take ownership of the handler object.
     reactive_wait_op* o(static_cast<reactive_wait_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -82,7 +88,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/reactor_op.hpp b/include/boost/asio/detail/reactor_op.hpp
index 4ec24326..5985e935 100644
--- a/include/boost/asio/detail/reactor_op.hpp
+++ b/include/boost/asio/detail/reactor_op.hpp
@@ -47,8 +47,10 @@ public:
 protected:
   typedef status (*perform_func_type)(reactor_op*);
 
-  reactor_op(perform_func_type perform_func, func_type complete_func)
+  reactor_op(const boost::system::error_code& success_ec,
+      perform_func_type perform_func, func_type complete_func)
     : operation(complete_func),
+      ec_(success_ec),
       bytes_transferred_(0),
       perform_func_(perform_func)
   {
diff --git a/include/boost/asio/detail/resolve_endpoint_op.hpp b/include/boost/asio/detail/resolve_endpoint_op.hpp
index aae503c4..6d6e37cc 100644
--- a/include/boost/asio/detail/resolve_endpoint_op.hpp
+++ b/include/boost/asio/detail/resolve_endpoint_op.hpp
@@ -16,15 +16,16 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
-#include <boost/asio/error.hpp>
-#include <boost/asio/ip/basic_resolver_results.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/resolve_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
+#include <boost/asio/error.hpp>
+#include <boost/asio/ip/basic_resolver_results.hpp>
 
 #if defined(BOOST_ASIO_HAS_IOCP)
 # include <boost/asio/detail/win_iocp_io_context.hpp>
@@ -61,9 +62,8 @@ public:
       endpoint_(endpoint),
       scheduler_(sched),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -96,11 +96,13 @@ public:
       // The operation has been returned to the main io_context. The completion
       // handler is ready to be delivered.
 
-      // Take ownership of the operation's outstanding work.
-      handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
-
       BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+      // Take ownership of the operation's outstanding work.
+      handler_work<Handler, IoExecutor> w(
+          BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+            o->work_));
+
       // Make a copy of the handler so that the memory can be deallocated
       // before the upcall is made. Even if we're not about to make an upcall,
       // a sub-object of the handler may be the true owner of the memory
@@ -127,7 +129,7 @@ private:
   endpoint_type endpoint_;
   scheduler_impl& scheduler_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
   results_type results_;
 };
 
diff --git a/include/boost/asio/detail/resolve_query_op.hpp b/include/boost/asio/detail/resolve_query_op.hpp
index d1e0717f..2b2ca2d9 100644
--- a/include/boost/asio/detail/resolve_query_op.hpp
+++ b/include/boost/asio/detail/resolve_query_op.hpp
@@ -16,16 +16,17 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
-#include <boost/asio/error.hpp>
-#include <boost/asio/ip/basic_resolver_query.hpp>
-#include <boost/asio/ip/basic_resolver_results.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/resolve_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
+#include <boost/asio/error.hpp>
+#include <boost/asio/ip/basic_resolver_query.hpp>
+#include <boost/asio/ip/basic_resolver_results.hpp>
 
 #if defined(BOOST_ASIO_HAS_IOCP)
 # include <boost/asio/detail/win_iocp_io_context.hpp>
@@ -62,10 +63,9 @@ public:
       query_(query),
       scheduler_(sched),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex),
+      work_(handler_, io_ex),
       addrinfo_(0)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   ~resolve_query_op()
@@ -101,11 +101,13 @@ public:
       // The operation has been returned to the main io_context. The completion
       // handler is ready to be delivered.
 
-      // Take ownership of the operation's outstanding work.
-      handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
-
       BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+      // Take ownership of the operation's outstanding work.
+      handler_work<Handler, IoExecutor> w(
+          BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+            o->work_));
+
       // Make a copy of the handler so that the memory can be deallocated
       // before the upcall is made. Even if we're not about to make an upcall,
       // a sub-object of the handler may be the true owner of the memory
@@ -137,7 +139,7 @@ private:
   query_type query_;
   scheduler_impl& scheduler_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
   boost::asio::detail::addrinfo_type* addrinfo_;
 };
 
diff --git a/include/boost/asio/detail/scheduler.hpp b/include/boost/asio/detail/scheduler.hpp
index fe6c9a81..148dbdc8 100644
--- a/include/boost/asio/detail/scheduler.hpp
+++ b/include/boost/asio/detail/scheduler.hpp
@@ -105,6 +105,9 @@ public:
     return thread_call_stack::contains(this) != 0;
   }
 
+  /// Capture the current exception so it can be rethrown from a run function.
+  BOOST_ASIO_DECL void capture_current_exception();
+
   // Request invocation of the given operation and return immediately. Assumes
   // that work_started() has not yet been called for the operation.
   BOOST_ASIO_DECL void post_immediate_completion(
diff --git a/include/boost/asio/detail/signal_handler.hpp b/include/boost/asio/detail/signal_handler.hpp
index 3bb35ecd..459b81ab 100644
--- a/include/boost/asio/detail/signal_handler.hpp
+++ b/include/boost/asio/detail/signal_handler.hpp
@@ -19,7 +19,6 @@
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
-#include <boost/asio/detail/handler_invoke_helpers.hpp>
 #include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/signal_op.hpp>
@@ -39,9 +38,8 @@ public:
   signal_handler(Handler& h, const IoExecutor& io_ex)
     : signal_op(&signal_handler::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(h)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -51,10 +49,14 @@ public:
     // Take ownership of the handler object.
     signal_handler* h(static_cast<signal_handler*>(base));
     ptr p = { boost::asio::detail::addressof(h->handler_), h, h };
-    handler_work<Handler, IoExecutor> w(h->handler_, h->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*h));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          h->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -78,7 +80,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/socket_ops.hpp b/include/boost/asio/detail/socket_ops.hpp
index aabcc84c..6f101888 100644
--- a/include/boost/asio/detail/socket_ops.hpp
+++ b/include/boost/asio/detail/socket_ops.hpp
@@ -140,9 +140,15 @@ BOOST_ASIO_DECL void init_buf(buf& b, const void* data, size_t size);
 BOOST_ASIO_DECL signed_size_type recv(socket_type s, buf* bufs,
     size_t count, int flags, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL signed_size_type recv1(socket_type s,
+    void* data, size_t size, int flags, boost::system::error_code& ec);
+
 BOOST_ASIO_DECL size_t sync_recv(socket_type s, state_type state, buf* bufs,
     size_t count, int flags, bool all_empty, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL size_t sync_recv1(socket_type s, state_type state,
+    void* data, size_t size, int flags, boost::system::error_code& ec);
+
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL void complete_iocp_recv(state_type state,
@@ -155,16 +161,28 @@ BOOST_ASIO_DECL bool non_blocking_recv(socket_type s,
     buf* bufs, size_t count, int flags, bool is_stream,
     boost::system::error_code& ec, size_t& bytes_transferred);
 
+BOOST_ASIO_DECL bool non_blocking_recv1(socket_type s,
+    void* data, size_t size, int flags, bool is_stream,
+    boost::system::error_code& ec, size_t& bytes_transferred);
+
 #endif // defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL signed_size_type recvfrom(socket_type s, buf* bufs,
     size_t count, int flags, socket_addr_type* addr,
     std::size_t* addrlen, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL signed_size_type recvfrom1(socket_type s, void* data,
+    size_t size, int flags, socket_addr_type* addr,
+    std::size_t* addrlen, boost::system::error_code& ec);
+
 BOOST_ASIO_DECL size_t sync_recvfrom(socket_type s, state_type state,
     buf* bufs, size_t count, int flags, socket_addr_type* addr,
     std::size_t* addrlen, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL size_t sync_recvfrom1(socket_type s, state_type state,
+    void* data, size_t size, int flags, socket_addr_type* addr,
+    std::size_t* addrlen, boost::system::error_code& ec);
+
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL void complete_iocp_recvfrom(
@@ -178,6 +196,11 @@ BOOST_ASIO_DECL bool non_blocking_recvfrom(socket_type s,
     socket_addr_type* addr, std::size_t* addrlen,
     boost::system::error_code& ec, size_t& bytes_transferred);
 
+BOOST_ASIO_DECL bool non_blocking_recvfrom1(socket_type s,
+    void* data, size_t size, int flags,
+    socket_addr_type* addr, std::size_t* addrlen,
+    boost::system::error_code& ec, size_t& bytes_transferred);
+
 #endif // defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL signed_size_type recvmsg(socket_type s, buf* bufs,
@@ -205,10 +228,16 @@ BOOST_ASIO_DECL bool non_blocking_recvmsg(socket_type s,
 BOOST_ASIO_DECL signed_size_type send(socket_type s, const buf* bufs,
     size_t count, int flags, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL signed_size_type send1(socket_type s,
+    const void* data, size_t size, int flags, boost::system::error_code& ec);
+
 BOOST_ASIO_DECL size_t sync_send(socket_type s, state_type state,
     const buf* bufs, size_t count, int flags,
     bool all_empty, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL size_t sync_send1(socket_type s, state_type state,
+    const void* data, size_t size, int flags, boost::system::error_code& ec);
+
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL void complete_iocp_send(
@@ -221,16 +250,28 @@ BOOST_ASIO_DECL bool non_blocking_send(socket_type s,
     const buf* bufs, size_t count, int flags,
     boost::system::error_code& ec, size_t& bytes_transferred);
 
+BOOST_ASIO_DECL bool non_blocking_send1(socket_type s,
+    const void* data, size_t size, int flags,
+    boost::system::error_code& ec, size_t& bytes_transferred);
+
 #endif // defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL signed_size_type sendto(socket_type s, const buf* bufs,
     size_t count, int flags, const socket_addr_type* addr,
     std::size_t addrlen, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL signed_size_type sendto1(socket_type s, const void* data,
+    size_t size, int flags, const socket_addr_type* addr,
+    std::size_t addrlen, boost::system::error_code& ec);
+
 BOOST_ASIO_DECL size_t sync_sendto(socket_type s, state_type state,
     const buf* bufs, size_t count, int flags, const socket_addr_type* addr,
     std::size_t addrlen, boost::system::error_code& ec);
 
+BOOST_ASIO_DECL size_t sync_sendto1(socket_type s, state_type state,
+    const void* data, size_t size, int flags, const socket_addr_type* addr,
+    std::size_t addrlen, boost::system::error_code& ec);
+
 #if !defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL bool non_blocking_sendto(socket_type s,
@@ -238,6 +279,11 @@ BOOST_ASIO_DECL bool non_blocking_sendto(socket_type s,
     const socket_addr_type* addr, std::size_t addrlen,
     boost::system::error_code& ec, size_t& bytes_transferred);
 
+BOOST_ASIO_DECL bool non_blocking_sendto1(socket_type s,
+    const void* data, size_t size, int flags,
+    const socket_addr_type* addr, std::size_t addrlen,
+    boost::system::error_code& ec, size_t& bytes_transferred);
+
 #endif // !defined(BOOST_ASIO_HAS_IOCP)
 
 BOOST_ASIO_DECL socket_type socket(int af, int type, int protocol,
diff --git a/include/boost/asio/detail/source_location.hpp b/include/boost/asio/detail/source_location.hpp
new file mode 100644
index 00000000..e36ef8c6
--- /dev/null
+++ b/include/boost/asio/detail/source_location.hpp
@@ -0,0 +1,47 @@
+//
+// detail/source_location.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_DETAIL_SOURCE_LOCATION_HPP
+#define BOOST_ASIO_DETAIL_SOURCE_LOCATION_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+
+#if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+
+#if defined(BOOST_ASIO_HAS_STD_SOURCE_LOCATION)
+# include <source_location>
+#elif defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+# include <experimental/source_location>
+#else // defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+# error BOOST_ASIO_HAS_SOURCE_LOCATION is set \
+  but no source_location is available
+#endif // defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+
+namespace boost {
+namespace asio {
+namespace detail {
+
+#if defined(BOOST_ASIO_HAS_STD_SOURCE_LOCATION)
+using std::source_location;
+#elif defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+using std::experimental::source_location;
+#endif // defined(BOOST_ASIO_HAS_STD_EXPERIMENTAL_SOURCE_LOCATION)
+
+} // namespace detail
+} // namespace asio
+} // namespace boost
+
+#endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+
+#endif // BOOST_ASIO_DETAIL_SOURCE_LOCATION_HPP
diff --git a/include/boost/asio/detail/std_event.hpp b/include/boost/asio/detail/std_event.hpp
index 914f9d93..32ad0441 100644
--- a/include/boost/asio/detail/std_event.hpp
+++ b/include/boost/asio/detail/std_event.hpp
@@ -74,6 +74,18 @@ public:
       cond_.notify_one();
   }
 
+  // Unlock the mutex and signal one waiter who may destroy us.
+  template <typename Lock>
+  void unlock_and_signal_one(Lock& lock)
+  {
+    BOOST_ASIO_ASSERT(lock.locked());
+    state_ |= 1;
+    bool have_waiters = (state_ > 1);
+    if (have_waiters)
+      cond_.notify_one();
+    lock.unlock();
+  }
+
   // If there's a waiter, unlock the mutex and signal it.
   template <typename Lock>
   bool maybe_unlock_and_signal_one(Lock& lock)
diff --git a/include/boost/asio/detail/strand_executor_service.hpp b/include/boost/asio/detail/strand_executor_service.hpp
index d710927b..0feabeb2 100644
--- a/include/boost/asio/detail/strand_executor_service.hpp
+++ b/include/boost/asio/detail/strand_executor_service.hpp
@@ -23,6 +23,8 @@
 #include <boost/asio/detail/op_queue.hpp>
 #include <boost/asio/detail/scheduler_operation.hpp>
 #include <boost/asio/detail/scoped_ptr.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution.hpp>
 #include <boost/asio/execution_context.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -86,6 +88,27 @@ public:
   // Create a new strand_executor implementation.
   BOOST_ASIO_DECL implementation_type create_implementation();
 
+  // Request invocation of the given function.
+  template <typename Executor, typename Function>
+  static void execute(const implementation_type& impl, Executor& ex,
+      BOOST_ASIO_MOVE_ARG(Function) function,
+      typename enable_if<
+        can_query<Executor, execution::allocator_t<void> >::value
+      >::type* = 0);
+
+  // Request invocation of the given function.
+  template <typename Executor, typename Function>
+  static void execute(const implementation_type& impl, Executor& ex,
+      BOOST_ASIO_MOVE_ARG(Function) function,
+      typename enable_if<
+        !can_query<Executor, execution::allocator_t<void> >::value
+      >::type* = 0);
+
+  // Request invocation of the given function.
+  template <typename Executor, typename Function, typename Allocator>
+  static void execute(const implementation_type& impl, Executor& ex,
+      BOOST_ASIO_MOVE_ARG(Function) function, const Allocator& a);
+
   // Request invocation of the given function.
   template <typename Executor, typename Function, typename Allocator>
   static void dispatch(const implementation_type& impl, Executor& ex,
@@ -107,7 +130,8 @@ public:
 
 private:
   friend class strand_impl;
-  template <typename Executor> class invoker;
+  template <typename F, typename Allocator> class allocator_binder;
+  template <typename Executor, typename = void> class invoker;
 
   // Adds a function to the strand. Returns true if it acquires the lock.
   BOOST_ASIO_DECL static bool enqueue(const implementation_type& impl,
diff --git a/include/boost/asio/detail/strand_service.hpp b/include/boost/asio/detail/strand_service.hpp
index 68635d62..17fdb749 100644
--- a/include/boost/asio/detail/strand_service.hpp
+++ b/include/boost/asio/detail/strand_service.hpp
@@ -109,8 +109,11 @@ private:
       operation* base, const boost::system::error_code& ec,
       std::size_t bytes_transferred);
 
+  // The io_context used to obtain an I/O executor.
+  io_context& io_context_;
+
   // The io_context implementation used to post completions.
-  io_context_impl& io_context_;
+  io_context_impl& io_context_impl_;
 
   // Mutex to protect access to the array of implementations.
   boost::asio::detail::mutex mutex_;
diff --git a/include/boost/asio/detail/thread_info_base.hpp b/include/boost/asio/detail/thread_info_base.hpp
index d5a8e818..091be139 100644
--- a/include/boost/asio/detail/thread_info_base.hpp
+++ b/include/boost/asio/detail/thread_info_base.hpp
@@ -15,10 +15,18 @@
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
+#include <boost/asio/detail/config.hpp>
 #include <climits>
 #include <cstddef>
 #include <boost/asio/detail/noncopyable.hpp>
 
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+# include <exception>
+# include <boost/asio/multiple_exceptions.hpp>
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       // && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
@@ -45,6 +53,11 @@ public:
   };
 
   thread_info_base()
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    : has_pending_exception_(0)
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       // && !defined(BOOST_ASIO_NO_EXCEPTIONS)
   {
     for (int i = 0; i < max_mem_index; ++i)
       reusable_memory_[i] = 0;
@@ -112,10 +125,55 @@ public:
     ::operator delete(pointer);
   }
 
+  void capture_current_exception()
+  {
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    switch (has_pending_exception_)
+    {
+    case 0:
+      has_pending_exception_ = 1;
+      pending_exception_ = std::current_exception();
+      break;
+    case 1:
+      has_pending_exception_ = 2;
+      pending_exception_ =
+        std::make_exception_ptr<multiple_exceptions>(
+            multiple_exceptions(pending_exception_));
+    default:
+      break;
+    }
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       // && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+
+  void rethrow_pending_exception()
+  {
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    if (has_pending_exception_ > 0)
+    {
+      has_pending_exception_ = 0;
+      std::exception_ptr ex(
+          BOOST_ASIO_MOVE_CAST(std::exception_ptr)(
+            pending_exception_));
+      std::rethrow_exception(ex);
+    }
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       // && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+
 private:
   enum { chunk_size = 4 };
   enum { max_mem_index = 3 };
   void* reusable_memory_[max_mem_index];
+
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  int has_pending_exception_;
+  std::exception_ptr pending_exception_;
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       // && !defined(BOOST_ASIO_NO_EXCEPTIONS)
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/type_traits.hpp b/include/boost/asio/detail/type_traits.hpp
index d5a8901c..a6a0d0e6 100644
--- a/include/boost/asio/detail/type_traits.hpp
+++ b/include/boost/asio/detail/type_traits.hpp
@@ -21,13 +21,19 @@
 # include <type_traits>
 #else // defined(BOOST_ASIO_HAS_STD_TYPE_TRAITS)
 # include <boost/type_traits/add_const.hpp>
+# include <boost/type_traits/aligned_storage.hpp>
+# include <boost/type_traits/alignment_of.hpp>
 # include <boost/type_traits/conditional.hpp>
 # include <boost/type_traits/decay.hpp>
+# include <boost/type_traits/has_nothrow_copy.hpp>
+# include <boost/type_traits/has_nothrow_destructor.hpp>
 # include <boost/type_traits/integral_constant.hpp>
 # include <boost/type_traits/is_base_of.hpp>
 # include <boost/type_traits/is_class.hpp>
 # include <boost/type_traits/is_const.hpp>
 # include <boost/type_traits/is_convertible.hpp>
+# include <boost/type_traits/is_copy_constructible.hpp>
+# include <boost/type_traits/is_destructible.hpp>
 # include <boost/type_traits/is_function.hpp>
 # include <boost/type_traits/is_same.hpp>
 # include <boost/type_traits/remove_pointer.hpp>
@@ -42,6 +48,8 @@ namespace asio {
 
 #if defined(BOOST_ASIO_HAS_STD_TYPE_TRAITS)
 using std::add_const;
+using std::aligned_storage;
+using std::alignment_of;
 using std::conditional;
 using std::decay;
 using std::declval;
@@ -52,8 +60,14 @@ using std::is_base_of;
 using std::is_class;
 using std::is_const;
 using std::is_convertible;
+using std::is_copy_constructible;
+using std::is_destructible;
 using std::is_function;
+using std::is_nothrow_copy_constructible;
+using std::is_nothrow_destructible;
+using std::is_reference;
 using std::is_same;
+using std::is_scalar;
 using std::remove_pointer;
 using std::remove_reference;
 #if defined(BOOST_ASIO_HAS_STD_INVOKE_RESULT)
@@ -66,6 +80,8 @@ using std::result_of;
 using std::true_type;
 #else // defined(BOOST_ASIO_HAS_STD_TYPE_TRAITS)
 using boost::add_const;
+using boost::aligned_storage;
+using boost::alignment_of;
 template <bool Condition, typename Type = void>
 struct enable_if : boost::enable_if_c<Condition, Type> {};
 using boost::conditional;
@@ -77,14 +93,24 @@ using boost::is_base_of;
 using boost::is_class;
 using boost::is_const;
 using boost::is_convertible;
+using boost::is_copy_constructible;
+using boost::is_destructible;
 using boost::is_function;
+template <typename T>
+struct is_nothrow_copy_constructible : boost::has_nothrow_copy<T> {};
+template <typename T>
+struct is_nothrow_destructible : boost::has_nothrow_destructor<T> {};
+using boost::is_reference;
 using boost::is_same;
+using boost::is_scalar;
 using boost::remove_pointer;
 using boost::remove_reference;
 using boost::result_of;
 using boost::true_type;
 #endif // defined(BOOST_ASIO_HAS_STD_TYPE_TRAITS)
 
+template <typename> struct void_type { typedef void type; };
+
 } // namespace asio
 } // namespace boost
 
diff --git a/include/boost/asio/detail/variadic_templates.hpp b/include/boost/asio/detail/variadic_templates.hpp
index f1a8bc6c..4408a816 100644
--- a/include/boost/asio/detail/variadic_templates.hpp
+++ b/include/boost/asio/detail/variadic_templates.hpp
@@ -31,6 +31,15 @@
   typename T1, typename T2, typename T3, typename T4
 # define BOOST_ASIO_VARIADIC_TPARAMS_5 \
   typename T1, typename T2, typename T3, typename T4, typename T5
+# define BOOST_ASIO_VARIADIC_TPARAMS_6 \
+  typename T1, typename T2, typename T3, typename T4, typename T5, \
+  typename T6
+# define BOOST_ASIO_VARIADIC_TPARAMS_7 \
+  typename T1, typename T2, typename T3, typename T4, typename T5, \
+  typename T6, typename T7
+# define BOOST_ASIO_VARIADIC_TPARAMS_8 \
+  typename T1, typename T2, typename T3, typename T4, typename T5, \
+  typename T6, typename T7, typename T8
 
 # define BOOST_ASIO_VARIADIC_TARGS(n) BOOST_ASIO_VARIADIC_TARGS_##n
 
@@ -39,6 +48,9 @@
 # define BOOST_ASIO_VARIADIC_TARGS_3 T1, T2, T3
 # define BOOST_ASIO_VARIADIC_TARGS_4 T1, T2, T3, T4
 # define BOOST_ASIO_VARIADIC_TARGS_5 T1, T2, T3, T4, T5
+# define BOOST_ASIO_VARIADIC_TARGS_6 T1, T2, T3, T4, T5, T6
+# define BOOST_ASIO_VARIADIC_TARGS_7 T1, T2, T3, T4, T5, T6, T7
+# define BOOST_ASIO_VARIADIC_TARGS_8 T1, T2, T3, T4, T5, T6, T7, T8
 
 # define BOOST_ASIO_VARIADIC_BYVAL_PARAMS(n) \
   BOOST_ASIO_VARIADIC_BYVAL_PARAMS_##n
@@ -48,6 +60,12 @@
 # define BOOST_ASIO_VARIADIC_BYVAL_PARAMS_3 T1 x1, T2 x2, T3 x3
 # define BOOST_ASIO_VARIADIC_BYVAL_PARAMS_4 T1 x1, T2 x2, T3 x3, T4 x4
 # define BOOST_ASIO_VARIADIC_BYVAL_PARAMS_5 T1 x1, T2 x2, T3 x3, T4 x4, T5 x5
+# define BOOST_ASIO_VARIADIC_BYVAL_PARAMS_6 T1 x1, T2 x2, T3 x3, T4 x4, T5 x5, \
+  T6 x6
+# define BOOST_ASIO_VARIADIC_BYVAL_PARAMS_7 T1 x1, T2 x2, T3 x3, T4 x4, T5 x5, \
+  T6 x6, T7 x7
+# define BOOST_ASIO_VARIADIC_BYVAL_PARAMS_8 T1 x1, T2 x2, T3 x3, T4 x4, T5 x5, \
+  T6 x6, T7 x7, T8 x8
 
 # define BOOST_ASIO_VARIADIC_BYVAL_ARGS(n) \
   BOOST_ASIO_VARIADIC_BYVAL_ARGS_##n
@@ -57,6 +75,9 @@
 # define BOOST_ASIO_VARIADIC_BYVAL_ARGS_3 x1, x2, x3
 # define BOOST_ASIO_VARIADIC_BYVAL_ARGS_4 x1, x2, x3, x4
 # define BOOST_ASIO_VARIADIC_BYVAL_ARGS_5 x1, x2, x3, x4, x5
+# define BOOST_ASIO_VARIADIC_BYVAL_ARGS_6 x1, x2, x3, x4, x5, x6
+# define BOOST_ASIO_VARIADIC_BYVAL_ARGS_7 x1, x2, x3, x4, x5, x6, x7
+# define BOOST_ASIO_VARIADIC_BYVAL_ARGS_8 x1, x2, x3, x4, x5, x6, x7, x8
 
 # define BOOST_ASIO_VARIADIC_CONSTREF_PARAMS(n) \
   BOOST_ASIO_VARIADIC_CONSTREF_PARAMS_##n
@@ -71,6 +92,15 @@
   const T1& x1, const T2& x2, const T3& x3, const T4& x4
 # define BOOST_ASIO_VARIADIC_CONSTREF_PARAMS_5 \
   const T1& x1, const T2& x2, const T3& x3, const T4& x4, const T5& x5
+# define BOOST_ASIO_VARIADIC_CONSTREF_PARAMS_6 \
+  const T1& x1, const T2& x2, const T3& x3, const T4& x4, const T5& x5, \
+  const T6& x6
+# define BOOST_ASIO_VARIADIC_CONSTREF_PARAMS_7 \
+  const T1& x1, const T2& x2, const T3& x3, const T4& x4, const T5& x5, \
+  const T6& x6, const T7& x7
+# define BOOST_ASIO_VARIADIC_CONSTREF_PARAMS_8 \
+  const T1& x1, const T2& x2, const T3& x3, const T4& x4, const T5& x5, \
+  const T6& x6, const T7& x7, const T8& x8
 
 # define BOOST_ASIO_VARIADIC_MOVE_PARAMS(n) \
   BOOST_ASIO_VARIADIC_MOVE_PARAMS_##n
@@ -89,6 +119,52 @@
   BOOST_ASIO_MOVE_ARG(T1) x1, BOOST_ASIO_MOVE_ARG(T2) x2, \
   BOOST_ASIO_MOVE_ARG(T3) x3, BOOST_ASIO_MOVE_ARG(T4) x4, \
   BOOST_ASIO_MOVE_ARG(T5) x5
+# define BOOST_ASIO_VARIADIC_MOVE_PARAMS_6 \
+  BOOST_ASIO_MOVE_ARG(T1) x1, BOOST_ASIO_MOVE_ARG(T2) x2, \
+  BOOST_ASIO_MOVE_ARG(T3) x3, BOOST_ASIO_MOVE_ARG(T4) x4, \
+  BOOST_ASIO_MOVE_ARG(T5) x5, BOOST_ASIO_MOVE_ARG(T6) x6
+# define BOOST_ASIO_VARIADIC_MOVE_PARAMS_7 \
+  BOOST_ASIO_MOVE_ARG(T1) x1, BOOST_ASIO_MOVE_ARG(T2) x2, \
+  BOOST_ASIO_MOVE_ARG(T3) x3, BOOST_ASIO_MOVE_ARG(T4) x4, \
+  BOOST_ASIO_MOVE_ARG(T5) x5, BOOST_ASIO_MOVE_ARG(T6) x6, \
+  BOOST_ASIO_MOVE_ARG(T7) x7
+# define BOOST_ASIO_VARIADIC_MOVE_PARAMS_8 \
+  BOOST_ASIO_MOVE_ARG(T1) x1, BOOST_ASIO_MOVE_ARG(T2) x2, \
+  BOOST_ASIO_MOVE_ARG(T3) x3, BOOST_ASIO_MOVE_ARG(T4) x4, \
+  BOOST_ASIO_MOVE_ARG(T5) x5, BOOST_ASIO_MOVE_ARG(T6) x6, \
+  BOOST_ASIO_MOVE_ARG(T7) x7, BOOST_ASIO_MOVE_ARG(T8) x8
+
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS(n) \
+  BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_##n
+
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_1 \
+  BOOST_ASIO_MOVE_ARG(T1)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_2 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_3 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2), \
+  BOOST_ASIO_MOVE_ARG(T3)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_4 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2), \
+  BOOST_ASIO_MOVE_ARG(T3), BOOST_ASIO_MOVE_ARG(T4)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_5 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2), \
+  BOOST_ASIO_MOVE_ARG(T3), BOOST_ASIO_MOVE_ARG(T4), \
+  BOOST_ASIO_MOVE_ARG(T5)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_6 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2), \
+  BOOST_ASIO_MOVE_ARG(T3), BOOST_ASIO_MOVE_ARG(T4), \
+  BOOST_ASIO_MOVE_ARG(T5), BOOST_ASIO_MOVE_ARG(T6)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_7 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2), \
+  BOOST_ASIO_MOVE_ARG(T3), BOOST_ASIO_MOVE_ARG(T4), \
+  BOOST_ASIO_MOVE_ARG(T5), BOOST_ASIO_MOVE_ARG(T6), \
+  BOOST_ASIO_MOVE_ARG(T7)
+# define BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS_8 \
+  BOOST_ASIO_MOVE_ARG(T1), BOOST_ASIO_MOVE_ARG(T2), \
+  BOOST_ASIO_MOVE_ARG(T3), BOOST_ASIO_MOVE_ARG(T4), \
+  BOOST_ASIO_MOVE_ARG(T5), BOOST_ASIO_MOVE_ARG(T6), \
+  BOOST_ASIO_MOVE_ARG(T7), BOOST_ASIO_MOVE_ARG(T8)
 
 # define BOOST_ASIO_VARIADIC_MOVE_ARGS(n) \
   BOOST_ASIO_VARIADIC_MOVE_ARGS_##n
@@ -107,6 +183,20 @@
   BOOST_ASIO_MOVE_CAST(T1)(x1), BOOST_ASIO_MOVE_CAST(T2)(x2), \
   BOOST_ASIO_MOVE_CAST(T3)(x3), BOOST_ASIO_MOVE_CAST(T4)(x4), \
   BOOST_ASIO_MOVE_CAST(T5)(x5)
+# define BOOST_ASIO_VARIADIC_MOVE_ARGS_6 \
+  BOOST_ASIO_MOVE_CAST(T1)(x1), BOOST_ASIO_MOVE_CAST(T2)(x2), \
+  BOOST_ASIO_MOVE_CAST(T3)(x3), BOOST_ASIO_MOVE_CAST(T4)(x4), \
+  BOOST_ASIO_MOVE_CAST(T5)(x5), BOOST_ASIO_MOVE_CAST(T6)(x6)
+# define BOOST_ASIO_VARIADIC_MOVE_ARGS_7 \
+  BOOST_ASIO_MOVE_CAST(T1)(x1), BOOST_ASIO_MOVE_CAST(T2)(x2), \
+  BOOST_ASIO_MOVE_CAST(T3)(x3), BOOST_ASIO_MOVE_CAST(T4)(x4), \
+  BOOST_ASIO_MOVE_CAST(T5)(x5), BOOST_ASIO_MOVE_CAST(T6)(x6), \
+  BOOST_ASIO_MOVE_CAST(T7)(x7)
+# define BOOST_ASIO_VARIADIC_MOVE_ARGS_8 \
+  BOOST_ASIO_MOVE_CAST(T1)(x1), BOOST_ASIO_MOVE_CAST(T2)(x2), \
+  BOOST_ASIO_MOVE_CAST(T3)(x3), BOOST_ASIO_MOVE_CAST(T4)(x4), \
+  BOOST_ASIO_MOVE_CAST(T5)(x5), BOOST_ASIO_MOVE_CAST(T6)(x6), \
+  BOOST_ASIO_MOVE_CAST(T7)(x7), BOOST_ASIO_MOVE_CAST(T8)(x8)
 
 # define BOOST_ASIO_VARIADIC_MOVE_DECLVAL(n) \
   BOOST_ASIO_VARIADIC_MOVE_DECLVAL_##n
@@ -125,6 +215,20 @@
   declval<BOOST_ASIO_MOVE_ARG(T1)>(), declval<BOOST_ASIO_MOVE_ARG(T2)>(), \
   declval<BOOST_ASIO_MOVE_ARG(T3)>(), declval<BOOST_ASIO_MOVE_ARG(T4)>(), \
   declval<BOOST_ASIO_MOVE_ARG(T5)>()
+# define BOOST_ASIO_VARIADIC_MOVE_DECLVAL_6 \
+  declval<BOOST_ASIO_MOVE_ARG(T1)>(), declval<BOOST_ASIO_MOVE_ARG(T2)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T3)>(), declval<BOOST_ASIO_MOVE_ARG(T4)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T5)>(), declval<BOOST_ASIO_MOVE_ARG(T6)>()
+# define BOOST_ASIO_VARIADIC_MOVE_DECLVAL_7 \
+  declval<BOOST_ASIO_MOVE_ARG(T1)>(), declval<BOOST_ASIO_MOVE_ARG(T2)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T3)>(), declval<BOOST_ASIO_MOVE_ARG(T4)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T5)>(), declval<BOOST_ASIO_MOVE_ARG(T6)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T7)>()
+# define BOOST_ASIO_VARIADIC_MOVE_DECLVAL_8 \
+  declval<BOOST_ASIO_MOVE_ARG(T1)>(), declval<BOOST_ASIO_MOVE_ARG(T2)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T3)>(), declval<BOOST_ASIO_MOVE_ARG(T4)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T5)>(), declval<BOOST_ASIO_MOVE_ARG(T6)>(), \
+  declval<BOOST_ASIO_MOVE_ARG(T7)>(), declval<BOOST_ASIO_MOVE_ARG(T8)>()
 
 # define BOOST_ASIO_VARIADIC_DECAY(n) \
   BOOST_ASIO_VARIADIC_DECAY_##n
@@ -143,8 +247,22 @@
   typename decay<T1>::type, typename decay<T2>::type, \
   typename decay<T3>::type, typename decay<T4>::type, \
   typename decay<T5>::type
+# define BOOST_ASIO_VARIADIC_DECAY_6 \
+  typename decay<T1>::type, typename decay<T2>::type, \
+  typename decay<T3>::type, typename decay<T4>::type, \
+  typename decay<T5>::type, typename decay<T6>::type
+# define BOOST_ASIO_VARIADIC_DECAY_7 \
+  typename decay<T1>::type, typename decay<T2>::type, \
+  typename decay<T3>::type, typename decay<T4>::type, \
+  typename decay<T5>::type, typename decay<T6>::type, \
+  typename decay<T7>::type
+# define BOOST_ASIO_VARIADIC_DECAY_8 \
+  typename decay<T1>::type, typename decay<T2>::type, \
+  typename decay<T3>::type, typename decay<T4>::type, \
+  typename decay<T5>::type, typename decay<T6>::type, \
+  typename decay<T7>::type, typename decay<T8>::type
 
-# define BOOST_ASIO_VARIADIC_GENERATE(m) m(1) m(2) m(3) m(4) m(5)
+# define BOOST_ASIO_VARIADIC_GENERATE(m) m(1) m(2) m(3) m(4) m(5) m(6) m(7) m(8)
 
 #endif // !defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
 
diff --git a/include/boost/asio/detail/wait_handler.hpp b/include/boost/asio/detail/wait_handler.hpp
index 7ec6a4f7..3f732640 100644
--- a/include/boost/asio/detail/wait_handler.hpp
+++ b/include/boost/asio/detail/wait_handler.hpp
@@ -16,9 +16,9 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
-#include <boost/asio/detail/handler_invoke_helpers.hpp>
 #include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/wait_op.hpp>
@@ -35,12 +35,11 @@ class wait_handler : public wait_op
 public:
   BOOST_ASIO_DEFINE_HANDLER_PTR(wait_handler);
 
-  wait_handler(Handler& h, const IoExecutor& ex)
+  wait_handler(Handler& h, const IoExecutor& io_ex)
     : wait_op(&wait_handler::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(h)),
-      io_executor_(ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -50,10 +49,14 @@ public:
     // Take ownership of the handler object.
     wait_handler* h(static_cast<wait_handler*>(base));
     ptr p = { boost::asio::detail::addressof(h->handler_), h, h };
-    handler_work<Handler, IoExecutor> w(h->handler_, h->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*h));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          h->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -77,7 +80,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_event.hpp b/include/boost/asio/detail/win_event.hpp
index 6d456713..617593e9 100644
--- a/include/boost/asio/detail/win_event.hpp
+++ b/include/boost/asio/detail/win_event.hpp
@@ -68,6 +68,18 @@ public:
       ::SetEvent(events_[1]);
   }
 
+  // Unlock the mutex and signal one waiter who may destroy us.
+  template <typename Lock>
+  void unlock_and_signal_one_for_destruction(Lock& lock)
+  {
+    BOOST_ASIO_ASSERT(lock.locked());
+    state_ |= 1;
+    bool have_waiters = (state_ > 1);
+    if (have_waiters)
+      ::SetEvent(events_[1]);
+    lock.unlock();
+  }
+
   // If there's a waiter, unlock the mutex and signal it.
   template <typename Lock>
   bool maybe_unlock_and_signal_one(Lock& lock)
diff --git a/include/boost/asio/detail/win_iocp_handle_read_op.hpp b/include/boost/asio/detail/win_iocp_handle_read_op.hpp
index b17f639c..13369f73 100644
--- a/include/boost/asio/detail/win_iocp_handle_read_op.hpp
+++ b/include/boost/asio/detail/win_iocp_handle_read_op.hpp
@@ -20,14 +20,15 @@
 
 #if defined(BOOST_ASIO_HAS_IOCP)
 
-#include <boost/asio/error.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
+#include <boost/asio/error.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -46,9 +47,8 @@ public:
     : operation(&win_iocp_handle_read_op::do_complete),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -60,10 +60,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_handle_read_op* o(static_cast<win_iocp_handle_read_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     if (owner)
     {
@@ -101,7 +105,7 @@ public:
 private:
   MutableBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_handle_write_op.hpp b/include/boost/asio/detail/win_iocp_handle_write_op.hpp
index b24ffad2..e1706f16 100644
--- a/include/boost/asio/detail/win_iocp_handle_write_op.hpp
+++ b/include/boost/asio/detail/win_iocp_handle_write_op.hpp
@@ -20,14 +20,15 @@
 
 #if defined(BOOST_ASIO_HAS_IOCP)
 
-#include <boost/asio/error.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
+#include <boost/asio/error.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -46,9 +47,8 @@ public:
     : operation(&win_iocp_handle_write_op::do_complete),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -57,10 +57,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_handle_write_op* o(static_cast<win_iocp_handle_write_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     if (owner)
     {
@@ -94,7 +98,7 @@ public:
 private:
   ConstBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_io_context.hpp b/include/boost/asio/detail/win_iocp_io_context.hpp
index 9cc7690a..049cdbcf 100644
--- a/include/boost/asio/detail/win_iocp_io_context.hpp
+++ b/include/boost/asio/detail/win_iocp_io_context.hpp
@@ -115,6 +115,9 @@ public:
     return thread_call_stack::contains(this) != 0;
   }
 
+  /// Capture the current exception so it can be rethrown from a run function.
+  BOOST_ASIO_DECL void capture_current_exception();
+
   // Request invocation of the given operation and return immediately. Assumes
   // that work_started() has not yet been called for the operation.
   void post_immediate_completion(win_iocp_operation* op, bool)
@@ -222,7 +225,8 @@ private:
   // Dequeues at most one operation from the I/O completion port, and then
   // executes it. Returns the number of operations that were dequeued (i.e.
   // either 0 or 1).
-  BOOST_ASIO_DECL size_t do_one(DWORD msec, boost::system::error_code& ec);
+  BOOST_ASIO_DECL size_t do_one(DWORD msec,
+      win_iocp_thread_info& this_thread, boost::system::error_code& ec);
 
   // Helper to calculate the GetQueuedCompletionStatus timeout.
   BOOST_ASIO_DECL static DWORD get_gqcs_timeout();
diff --git a/include/boost/asio/detail/win_iocp_null_buffers_op.hpp b/include/boost/asio/detail/win_iocp_null_buffers_op.hpp
index f0615659..ec636dbd 100644
--- a/include/boost/asio/detail/win_iocp_null_buffers_op.hpp
+++ b/include/boost/asio/detail/win_iocp_null_buffers_op.hpp
@@ -20,10 +20,10 @@
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 #include <boost/asio/detail/bind_handler.hpp>
-#include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -43,13 +43,13 @@ public:
 
   win_iocp_null_buffers_op(socket_ops::weak_cancel_token_type cancel_token,
       Handler& handler, const IoExecutor& io_ex)
-    : reactor_op(&win_iocp_null_buffers_op::do_perform,
+    : reactor_op(boost::system::error_code(),
+        &win_iocp_null_buffers_op::do_perform,
         &win_iocp_null_buffers_op::do_complete),
       cancel_token_(cancel_token),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static status do_perform(reactor_op*)
@@ -66,10 +66,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_null_buffers_op* o(static_cast<win_iocp_null_buffers_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // The reactor may have stored a result in the operation object.
     if (o->ec_)
       ec = o->ec_;
@@ -111,7 +115,7 @@ public:
 private:
   socket_ops::weak_cancel_token_type cancel_token_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_overlapped_op.hpp b/include/boost/asio/detail/win_iocp_overlapped_op.hpp
index 57bbe2df..be3f2929 100644
--- a/include/boost/asio/detail/win_iocp_overlapped_op.hpp
+++ b/include/boost/asio/detail/win_iocp_overlapped_op.hpp
@@ -19,13 +19,14 @@
 
 #if defined(BOOST_ASIO_HAS_IOCP)
 
-#include <boost/asio/error.hpp>
 #include <boost/asio/detail/bind_handler.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
+#include <boost/asio/error.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -42,9 +43,8 @@ public:
   win_iocp_overlapped_op(Handler& handler, const IoExecutor& io_ex)
     : operation(&win_iocp_overlapped_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -53,10 +53,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_overlapped_op* o(static_cast<win_iocp_overlapped_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -80,7 +84,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_overlapped_ptr.hpp b/include/boost/asio/detail/win_iocp_overlapped_ptr.hpp
index 061ce3f9..ad32f87e 100644
--- a/include/boost/asio/detail/win_iocp_overlapped_ptr.hpp
+++ b/include/boost/asio/detail/win_iocp_overlapped_ptr.hpp
@@ -21,7 +21,6 @@
 
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
-#include <boost/asio/detail/io_object_executor.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/noncopyable.hpp>
 #include <boost/asio/detail/win_iocp_overlapped_op.hpp>
@@ -81,10 +80,10 @@ public:
     const bool native = is_same<Executor, io_context::executor_type>::value;
     win_iocp_io_context* iocp_service = this->get_iocp_service(ex);
 
-    typedef win_iocp_overlapped_op<Handler, io_object_executor<Executor> > op;
+    typedef win_iocp_overlapped_op<Handler, Executor> op;
     typename op::ptr p = { boost::asio::detail::addressof(handler),
       op::ptr::allocate(handler), 0 };
-    p.p = new (p.v) op(handler, io_object_executor<Executor>(ex, native));
+    p.p = new (p.v) op(handler, ex);
 
     BOOST_ASIO_HANDLER_CREATION((ex.context(), *p.p,
           "iocp_service", iocp_service, 0, "overlapped"));
diff --git a/include/boost/asio/detail/win_iocp_socket_accept_op.hpp b/include/boost/asio/detail/win_iocp_socket_accept_op.hpp
index 39fc5da0..eac8f77d 100644
--- a/include/boost/asio/detail/win_iocp_socket_accept_op.hpp
+++ b/include/boost/asio/detail/win_iocp_socket_accept_op.hpp
@@ -20,10 +20,10 @@
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 #include <boost/asio/detail/bind_handler.hpp>
-#include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -55,9 +55,8 @@ public:
       peer_endpoint_(peer_endpoint),
       enable_connection_aborted_(enable_connection_aborted),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   socket_holder& new_socket()
@@ -84,7 +83,6 @@ public:
     // Take ownership of the operation object.
     win_iocp_socket_accept_op* o(static_cast<win_iocp_socket_accept_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     if (owner)
     {
@@ -100,7 +98,6 @@ public:
       if (ec == boost::asio::error::connection_aborted
           && !o->enable_connection_aborted_)
       {
-        handler_work<Handler, IoExecutor>::start(o->handler_, o->io_executor_);
         o->reset();
         o->socket_service_.restart_accept_op(o->socket_,
             o->new_socket_, o->protocol_.family(),
@@ -128,6 +125,11 @@ public:
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -159,7 +161,7 @@ private:
   unsigned char output_buffer_[(sizeof(sockaddr_storage_type) + 16) * 2];
   bool enable_connection_aborted_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 #if defined(BOOST_ASIO_HAS_MOVE)
@@ -184,9 +186,8 @@ public:
       peer_endpoint_(peer_endpoint),
       enable_connection_aborted_(enable_connection_aborted),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   socket_holder& new_socket()
@@ -214,7 +215,6 @@ public:
     win_iocp_socket_move_accept_op* o(
         static_cast<win_iocp_socket_move_accept_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     if (owner)
     {
@@ -230,7 +230,6 @@ public:
       if (ec == boost::asio::error::connection_aborted
           && !o->enable_connection_aborted_)
       {
-        handler_work<Handler, IoExecutor>::start(o->handler_, o->io_executor_);
         o->reset();
         o->socket_service_.restart_accept_op(o->socket_,
             o->new_socket_, o->protocol_.family(),
@@ -258,6 +257,11 @@ public:
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -294,7 +298,7 @@ private:
   unsigned char output_buffer_[(sizeof(sockaddr_storage_type) + 16) * 2];
   bool enable_connection_aborted_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 #endif // defined(BOOST_ASIO_HAS_MOVE)
diff --git a/include/boost/asio/detail/win_iocp_socket_connect_op.hpp b/include/boost/asio/detail/win_iocp_socket_connect_op.hpp
index 5b53fe25..67d94b7c 100644
--- a/include/boost/asio/detail/win_iocp_socket_connect_op.hpp
+++ b/include/boost/asio/detail/win_iocp_socket_connect_op.hpp
@@ -23,6 +23,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -38,7 +39,8 @@ class win_iocp_socket_connect_op_base : public reactor_op
 {
 public:
   win_iocp_socket_connect_op_base(socket_type socket, func_type complete_func)
-    : reactor_op(&win_iocp_socket_connect_op_base::do_perform, complete_func),
+    : reactor_op(boost::system::error_code(),
+        &win_iocp_socket_connect_op_base::do_perform, complete_func),
       socket_(socket),
       connect_ex_(false)
   {
@@ -68,9 +70,8 @@ public:
     : win_iocp_socket_connect_op_base(socket,
         &win_iocp_socket_connect_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -83,7 +84,6 @@ public:
     win_iocp_socket_connect_op* o(
         static_cast<win_iocp_socket_connect_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     if (owner)
     {
@@ -95,6 +95,11 @@ public:
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -118,7 +123,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_socket_recv_op.hpp b/include/boost/asio/detail/win_iocp_socket_recv_op.hpp
index 120742e0..520678cb 100644
--- a/include/boost/asio/detail/win_iocp_socket_recv_op.hpp
+++ b/include/boost/asio/detail/win_iocp_socket_recv_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -50,9 +51,8 @@ public:
       cancel_token_(cancel_token),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -64,10 +64,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_socket_recv_op* o(static_cast<win_iocp_socket_recv_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     // Check whether buffers are still valid.
     if (owner)
@@ -108,7 +112,7 @@ private:
   socket_ops::weak_cancel_token_type cancel_token_;
   MutableBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_socket_recvfrom_op.hpp b/include/boost/asio/detail/win_iocp_socket_recvfrom_op.hpp
index e97d4be4..27524f7c 100644
--- a/include/boost/asio/detail/win_iocp_socket_recvfrom_op.hpp
+++ b/include/boost/asio/detail/win_iocp_socket_recvfrom_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -52,9 +53,8 @@ public:
       cancel_token_(cancel_token),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   int& endpoint_size()
@@ -72,10 +72,14 @@ public:
     win_iocp_socket_recvfrom_op* o(
         static_cast<win_iocp_socket_recvfrom_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     // Check whether buffers are still valid.
     if (owner)
@@ -117,7 +121,7 @@ private:
   socket_ops::weak_cancel_token_type cancel_token_;
   MutableBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_socket_recvmsg_op.hpp b/include/boost/asio/detail/win_iocp_socket_recvmsg_op.hpp
index 44d99d19..62dee6b8 100644
--- a/include/boost/asio/detail/win_iocp_socket_recvmsg_op.hpp
+++ b/include/boost/asio/detail/win_iocp_socket_recvmsg_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -52,9 +53,8 @@ public:
       buffers_(buffers),
       out_flags_(out_flags),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -67,10 +67,14 @@ public:
     win_iocp_socket_recvmsg_op* o(
         static_cast<win_iocp_socket_recvmsg_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     // Check whether buffers are still valid.
     if (owner)
@@ -109,7 +113,7 @@ private:
   MutableBufferSequence buffers_;
   socket_base::message_flags& out_flags_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_socket_send_op.hpp b/include/boost/asio/detail/win_iocp_socket_send_op.hpp
index 394431cc..6d20d741 100644
--- a/include/boost/asio/detail/win_iocp_socket_send_op.hpp
+++ b/include/boost/asio/detail/win_iocp_socket_send_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/operation.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -48,9 +49,8 @@ public:
       cancel_token_(cancel_token),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -62,10 +62,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_socket_send_op* o(static_cast<win_iocp_socket_send_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     // Check whether buffers are still valid.
     if (owner)
@@ -102,7 +106,7 @@ private:
   socket_ops::weak_cancel_token_type cancel_token_;
   ConstBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/win_iocp_wait_op.hpp b/include/boost/asio/detail/win_iocp_wait_op.hpp
index bf93e4a6..54d42206 100644
--- a/include/boost/asio/detail/win_iocp_wait_op.hpp
+++ b/include/boost/asio/detail/win_iocp_wait_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/reactor_op.hpp>
 #include <boost/asio/detail/socket_ops.hpp>
@@ -43,13 +44,13 @@ public:
 
   win_iocp_wait_op(socket_ops::weak_cancel_token_type cancel_token,
       Handler& handler, const IoExecutor& io_ex)
-    : reactor_op(&win_iocp_wait_op::do_perform,
+    : reactor_op(boost::system::error_code(),
+        &win_iocp_wait_op::do_perform,
         &win_iocp_wait_op::do_complete),
       cancel_token_(cancel_token),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static status do_perform(reactor_op*)
@@ -66,10 +67,14 @@ public:
     // Take ownership of the operation object.
     win_iocp_wait_op* o(static_cast<win_iocp_wait_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // The reactor may have stored a result in the operation object.
     if (o->ec_)
       ec = o->ec_;
@@ -111,7 +116,7 @@ public:
 private:
   socket_ops::weak_cancel_token_type cancel_token_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> work_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/winrt_resolve_op.hpp b/include/boost/asio/detail/winrt_resolve_op.hpp
index 2b025efd..d75fbefd 100644
--- a/include/boost/asio/detail/winrt_resolve_op.hpp
+++ b/include/boost/asio/detail/winrt_resolve_op.hpp
@@ -23,6 +23,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/winrt_async_op.hpp>
 #include <boost/asio/ip/basic_resolver_results.hpp>
@@ -55,9 +56,8 @@ public:
             &winrt_resolve_op::do_complete),
       query_(query),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -66,10 +66,14 @@ public:
     // Take ownership of the operation object.
     winrt_resolve_op* o(static_cast<winrt_resolve_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     results_type results = results_type();
     if (!o->ec_)
     {
@@ -109,7 +113,7 @@ public:
 private:
   query_type query_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> executor_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/winrt_socket_connect_op.hpp b/include/boost/asio/detail/winrt_socket_connect_op.hpp
index cadfe435..7cd6e8e8 100644
--- a/include/boost/asio/detail/winrt_socket_connect_op.hpp
+++ b/include/boost/asio/detail/winrt_socket_connect_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/winrt_async_op.hpp>
 #include <boost/asio/error.hpp>
@@ -44,9 +45,8 @@ public:
   winrt_socket_connect_op(Handler& handler, const IoExecutor& io_ex)
     : winrt_async_op<void>(&winrt_socket_connect_op::do_complete),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -55,10 +55,14 @@ public:
     // Take ownership of the operation object.
     winrt_socket_connect_op* o(static_cast<winrt_socket_connect_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
     // Make a copy of the handler so that the memory can be deallocated before
     // the upcall is made. Even if we're not about to make an upcall, a
     // sub-object of the handler may be the true owner of the memory associated
@@ -82,7 +86,7 @@ public:
 
 private:
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> executor_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/winrt_socket_recv_op.hpp b/include/boost/asio/detail/winrt_socket_recv_op.hpp
index 5539f35f..80cb056b 100644
--- a/include/boost/asio/detail/winrt_socket_recv_op.hpp
+++ b/include/boost/asio/detail/winrt_socket_recv_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/winrt_async_op.hpp>
 #include <boost/asio/error.hpp>
@@ -47,9 +48,8 @@ public:
           &winrt_socket_recv_op::do_complete),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -58,10 +58,14 @@ public:
     // Take ownership of the operation object.
     winrt_socket_recv_op* o(static_cast<winrt_socket_recv_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     // Check whether buffers are still valid.
     if (owner)
@@ -103,7 +107,7 @@ public:
 private:
   MutableBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> executor_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/winrt_socket_send_op.hpp b/include/boost/asio/detail/winrt_socket_send_op.hpp
index c1ec3dd5..f9624d04 100644
--- a/include/boost/asio/detail/winrt_socket_send_op.hpp
+++ b/include/boost/asio/detail/winrt_socket_send_op.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/detail/fenced_block.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_work.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/winrt_async_op.hpp>
 #include <boost/asio/error.hpp>
@@ -46,9 +47,8 @@ public:
     : winrt_async_op<unsigned int>(&winrt_socket_send_op::do_complete),
       buffers_(buffers),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
-      io_executor_(io_ex)
+      work_(handler_, io_ex)
   {
-    handler_work<Handler, IoExecutor>::start(handler_, io_executor_);
   }
 
   static void do_complete(void* owner, operation* base,
@@ -57,10 +57,14 @@ public:
     // Take ownership of the operation object.
     winrt_socket_send_op* o(static_cast<winrt_socket_send_op*>(base));
     ptr p = { boost::asio::detail::addressof(o->handler_), o, o };
-    handler_work<Handler, IoExecutor> w(o->handler_, o->io_executor_);
 
     BOOST_ASIO_HANDLER_COMPLETION((*o));
 
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        BOOST_ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
+          o->work_));
+
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     // Check whether buffers are still valid.
     if (owner)
@@ -94,7 +98,7 @@ public:
 private:
   ConstBufferSequence buffers_;
   Handler handler_;
-  IoExecutor io_executor_;
+  handler_work<Handler, IoExecutor> executor_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/work_dispatcher.hpp b/include/boost/asio/detail/work_dispatcher.hpp
index 3416ead2..700eceec 100644
--- a/include/boost/asio/detail/work_dispatcher.hpp
+++ b/include/boost/asio/detail/work_dispatcher.hpp
@@ -19,6 +19,11 @@
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/associated_allocator.hpp>
 #include <boost/asio/executor_work_guard.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/outstanding_work.hpp>
+#include <boost/asio/prefer.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -26,13 +31,64 @@ namespace boost {
 namespace asio {
 namespace detail {
 
-template <typename Handler>
+template <typename Handler, typename Executor, typename = void>
 class work_dispatcher
 {
 public:
   template <typename CompletionHandler>
-  explicit work_dispatcher(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler)
-    : work_((get_associated_executor)(handler)),
+  work_dispatcher(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      const Executor& handler_ex)
+    : handler_(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler)),
+      executor_(boost::asio::prefer(handler_ex,
+          execution::outstanding_work.tracked))
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  work_dispatcher(const work_dispatcher& other)
+    : handler_(other.handler_),
+      executor_(other.executor_)
+  {
+  }
+
+  work_dispatcher(work_dispatcher&& other)
+    : handler_(BOOST_ASIO_MOVE_CAST(Handler)(other.handler_)),
+      executor_(BOOST_ASIO_MOVE_CAST(work_executor_type)(other.executor_))
+  {
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  void operator()()
+  {
+    execution::execute(
+        boost::asio::prefer(executor_,
+          execution::blocking.possibly,
+          execution::allocator((get_associated_allocator)(handler_))),
+        BOOST_ASIO_MOVE_CAST(Handler)(handler_));
+  }
+
+private:
+  typedef typename decay<
+      typename prefer_result_type<const Executor&,
+        execution::outstanding_work_t::tracked_t
+      >::type
+    >::type work_executor_type;
+
+  Handler handler_;
+  work_executor_type executor_;
+};
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+template <typename Handler, typename Executor>
+class work_dispatcher<Handler, Executor,
+    typename enable_if<!execution::is_executor<Executor>::value>::type>
+{
+public:
+  template <typename CompletionHandler>
+  work_dispatcher(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      const Executor& handler_ex)
+    : work_(handler_ex),
       handler_(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler))
   {
   }
@@ -45,8 +101,7 @@ public:
   }
 
   work_dispatcher(work_dispatcher&& other)
-    : work_(BOOST_ASIO_MOVE_CAST(executor_work_guard<
-        typename associated_executor<Handler>::type>)(other.work_)),
+    : work_(BOOST_ASIO_MOVE_CAST(executor_work_guard<Executor>)(other.work_)),
       handler_(BOOST_ASIO_MOVE_CAST(Handler)(other.handler_))
   {
   }
@@ -62,10 +117,12 @@ public:
   }
 
 private:
-  executor_work_guard<typename associated_executor<Handler>::type> work_;
+  executor_work_guard<Executor> work_;
   Handler handler_;
 };
 
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 } // namespace detail
 } // namespace asio
 } // namespace boost
diff --git a/include/boost/asio/detail/wrapped_handler.hpp b/include/boost/asio/detail/wrapped_handler.hpp
index 49e7fe7d..3441223e 100644
--- a/include/boost/asio/detail/wrapped_handler.hpp
+++ b/include/boost/asio/detail/wrapped_handler.hpp
@@ -202,19 +202,29 @@ public:
 };
 
 template <typename Dispatcher, typename Handler, typename IsContinuation>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     wrapped_handler<Dispatcher, Handler, IsContinuation>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Dispatcher, typename Handler, typename IsContinuation>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     wrapped_handler<Dispatcher, Handler, IsContinuation>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Dispatcher, typename Handler, typename IsContinuation>
@@ -226,38 +236,56 @@ inline bool asio_handler_is_continuation(
 
 template <typename Function, typename Dispatcher,
     typename Handler, typename IsContinuation>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     wrapped_handler<Dispatcher, Handler, IsContinuation>* this_handler)
 {
   this_handler->dispatcher_.dispatch(
       rewrapped_handler<Function, Handler>(
         function, this_handler->handler_));
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Dispatcher,
     typename Handler, typename IsContinuation>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     wrapped_handler<Dispatcher, Handler, IsContinuation>* this_handler)
 {
   this_handler->dispatcher_.dispatch(
       rewrapped_handler<Function, Handler>(
         function, this_handler->handler_));
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Context>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     rewrapped_handler<Handler, Context>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
-      size, this_handler->context_);
+      size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler, typename Context>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     rewrapped_handler<Handler, Context>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->context_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Dispatcher, typename Context>
@@ -269,19 +297,27 @@ inline bool asio_handler_is_continuation(
 }
 
 template <typename Function, typename Handler, typename Context>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     rewrapped_handler<Handler, Context>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->context_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler, typename Context>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     rewrapped_handler<Handler, Context>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->context_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 } // namespace detail
diff --git a/include/boost/asio/dispatch.hpp b/include/boost/asio/dispatch.hpp
index 77eefcae..bf278f13 100644
--- a/include/boost/asio/dispatch.hpp
+++ b/include/boost/asio/dispatch.hpp
@@ -19,6 +19,7 @@
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/execution_context.hpp>
+#include <boost/asio/execution/executor.hpp>
 #include <boost/asio/is_executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -91,7 +92,9 @@ BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) dispatch(
     const Executor& ex,
     BOOST_ASIO_MOVE_ARG(CompletionToken) token
       BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
-    typename enable_if<is_executor<Executor>::value>::type* = 0);
+    typename enable_if<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    >::type* = 0);
 
 /// Submits a completion token or function object for execution.
 /**
diff --git a/include/boost/asio/execution.hpp b/include/boost/asio/execution.hpp
new file mode 100644
index 00000000..1a2985c6
--- /dev/null
+++ b/include/boost/asio/execution.hpp
@@ -0,0 +1,35 @@
+//
+// execution.hpp
+// ~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_HPP
+#define BOOST_ASIO_EXECUTION_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/any_executor.hpp>
+#include <boost/asio/execution/bad_executor.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/blocking_adaptation.hpp>
+#include <boost/asio/execution/bulk_guarantee.hpp>
+#include <boost/asio/execution/context.hpp>
+#include <boost/asio/execution/context_as.hpp>
+#include <boost/asio/execution/execute.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/execution/invocable_archetype.hpp>
+#include <boost/asio/execution/mapping.hpp>
+#include <boost/asio/execution/occupancy.hpp>
+#include <boost/asio/execution/outstanding_work.hpp>
+#include <boost/asio/execution/prefer_only.hpp>
+#include <boost/asio/execution/relationship.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_HPP
diff --git a/include/boost/asio/execution/allocator.hpp b/include/boost/asio/execution/allocator.hpp
new file mode 100644
index 00000000..60ae1ad7
--- /dev/null
+++ b/include/boost/asio/execution/allocator.hpp
@@ -0,0 +1,243 @@
+//
+// execution/allocator.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_ALLOCATOR_HPP
+#define BOOST_ASIO_EXECUTION_ALLOCATOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe which allocator an executor will use to allocate the
+/// memory required to store a submitted function object.
+template <typename ProtoAllocator>
+struct allocator_t
+{
+  /// The allocator_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The allocator_t property can be required.
+  static constexpr bool is_requirable = true;
+
+  /// The allocator_t property can be preferred.
+  static constexpr bool is_preferable = true;
+
+  /// Default constructor.
+  constexpr allocator_t();
+
+  /// Obtain the allocator stored in the allocator_t property object.
+  /**
+   * Present only if @c ProtoAllocator is non-void.
+   */
+  constexpr ProtoAllocator value() const;
+
+  /// Create an allocator_t object with a different allocator.
+  /**
+   * Present only if @c ProtoAllocator is void.
+   */
+  template <typename OtherAllocator>
+  allocator_t<OtherAllocator operator()(const OtherAllocator& a);
+};
+
+/// A special value used for accessing the allocator_t property.
+constexpr allocator_t<void> allocator;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+template <typename ProtoAllocator>
+struct allocator_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, allocator_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, allocator_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, allocator_t>::value();
+  }
+
+  template <typename E, typename T = decltype(allocator_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = allocator_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_CONSTEXPR ProtoAllocator value() const
+  {
+    return a_;
+  }
+
+private:
+  friend struct allocator_t<void>;
+
+  explicit BOOST_ASIO_CONSTEXPR allocator_t(const ProtoAllocator& a)
+    : a_(a)
+  {
+  }
+
+  ProtoAllocator a_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename ProtoAllocator> template <typename E, typename T>
+const T allocator_t<ProtoAllocator>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <>
+struct allocator_t<void>
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+
+  BOOST_ASIO_CONSTEXPR allocator_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, allocator_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, allocator_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, allocator_t>::value();
+  }
+
+  template <typename E, typename T = decltype(allocator_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = allocator_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  template <typename OtherProtoAllocator>
+  BOOST_ASIO_CONSTEXPR allocator_t<OtherProtoAllocator> operator()(
+      const OtherProtoAllocator& a) const
+  {
+    return allocator_t<OtherProtoAllocator>(a);
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename E, typename T>
+const T allocator_t<void>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr allocator_t<void> allocator;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+template <typename T>
+struct allocator_instance
+{
+  static allocator_t<T> instance;
+};
+
+template <typename T>
+allocator_t<T> allocator_instance<T>::instance;
+
+namespace {
+static const allocator_t<void>& allocator = allocator_instance<void>::instance;
+} // namespace
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename ProtoAllocator>
+struct is_applicable_property<T, execution::allocator_t<ProtoAllocator> >
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T, typename ProtoAllocator>
+struct static_query<T, execution::allocator_t<ProtoAllocator>,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::allocator_t<ProtoAllocator> >::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::allocator_t<ProtoAllocator> >::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::allocator_t<ProtoAllocator> >::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_ALLOCATOR_HPP
diff --git a/include/boost/asio/execution/any_executor.hpp b/include/boost/asio/execution/any_executor.hpp
new file mode 100644
index 00000000..fd6efc73
--- /dev/null
+++ b/include/boost/asio/execution/any_executor.hpp
@@ -0,0 +1,1972 @@
+//
+// execution/any_executor.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_ANY_EXECUTOR_HPP
+#define BOOST_ASIO_EXECUTION_ANY_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <new>
+#include <typeinfo>
+#include <boost/asio/detail/assert.hpp>
+#include <boost/asio/detail/executor_function.hpp>
+#include <boost/asio/detail/memory.hpp>
+#include <boost/asio/detail/non_const_lvalue.hpp>
+#include <boost/asio/detail/scoped_ptr.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/detail/throw_exception.hpp>
+#include <boost/asio/detail/variadic_templates.hpp>
+#include <boost/asio/execution/bad_executor.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// Polymorphic executor wrapper.
+template <typename... SupportableProperties>
+class any_executor
+{
+public:
+  /// Default constructor.
+  any_executor() noexcept;
+
+  /// Copy constructor.
+  any_executor(const any_executor& e) noexcept;
+
+  /// Move constructor.
+  any_executor(any_executor&& e) noexcept;
+
+  /// Construct to point to the same target as another any_executor.
+  template <class... OtherSupportableProperties>
+    any_executor(any_executor<OtherSupportableProperties...> e);
+
+  /// Construct a polymorphic wrapper for the specified executor.
+  template <typename Executor>
+  any_executor(Executor e);
+
+  /// Assignment operator.
+  any_executor& operator=(const any_executor& e) noexcept;
+
+  /// Move assignment operator.
+  any_executor& operator=(any_executor&& e) noexcept;
+
+  /// Assignment operator to create a polymorphic wrapper for the specified
+  /// executor.
+  template <typename Executor>
+  any_executor& operator=(Executor e);
+
+  /// Destructor.
+  ~any_executor();
+
+  //void swap(any_executor& other) noexcept;
+
+  /// Obtain a polymorphic wrapper with the specified property.
+  /**
+   * Do not call this function directly. It is intended for use with the
+   * boost::asio::require and boost::asio::prefer customisation points.
+   *
+   * For example:
+   * @code execution::any_executor<execution::blocking_t::possibly_t> ex = ...;
+   * auto ex2 = boost::asio::requre(ex, execution::blocking.possibly); @endcode
+   */
+  template <typename Property>
+  any_executor require(Property) const;
+
+  /// Obtain a polymorphic wrapper with the specified property.
+  /**
+   * Do not call this function directly. It is intended for use with the
+   * boost::asio::prefer customisation point.
+   *
+   * For example:
+   * @code execution::any_executor<execution::blocking_t::possibly_t> ex = ...;
+   * auto ex2 = boost::asio::prefer(ex, execution::blocking.possibly); @endcode
+   */
+  template <typename Property>
+  any_executor prefer(Property) const;
+
+  /// Obtain the value associated with the specified property.
+  /**
+   * Do not call this function directly. It is intended for use with the
+   * boost::asio::query customisation point.
+   *
+   * For example:
+   * @code execution::any_executor<execution::occupancy_t> ex = ...;
+   * size_t n = boost::asio::query(ex, execution::occupancy); @endcode
+   */
+  template <typename Property>
+  typename Property::polymorphic_query_result_type query(Property) const;
+
+  /// Execute the function on the target executor.
+  /**
+   * Do not call this function directly. It is intended for use with the
+   * execution::execute customisation point.
+   *
+   * For example:
+   * @code execution::any_executor<> ex = ...;
+   * execution::execute(ex, my_function_object); @endcode
+   *
+   * Throws boost::asio::bad_executor if the polymorphic wrapper has no target.
+   */
+  template <typename Function>
+  void execute(Function&& f) const;
+
+  /// Obtain the underlying execution context.
+  /**
+   * This function is provided for backward compatibility. It is automatically
+   * defined when the @c SupportableProperties... list includes a property of
+   * type <tt>execution::context_as<U></tt>, for some type <tt>U</tt>.
+   */
+  automatically_determined context() const;
+
+  /// Determine whether the wrapper has a target executor.
+  /**
+   * @returns @c true if the polymorphic wrapper has a target executor,
+   * otherwise false.
+   */
+  explicit operator bool() const noexcept;
+
+  /// Get the type of the target executor.
+  const type_info& target_type() const noexcept;
+
+  /// Get a pointer to the target executor.
+  template <typename Executor> Executor* target() noexcept;
+
+  /// Get a pointer to the target executor.
+  template <typename Executor> const Executor* target() const noexcept;
+};
+
+/// Equality operator.
+/**
+ * @relates any_executor
+ */
+template <typename... SupportableProperties>
+bool operator==(const any_executor<SupportableProperties...>& a,
+    const any_executor<SupportableProperties...>& b) noexcept;
+
+/// Inequality operator.
+/**
+ * @relates any_executor
+ */
+template <typename... SupportableProperties>
+bool operator!=(const any_executor<SupportableProperties...>& a,
+    const any_executor<SupportableProperties...>& b) noexcept;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename... SupportableProperties>
+class any_executor;
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void>
+class any_executor;
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename U>
+struct context_as_t;
+
+namespace detail {
+
+// Traits used to detect whether a property is requirable or preferable, taking
+// into account that T::is_requirable or T::is_preferable may not not be well
+// formed.
+
+template <typename T, typename = void>
+struct is_requirable : false_type {};
+
+template <typename T>
+struct is_requirable<T, typename enable_if<T::is_requirable>::type> :
+  true_type {};
+
+template <typename T, typename = void>
+struct is_preferable : false_type {};
+
+template <typename T>
+struct is_preferable<T, typename enable_if<T::is_preferable>::type> :
+  true_type {};
+
+// Trait used to detect context_as property, for backward compatibility.
+
+template <typename T>
+struct is_context_as : false_type {};
+
+template <typename U>
+struct is_context_as<context_as_t<U> > : true_type {};
+
+// Helper template to:
+// - Check if a target can supply the supportable properties.
+// - Find the first convertible-from-T property in the list.
+
+template <std::size_t I, typename Props>
+struct supportable_properties;
+
+template <std::size_t I, typename Prop>
+struct supportable_properties<I, void(Prop)>
+{
+  template <typename T>
+  struct is_valid_target : integral_constant<bool,
+      (
+        is_requirable<Prop>::value
+          ? can_require<T, Prop>::value
+          : true
+      )
+      &&
+      (
+        is_preferable<Prop>::value
+          ? can_prefer<T, Prop>::value
+          : true
+      )
+      &&
+      (
+        !is_requirable<Prop>::value && !is_preferable<Prop>::value
+          ? can_query<T, Prop>::value
+          : true
+      )
+    >
+  {
+  };
+
+  struct found
+  {
+    BOOST_ASIO_STATIC_CONSTEXPR(bool, value = true);
+    typedef Prop type;
+    typedef typename Prop::polymorphic_query_result_type query_result_type;
+    BOOST_ASIO_STATIC_CONSTEXPR(std::size_t, index = I);
+  };
+
+  struct not_found
+  {
+    BOOST_ASIO_STATIC_CONSTEXPR(bool, value = false);
+  };
+
+  template <typename T>
+  struct find_convertible_property :
+      conditional<
+        is_same<T, Prop>::value || is_convertible<T, Prop>::value,
+        found,
+        not_found
+      >::type {};
+
+  template <typename T>
+  struct find_convertible_requirable_property :
+      conditional<
+        is_requirable<Prop>::value
+          && (is_same<T, Prop>::value || is_convertible<T, Prop>::value),
+        found,
+        not_found
+      >::type {};
+
+  template <typename T>
+  struct find_convertible_preferable_property :
+      conditional<
+        is_preferable<Prop>::value
+          && (is_same<T, Prop>::value || is_convertible<T, Prop>::value),
+        found,
+        not_found
+      >::type {};
+
+  struct find_context_as_property :
+      conditional<
+        is_context_as<Prop>::value,
+        found,
+        not_found
+      >::type {};
+};
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <std::size_t I, typename Head, typename... Tail>
+struct supportable_properties<I, void(Head, Tail...)>
+{
+  template <typename T>
+  struct is_valid_target : integral_constant<bool,
+      (
+        supportable_properties<I,
+          void(Head)>::template is_valid_target<T>::value
+        &&
+        supportable_properties<I + 1,
+          void(Tail...)>::template is_valid_target<T>::value
+      )
+    >
+  {
+  };
+
+  template <typename T>
+  struct find_convertible_property :
+      conditional<
+        is_convertible<T, Head>::value,
+        typename supportable_properties<I, void(Head)>::found,
+        typename supportable_properties<I + 1,
+            void(Tail...)>::template find_convertible_property<T>
+      >::type {};
+
+  template <typename T>
+  struct find_convertible_requirable_property :
+      conditional<
+        is_requirable<Head>::value
+          && is_convertible<T, Head>::value,
+        typename supportable_properties<I, void(Head)>::found,
+        typename supportable_properties<I + 1,
+            void(Tail...)>::template find_convertible_requirable_property<T>
+      >::type {};
+
+  template <typename T>
+  struct find_convertible_preferable_property :
+      conditional<
+        is_preferable<Head>::value
+          && is_convertible<T, Head>::value,
+        typename supportable_properties<I, void(Head)>::found,
+        typename supportable_properties<I + 1,
+            void(Tail...)>::template find_convertible_preferable_property<T>
+      >::type {};
+
+  struct find_context_as_property :
+      conditional<
+        is_context_as<Head>::value,
+        typename supportable_properties<I, void(Head)>::found,
+        typename supportable_properties<I + 1,
+            void(Tail...)>::find_context_as_property
+      >::type {};
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROPS_BASE_DEF(n) \
+  template <std::size_t I, \
+    typename Head, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  struct supportable_properties<I, \
+      void(Head, BOOST_ASIO_VARIADIC_TARGS(n))> \
+  { \
+    template <typename T> \
+    struct is_valid_target : integral_constant<bool, \
+        ( \
+          supportable_properties<I, \
+            void(Head)>::template is_valid_target<T>::value \
+          && \
+          supportable_properties<I + 1, \
+              void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+                is_valid_target<T>::value \
+        ) \
+      > \
+    { \
+    }; \
+  \
+    template <typename T> \
+    struct find_convertible_property : \
+        conditional< \
+          is_convertible<T, Head>::value, \
+          typename supportable_properties<I, void(Head)>::found, \
+          typename supportable_properties<I + 1, \
+              void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+                find_convertible_property<T> \
+        >::type {}; \
+  \
+    template <typename T> \
+    struct find_convertible_requirable_property : \
+        conditional< \
+          is_requirable<Head>::value \
+            && is_convertible<T, Head>::value, \
+          typename supportable_properties<I, void(Head)>::found, \
+          typename supportable_properties<I + 1, \
+              void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+                find_convertible_requirable_property<T> \
+        >::type {}; \
+  \
+    template <typename T> \
+    struct find_convertible_preferable_property : \
+        conditional< \
+          is_preferable<Head>::value \
+            && is_convertible<T, Head>::value, \
+          typename supportable_properties<I, void(Head)>::found, \
+          typename supportable_properties<I + 1, \
+              void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+                find_convertible_preferable_property<T> \
+        >::type {}; \
+  \
+    struct find_context_as_property : \
+        conditional< \
+          is_context_as<Head>::value, \
+          typename supportable_properties<I, void(Head)>::found, \
+          typename supportable_properties<I + 1, void( \
+            BOOST_ASIO_VARIADIC_TARGS(n))>::find_context_as_property \
+        >::type {}; \
+  }; \
+  /**/
+BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROPS_BASE_DEF)
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROPS_BASE_DEF
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+class any_executor_base
+{
+public:
+  any_executor_base() BOOST_ASIO_NOEXCEPT
+    : object_fns_(object_fns_table<void>()),
+      target_(0),
+      target_fns_(target_fns_table<void>()),
+      blocking_()
+  {
+  }
+
+  template <BOOST_ASIO_EXECUTION_EXECUTOR Executor>
+  any_executor_base(Executor ex, false_type)
+    : target_fns_(target_fns_table<Executor>()),
+      blocking_(
+          any_executor_base::query_blocking(
+            ex, can_query<const Executor&, const execution::blocking_t&>()))
+  {
+    any_executor_base::construct_object(ex,
+        integral_constant<bool,
+          sizeof(Executor) <= sizeof(object_type)
+            && alignment_of<Executor>::value <= alignment_of<object_type>::value
+        >());
+  }
+
+  template <BOOST_ASIO_EXECUTION_EXECUTOR Executor>
+  any_executor_base(Executor other, true_type)
+    : object_fns_(object_fns_table<boost::asio::detail::shared_ptr<void> >()),
+      target_fns_(other.target_fns_),
+      blocking_(other.blocking_)
+  {
+    boost::asio::detail::shared_ptr<Executor> p =
+      boost::asio::detail::make_shared<Executor>(
+          BOOST_ASIO_MOVE_CAST(Executor)(other));
+    target_ = p->template target<void>();
+    new (&object_) boost::asio::detail::shared_ptr<void>(
+        BOOST_ASIO_MOVE_CAST(boost::asio::detail::shared_ptr<Executor>)(p));
+  }
+
+  any_executor_base(const any_executor_base& other) BOOST_ASIO_NOEXCEPT
+    : object_fns_(other.object_fns_),
+      target_fns_(other.target_fns_),
+      blocking_(other.blocking_)
+  {
+    object_fns_->copy(*this, other);
+  }
+
+  ~any_executor_base()
+  {
+    object_fns_->destroy(*this);
+  }
+
+  any_executor_base& operator=(
+      const any_executor_base& other) BOOST_ASIO_NOEXCEPT
+  {
+    if (this != &other)
+    {
+      object_fns_->destroy(*this);
+      object_fns_ = other.object_fns_;
+      target_fns_ = other.target_fns_;
+      blocking_ = other.blocking_;
+      object_fns_->copy(*this, other);
+    }
+    return *this;
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+
+  any_executor_base(any_executor_base&& other) BOOST_ASIO_NOEXCEPT
+    : object_fns_(other.object_fns_),
+      target_fns_(other.target_fns_),
+      blocking_(other.blocking_)
+  {
+    other.object_fns_ = object_fns_table<void>();
+    other.target_fns_ = target_fns_table<void>();
+    other.blocking_ = execution::blocking_t();
+    object_fns_->move(*this, other);
+    other.target_ = 0;
+  }
+
+  any_executor_base& operator=(
+      any_executor_base&& other) BOOST_ASIO_NOEXCEPT
+  {
+    if (this != &other)
+    {
+      object_fns_->destroy(*this);
+      object_fns_ = other.object_fns_;
+      other.object_fns_ = object_fns_table<void>();
+      target_fns_ = other.target_fns_;
+      other.target_fns_ = target_fns_table<void>();
+      blocking_ = other.blocking_;
+      other.blocking_ = execution::blocking_t();
+      object_fns_->move(*this, other);
+      other.target_ = 0;
+    }
+    return *this;
+  }
+
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  template <typename F>
+  void execute(BOOST_ASIO_MOVE_ARG(F) f) const
+  {
+    if (blocking_ == execution::blocking.always)
+    {
+      boost::asio::detail::non_const_lvalue<F> f2(f);
+      target_fns_->blocking_execute(*this, function_view(f2.value));
+    }
+    else
+    {
+      target_fns_->execute(*this,
+          function(BOOST_ASIO_MOVE_CAST(F)(f), std::allocator<void>()));
+    }
+  }
+
+  template <typename Executor>
+  Executor* target()
+  {
+    return static_cast<Executor*>(target_);
+  }
+
+  template <typename Executor>
+  const Executor* target() const
+  {
+    return static_cast<Executor*>(target_);
+  }
+
+  const std::type_info& target_type() const
+  {
+    return target_fns_->target_type();
+  }
+
+  struct unspecified_bool_type_t {};
+  typedef void (*unspecified_bool_type)(unspecified_bool_type_t);
+  static void unspecified_bool_true(unspecified_bool_type_t) {}
+
+  operator unspecified_bool_type() const BOOST_ASIO_NOEXCEPT
+  {
+    return target_ ? &any_executor_base::unspecified_bool_true : 0;
+  }
+
+  bool operator!() const BOOST_ASIO_NOEXCEPT
+  {
+    return target_ == 0;
+  }
+
+protected:
+  bool equality_helper(const any_executor_base& other) const BOOST_ASIO_NOEXCEPT
+  {
+    if (target_ == other.target_)
+      return true;
+    if (target_ && !other.target_)
+      return false;
+    if (!target_ && other.target_)
+      return false;
+    if (target_fns_ != other.target_fns_)
+      return false;
+    return target_fns_->equal(*this, other);
+  }
+
+  template <typename Ex>
+  Ex& object()
+  {
+    return *static_cast<Ex*>(static_cast<void*>(&object_));
+  }
+
+  template <typename Ex>
+  const Ex& object() const
+  {
+    return *static_cast<const Ex*>(static_cast<const void*>(&object_));
+  }
+
+  struct object_fns
+  {
+    void (*destroy)(any_executor_base&);
+    void (*copy)(any_executor_base&, const any_executor_base&);
+    void (*move)(any_executor_base&, any_executor_base&);
+    const void* (*target)(const any_executor_base&);
+  };
+
+  static void destroy_void(any_executor_base&)
+  {
+  }
+
+  static void copy_void(any_executor_base&, const any_executor_base&)
+  {
+  }
+
+  static void move_void(any_executor_base&, any_executor_base&)
+  {
+  }
+
+  static const void* target_void(const any_executor_base&)
+  {
+    return 0;
+  }
+
+  template <typename Obj>
+  static const object_fns* object_fns_table(
+      typename enable_if<
+        is_same<Obj, void>::value
+      >::type* = 0)
+  {
+    static const object_fns fns =
+    {
+      &any_executor_base::destroy_void,
+      &any_executor_base::copy_void,
+      &any_executor_base::move_void,
+      &any_executor_base::target_void
+    };
+    return &fns;
+  }
+
+  static void destroy_shared(any_executor_base& ex)
+  {
+    typedef boost::asio::detail::shared_ptr<void> type;
+    ex.object<type>().~type();
+  }
+
+  static void copy_shared(any_executor_base& ex1, const any_executor_base& ex2)
+  {
+    typedef boost::asio::detail::shared_ptr<void> type;
+    new (&ex1.object_) type(ex2.object<type>());
+    ex1.target_ = ex2.target_;
+  }
+
+  static void move_shared(any_executor_base& ex1, any_executor_base& ex2)
+  {
+    typedef boost::asio::detail::shared_ptr<void> type;
+    new (&ex1.object_) type(BOOST_ASIO_MOVE_CAST(type)(ex2.object<type>()));
+    ex1.target_ = ex2.target_;
+    ex2.object<type>().~type();
+  }
+
+  static const void* target_shared(const any_executor_base& ex)
+  {
+    typedef boost::asio::detail::shared_ptr<void> type;
+    return ex.object<type>().get();
+  }
+
+  template <typename Obj>
+  static const object_fns* object_fns_table(
+      typename enable_if<
+        is_same<Obj, boost::asio::detail::shared_ptr<void> >::value
+      >::type* = 0)
+  {
+    static const object_fns fns =
+    {
+      &any_executor_base::destroy_shared,
+      &any_executor_base::copy_shared,
+      &any_executor_base::move_shared,
+      &any_executor_base::target_shared
+    };
+    return &fns;
+  }
+
+  template <typename Obj>
+  static void destroy_object(any_executor_base& ex)
+  {
+    ex.object<Obj>().~Obj();
+  }
+
+  template <typename Obj>
+  static void copy_object(any_executor_base& ex1, const any_executor_base& ex2)
+  {
+    new (&ex1.object_) Obj(ex2.object<Obj>());
+    ex1.target_ = &ex1.object<Obj>();
+  }
+
+  template <typename Obj>
+  static void move_object(any_executor_base& ex1, any_executor_base& ex2)
+  {
+    new (&ex1.object_) Obj(BOOST_ASIO_MOVE_CAST(Obj)(ex2.object<Obj>()));
+    ex1.target_ = &ex1.object<Obj>();
+    ex2.object<Obj>().~Obj();
+  }
+
+  template <typename Obj>
+  static const void* target_object(const any_executor_base& ex)
+  {
+    return &ex.object<Obj>();
+  }
+
+  template <typename Obj>
+  static const object_fns* object_fns_table(
+      typename enable_if<
+        !is_same<Obj, void>::value
+          && !is_same<Obj, boost::asio::detail::shared_ptr<void> >::value
+      >::type* = 0)
+  {
+    static const object_fns fns =
+    {
+      &any_executor_base::destroy_object<Obj>,
+      &any_executor_base::copy_object<Obj>,
+      &any_executor_base::move_object<Obj>,
+      &any_executor_base::target_object<Obj>
+    };
+    return &fns;
+  }
+
+  typedef boost::asio::detail::executor_function function;
+  typedef boost::asio::detail::executor_function_view function_view;
+
+  struct target_fns
+  {
+    const std::type_info& (*target_type)();
+    bool (*equal)(const any_executor_base&, const any_executor_base&);
+    void (*execute)(const any_executor_base&, BOOST_ASIO_MOVE_ARG(function));
+    void (*blocking_execute)(const any_executor_base&, function_view);
+  };
+
+  static const std::type_info& target_type_void()
+  {
+    return typeid(void);
+  }
+
+  static bool equal_void(const any_executor_base&, const any_executor_base&)
+  {
+    return true;
+  }
+
+  static void execute_void(const any_executor_base&,
+      BOOST_ASIO_MOVE_ARG(function))
+  {
+    bad_executor ex;
+    boost::asio::detail::throw_exception(ex);
+  }
+
+  static void blocking_execute_void(const any_executor_base&, function_view)
+  {
+    bad_executor ex;
+    boost::asio::detail::throw_exception(ex);
+  }
+
+  template <typename Ex>
+  static const target_fns* target_fns_table(
+      typename enable_if<
+        is_same<Ex, void>::value
+      >::type* = 0)
+  {
+    static const target_fns fns =
+    {
+      &any_executor_base::target_type_void,
+      &any_executor_base::equal_void,
+      &any_executor_base::execute_void,
+      &any_executor_base::blocking_execute_void
+    };
+    return &fns;
+  }
+
+  template <typename Ex>
+  static const std::type_info& target_type_ex()
+  {
+    return typeid(Ex);
+  }
+
+  template <typename Ex>
+  static bool equal_ex(const any_executor_base& ex1,
+      const any_executor_base& ex2)
+  {
+    return *ex1.target<Ex>() == *ex2.target<Ex>();
+  }
+
+  template <typename Ex>
+  static void execute_ex(const any_executor_base& ex,
+      BOOST_ASIO_MOVE_ARG(function) f)
+  {
+    ex.target<Ex>()->execute(BOOST_ASIO_MOVE_CAST(function)(f));
+  }
+
+  template <typename Ex>
+  static void blocking_execute_ex(const any_executor_base& ex, function_view f)
+  {
+    ex.target<Ex>()->execute(f);
+  }
+
+  template <typename Ex>
+  static const target_fns* target_fns_table(
+      typename enable_if<
+        !is_same<Ex, void>::value
+      >::type* = 0)
+  {
+    static const target_fns fns =
+    {
+      &any_executor_base::target_type_ex<Ex>,
+      &any_executor_base::equal_ex<Ex>,
+      &any_executor_base::execute_ex<Ex>,
+      &any_executor_base::blocking_execute_ex<Ex>
+    };
+    return &fns;
+  }
+
+#if defined(BOOST_ASIO_MSVC)
+# pragma warning (push)
+# pragma warning (disable:4702)
+#endif // defined(BOOST_ASIO_MSVC)
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void*, const void*, const void*,
+      typename enable_if<
+        is_same<Ex, void>::value
+      >::type*)
+  {
+    bad_executor ex;
+    boost::asio::detail::throw_exception(ex);
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void*, const void* ex, const void* prop,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && boost::asio::can_query<const Ex&, const Prop&>::value
+          && is_same<typename Prop::polymorphic_query_result_type, void>::value
+      >::type*)
+  {
+    boost::asio::query(*static_cast<const Ex*>(ex),
+        *static_cast<const Prop*>(prop));
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void*, const void*, const void*,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && !boost::asio::can_query<const Ex&, const Prop&>::value
+          && is_same<typename Prop::polymorphic_query_result_type, void>::value
+      >::type*)
+  {
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void* result, const void* ex, const void* prop,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && boost::asio::can_query<const Ex&, const Prop&>::value
+          && !is_same<typename Prop::polymorphic_query_result_type, void>::value
+          && is_reference<typename Prop::polymorphic_query_result_type>::value
+      >::type*)
+  {
+    *static_cast<typename remove_reference<
+      typename Prop::polymorphic_query_result_type>::type**>(result)
+        = &static_cast<typename Prop::polymorphic_query_result_type>(
+            boost::asio::query(*static_cast<const Ex*>(ex),
+              *static_cast<const Prop*>(prop)));
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void*, const void*, const void*,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && !boost::asio::can_query<const Ex&, const Prop&>::value
+          && !is_same<typename Prop::polymorphic_query_result_type, void>::value
+          && is_reference<typename Prop::polymorphic_query_result_type>::value
+      >::type*)
+  {
+    std::terminate(); // Combination should not be possible.
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void* result, const void* ex, const void* prop,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && boost::asio::can_query<const Ex&, const Prop&>::value
+          && !is_same<typename Prop::polymorphic_query_result_type, void>::value
+          && is_scalar<typename Prop::polymorphic_query_result_type>::value
+      >::type*)
+  {
+    *static_cast<typename Prop::polymorphic_query_result_type*>(result)
+      = static_cast<typename Prop::polymorphic_query_result_type>(
+          boost::asio::query(*static_cast<const Ex*>(ex),
+            *static_cast<const Prop*>(prop)));
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void* result, const void*, const void*,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && !boost::asio::can_query<const Ex&, const Prop&>::value
+          && !is_same<typename Prop::polymorphic_query_result_type, void>::value
+          && is_scalar<typename Prop::polymorphic_query_result_type>::value
+      >::type*)
+  {
+    *static_cast<typename Prop::polymorphic_query_result_type*>(result)
+      = typename Prop::polymorphic_query_result_type();
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void* result, const void* ex, const void* prop,
+      typename enable_if<
+        !is_same<Ex, void>::value
+          && boost::asio::can_query<const Ex&, const Prop&>::value
+          && !is_same<typename Prop::polymorphic_query_result_type, void>::value
+          && !is_reference<typename Prop::polymorphic_query_result_type>::value
+          && !is_scalar<typename Prop::polymorphic_query_result_type>::value
+      >::type*)
+  {
+    *static_cast<typename Prop::polymorphic_query_result_type**>(result)
+      = new typename Prop::polymorphic_query_result_type(
+          boost::asio::query(*static_cast<const Ex*>(ex),
+            *static_cast<const Prop*>(prop)));
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn_impl(void* result, const void*, const void*, ...)
+  {
+    *static_cast<typename Prop::polymorphic_query_result_type**>(result)
+      = new typename Prop::polymorphic_query_result_type();
+  }
+
+  template <typename Ex, class Prop>
+  static void query_fn(void* result, const void* ex, const void* prop)
+  {
+    query_fn_impl<Ex, Prop>(result, ex, prop, 0);
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly require_fn_impl(const void*, const void*,
+      typename enable_if<
+        is_same<Ex, void>::value
+      >::type*)
+  {
+    bad_executor ex;
+    boost::asio::detail::throw_exception(ex);
+    return Poly();
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly require_fn_impl(const void* ex, const void* prop,
+      typename enable_if<
+        !is_same<Ex, void>::value && Prop::is_requirable
+      >::type*)
+  {
+    return boost::asio::require(*static_cast<const Ex*>(ex),
+        *static_cast<const Prop*>(prop));
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly require_fn_impl(const void*, const void*, ...)
+  {
+    return Poly();
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly require_fn(const void* ex, const void* prop)
+  {
+    return require_fn_impl<Poly, Ex, Prop>(ex, prop, 0);
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly prefer_fn_impl(const void*, const void*,
+      typename enable_if<
+        is_same<Ex, void>::value
+      >::type*)
+  {
+    bad_executor ex;
+    boost::asio::detail::throw_exception(ex);
+    return Poly();
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly prefer_fn_impl(const void* ex, const void* prop,
+      typename enable_if<
+        !is_same<Ex, void>::value && Prop::is_preferable
+      >::type*)
+  {
+    return boost::asio::prefer(*static_cast<const Ex*>(ex),
+        *static_cast<const Prop*>(prop));
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly prefer_fn_impl(const void*, const void*, ...)
+  {
+    return Poly();
+  }
+
+  template <typename Poly, typename Ex, class Prop>
+  static Poly prefer_fn(const void* ex, const void* prop)
+  {
+    return prefer_fn_impl<Poly, Ex, Prop>(ex, prop, 0);
+  }
+
+  template <typename Poly>
+  struct prop_fns
+  {
+    void (*query)(void*, const void*, const void*);
+    Poly (*require)(const void*, const void*);
+    Poly (*prefer)(const void*, const void*);
+  };
+
+#if defined(BOOST_ASIO_MSVC)
+# pragma warning (pop)
+#endif // defined(BOOST_ASIO_MSVC)
+
+private:
+  template <typename Executor>
+  static execution::blocking_t query_blocking(const Executor& ex, true_type)
+  {
+    return boost::asio::query(ex, execution::blocking);
+  }
+
+  template <typename Executor>
+  static execution::blocking_t query_blocking(const Executor&, false_type)
+  {
+    return execution::blocking_t();
+  }
+
+  template <typename Executor>
+  void construct_object(Executor& ex, true_type)
+  {
+    object_fns_ = object_fns_table<Executor>();
+    target_ = new (&object_) Executor(BOOST_ASIO_MOVE_CAST(Executor)(ex));
+  }
+
+  template <typename Executor>
+  void construct_object(Executor& ex, false_type)
+  {
+    object_fns_ = object_fns_table<boost::asio::detail::shared_ptr<void> >();
+    boost::asio::detail::shared_ptr<Executor> p =
+      boost::asio::detail::make_shared<Executor>(
+          BOOST_ASIO_MOVE_CAST(Executor)(ex));
+    target_ = p.get();
+    new (&object_) boost::asio::detail::shared_ptr<void>(
+        BOOST_ASIO_MOVE_CAST(boost::asio::detail::shared_ptr<Executor>)(p));
+  }
+
+/*private:*/public:
+//  template <typename...> friend class any_executor;
+
+  typedef aligned_storage<
+      sizeof(boost::asio::detail::shared_ptr<void>),
+      alignment_of<boost::asio::detail::shared_ptr<void> >::value
+    >::type object_type;
+
+  object_type object_;
+  const object_fns* object_fns_;
+  void* target_;
+  const target_fns* target_fns_;
+  execution::blocking_t blocking_;
+};
+
+template <typename Derived, typename Property, typename = void>
+struct any_executor_context
+{
+};
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+template <typename Derived, typename Property>
+struct any_executor_context<Derived, Property,
+    typename enable_if<Property::value>::type>
+{
+  typename Property::query_result_type context() const
+  {
+    return static_cast<const Derived*>(this)->query(typename Property::type());
+  }
+};
+
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+} // namespace detail
+
+template <>
+class any_executor<> : public detail::any_executor_base
+{
+public:
+  any_executor() BOOST_ASIO_NOEXCEPT
+    : detail::any_executor_base()
+  {
+  }
+
+  template <typename Executor>
+  any_executor(Executor ex)
+    : detail::any_executor_base(
+        BOOST_ASIO_MOVE_CAST(Executor)(ex), false_type())
+  {
+    BOOST_ASIO_STATIC_ASSERT(is_executor<Executor>::value,
+        any_executor_target_must_be_an_executor,
+        "any_executor target must be an executor");
+  }
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename... OtherSupportableProperties>
+  any_executor(any_executor<OtherSupportableProperties...> other)
+    : detail::any_executor_base(
+        static_cast<const detail::any_executor_base&>(other))
+  {
+  }
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename U0, typename U1, typename U2, typename U3,
+      typename U4, typename U5, typename U6, typename U7>
+  any_executor(any_executor<U0, U1, U2, U3, U4, U5, U6, U7> other)
+    : detail::any_executor_base(
+        static_cast<const detail::any_executor_base&>(other))
+  {
+  }
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+  any_executor(const any_executor& other) BOOST_ASIO_NOEXCEPT
+    : detail::any_executor_base(
+        static_cast<const detail::any_executor_base&>(other))
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+
+  any_executor(any_executor&& other) BOOST_ASIO_NOEXCEPT
+    : detail::any_executor_base(
+        static_cast<any_executor_base&&>(
+          static_cast<any_executor_base&>(other)))
+  {
+  }
+
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  using detail::any_executor_base::operator=;
+  using detail::any_executor_base::execute;
+  using detail::any_executor_base::target;
+  using detail::any_executor_base::target_type;
+  using detail::any_executor_base::operator unspecified_bool_type;
+  using detail::any_executor_base::operator!;
+
+  bool equality_helper(const any_executor& other) const BOOST_ASIO_NOEXCEPT
+  {
+    return any_executor_base::equality_helper(other);
+  }
+};
+
+inline bool operator==(const any_executor<>& a,
+    const any_executor<>& b) BOOST_ASIO_NOEXCEPT
+{
+  return a.equality_helper(b);
+}
+
+inline bool operator!=(const any_executor<>& a,
+    const any_executor<>& b) BOOST_ASIO_NOEXCEPT
+{
+  return !a.equality_helper(b);
+}
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename... SupportableProperties>
+class any_executor :
+  public detail::any_executor_base,
+  public detail::any_executor_context<
+    any_executor<SupportableProperties...>,
+      typename detail::supportable_properties<
+        0, void(SupportableProperties...)>::find_context_as_property>
+{
+public:
+  any_executor() BOOST_ASIO_NOEXCEPT
+    : detail::any_executor_base(),
+      prop_fns_(prop_fns_table<void>())
+  {
+  }
+
+  template <typename Executor>
+  any_executor(Executor ex)
+    : detail::any_executor_base(
+        BOOST_ASIO_MOVE_CAST(Executor)(ex), false_type()),
+      prop_fns_(prop_fns_table<Executor>())
+  {
+    BOOST_ASIO_STATIC_ASSERT(is_executor<Executor>::value,
+        any_executor_target_must_be_an_executor,
+        "any_executor target must be an executor");
+
+    BOOST_ASIO_STATIC_ASSERT(
+        (detail::supportable_properties<
+          0, void(SupportableProperties...)>::template
+            is_valid_target<Executor>::value),
+        any_executor_target_must_support_listed_properties,
+        "any_executor target must support listed properties");
+  }
+
+  template <typename... OtherSupportableProperties>
+  any_executor(any_executor<OtherSupportableProperties...> other)
+    : detail::any_executor_base(BOOST_ASIO_MOVE_CAST(
+          any_executor<OtherSupportableProperties...>)(other), true_type()),
+      prop_fns_(prop_fns_table<any_executor<OtherSupportableProperties...> >())
+  {
+    BOOST_ASIO_STATIC_ASSERT(
+        (detail::supportable_properties<
+          0, void(SupportableProperties...)>::template is_valid_target<
+            any_executor<OtherSupportableProperties...> >::value),
+        any_executor_target_must_support_listed_properties,
+        "any_executor target must support listed properties");
+  }
+
+  any_executor(const any_executor& other) BOOST_ASIO_NOEXCEPT
+    : detail::any_executor_base(
+        static_cast<const detail::any_executor_base&>(other)),
+      prop_fns_(other.prop_fns_)
+  {
+  }
+
+  any_executor& operator=(const any_executor& other) BOOST_ASIO_NOEXCEPT
+  {
+    if (this != &other)
+    {
+      prop_fns_ = other.prop_fns_;
+      detail::any_executor_base::operator=(
+          static_cast<const detail::any_executor_base&>(other));
+    }
+    return *this;
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+
+  any_executor(any_executor&& other) BOOST_ASIO_NOEXCEPT
+    : detail::any_executor_base(
+        static_cast<any_executor_base&&>(
+          static_cast<any_executor_base&>(other))),
+      prop_fns_(other.prop_fns_)
+  {
+    other.prop_fns_ = prop_fns_table<void>();
+  }
+
+  any_executor& operator=(any_executor&& other) BOOST_ASIO_NOEXCEPT
+  {
+    if (this != &other)
+    {
+      prop_fns_ = other.prop_fns_;
+      detail::any_executor_base::operator=(
+          static_cast<detail::any_executor_base&&>(
+            static_cast<detail::any_executor_base&>(other)));
+    }
+    return *this;
+  }
+
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+  using detail::any_executor_base::execute;
+  using detail::any_executor_base::target;
+  using detail::any_executor_base::target_type;
+  using detail::any_executor_base::operator unspecified_bool_type;
+  using detail::any_executor_base::operator!;
+
+  bool equality_helper(const any_executor& other) const BOOST_ASIO_NOEXCEPT
+  {
+    return any_executor_base::equality_helper(other);
+  }
+
+  template <typename T>
+  struct find_convertible_property :
+      detail::supportable_properties<
+        0, void(SupportableProperties...)>::template
+          find_convertible_property<T> {};
+
+  template <typename Property>
+  void query(const Property& p,
+      typename enable_if<
+        is_same<
+          typename find_convertible_property<Property>::query_result_type,
+          void
+        >::value
+      >::type* = 0) const
+  {
+    typedef find_convertible_property<Property> found;
+    prop_fns_[found::index].query(0, object_fns_->target(*this),
+        &static_cast<const typename found::type&>(p));
+  }
+
+  template <typename Property>
+  typename find_convertible_property<Property>::query_result_type
+  query(const Property& p,
+      typename enable_if<
+        !is_same<
+          typename find_convertible_property<Property>::query_result_type,
+          void
+        >::value
+        &&
+        is_reference<
+          typename find_convertible_property<Property>::query_result_type
+        >::value
+      >::type* = 0) const
+  {
+    typedef find_convertible_property<Property> found;
+    typename remove_reference<
+      typename found::query_result_type>::type* result = 0;
+    prop_fns_[found::index].query(&result, object_fns_->target(*this),
+        &static_cast<const typename found::type&>(p));
+    return *result;
+  }
+
+  template <typename Property>
+  typename find_convertible_property<Property>::query_result_type
+  query(const Property& p,
+      typename enable_if<
+        !is_same<
+          typename find_convertible_property<Property>::query_result_type,
+          void
+        >::value
+        &&
+        is_scalar<
+          typename find_convertible_property<Property>::query_result_type
+        >::value
+      >::type* = 0) const
+  {
+    typedef find_convertible_property<Property> found;
+    typename found::query_result_type result;
+    prop_fns_[found::index].query(&result, object_fns_->target(*this),
+        &static_cast<const typename found::type&>(p));
+    return result;
+  }
+
+  template <typename Property>
+  typename find_convertible_property<Property>::query_result_type
+  query(const Property& p,
+      typename enable_if<
+        !is_same<
+          typename find_convertible_property<Property>::query_result_type,
+          void
+        >::value
+        &&
+        !is_reference<
+          typename find_convertible_property<Property>::query_result_type
+        >::value
+        &&
+        !is_scalar<
+          typename find_convertible_property<Property>::query_result_type
+        >::value
+      >::type* = 0) const
+  {
+    typedef find_convertible_property<Property> found;
+    typename found::query_result_type* result;
+    prop_fns_[found::index].query(&result, object_fns_->target(*this),
+        &static_cast<const typename found::type&>(p));
+    return *boost::asio::detail::scoped_ptr<
+      typename found::query_result_type>(result);
+  }
+
+  template <typename T>
+  struct find_convertible_requirable_property :
+      detail::supportable_properties<
+        0, void(SupportableProperties...)>::template
+          find_convertible_requirable_property<T> {};
+
+  template <typename Property>
+  any_executor require(const Property& p,
+      typename enable_if<
+        find_convertible_requirable_property<Property>::value
+      >::type* = 0) const
+  {
+    typedef find_convertible_requirable_property<Property> found;
+    return prop_fns_[found::index].require(object_fns_->target(*this),
+        &static_cast<const typename found::type&>(p));
+  }
+
+  template <typename T>
+  struct find_convertible_preferable_property :
+      detail::supportable_properties<
+        0, void(SupportableProperties...)>::template
+          find_convertible_preferable_property<T> {};
+
+  template <typename Property>
+  any_executor prefer(const Property& p,
+      typename enable_if<
+        find_convertible_preferable_property<Property>::value
+      >::type* = 0) const
+  {
+    typedef find_convertible_preferable_property<Property> found;
+    return prop_fns_[found::index].prefer(object_fns_->target(*this),
+        &static_cast<const typename found::type&>(p));
+  }
+
+//private:
+  template <typename Ex>
+  static const prop_fns<any_executor>* prop_fns_table()
+  {
+    static const prop_fns<any_executor> fns[] =
+    {
+      {
+        &detail::any_executor_base::query_fn<
+            Ex, SupportableProperties>,
+        &detail::any_executor_base::require_fn<
+            any_executor, Ex, SupportableProperties>,
+        &detail::any_executor_base::prefer_fn<
+            any_executor, Ex, SupportableProperties>
+      }...
+    };
+    return fns;
+  }
+
+  const prop_fns<any_executor>* prop_fns_;
+};
+
+template <typename... SupportableProperties>
+inline bool operator==(const any_executor<SupportableProperties...>& a,
+    const any_executor<SupportableProperties...>& b) BOOST_ASIO_NOEXCEPT
+{
+  return a.equality_helper(b);
+}
+
+template <typename... SupportableProperties>
+inline bool operator!=(const any_executor<SupportableProperties...>& a,
+    const any_executor<SupportableProperties...>& b) BOOST_ASIO_NOEXCEPT
+{
+  return !a.equality_helper(b);
+}
+
+template <typename... SupportableProperties>
+struct is_executor<any_executor<SupportableProperties...> > : true_type
+{
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS(n) \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_##n
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_1 \
+  {  \
+    &detail::any_executor_base::query_fn<Ex, T1>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T1>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T1> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_2 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_1, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T2>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T2>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T2> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_3 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_2, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T3>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T3>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T3> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_4 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_3, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T4>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T4>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T4> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_5 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_4, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T5>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T5>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T5> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_6 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_5, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T6>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T6>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T6> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_7 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_6, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T7>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T7>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T7> \
+  }
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_8 \
+  BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_7, \
+  { \
+    &detail::any_executor_base::query_fn<Ex, T8>, \
+    &detail::any_executor_base::require_fn<any_executor, Ex, T8>, \
+    &detail::any_executor_base::prefer_fn<any_executor, Ex, T8> \
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+
+# define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_MOVE_OPS \
+  any_executor(any_executor&& other) BOOST_ASIO_NOEXCEPT \
+    : detail::any_executor_base( \
+        static_cast<any_executor_base&&>( \
+          static_cast<any_executor_base&>(other))), \
+      prop_fns_(other.prop_fns_) \
+  { \
+    other.prop_fns_ = prop_fns_table<void>(); \
+  } \
+  \
+  any_executor& operator=(any_executor&& other) BOOST_ASIO_NOEXCEPT \
+  { \
+    if (this != &other) \
+    { \
+      prop_fns_ = other.prop_fns_; \
+      detail::any_executor_base::operator=( \
+          static_cast<detail::any_executor_base&&>( \
+            static_cast<detail::any_executor_base&>(other))); \
+    } \
+    return *this; \
+  } \
+  /**/
+#else // defined(BOOST_ASIO_HAS_MOVE)
+
+# define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_MOVE_OPS
+
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_DEF(n) \
+  template <BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  class any_executor<BOOST_ASIO_VARIADIC_TARGS(n)> : \
+    public detail::any_executor_base, \
+    public detail::any_executor_context< \
+      any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>, \
+        typename detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::find_context_as_property> \
+  { \
+  public: \
+    any_executor() BOOST_ASIO_NOEXCEPT \
+      : detail::any_executor_base(), \
+        prop_fns_(prop_fns_table<void>()) \
+    { \
+    } \
+    \
+    template <BOOST_ASIO_EXECUTION_EXECUTOR Executor> \
+    any_executor(Executor ex, \
+        typename enable_if< \
+          !is_base_of< \
+            detail::any_executor_base, \
+            Executor \
+          >::value \
+        >::type* = 0) \
+      : detail::any_executor_base(BOOST_ASIO_MOVE_CAST( \
+            Executor)(ex), false_type()), \
+        prop_fns_(prop_fns_table<Executor>()) \
+    { \
+      BOOST_ASIO_STATIC_ASSERT(is_executor<Executor>::value, \
+          any_executor_target_must_be_an_executor, \
+          "any_executor target must be an executor"); \
+    \
+      BOOST_ASIO_STATIC_ASSERT( \
+          (detail::supportable_properties< \
+            0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+              is_valid_target<Executor>::value), \
+          any_executor_target_must_support_listed_properties, \
+          "any_executor target must support listed properties"); \
+    } \
+    \
+    any_executor(const any_executor& other) BOOST_ASIO_NOEXCEPT \
+      : detail::any_executor_base( \
+          static_cast<const detail::any_executor_base&>(other)), \
+        prop_fns_(other.prop_fns_) \
+    { \
+    } \
+    \
+    any_executor(any_executor<> other) \
+      : detail::any_executor_base(BOOST_ASIO_MOVE_CAST( \
+            any_executor<>)(other), true_type()), \
+        prop_fns_(prop_fns_table<any_executor<> >()) \
+    { \
+    } \
+    \
+    template <typename OtherAnyExecutor> \
+    any_executor(OtherAnyExecutor other, \
+        typename enable_if< \
+          is_base_of< \
+            detail::any_executor_base, \
+            OtherAnyExecutor \
+          >::value \
+        >::type* = 0) \
+      : detail::any_executor_base(BOOST_ASIO_MOVE_CAST( \
+            OtherAnyExecutor)(other), true_type()), \
+        prop_fns_(prop_fns_table<OtherAnyExecutor>()) \
+    { \
+      BOOST_ASIO_STATIC_ASSERT( \
+          OtherAnyExecutor::supportable_properties_type::template \
+            is_valid_target<any_executor<OtherAnyExecutor> >::value, \
+          any_executor_target_must_support_listed_properties, \
+          "any_executor target must support listed properties"); \
+    } \
+    \
+    any_executor& operator=(const any_executor& other) BOOST_ASIO_NOEXCEPT \
+    { \
+      if (this != &other) \
+      { \
+        prop_fns_ = other.prop_fns_; \
+        detail::any_executor_base::operator=( \
+            static_cast<const detail::any_executor_base&>(other)); \
+      } \
+      return *this; \
+    } \
+    \
+    BOOST_ASIO_PRIVATE_ANY_EXECUTOR_MOVE_OPS \
+    \
+    using detail::any_executor_base::execute; \
+    using detail::any_executor_base::target; \
+    using detail::any_executor_base::target_type; \
+    using detail::any_executor_base::operator unspecified_bool_type; \
+    using detail::any_executor_base::operator!; \
+    \
+    bool equality_helper(const any_executor& other) const BOOST_ASIO_NOEXCEPT \
+    { \
+      return any_executor_base::equality_helper(other); \
+    } \
+    \
+    template <typename T> \
+    struct find_convertible_property : \
+        detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+            find_convertible_property<T> {}; \
+    \
+    template <typename Property> \
+    void query(const Property& p, \
+        typename enable_if< \
+          is_same< \
+            typename find_convertible_property<Property>::query_result_type, \
+            void \
+          >::value \
+        >::type* = 0) const \
+    { \
+      typedef find_convertible_property<Property> found; \
+      prop_fns_[found::index].query(0, object_fns_->target(*this), \
+          &static_cast<const typename found::type&>(p)); \
+    } \
+    \
+    template <typename Property> \
+    typename find_convertible_property<Property>::query_result_type \
+    query(const Property& p, \
+        typename enable_if< \
+          !is_same< \
+            typename find_convertible_property<Property>::query_result_type, \
+            void \
+          >::value \
+          && \
+          is_reference< \
+            typename find_convertible_property<Property>::query_result_type \
+          >::value \
+        >::type* = 0) const \
+    { \
+      typedef find_convertible_property<Property> found; \
+      typename remove_reference< \
+        typename found::query_result_type>::type* result; \
+      prop_fns_[found::index].query(&result, object_fns_->target(*this), \
+          &static_cast<const typename found::type&>(p)); \
+      return *result; \
+    } \
+    \
+    template <typename Property> \
+    typename find_convertible_property<Property>::query_result_type \
+    query(const Property& p, \
+        typename enable_if< \
+          !is_same< \
+            typename find_convertible_property<Property>::query_result_type, \
+            void \
+          >::value \
+          && \
+          is_scalar< \
+            typename find_convertible_property<Property>::query_result_type \
+          >::value \
+        >::type* = 0) const \
+    { \
+      typedef find_convertible_property<Property> found; \
+      typename found::query_result_type result; \
+      prop_fns_[found::index].query(&result, object_fns_->target(*this), \
+          &static_cast<const typename found::type&>(p)); \
+      return result; \
+    } \
+    \
+    template <typename Property> \
+    typename find_convertible_property<Property>::query_result_type \
+    query(const Property& p, \
+        typename enable_if< \
+          !is_same< \
+            typename find_convertible_property<Property>::query_result_type, \
+            void \
+          >::value \
+          && \
+          !is_reference< \
+            typename find_convertible_property<Property>::query_result_type \
+          >::value \
+          && \
+          !is_scalar< \
+            typename find_convertible_property<Property>::query_result_type \
+          >::value \
+        >::type* = 0) const \
+    { \
+      typedef find_convertible_property<Property> found; \
+      typename found::query_result_type* result; \
+      prop_fns_[found::index].query(&result, object_fns_->target(*this), \
+          &static_cast<const typename found::type&>(p)); \
+      return *boost::asio::detail::scoped_ptr< \
+        typename found::query_result_type>(result); \
+    } \
+    \
+    template <typename T> \
+    struct find_convertible_requirable_property : \
+        detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+            find_convertible_requirable_property<T> {}; \
+    \
+    template <typename Property> \
+    any_executor require(const Property& p, \
+        typename enable_if< \
+          find_convertible_requirable_property<Property>::value \
+        >::type* = 0) const \
+    { \
+      typedef find_convertible_requirable_property<Property> found; \
+      return prop_fns_[found::index].require(object_fns_->target(*this), \
+          &static_cast<const typename found::type&>(p)); \
+    } \
+    \
+    template <typename T> \
+    struct find_convertible_preferable_property : \
+        detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+            find_convertible_preferable_property<T> {}; \
+    \
+    template <typename Property> \
+    any_executor prefer(const Property& p, \
+        typename enable_if< \
+          find_convertible_preferable_property<Property>::value \
+        >::type* = 0) const \
+    { \
+      typedef find_convertible_preferable_property<Property> found; \
+      return prop_fns_[found::index].prefer(object_fns_->target(*this), \
+          &static_cast<const typename found::type&>(p)); \
+    } \
+    \
+    template <typename Ex> \
+    static const prop_fns<any_executor>* prop_fns_table() \
+    { \
+      static const prop_fns<any_executor> fns[] = \
+      { \
+        BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS(n) \
+      }; \
+      return fns; \
+    } \
+    \
+    const prop_fns<any_executor>* prop_fns_; \
+    typedef detail::supportable_properties<0, \
+        void(BOOST_ASIO_VARIADIC_TARGS(n))> supportable_properties_type; \
+  }; \
+  \
+  template <BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  inline bool operator==(const any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>& a, \
+      const any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>& b) BOOST_ASIO_NOEXCEPT \
+  { \
+    return a.equality_helper(b); \
+  } \
+  \
+  template <BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  inline bool operator!=(const any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>& a, \
+      const any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>& b) BOOST_ASIO_NOEXCEPT \
+  { \
+    return !a.equality_helper(b); \
+  } \
+  \
+  template <BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  struct is_executor<any_executor<BOOST_ASIO_VARIADIC_TARGS(n)> > : true_type \
+  { \
+  }; \
+  /**/
+  BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_ANY_EXECUTOR_DEF)
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_DEF
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_MOVE_OPS
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_1
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_2
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_3
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_4
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_5
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_6
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_7
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PROP_FNS_8
+
+#endif // if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+} // namespace execution
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename F, typename... SupportableProperties>
+struct execute_member<execution::any_executor<SupportableProperties...>, F>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = false;
+  typedef void result_type;
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename F>
+struct execute_member<execution::any_executor<>, F>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = false;
+  typedef void result_type;
+};
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_EXECUTE_MEMBER_DEF(n) \
+  template <typename F, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  struct execute_member< \
+      execution::any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>, F> \
+  { \
+    static const bool is_valid = true; \
+    static const bool is_noexcept = false; \
+    typedef void result_type; \
+  }; \
+  /**/
+  BOOST_ASIO_VARIADIC_GENERATE(
+      BOOST_ASIO_PRIVATE_ANY_EXECUTOR_EXECUTE_MEMBER_DEF)
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_EXECUTE_MEMBER_DEF
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename Prop, typename... SupportableProperties>
+struct query_member<
+    execution::any_executor<SupportableProperties...>, Prop,
+    typename enable_if<
+      execution::detail::supportable_properties<
+        0, void(SupportableProperties...)>::template
+          find_convertible_property<Prop>::value
+    >::type>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = false;
+  typedef typename execution::detail::supportable_properties<
+      0, void(SupportableProperties...)>::template
+        find_convertible_property<Prop>::query_result_type result_type;
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_QUERY_MEMBER_DEF(n) \
+  template <typename Prop, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  struct query_member< \
+      execution::any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>, Prop, \
+      typename enable_if< \
+        execution::detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+            find_convertible_property<Prop>::value \
+    >::type> \
+  { \
+    static const bool is_valid = true; \
+    static const bool is_noexcept = false; \
+    typedef typename execution::detail::supportable_properties< \
+        0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+          find_convertible_property<Prop>::query_result_type result_type; \
+  }; \
+  /**/
+  BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_ANY_EXECUTOR_QUERY_MEMBER_DEF)
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_QUERY_MEMBER_DEF
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename Prop, typename... SupportableProperties>
+struct require_member<
+    execution::any_executor<SupportableProperties...>, Prop,
+    typename enable_if<
+      execution::detail::supportable_properties<
+        0, void(SupportableProperties...)>::template
+          find_convertible_requirable_property<Prop>::value
+    >::type>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = false;
+  typedef execution::any_executor<SupportableProperties...> result_type;
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_REQUIRE_MEMBER_DEF(n) \
+  template <typename Prop, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  struct require_member< \
+      execution::any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>, Prop, \
+      typename enable_if< \
+        execution::detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+            find_convertible_requirable_property<Prop>::value \
+      >::type> \
+  { \
+    static const bool is_valid = true; \
+    static const bool is_noexcept = false; \
+    typedef execution::any_executor<BOOST_ASIO_VARIADIC_TARGS(n)> result_type; \
+  }; \
+  /**/
+  BOOST_ASIO_VARIADIC_GENERATE(
+      BOOST_ASIO_PRIVATE_ANY_EXECUTOR_REQUIRE_MEMBER_DEF)
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_REQUIRE_MEMBER_DEF
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename Prop, typename... SupportableProperties>
+struct prefer_member<
+    execution::any_executor<SupportableProperties...>, Prop,
+    typename enable_if<
+      execution::detail::supportable_properties<
+        0, void(SupportableProperties...)>::template
+          find_convertible_preferable_property<Prop>::value
+    >::type>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = false;
+  typedef execution::any_executor<SupportableProperties...> result_type;
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#define BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PREFER_FREE_DEF(n) \
+  template <typename Prop, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  struct prefer_member< \
+      execution::any_executor<BOOST_ASIO_VARIADIC_TARGS(n)>, Prop, \
+      typename enable_if< \
+        execution::detail::supportable_properties< \
+          0, void(BOOST_ASIO_VARIADIC_TARGS(n))>::template \
+            find_convertible_preferable_property<Prop>::value \
+      >::type> \
+  { \
+    static const bool is_valid = true; \
+    static const bool is_noexcept = false; \
+    typedef execution::any_executor<BOOST_ASIO_VARIADIC_TARGS(n)> result_type; \
+  }; \
+  /**/
+  BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PREFER_FREE_DEF)
+#undef BOOST_ASIO_PRIVATE_ANY_EXECUTOR_PREFER_FREE_DEF
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_ANY_EXECUTOR_HPP
diff --git a/include/boost/asio/execution/bad_executor.hpp b/include/boost/asio/execution/bad_executor.hpp
new file mode 100644
index 00000000..c73d8763
--- /dev/null
+++ b/include/boost/asio/execution/bad_executor.hpp
@@ -0,0 +1,49 @@
+//
+// execution/bad_executor.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_BAD_EXECUTOR_HPP
+#define BOOST_ASIO_EXECUTION_BAD_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <exception>
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+/// Exception thrown when trying to access an empty polymorphic executor.
+class bad_executor
+  : public std::exception
+{
+public:
+  /// Constructor.
+  BOOST_ASIO_DECL bad_executor() BOOST_ASIO_NOEXCEPT;
+
+  /// Obtain message associated with exception.
+  BOOST_ASIO_DECL virtual const char* what() const
+    BOOST_ASIO_NOEXCEPT_OR_NOTHROW;
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#if defined(BOOST_ASIO_HEADER_ONLY)
+# include <boost/asio/execution/impl/bad_executor.ipp>
+#endif // defined(BOOST_ASIO_HEADER_ONLY)
+
+#endif // BOOST_ASIO_EXECUTION_BAD_EXECUTOR_HPP
diff --git a/include/boost/asio/execution/blocking.hpp b/include/boost/asio/execution/blocking.hpp
new file mode 100644
index 00000000..2b59e1b4
--- /dev/null
+++ b/include/boost/asio/execution/blocking.hpp
@@ -0,0 +1,962 @@
+//
+// execution/blocking.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_BLOCKING_HPP
+#define BOOST_ASIO_EXECUTION_BLOCKING_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe what guarantees an executor makes about the blocking
+/// behaviour of their execution functions.
+struct blocking_t
+{
+  /// The blocking_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The top-level blocking_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level blocking_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef blocking_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that invocation of an executor's execution
+  /// function may block pending completion of one or more invocations of the
+  /// submitted function object.
+  struct possibly_t
+  {
+    /// The blocking_t::possibly_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The blocking_t::possibly_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The blocking_t::possibly_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef blocking_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr possibly_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns possibly_t();
+     */
+    static constexpr blocking_t value();
+  };
+
+  /// A sub-property that indicates that invocation of an executor's execution
+  /// function shall block until completion of all invocations of the submitted
+  /// function object.
+  struct always_t
+  {
+    /// The blocking_t::always_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The blocking_t::always_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The blocking_t::always_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef blocking_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr always_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns always_t();
+     */
+    static constexpr blocking_t value();
+  };
+
+  /// A sub-property that indicates that invocation of an executor's execution
+  /// function shall not block pending completion of the invocations of the
+  /// submitted function object.
+  struct never_t
+  {
+    /// The blocking_t::never_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The blocking_t::never_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The blocking_t::never_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef blocking_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr never_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns never_t();
+     */
+    static constexpr blocking_t value();
+  };
+
+  /// A special value used for accessing the blocking_t::possibly_t property.
+  static constexpr possibly_t possibly;
+
+  /// A special value used for accessing the blocking_t::always_t property.
+  static constexpr always_t always;
+
+  /// A special value used for accessing the blocking_t::never_t property.
+  static constexpr never_t never;
+
+  /// Default constructor.
+  constexpr blocking_t();
+
+  /// Construct from a sub-property value.
+  constexpr blocking_t(possibly_t);
+
+  /// Construct from a sub-property value.
+  constexpr blocking_t(always_t);
+
+  /// Construct from a sub-property value.
+  constexpr blocking_t(never_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const blocking_t& a, const blocking_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const blocking_t& a, const blocking_t& b) noexcept;
+};
+
+/// A special value used for accessing the blocking_t property.
+constexpr blocking_t blocking;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace blocking {
+
+template <int I> struct possibly_t;
+template <int I> struct always_t;
+template <int I> struct never_t;
+
+} // namespace blocking
+
+template <int I = 0>
+struct blocking_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef blocking_t polymorphic_query_result_type;
+
+  typedef detail::blocking::possibly_t<I> possibly_t;
+  typedef detail::blocking::always_t<I> always_t;
+  typedef detail::blocking::never_t<I> never_t;
+
+  BOOST_ASIO_CONSTEXPR blocking_t()
+    : value_(-1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR blocking_t(possibly_t)
+    : value_(0)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR blocking_t(always_t)
+    : value_(1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR blocking_t(never_t)
+    : value_(2)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, blocking_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, blocking_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, blocking_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, possibly_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, blocking_t>::is_valid
+          && !traits::query_member<T, blocking_t>::is_valid
+          && traits::static_query<T, possibly_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, possibly_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, always_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, blocking_t>::is_valid
+          && !traits::query_member<T, blocking_t>::is_valid
+          && !traits::static_query<T, possibly_t>::is_valid
+          && traits::static_query<T, always_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, always_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, never_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, blocking_t>::is_valid
+          && !traits::query_member<T, blocking_t>::is_valid
+          && !traits::static_query<T, possibly_t>::is_valid
+          && !traits::static_query<T, always_t>::is_valid
+          && traits::static_query<T, never_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, never_t>::value();
+  }
+
+  template <typename E, typename T = decltype(blocking_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = blocking_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const blocking_t& a, const blocking_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const blocking_t& a, const blocking_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_blocking_t
+  {
+    BOOST_ASIO_CONSTEXPR convertible_from_blocking_t(blocking_t) {}
+  };
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR blocking_t query(
+      const Executor& ex, convertible_from_blocking_t,
+      typename enable_if<
+        can_query<const Executor&, possibly_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, blocking_t<>::possibly_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, possibly_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, possibly_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR blocking_t query(
+      const Executor& ex, convertible_from_blocking_t,
+      typename enable_if<
+        !can_query<const Executor&, possibly_t>::value
+          && can_query<const Executor&, always_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, blocking_t<>::always_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, always_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, always_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR blocking_t query(
+      const Executor& ex, convertible_from_blocking_t,
+      typename enable_if<
+        !can_query<const Executor&, possibly_t>::value
+          && !can_query<const Executor&, always_t>::value
+          && can_query<const Executor&, never_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, blocking_t<>::never_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, never_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, never_t());
+  }
+
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(possibly_t, possibly);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(always_t, always);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(never_t, never);
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const blocking_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T blocking_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const blocking_t<I> blocking_t<I>::instance;
+#endif
+
+template <int I>
+const typename blocking_t<I>::possibly_t blocking_t<I>::possibly;
+
+template <int I>
+const typename blocking_t<I>::always_t blocking_t<I>::always;
+
+template <int I>
+const typename blocking_t<I>::never_t blocking_t<I>::never;
+
+namespace blocking {
+
+template <int I = 0>
+struct possibly_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef blocking_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR possibly_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, possibly_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, possibly_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, possibly_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR possibly_t static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, possibly_t>::is_valid
+          && !traits::query_member<T, possibly_t>::is_valid
+          && !traits::query_free<T, possibly_t>::is_valid
+          && !can_query<T, always_t<I> >::value
+          && !can_query<T, never_t<I> >::value
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return possibly_t();
+  }
+
+  template <typename E, typename T = decltype(possibly_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = possibly_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR blocking_t<I> value()
+  {
+    return possibly_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const possibly_t&, const possibly_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const possibly_t&, const possibly_t&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const possibly_t&, const always_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const possibly_t&, const always_t<I>&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const possibly_t&, const never_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const possibly_t&, const never_t<I>&)
+  {
+    return true;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T possibly_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct always_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef blocking_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR always_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, always_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, always_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, always_t>::value();
+  }
+
+  template <typename E, typename T = decltype(always_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = always_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR blocking_t<I> value()
+  {
+    return always_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const always_t&, const always_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const always_t&, const always_t&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const always_t&, const possibly_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const always_t&, const possibly_t<I>&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const always_t&, const never_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const always_t&, const never_t<I>&)
+  {
+    return true;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T always_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I>
+struct never_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef blocking_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR never_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, never_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, never_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, never_t>::value();
+  }
+
+  template <typename E, typename T = decltype(never_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = never_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR blocking_t<I> value()
+  {
+    return never_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const never_t&, const never_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const never_t&, const never_t&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const never_t&, const possibly_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const never_t&, const possibly_t<I>&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const never_t&, const always_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const never_t&, const always_t<I>&)
+  {
+    return true;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T never_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace blocking
+} // namespace detail
+
+typedef detail::blocking_t<> blocking_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr blocking_t blocking;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const blocking_t& blocking = blocking_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_t::possibly_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_t::always_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_t::never_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::blocking_t,
+  typename enable_if<
+    can_query<T, execution::blocking_t::possibly_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::blocking_t::possibly_t>::value));
+
+  typedef execution::blocking_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::blocking_t,
+  typename enable_if<
+    !can_query<T, execution::blocking_t::possibly_t>::value
+      && can_query<T, execution::blocking_t::always_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::blocking_t::always_t>::value));
+
+  typedef execution::blocking_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::blocking_t,
+  typename enable_if<
+    !can_query<T, execution::blocking_t::possibly_t>::value
+      && !can_query<T, execution::blocking_t::always_t>::value
+      && can_query<T, execution::blocking_t::never_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::blocking_t::never_t>::value));
+
+  typedef execution::blocking_t result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::blocking_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T, execution::blocking_t>::is_valid
+      && !traits::query_member<T, execution::blocking_t>::is_valid
+      && traits::static_query<T, execution::blocking_t::possibly_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::blocking_t::possibly_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T, execution::blocking_t::possibly_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T, execution::blocking_t>::is_valid
+      && !traits::query_member<T, execution::blocking_t>::is_valid
+      && !traits::static_query<T, execution::blocking_t::possibly_t>::is_valid
+      && traits::static_query<T, execution::blocking_t::always_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::blocking_t::always_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T, execution::blocking_t::always_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T, execution::blocking_t>::is_valid
+      && !traits::query_member<T, execution::blocking_t>::is_valid
+      && !traits::static_query<T, execution::blocking_t::possibly_t>::is_valid
+      && !traits::static_query<T, execution::blocking_t::always_t>::is_valid
+      && traits::static_query<T, execution::blocking_t::never_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::blocking_t::never_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T, execution::blocking_t::never_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t::possibly_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_t::possibly_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_t::possibly_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_t::possibly_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t::possibly_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+      execution::blocking_t::possibly_t>::is_valid
+      && !traits::query_member<T, execution::blocking_t::possibly_t>::is_valid
+      && !traits::query_free<T, execution::blocking_t::possibly_t>::is_valid
+      && !can_query<T, execution::blocking_t::always_t>::value
+      && !can_query<T, execution::blocking_t::never_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::blocking_t::possibly_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t::always_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_t::always_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_t::always_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_t::always_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_t::never_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_t::never_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_t::never_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_t::never_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::blocking_t::possibly_t,
+  typename enable_if<
+    static_query<T, execution::blocking_t::possibly_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::blocking_t::possibly_t>::result_type,
+        execution::blocking_t::possibly_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::blocking_t::always_t,
+  typename enable_if<
+    static_query<T, execution::blocking_t::always_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::blocking_t::always_t>::result_type,
+        execution::blocking_t::always_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::blocking_t::never_t,
+  typename enable_if<
+    static_query<T, execution::blocking_t::never_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::blocking_t::never_t>::result_type,
+        execution::blocking_t::never_t>::value));
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_BLOCKING_HPP
diff --git a/include/boost/asio/execution/blocking_adaptation.hpp b/include/boost/asio/execution/blocking_adaptation.hpp
new file mode 100644
index 00000000..56f197c9
--- /dev/null
+++ b/include/boost/asio/execution/blocking_adaptation.hpp
@@ -0,0 +1,699 @@
+//
+// execution/blocking_adaptation.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_BLOCKING_ADAPTATION_HPP
+#define BOOST_ASIO_EXECUTION_BLOCKING_ADAPTATION_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe whether automatic adaptation of an executor is
+/// allowed in order to apply the blocking_adaptation_t::allowed_t property.
+struct blocking_adaptation_t
+{
+  /// The blocking_adaptation_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The top-level blocking_adaptation_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level blocking_adaptation_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef blocking_adaptation_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that automatic adaptation is not allowed.
+  struct disallowed_t
+  {
+    /// The blocking_adaptation_t::disallowed_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The blocking_adaptation_t::disallowed_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The blocking_adaptation_t::disallowed_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef blocking_adaptation_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr disallowed_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns disallowed_t();
+     */
+    static constexpr blocking_adaptation_t value();
+  };
+
+  /// A sub-property that indicates that automatic adaptation is allowed.
+  struct allowed_t
+  {
+    /// The blocking_adaptation_t::allowed_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The blocking_adaptation_t::allowed_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The blocking_adaptation_t::allowed_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef blocking_adaptation_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr allowed_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns allowed_t();
+     */
+    static constexpr blocking_adaptation_t value();
+  };
+
+  /// A special value used for accessing the blocking_adaptation_t::disallowed_t
+  /// property.
+  static constexpr disallowed_t disallowed;
+
+  /// A special value used for accessing the blocking_adaptation_t::allowed_t
+  /// property.
+  static constexpr allowed_t allowed;
+
+  /// Default constructor.
+  constexpr blocking_adaptation_t();
+
+  /// Construct from a sub-property value.
+  constexpr blocking_adaptation_t(disallowed_t);
+
+  /// Construct from a sub-property value.
+  constexpr blocking_adaptation_t(allowed_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const blocking_adaptation_t& a, const blocking_adaptation_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const blocking_adaptation_t& a, const blocking_adaptation_t& b) noexcept;
+};
+
+/// A special value used for accessing the blocking_adaptation_t property.
+constexpr blocking_adaptation_t blocking_adaptation;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace blocking_adaptation {
+
+template <int I> struct disallowed_t;
+template <int I> struct allowed_t;
+
+} // namespace blocking_adaptation
+
+template <int I = 0>
+struct blocking_adaptation_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef blocking_adaptation_t polymorphic_query_result_type;
+
+  typedef detail::blocking_adaptation::disallowed_t<I> disallowed_t;
+  typedef detail::blocking_adaptation::allowed_t<I> allowed_t;
+
+  BOOST_ASIO_CONSTEXPR blocking_adaptation_t()
+    : value_(-1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR blocking_adaptation_t(disallowed_t)
+    : value_(0)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR blocking_adaptation_t(allowed_t)
+    : value_(1)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<
+      T, blocking_adaptation_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<
+        T, blocking_adaptation_t
+      >::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<
+        T, blocking_adaptation_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, disallowed_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<
+            T, blocking_adaptation_t>::is_valid
+          && !traits::query_member<T, blocking_adaptation_t>::is_valid
+          && traits::static_query<T, disallowed_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, disallowed_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, allowed_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<
+            T, blocking_adaptation_t>::is_valid
+          && !traits::query_member<T, blocking_adaptation_t>::is_valid
+          && !traits::static_query<T, disallowed_t>::is_valid
+          && traits::static_query<T, allowed_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, allowed_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(blocking_adaptation_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = blocking_adaptation_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const blocking_adaptation_t& a, const blocking_adaptation_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const blocking_adaptation_t& a, const blocking_adaptation_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_blocking_adaptation_t
+  {
+    BOOST_ASIO_CONSTEXPR convertible_from_blocking_adaptation_t(
+        blocking_adaptation_t)
+    {
+    }
+  };
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR blocking_adaptation_t query(
+      const Executor& ex, convertible_from_blocking_adaptation_t,
+      typename enable_if<
+        can_query<const Executor&, disallowed_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        blocking_adaptation_t<>::disallowed_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, disallowed_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, disallowed_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR blocking_adaptation_t query(
+      const Executor& ex, convertible_from_blocking_adaptation_t,
+      typename enable_if<
+        !can_query<const Executor&, disallowed_t>::value
+          && can_query<const Executor&, allowed_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        blocking_adaptation_t<>::allowed_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, allowed_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, allowed_t());
+  }
+
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(disallowed_t, disallowed);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(allowed_t, allowed);
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const blocking_adaptation_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T blocking_adaptation_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const blocking_adaptation_t<I> blocking_adaptation_t<I>::instance;
+#endif
+
+template <int I>
+const typename blocking_adaptation_t<I>::disallowed_t
+blocking_adaptation_t<I>::disallowed;
+
+template <int I>
+const typename blocking_adaptation_t<I>::allowed_t
+blocking_adaptation_t<I>::allowed;
+
+namespace blocking_adaptation {
+
+template <int I = 0>
+struct disallowed_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef blocking_adaptation_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR disallowed_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, disallowed_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, disallowed_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, disallowed_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR disallowed_t static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, disallowed_t>::is_valid
+          && !traits::query_member<T, disallowed_t>::is_valid
+          && !traits::query_free<T, disallowed_t>::is_valid
+          && !can_query<T, allowed_t<I> >::value
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return disallowed_t();
+  }
+
+  template <typename E, typename T = decltype(disallowed_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = disallowed_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR blocking_adaptation_t<I> value()
+  {
+    return disallowed_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const disallowed_t&, const disallowed_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const disallowed_t&, const disallowed_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T disallowed_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct allowed_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef blocking_adaptation_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR allowed_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, allowed_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, allowed_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, allowed_t>::value();
+  }
+
+  template <typename E, typename T = decltype(allowed_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = allowed_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR blocking_adaptation_t<I> value()
+  {
+    return allowed_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const allowed_t&, const allowed_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const allowed_t&, const allowed_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T allowed_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace blocking_adaptation
+} // namespace detail
+
+typedef detail::blocking_adaptation_t<> blocking_adaptation_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr blocking_adaptation_t blocking_adaptation;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const blocking_adaptation_t&
+  blocking_adaptation = blocking_adaptation_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_adaptation_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_adaptation_t::disallowed_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::blocking_adaptation_t::allowed_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::blocking_adaptation_t,
+  typename enable_if<
+    can_query<T, execution::blocking_adaptation_t::disallowed_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = (is_nothrow_query<T,
+      execution::blocking_adaptation_t::disallowed_t>::value));
+
+  typedef execution::blocking_adaptation_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::blocking_adaptation_t,
+  typename enable_if<
+    !can_query<T, execution::blocking_adaptation_t::disallowed_t>::value
+      && can_query<T, execution::blocking_adaptation_t::allowed_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::blocking_adaptation_t::allowed_t>::value));
+
+  typedef execution::blocking_adaptation_t result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::blocking_adaptation_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_adaptation_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_adaptation_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_adaptation_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_adaptation_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::blocking_adaptation_t>::is_valid
+      && !traits::query_member<T,
+        execution::blocking_adaptation_t>::is_valid
+      && traits::static_query<T,
+        execution::blocking_adaptation_t::disallowed_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::blocking_adaptation_t::disallowed_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::blocking_adaptation_t::disallowed_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_adaptation_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::blocking_adaptation_t>::is_valid
+      && !traits::query_member<T,
+        execution::blocking_adaptation_t>::is_valid
+      && !traits::static_query<T,
+        execution::blocking_adaptation_t::disallowed_t>::is_valid
+      && traits::static_query<T,
+        execution::blocking_adaptation_t::allowed_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::blocking_adaptation_t::allowed_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::blocking_adaptation_t::allowed_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_adaptation_t::disallowed_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_adaptation_t::disallowed_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_adaptation_t::disallowed_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_adaptation_t::disallowed_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_adaptation_t::disallowed_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::blocking_adaptation_t::disallowed_t>::is_valid
+      && !traits::query_member<T,
+        execution::blocking_adaptation_t::disallowed_t>::is_valid
+      && !traits::query_free<T,
+        execution::blocking_adaptation_t::disallowed_t>::is_valid
+      && !can_query<T, execution::blocking_adaptation_t::allowed_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::blocking_adaptation_t::disallowed_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::blocking_adaptation_t::allowed_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::blocking_adaptation_t::allowed_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::blocking_adaptation_t::allowed_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::blocking_adaptation_t::allowed_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::blocking_adaptation_t::disallowed_t,
+  typename enable_if<
+    static_query<T, execution::blocking_adaptation_t::disallowed_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::blocking_adaptation_t::disallowed_t>::result_type,
+        execution::blocking_adaptation_t::disallowed_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::blocking_adaptation_t::allowed_t,
+  typename enable_if<
+    static_query<T, execution::blocking_adaptation_t::allowed_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::blocking_adaptation_t::allowed_t>::result_type,
+        execution::blocking_adaptation_t::allowed_t>::value));
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_BLOCKING_ADAPTATION_HPP
diff --git a/include/boost/asio/execution/bulk_guarantee.hpp b/include/boost/asio/execution/bulk_guarantee.hpp
new file mode 100644
index 00000000..ced2fe2e
--- /dev/null
+++ b/include/boost/asio/execution/bulk_guarantee.hpp
@@ -0,0 +1,988 @@
+//
+// execution/bulk_guarantee.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_BULK_GUARANTEE_HPP
+#define BOOST_ASIO_EXECUTION_BULK_GUARANTEE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to communicate the forward progress and ordering guarantees of
+/// execution agents associated with the bulk execution.
+struct bulk_guarantee_t
+{
+  /// The bulk_guarantee_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The top-level bulk_guarantee_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level bulk_guarantee_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef bulk_guarantee_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that execution agents within the same bulk
+  /// execution may be parallelised and vectorised.
+  struct unsequenced_t
+  {
+    /// The bulk_guarantee_t::unsequenced_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The bulk_guarantee_t::unsequenced_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The bulk_guarantee_t::unsequenced_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef bulk_guarantee_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr unsequenced_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns unsequenced_t();
+     */
+    static constexpr bulk_guarantee_t value();
+  };
+
+  /// A sub-property that indicates that execution agents within the same bulk
+  /// execution may not be parallelised and vectorised.
+  struct sequenced_t
+  {
+    /// The bulk_guarantee_t::sequenced_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The bulk_guarantee_t::sequenced_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The bulk_guarantee_t::sequenced_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef bulk_guarantee_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr sequenced_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns sequenced_t();
+     */
+    static constexpr bulk_guarantee_t value();
+  };
+
+  /// A sub-property that indicates that execution agents within the same bulk
+  /// execution may be parallelised.
+  struct parallel_t
+  {
+    /// The bulk_guarantee_t::parallel_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The bulk_guarantee_t::parallel_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The bulk_guarantee_t::parallel_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef bulk_guarantee_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr parallel_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns parallel_t();
+     */
+    static constexpr bulk_guarantee_t value();
+  };
+
+  /// A special value used for accessing the bulk_guarantee_t::unsequenced_t
+  /// property.
+  static constexpr unsequenced_t unsequenced;
+
+  /// A special value used for accessing the bulk_guarantee_t::sequenced_t
+  /// property.
+  static constexpr sequenced_t sequenced;
+
+  /// A special value used for accessing the bulk_guarantee_t::parallel_t
+  /// property.
+  static constexpr parallel_t parallel;
+
+  /// Default constructor.
+  constexpr bulk_guarantee_t();
+
+  /// Construct from a sub-property value.
+  constexpr bulk_guarantee_t(unsequenced_t);
+
+  /// Construct from a sub-property value.
+  constexpr bulk_guarantee_t(sequenced_t);
+
+  /// Construct from a sub-property value.
+  constexpr bulk_guarantee_t(parallel_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const bulk_guarantee_t& a, const bulk_guarantee_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const bulk_guarantee_t& a, const bulk_guarantee_t& b) noexcept;
+};
+
+/// A special value used for accessing the bulk_guarantee_t property.
+constexpr bulk_guarantee_t bulk_guarantee;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace bulk_guarantee {
+
+template <int I> struct unsequenced_t;
+template <int I> struct sequenced_t;
+template <int I> struct parallel_t;
+
+} // namespace bulk_guarantee
+
+template <int I = 0>
+struct bulk_guarantee_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef bulk_guarantee_t polymorphic_query_result_type;
+
+  typedef detail::bulk_guarantee::unsequenced_t<I> unsequenced_t;
+  typedef detail::bulk_guarantee::sequenced_t<I> sequenced_t;
+  typedef detail::bulk_guarantee::parallel_t<I> parallel_t;
+
+  BOOST_ASIO_CONSTEXPR bulk_guarantee_t()
+    : value_(-1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR bulk_guarantee_t(unsequenced_t)
+    : value_(0)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR bulk_guarantee_t(sequenced_t)
+    : value_(1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR bulk_guarantee_t(parallel_t)
+    : value_(2)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<
+      T, bulk_guarantee_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, bulk_guarantee_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, bulk_guarantee_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, unsequenced_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, bulk_guarantee_t>::is_valid
+          && !traits::query_member<T, bulk_guarantee_t>::is_valid
+          && traits::static_query<T, unsequenced_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, unsequenced_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, sequenced_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, bulk_guarantee_t>::is_valid
+          && !traits::query_member<T, bulk_guarantee_t>::is_valid
+          && !traits::static_query<T, unsequenced_t>::is_valid
+          && traits::static_query<T, sequenced_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, sequenced_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, parallel_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, bulk_guarantee_t>::is_valid
+          && !traits::query_member<T, bulk_guarantee_t>::is_valid
+          && !traits::static_query<T, unsequenced_t>::is_valid
+          && !traits::static_query<T, sequenced_t>::is_valid
+          && traits::static_query<T, parallel_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, parallel_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(bulk_guarantee_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = bulk_guarantee_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const bulk_guarantee_t& a, const bulk_guarantee_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const bulk_guarantee_t& a, const bulk_guarantee_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_bulk_guarantee_t
+  {
+    BOOST_ASIO_CONSTEXPR convertible_from_bulk_guarantee_t(bulk_guarantee_t) {}
+  };
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR bulk_guarantee_t query(
+      const Executor& ex, convertible_from_bulk_guarantee_t,
+      typename enable_if<
+        can_query<const Executor&, unsequenced_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        bulk_guarantee_t<>::unsequenced_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, unsequenced_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, unsequenced_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR bulk_guarantee_t query(
+      const Executor& ex, convertible_from_bulk_guarantee_t,
+      typename enable_if<
+        !can_query<const Executor&, unsequenced_t>::value
+          && can_query<const Executor&, sequenced_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        bulk_guarantee_t<>::sequenced_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, sequenced_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, sequenced_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR bulk_guarantee_t query(
+      const Executor& ex, convertible_from_bulk_guarantee_t,
+      typename enable_if<
+        !can_query<const Executor&, unsequenced_t>::value
+          && !can_query<const Executor&, sequenced_t>::value
+          && can_query<const Executor&, parallel_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, bulk_guarantee_t<>::parallel_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, parallel_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, parallel_t());
+  }
+
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(unsequenced_t, unsequenced);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(sequenced_t, sequenced);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(parallel_t, parallel);
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const bulk_guarantee_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T bulk_guarantee_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const bulk_guarantee_t<I> bulk_guarantee_t<I>::instance;
+#endif
+
+template <int I>
+const typename bulk_guarantee_t<I>::unsequenced_t
+bulk_guarantee_t<I>::unsequenced;
+
+template <int I>
+const typename bulk_guarantee_t<I>::sequenced_t
+bulk_guarantee_t<I>::sequenced;
+
+template <int I>
+const typename bulk_guarantee_t<I>::parallel_t
+bulk_guarantee_t<I>::parallel;
+
+namespace bulk_guarantee {
+
+template <int I = 0>
+struct unsequenced_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef bulk_guarantee_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR unsequenced_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, unsequenced_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, unsequenced_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, unsequenced_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR unsequenced_t static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, unsequenced_t>::is_valid
+          && !traits::query_member<T, unsequenced_t>::is_valid
+          && !traits::query_free<T, unsequenced_t>::is_valid
+          && !can_query<T, sequenced_t<I> >::value
+          && !can_query<T, parallel_t<I> >::value
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return unsequenced_t();
+  }
+
+  template <typename E, typename T = decltype(unsequenced_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = unsequenced_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR bulk_guarantee_t<I> value()
+  {
+    return unsequenced_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const unsequenced_t&, const unsequenced_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const unsequenced_t&, const unsequenced_t&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const unsequenced_t&, const sequenced_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const unsequenced_t&, const sequenced_t<I>&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const unsequenced_t&, const parallel_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const unsequenced_t&, const parallel_t<I>&)
+  {
+    return true;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T unsequenced_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct sequenced_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef bulk_guarantee_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR sequenced_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, sequenced_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, sequenced_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, sequenced_t>::value();
+  }
+
+  template <typename E, typename T = decltype(sequenced_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = sequenced_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR bulk_guarantee_t<I> value()
+  {
+    return sequenced_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const sequenced_t&, const sequenced_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const sequenced_t&, const sequenced_t&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const sequenced_t&, const unsequenced_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const sequenced_t&, const unsequenced_t<I>&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const sequenced_t&, const parallel_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const sequenced_t&, const parallel_t<I>&)
+  {
+    return true;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T sequenced_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I>
+struct parallel_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef bulk_guarantee_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR parallel_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, parallel_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, parallel_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, parallel_t>::value();
+  }
+
+  template <typename E, typename T = decltype(parallel_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = parallel_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR bulk_guarantee_t<I> value()
+  {
+    return parallel_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const parallel_t&, const parallel_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const parallel_t&, const parallel_t&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const parallel_t&, const unsequenced_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const parallel_t&, const unsequenced_t<I>&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const parallel_t&, const sequenced_t<I>&)
+  {
+    return false;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const parallel_t&, const sequenced_t<I>&)
+  {
+    return true;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T parallel_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace bulk_guarantee
+} // namespace detail
+
+typedef detail::bulk_guarantee_t<> bulk_guarantee_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr bulk_guarantee_t bulk_guarantee;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const bulk_guarantee_t&
+  bulk_guarantee = bulk_guarantee_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::bulk_guarantee_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::bulk_guarantee_t::unsequenced_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::bulk_guarantee_t::sequenced_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::bulk_guarantee_t::parallel_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    can_query<T, execution::bulk_guarantee_t::unsequenced_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::bulk_guarantee_t::unsequenced_t>::value));
+
+  typedef execution::bulk_guarantee_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    !can_query<T, execution::bulk_guarantee_t::unsequenced_t>::value
+      && can_query<T, execution::bulk_guarantee_t::sequenced_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::bulk_guarantee_t::sequenced_t>::value));
+
+  typedef execution::bulk_guarantee_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    !can_query<T, execution::bulk_guarantee_t::unsequenced_t>::value
+      && !can_query<T, execution::bulk_guarantee_t::sequenced_t>::value
+      && can_query<T, execution::bulk_guarantee_t::parallel_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::bulk_guarantee_t::parallel_t>::value));
+
+  typedef execution::bulk_guarantee_t result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::bulk_guarantee_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::bulk_guarantee_t>::is_valid
+      && !traits::query_member<T,
+        execution::bulk_guarantee_t>::is_valid
+      && traits::static_query<T,
+        execution::bulk_guarantee_t::unsequenced_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::bulk_guarantee_t::unsequenced_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::bulk_guarantee_t::unsequenced_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::bulk_guarantee_t>::is_valid
+      && !traits::query_member<T,
+        execution::bulk_guarantee_t>::is_valid
+      && !traits::static_query<T,
+        execution::bulk_guarantee_t::unsequenced_t>::is_valid
+      && traits::static_query<T,
+        execution::bulk_guarantee_t::sequenced_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::bulk_guarantee_t::sequenced_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::bulk_guarantee_t::sequenced_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::bulk_guarantee_t>::is_valid
+      && !traits::query_member<T,
+        execution::bulk_guarantee_t>::is_valid
+      && !traits::static_query<T,
+        execution::bulk_guarantee_t::unsequenced_t>::is_valid
+      && !traits::static_query<T,
+        execution::bulk_guarantee_t::sequenced_t>::is_valid
+      && traits::static_query<T,
+        execution::bulk_guarantee_t::parallel_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::bulk_guarantee_t::parallel_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::bulk_guarantee_t::parallel_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t::unsequenced_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::unsequenced_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::bulk_guarantee_t::unsequenced_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::unsequenced_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t::unsequenced_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::unsequenced_t>::is_valid
+      && !traits::query_member<T,
+        execution::bulk_guarantee_t::unsequenced_t>::is_valid
+      && !traits::query_free<T,
+        execution::bulk_guarantee_t::unsequenced_t>::is_valid
+      && !can_query<T, execution::bulk_guarantee_t::sequenced_t>::value
+      && !can_query<T, execution::bulk_guarantee_t::parallel_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::bulk_guarantee_t::unsequenced_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t::sequenced_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::sequenced_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::bulk_guarantee_t::sequenced_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::sequenced_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::bulk_guarantee_t::parallel_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::parallel_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::bulk_guarantee_t::parallel_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::bulk_guarantee_t::parallel_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::bulk_guarantee_t::unsequenced_t,
+  typename enable_if<
+    static_query<T, execution::bulk_guarantee_t::unsequenced_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::bulk_guarantee_t::unsequenced_t>::result_type,
+        execution::bulk_guarantee_t::unsequenced_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::bulk_guarantee_t::sequenced_t,
+  typename enable_if<
+    static_query<T, execution::bulk_guarantee_t::sequenced_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::bulk_guarantee_t::sequenced_t>::result_type,
+        execution::bulk_guarantee_t::sequenced_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::bulk_guarantee_t::parallel_t,
+  typename enable_if<
+    static_query<T, execution::bulk_guarantee_t::parallel_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::bulk_guarantee_t::parallel_t>::result_type,
+        execution::bulk_guarantee_t::parallel_t>::value));
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_BULK_GUARANTEE_HPP
diff --git a/include/boost/asio/execution/context.hpp b/include/boost/asio/execution/context.hpp
new file mode 100644
index 00000000..35e8da8a
--- /dev/null
+++ b/include/boost/asio/execution/context.hpp
@@ -0,0 +1,169 @@
+//
+// execution/context.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_CONTEXT2_HPP
+#define BOOST_ASIO_EXECUTION_CONTEXT2_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that is used to obtain the execution context that is associated
+/// with an executor.
+struct context_t
+{
+  /// The context_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The context_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The context_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+};
+
+/// A special value used for accessing the context_t property.
+constexpr context_t context;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+
+template <int I = 0>
+struct context_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+
+  BOOST_ASIO_CONSTEXPR context_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, context_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, context_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, context_t>::value();
+  }
+
+  template <typename E, typename T = decltype(context_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = context_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const context_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T context_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const context_t<I> context_t<I>::instance;
+#endif
+
+} // namespace detail
+
+typedef detail::context_t<> context_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr context_t context;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const context_t& context = context_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::context_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::context_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::context_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::context_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::context_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_CONTEXT2_HPP
diff --git a/include/boost/asio/execution/context_as.hpp b/include/boost/asio/execution/context_as.hpp
new file mode 100644
index 00000000..99fd10de
--- /dev/null
+++ b/include/boost/asio/execution/context_as.hpp
@@ -0,0 +1,194 @@
+//
+// execution/context_as.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_CONTEXT_AS_HPP
+#define BOOST_ASIO_EXECUTION_CONTEXT_AS_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/context.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that is used to obtain the execution context that is associated
+/// with an executor.
+template <typename U>
+struct context_as_t
+{
+  /// The context_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The context_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The context_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef T polymorphic_query_result_type;
+};
+
+/// A special value used for accessing the context_as_t property.
+template <typename U>
+constexpr context_as_t context_as;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+template <typename T>
+struct context_as_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename U>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<U>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+
+  typedef T polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR context_as_t()
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR context_as_t(context_t)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename E>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<E, context_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<E, context_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<E, context_t>::value();
+  }
+
+  template <typename E, typename U = decltype(context_as_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const U static_query_v
+    = context_as_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  template <typename Executor, typename U>
+  friend BOOST_ASIO_CONSTEXPR U query(
+      const Executor& ex, const context_as_t<U>&,
+      typename enable_if<
+        is_same<T, U>::value
+          && can_query<const Executor&, const context_t&>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, const context_t&>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, const context_t&>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, context);
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename T> template <typename E, typename U>
+const U context_as_t<T>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if (defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES) \
+    && defined(BOOST_ASIO_HAS_CONSTEXPR)) \
+  || defined(GENERATING_DOCUMENTATION)
+template <typename T>
+constexpr context_as_t<T> context_as{};
+#endif // (defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+       //     && defined(BOOST_ASIO_HAS_CONSTEXPR))
+       //   || defined(GENERATING_DOCUMENTATION)
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename U>
+struct is_applicable_property<T, execution::context_as_t<U> >
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T, typename U>
+struct static_query<T, execution::context_as_t<U>,
+  typename enable_if<
+    static_query<T, execution::context_t>::is_valid
+  >::type> : static_query<T, execution::context_t>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T, typename U>
+struct query_free<T, execution::context_as_t<U>,
+    typename enable_if<
+      can_query<const T&, const execution::context_t&>::value
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<const T&, const execution::context_t&>::value));
+
+  typedef U result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_CONTEXT_AS_HPP
diff --git a/include/boost/asio/execution/execute.hpp b/include/boost/asio/execution/execute.hpp
new file mode 100644
index 00000000..04b5c074
--- /dev/null
+++ b/include/boost/asio/execution/execute.hpp
@@ -0,0 +1,196 @@
+//
+// execution/execute.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_EXECUTE_HPP
+#define BOOST_ASIO_EXECUTION_EXECUTE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/traits/execute_member.hpp>
+#include <boost/asio/traits/execute_free.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+/// A customisation point that executes a function on an executor.
+/**
+ * The name <tt>execution::execute</tt> denotes a customization point object.
+ *
+ * For some subexpressions <tt>e</tt> and <tt>f</tt>, let <tt>E</tt> be a type
+ * such that <tt>decltype((e))</tt> is <tt>E</tt> and let <tt>F</tt> be a type
+ * such that <tt>decltype((f))</tt> is <tt>F</tt>. The expression
+ * <tt>execution::execute(e, f)</tt> is ill-formed if <tt>F</tt> does not model
+ * <tt>invocable</tt>, or if <tt>E</tt> does not model either <tt>executor</tt>
+ * or <tt>sender</tt>. Otherwise, it is expression-equivalent to:
+ *
+ * @li <tt>e.execute(f)</tt>, if that expression is valid. If the function
+ *   selected does not execute the function object <tt>f</tt> on the executor
+ *   <tt>e</tt>, the program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>execute(e, f)</tt>, if that expression is valid, with
+ *   overload resolution performed in a context that includes the declaration
+ *   <tt>void execute();</tt> and that does not include a declaration of
+ *   <tt>execution::execute</tt>. If the function selected by overload
+ *   resolution does not execute the function object <tt>f</tt> on the executor
+ *   <tt>e</tt>, the program is ill-formed with no diagnostic required.
+ */
+inline constexpr unspecified execute = unspecified;
+
+/// A type trait that determines whether a @c execute expression is well-formed.
+/**
+ * Class template @c can_execute is a trait that is derived from
+ * @c true_type if the expression <tt>execution::execute(std::declval<T>(),
+ * std::declval<F>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename T, typename F>
+struct can_execute :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_execute_fn {
+
+using boost::asio::decay;
+using boost::asio::declval;
+using boost::asio::enable_if;
+using boost::asio::traits::execute_free;
+using boost::asio::traits::execute_member;
+
+void execute();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename T, typename F, typename = void>
+struct call_traits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+};
+
+template <typename T, typename F>
+struct call_traits<T, void(F),
+  typename enable_if<
+    (
+      execute_member<T, F>::is_valid
+    )
+  >::type> :
+  execute_member<T, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename T, typename F>
+struct call_traits<T, void(F),
+  typename enable_if<
+    (
+      !execute_member<T, F>::is_valid
+      &&
+      execute_free<T, F>::is_valid
+    )
+  >::type> :
+  execute_free<T, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+  template <typename T, typename F>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(F)>::overload == call_member,
+    typename call_traits<T, void(F)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(F) f) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(F)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t).execute(BOOST_ASIO_MOVE_CAST(F)(f));
+  }
+
+  template <typename T, typename F>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(F)>::overload == call_free,
+    typename call_traits<T, void(F)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(F) f) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(F)>::is_noexcept))
+  {
+    return execute(BOOST_ASIO_MOVE_CAST(T)(t), BOOST_ASIO_MOVE_CAST(F)(f));
+  }
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_execute_fn
+namespace boost {
+namespace asio {
+namespace execution {
+namespace {
+
+static BOOST_ASIO_CONSTEXPR const asio_execution_execute_fn::impl&
+  execute = asio_execution_execute_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename T, typename F>
+struct can_execute :
+  integral_constant<bool,
+    asio_execution_execute_fn::call_traits<T, void(F)>::overload !=
+      asio_execution_execute_fn::ill_formed>
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename F>
+constexpr bool can_execute_v = can_execute<T, F>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_EXECUTE_HPP
diff --git a/include/boost/asio/execution/executor.hpp b/include/boost/asio/execution/executor.hpp
new file mode 100644
index 00000000..f9842a21
--- /dev/null
+++ b/include/boost/asio/execution/executor.hpp
@@ -0,0 +1,92 @@
+//
+// execution/executor.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_EXECUTOR_HPP
+#define BOOST_ASIO_EXECUTION_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/execute.hpp>
+#include <boost/asio/execution/invocable_archetype.hpp>
+#include <boost/asio/traits/equality_comparable.hpp>
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT) \
+  && defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT) \
+  && defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+# define BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+/// The is_executor trait detects whether a type T satisfies the
+/// execution::executor concept.
+/**
+ * Class template @c is_executor is a UnaryTypeTrait that is derived from @c
+ * true_type if the type @c T meets the concept definition for an executor,
+ * otherwise @c false_type.
+ */
+template <typename T>
+struct is_executor :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool,
+    can_execute<const T, invocable_archetype>::value
+#if defined(BOOST_ASIO_HAS_NOEXCEPT)
+      && is_nothrow_copy_constructible<T>::value
+      && is_nothrow_destructible<T>::value
+#else // defined(BOOST_ASIO_HAS_NOEXCEPT)
+      && is_copy_constructible<T>::value
+      && is_destructible<T>::value
+#endif // defined(BOOST_ASIO_HAS_NOEXCEPT)
+      && traits::equality_comparable<typename decay<T>::type>::is_valid
+      && traits::equality_comparable<typename decay<T>::type>::is_noexcept
+  >
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+BOOST_ASIO_CONSTEXPR const bool is_executor_v = is_executor<T>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_CONCEPTS)
+
+template <typename T>
+BOOST_ASIO_CONCEPT executor = is_executor<T>::value;
+
+#define BOOST_ASIO_EXECUTION_EXECUTOR ::boost::asio::execution::executor
+
+#else // defined(BOOST_ASIO_HAS_CONCEPTS)
+
+#define BOOST_ASIO_EXECUTION_EXECUTOR typename
+
+#endif // defined(BOOST_ASIO_HAS_CONCEPTS)
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_EXECUTOR_HPP
diff --git a/include/boost/asio/execution/impl/bad_executor.ipp b/include/boost/asio/execution/impl/bad_executor.ipp
new file mode 100644
index 00000000..4729a64b
--- /dev/null
+++ b/include/boost/asio/execution/impl/bad_executor.ipp
@@ -0,0 +1,42 @@
+//
+// exection/impl/bad_executor.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_IMPL_BAD_EXECUTOR_IPP
+#define BOOST_ASIO_EXECUTION_IMPL_BAD_EXECUTOR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/execution/bad_executor.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+bad_executor::bad_executor() BOOST_ASIO_NOEXCEPT
+{
+}
+
+const char* bad_executor::what() const BOOST_ASIO_NOEXCEPT_OR_NOTHROW
+{
+  return "bad executor";
+}
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_IMPL_BAD_EXECUTOR_IPP
diff --git a/include/boost/asio/execution/invocable_archetype.hpp b/include/boost/asio/execution/invocable_archetype.hpp
new file mode 100644
index 00000000..75715965
--- /dev/null
+++ b/include/boost/asio/execution/invocable_archetype.hpp
@@ -0,0 +1,68 @@
+//
+// execution/invocable_archetype.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_INVOCABLE_ARCHETYPE_HPP
+#define BOOST_ASIO_EXECUTION_INVOCABLE_ARCHETYPE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/detail/variadic_templates.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+/// An archetypal function object used for determining adherence to the
+/// execution::executor concept.
+struct invocable_archetype
+{
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+
+  /// Function call operator.
+  template <typename... Args>
+  void operator()(BOOST_ASIO_MOVE_ARG(Args)...)
+  {
+  }
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+      //   || defined(GENERATING_DOCUMENTATION)
+
+  void operator()()
+  {
+  }
+
+#define BOOST_ASIO_PRIVATE_INVOCABLE_ARCHETYPE_CALL_DEF(n) \
+  template <BOOST_ASIO_VARIADIC_TPARAMS(n)> \
+  void operator()(BOOST_ASIO_VARIADIC_UNNAMED_MOVE_PARAMS(n)) \
+  { \
+  } \
+  /**/
+  BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_INVOCABLE_ARCHETYPE_CALL_DEF)
+#undef BOOST_ASIO_PRIVATE_INVOCABLE_ARCHETYPE_CALL_DEF
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_INVOCABLE_ARCHETYPE_HPP
+
diff --git a/include/boost/asio/execution/mapping.hpp b/include/boost/asio/execution/mapping.hpp
new file mode 100644
index 00000000..b28ccd6a
--- /dev/null
+++ b/include/boost/asio/execution/mapping.hpp
@@ -0,0 +1,888 @@
+//
+// execution/mapping.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_MAPPING_HPP
+#define BOOST_ASIO_EXECUTION_MAPPING_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe what guarantees an executor makes about the mapping
+/// of execution agents on to threads of execution.
+struct mapping_t
+{
+  /// The mapping_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The top-level mapping_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level mapping_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef mapping_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that execution agents are mapped on to
+  /// threads of execution.
+  struct thread_t
+  {
+    /// The mapping_t::thread_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The mapping_t::thread_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The mapping_t::thread_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef mapping_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr thread_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns thread_t();
+     */
+    static constexpr mapping_t value();
+  };
+
+  /// A sub-property that indicates that execution agents are mapped on to
+  /// new threads of execution.
+  struct new_thread_t
+  {
+    /// The mapping_t::new_thread_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The mapping_t::new_thread_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The mapping_t::new_thread_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef mapping_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr new_thread_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns new_thread_t();
+     */
+    static constexpr mapping_t value();
+  };
+
+  /// A sub-property that indicates that the mapping of execution agents is
+  /// implementation-defined.
+  struct other_t
+  {
+    /// The mapping_t::other_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The mapping_t::other_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The mapping_t::other_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef mapping_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr other_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns other_t();
+     */
+    static constexpr mapping_t value();
+  };
+
+  /// A special value used for accessing the mapping_t::thread_t property.
+  static constexpr thread_t thread;
+
+  /// A special value used for accessing the mapping_t::new_thread_t property.
+  static constexpr new_thread_t new_thread;
+
+  /// A special value used for accessing the mapping_t::other_t property.
+  static constexpr other_t other;
+
+  /// Default constructor.
+  constexpr mapping_t();
+
+  /// Construct from a sub-property value.
+  constexpr mapping_t(thread_t);
+
+  /// Construct from a sub-property value.
+  constexpr mapping_t(new_thread_t);
+
+  /// Construct from a sub-property value.
+  constexpr mapping_t(other_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const mapping_t& a, const mapping_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const mapping_t& a, const mapping_t& b) noexcept;
+};
+
+/// A special value used for accessing the mapping_t property.
+constexpr mapping_t mapping;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace mapping {
+
+template <int I> struct thread_t;
+template <int I> struct new_thread_t;
+template <int I> struct other_t;
+
+} // namespace mapping
+
+template <int I = 0>
+struct mapping_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef mapping_t polymorphic_query_result_type;
+
+  typedef detail::mapping::thread_t<I> thread_t;
+  typedef detail::mapping::new_thread_t<I> new_thread_t;
+  typedef detail::mapping::other_t<I> other_t;
+
+  BOOST_ASIO_CONSTEXPR mapping_t()
+    : value_(-1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR mapping_t(thread_t)
+    : value_(0)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR mapping_t(new_thread_t)
+    : value_(1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR mapping_t(other_t)
+    : value_(2)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, mapping_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, mapping_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, mapping_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, thread_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, mapping_t>::is_valid
+          && !traits::query_member<T, mapping_t>::is_valid
+          && traits::static_query<T, thread_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, thread_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, new_thread_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, mapping_t>::is_valid
+          && !traits::query_member<T, mapping_t>::is_valid
+          && !traits::static_query<T, thread_t>::is_valid
+          && traits::static_query<T, new_thread_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, new_thread_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, other_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, mapping_t>::is_valid
+          && !traits::query_member<T, mapping_t>::is_valid
+          && !traits::static_query<T, thread_t>::is_valid
+          && !traits::static_query<T, new_thread_t>::is_valid
+          && traits::static_query<T, other_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, other_t>::value();
+  }
+
+  template <typename E, typename T = decltype(mapping_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = mapping_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const mapping_t& a, const mapping_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const mapping_t& a, const mapping_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_mapping_t
+  {
+    BOOST_ASIO_CONSTEXPR convertible_from_mapping_t(mapping_t) {}
+  };
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR mapping_t query(
+      const Executor& ex, convertible_from_mapping_t,
+      typename enable_if<
+        can_query<const Executor&, thread_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, mapping_t<>::thread_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, thread_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, thread_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR mapping_t query(
+      const Executor& ex, convertible_from_mapping_t,
+      typename enable_if<
+        !can_query<const Executor&, thread_t>::value
+          && can_query<const Executor&, new_thread_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, mapping_t<>::new_thread_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, new_thread_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, new_thread_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR mapping_t query(
+      const Executor& ex, convertible_from_mapping_t,
+      typename enable_if<
+        !can_query<const Executor&, thread_t>::value
+          && !can_query<const Executor&, new_thread_t>::value
+          && can_query<const Executor&, other_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, mapping_t<>::other_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, other_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, other_t());
+  }
+
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(thread_t, thread);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(new_thread_t, new_thread);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(other_t, other);
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const mapping_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T mapping_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const mapping_t<I> mapping_t<I>::instance;
+#endif
+
+template <int I>
+const typename mapping_t<I>::thread_t mapping_t<I>::thread;
+
+template <int I>
+const typename mapping_t<I>::new_thread_t mapping_t<I>::new_thread;
+
+template <int I>
+const typename mapping_t<I>::other_t mapping_t<I>::other;
+
+namespace mapping {
+
+template <int I = 0>
+struct thread_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef mapping_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR thread_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, thread_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, thread_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, thread_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR thread_t static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, thread_t>::is_valid
+          && !traits::query_member<T, thread_t>::is_valid
+          && !traits::query_free<T, thread_t>::is_valid
+          && !can_query<T, new_thread_t<I> >::value
+          && !can_query<T, other_t<I> >::value
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return thread_t();
+  }
+
+  template <typename E, typename T = decltype(thread_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = thread_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR mapping_t<I> value()
+  {
+    return thread_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const thread_t&, const thread_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const thread_t&, const thread_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T thread_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct new_thread_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef mapping_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR new_thread_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, new_thread_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, new_thread_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, new_thread_t>::value();
+  }
+
+  template <typename E, typename T = decltype(new_thread_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = new_thread_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR mapping_t<I> value()
+  {
+    return new_thread_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const new_thread_t&, const new_thread_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const new_thread_t&, const new_thread_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T new_thread_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I>
+struct other_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef mapping_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR other_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, other_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, other_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, other_t>::value();
+  }
+
+  template <typename E, typename T = decltype(other_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = other_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR mapping_t<I> value()
+  {
+    return other_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const other_t&, const other_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const other_t&, const other_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T other_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace mapping
+} // namespace detail
+
+typedef detail::mapping_t<> mapping_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr mapping_t mapping;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const mapping_t& mapping = mapping_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::mapping_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::mapping_t::thread_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::mapping_t::new_thread_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::mapping_t::other_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::mapping_t,
+  typename enable_if<
+    can_query<T, execution::mapping_t::thread_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::mapping_t::thread_t>::value));
+
+  typedef execution::mapping_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::mapping_t,
+  typename enable_if<
+    !can_query<T, execution::mapping_t::thread_t>::value
+      && can_query<T, execution::mapping_t::new_thread_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::mapping_t::new_thread_t>::value));
+
+  typedef execution::mapping_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::mapping_t,
+  typename enable_if<
+    !can_query<T, execution::mapping_t::thread_t>::value
+      && !can_query<T, execution::mapping_t::new_thread_t>::value
+      && can_query<T, execution::mapping_t::other_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::mapping_t::other_t>::value));
+
+  typedef execution::mapping_t result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::mapping_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::mapping_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::mapping_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::mapping_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T, execution::mapping_t>::is_valid
+      && !traits::query_member<T, execution::mapping_t>::is_valid
+      && traits::static_query<T, execution::mapping_t::thread_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::mapping_t::thread_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T, execution::mapping_t::thread_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T, execution::mapping_t>::is_valid
+      && !traits::query_member<T, execution::mapping_t>::is_valid
+      && !traits::static_query<T, execution::mapping_t::thread_t>::is_valid
+      && traits::static_query<T, execution::mapping_t::new_thread_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::mapping_t::new_thread_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T, execution::mapping_t::new_thread_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T, execution::mapping_t>::is_valid
+      && !traits::query_member<T, execution::mapping_t>::is_valid
+      && !traits::static_query<T, execution::mapping_t::thread_t>::is_valid
+      && !traits::static_query<T, execution::mapping_t::new_thread_t>::is_valid
+      && traits::static_query<T, execution::mapping_t::other_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::mapping_t::other_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T, execution::mapping_t::other_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t::thread_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::mapping_t::thread_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::mapping_t::thread_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::mapping_t::thread_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t::thread_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+      execution::mapping_t::thread_t>::is_valid
+      && !traits::query_member<T, execution::mapping_t::thread_t>::is_valid
+      && !traits::query_free<T, execution::mapping_t::thread_t>::is_valid
+      && !can_query<T, execution::mapping_t::new_thread_t>::value
+      && !can_query<T, execution::mapping_t::other_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::mapping_t::thread_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t::new_thread_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::mapping_t::new_thread_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::mapping_t::new_thread_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::mapping_t::new_thread_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::mapping_t::other_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::mapping_t::other_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::mapping_t::other_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::mapping_t::other_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::mapping_t::thread_t,
+  typename enable_if<
+    static_query<T, execution::mapping_t::thread_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::mapping_t::thread_t>::result_type,
+        execution::mapping_t::thread_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::mapping_t::new_thread_t,
+  typename enable_if<
+    static_query<T, execution::mapping_t::new_thread_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::mapping_t::new_thread_t>::result_type,
+        execution::mapping_t::new_thread_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::mapping_t::other_t,
+  typename enable_if<
+    static_query<T, execution::mapping_t::other_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::mapping_t::other_t>::result_type,
+        execution::mapping_t::other_t>::value));
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_MAPPING_HPP
diff --git a/include/boost/asio/execution/occupancy.hpp b/include/boost/asio/execution/occupancy.hpp
new file mode 100644
index 00000000..39850aa2
--- /dev/null
+++ b/include/boost/asio/execution/occupancy.hpp
@@ -0,0 +1,173 @@
+//
+// execution/occupancy.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_OCCUPANCY_HPP
+#define BOOST_ASIO_EXECUTION_OCCUPANCY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that gives an estimate of the number of execution agents that
+/// should occupy the associated execution context.
+struct occupancy_t
+{
+  /// The occupancy_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The occupancy_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The occupancy_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef std::size_t polymorphic_query_result_type;
+};
+
+/// A special value used for accessing the occupancy_t property.
+constexpr occupancy_t occupancy;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+
+template <int I = 0>
+struct occupancy_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef std::size_t polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR occupancy_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, occupancy_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, occupancy_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, occupancy_t>::value();
+  }
+
+  template <typename E, typename T = decltype(occupancy_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = occupancy_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const occupancy_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T occupancy_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const occupancy_t<I> occupancy_t<I>::instance;
+#endif
+
+} // namespace detail
+
+typedef detail::occupancy_t<> occupancy_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr occupancy_t occupancy;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const occupancy_t& occupancy = occupancy_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::occupancy_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::occupancy_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::occupancy_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::occupancy_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::occupancy_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_OCCUPANCY_HPP
diff --git a/include/boost/asio/execution/outstanding_work.hpp b/include/boost/asio/execution/outstanding_work.hpp
new file mode 100644
index 00000000..19ba4c40
--- /dev/null
+++ b/include/boost/asio/execution/outstanding_work.hpp
@@ -0,0 +1,699 @@
+//
+// execution/outstanding_work.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_OUTSTANDING_WORK_HPP
+#define BOOST_ASIO_EXECUTION_OUTSTANDING_WORK_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe whether task submission is likely in the future.
+struct outstanding_work_t
+{
+  /// The outstanding_work_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The top-level outstanding_work_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level outstanding_work_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that the executor does not represent likely
+  /// future submission of a function object.
+  struct untracked_t
+  {
+    /// The outstanding_work_t::untracked_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The outstanding_work_t::untracked_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The outstanding_work_t::untracked_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef outstanding_work_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr untracked_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns untracked_t();
+     */
+    static constexpr outstanding_work_t value();
+  };
+
+  /// A sub-property that indicates that the executor represents likely
+  /// future submission of a function object.
+  struct tracked_t
+  {
+    /// The outstanding_work_t::tracked_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The outstanding_work_t::tracked_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The outstanding_work_t::tracked_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef outstanding_work_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr tracked_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns tracked_t();
+     */
+    static constexpr outstanding_work_t value();
+  };
+
+  /// A special value used for accessing the outstanding_work_t::untracked_t
+  /// property.
+  static constexpr untracked_t untracked;
+
+  /// A special value used for accessing the outstanding_work_t::tracked_t
+  /// property.
+  static constexpr tracked_t tracked;
+
+  /// Default constructor.
+  constexpr outstanding_work_t();
+
+  /// Construct from a sub-property value.
+  constexpr outstanding_work_t(untracked_t);
+
+  /// Construct from a sub-property value.
+  constexpr outstanding_work_t(tracked_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const outstanding_work_t& a, const outstanding_work_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const outstanding_work_t& a, const outstanding_work_t& b) noexcept;
+};
+
+/// A special value used for accessing the outstanding_work_t property.
+constexpr outstanding_work_t outstanding_work;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace outstanding_work {
+
+template <int I> struct untracked_t;
+template <int I> struct tracked_t;
+
+} // namespace outstanding_work
+
+template <int I = 0>
+struct outstanding_work_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+  typedef detail::outstanding_work::untracked_t<I> untracked_t;
+  typedef detail::outstanding_work::tracked_t<I> tracked_t;
+
+  BOOST_ASIO_CONSTEXPR outstanding_work_t()
+    : value_(-1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR outstanding_work_t(untracked_t)
+    : value_(0)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR outstanding_work_t(tracked_t)
+    : value_(1)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<
+      T, outstanding_work_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<
+        T, outstanding_work_t
+      >::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<
+        T, outstanding_work_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, untracked_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<
+            T, outstanding_work_t>::is_valid
+          && !traits::query_member<T, outstanding_work_t>::is_valid
+          && traits::static_query<T, untracked_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, untracked_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, tracked_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<
+            T, outstanding_work_t>::is_valid
+          && !traits::query_member<T, outstanding_work_t>::is_valid
+          && !traits::static_query<T, untracked_t>::is_valid
+          && traits::static_query<T, tracked_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, tracked_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(outstanding_work_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = outstanding_work_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const outstanding_work_t& a, const outstanding_work_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const outstanding_work_t& a, const outstanding_work_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_outstanding_work_t
+  {
+    BOOST_ASIO_CONSTEXPR convertible_from_outstanding_work_t(outstanding_work_t)
+    {
+    }
+  };
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR outstanding_work_t query(
+      const Executor& ex, convertible_from_outstanding_work_t,
+      typename enable_if<
+        can_query<const Executor&, untracked_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        outstanding_work_t<>::untracked_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, untracked_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, untracked_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR outstanding_work_t query(
+      const Executor& ex, convertible_from_outstanding_work_t,
+      typename enable_if<
+        !can_query<const Executor&, untracked_t>::value
+          && can_query<const Executor&, tracked_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        outstanding_work_t<>::tracked_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, tracked_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, tracked_t());
+  }
+
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(untracked_t, untracked);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(tracked_t, tracked);
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const outstanding_work_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T outstanding_work_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const outstanding_work_t<I> outstanding_work_t<I>::instance;
+#endif
+
+template <int I>
+const typename outstanding_work_t<I>::untracked_t
+outstanding_work_t<I>::untracked;
+
+template <int I>
+const typename outstanding_work_t<I>::tracked_t
+outstanding_work_t<I>::tracked;
+
+namespace outstanding_work {
+
+template <int I = 0>
+struct untracked_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef outstanding_work_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR untracked_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, untracked_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, untracked_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, untracked_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR untracked_t static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, untracked_t>::is_valid
+          && !traits::query_member<T, untracked_t>::is_valid
+          && !traits::query_free<T, untracked_t>::is_valid
+          && !can_query<T, tracked_t<I> >::value
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return untracked_t();
+  }
+
+  template <typename E, typename T = decltype(untracked_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = untracked_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR outstanding_work_t<I> value()
+  {
+    return untracked_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const untracked_t&, const untracked_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const untracked_t&, const untracked_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T untracked_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct tracked_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef outstanding_work_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR tracked_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, tracked_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, tracked_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, tracked_t>::value();
+  }
+
+  template <typename E, typename T = decltype(tracked_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = tracked_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR outstanding_work_t<I> value()
+  {
+    return tracked_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const tracked_t&, const tracked_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const tracked_t&, const tracked_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T tracked_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace outstanding_work
+} // namespace detail
+
+typedef detail::outstanding_work_t<> outstanding_work_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr outstanding_work_t outstanding_work;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const outstanding_work_t&
+  outstanding_work = outstanding_work_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::outstanding_work_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::outstanding_work_t::untracked_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::outstanding_work_t::tracked_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::outstanding_work_t,
+  typename enable_if<
+    can_query<T, execution::outstanding_work_t::untracked_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::outstanding_work_t::untracked_t>::value));
+
+  typedef execution::outstanding_work_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::outstanding_work_t,
+  typename enable_if<
+    !can_query<T, execution::outstanding_work_t::untracked_t>::value
+      && can_query<T, execution::outstanding_work_t::tracked_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::outstanding_work_t::tracked_t>::value));
+
+  typedef execution::outstanding_work_t result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::outstanding_work_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::outstanding_work_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::outstanding_work_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::outstanding_work_t>::is_valid
+      && !traits::query_member<T,
+        execution::outstanding_work_t>::is_valid
+      && traits::static_query<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::outstanding_work_t::untracked_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::outstanding_work_t::untracked_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::outstanding_work_t>::is_valid
+      && !traits::query_member<T,
+        execution::outstanding_work_t>::is_valid
+      && !traits::static_query<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+      && traits::static_query<T,
+        execution::outstanding_work_t::tracked_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::outstanding_work_t::tracked_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::outstanding_work_t::tracked_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t::untracked_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::outstanding_work_t::untracked_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::outstanding_work_t::untracked_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::outstanding_work_t::untracked_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t::untracked_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+      && !traits::query_member<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+      && !traits::query_free<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+      && !can_query<T, execution::outstanding_work_t::tracked_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::outstanding_work_t::untracked_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t::tracked_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::outstanding_work_t::tracked_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::outstanding_work_t::tracked_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::outstanding_work_t::tracked_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::outstanding_work_t::untracked_t,
+  typename enable_if<
+    static_query<T, execution::outstanding_work_t::untracked_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::outstanding_work_t::untracked_t>::result_type,
+        execution::outstanding_work_t::untracked_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::outstanding_work_t::tracked_t,
+  typename enable_if<
+    static_query<T, execution::outstanding_work_t::tracked_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::outstanding_work_t::tracked_t>::result_type,
+        execution::outstanding_work_t::tracked_t>::value));
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_OUTSTANDING_WORK_HPP
diff --git a/include/boost/asio/execution/prefer_only.hpp b/include/boost/asio/execution/prefer_only.hpp
new file mode 100644
index 00000000..88d43015
--- /dev/null
+++ b/include/boost/asio/execution/prefer_only.hpp
@@ -0,0 +1,329 @@
+//
+// execution/prefer_only.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_PREFER_ONLY_HPP
+#define BOOST_ASIO_EXECUTION_PREFER_ONLY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that is used to obtain the execution context that is associated
+/// with an executor.
+template <typename Property>
+struct prefer_only
+{
+  /// The context_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The context_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The context_t property can be preferred, it the underlying property can
+  /// be preferred.
+  /**
+   * @c true if @c Property::is_preferable is @c true, otherwise @c false.
+   */
+  static constexpr bool is_preferable = automatically_determined;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef typename Property::polymorphic_query_result_type
+    polymorphic_query_result_type;
+};
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+
+template <typename InnerProperty, typename = void>
+struct prefer_only_is_preferable
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+};
+
+template <typename InnerProperty>
+struct prefer_only_is_preferable<InnerProperty,
+    typename enable_if<
+      InnerProperty::is_preferable
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+};
+
+template <typename InnerProperty, typename = void>
+struct prefer_only_polymorphic_query_result_type
+{
+};
+
+template <typename InnerProperty>
+struct prefer_only_polymorphic_query_result_type<InnerProperty,
+    typename void_type<
+      typename InnerProperty::polymorphic_query_result_type
+    >::type>
+{
+  typedef typename InnerProperty::polymorphic_query_result_type
+    polymorphic_query_result_type;
+};
+
+template <typename InnerProperty, typename = void>
+struct prefer_only_property
+{
+  InnerProperty property;
+
+  prefer_only_property(const InnerProperty& p)
+    : property(p)
+  {
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+template <typename InnerProperty>
+struct prefer_only_property<InnerProperty,
+    typename void_type<
+      decltype(boost::asio::declval<const InnerProperty>().value())
+    >::type>
+{
+  InnerProperty property;
+
+  prefer_only_property(const InnerProperty& p)
+    : property(p)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR auto value() const
+    BOOST_ASIO_NOEXCEPT_IF((
+      noexcept(boost::asio::declval<const InnerProperty>().value())))
+    -> decltype(boost::asio::declval<const InnerProperty>().value())
+  {
+    return property.value();
+  }
+};
+
+#else // defined(BOOST_ASIO_HAS_DECLTYPE)
+      //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+struct prefer_only_memfns_base
+{
+  void value();
+};
+
+template <typename T>
+struct prefer_only_memfns_derived
+  : T, prefer_only_memfns_base
+{
+};
+
+template <typename T, T>
+struct prefer_only_memfns_check
+{
+};
+
+template <typename>
+char (&prefer_only_value_memfn_helper(...))[2];
+
+template <typename T>
+char prefer_only_value_memfn_helper(
+    prefer_only_memfns_check<
+      void (prefer_only_memfns_base::*)(),
+      &prefer_only_memfns_derived<T>::value>*);
+
+template <typename InnerProperty>
+struct prefer_only_property<InnerProperty,
+    typename enable_if<
+      sizeof(prefer_only_value_memfn_helper<InnerProperty>(0)) != 1
+        && !is_same<typename InnerProperty::polymorphic_query_result_type,
+          void>::value
+    >::type>
+{
+  InnerProperty property;
+
+  prefer_only_property(const InnerProperty& p)
+    : property(p)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR typename InnerProperty::polymorphic_query_result_type
+  value() const
+  {
+    return property.value();
+  }
+};
+
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+} // namespace detail
+
+template <typename InnerProperty>
+struct prefer_only :
+  detail::prefer_only_is_preferable<InnerProperty>,
+  detail::prefer_only_polymorphic_query_result_type<InnerProperty>,
+  detail::prefer_only_property<InnerProperty>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+
+  BOOST_ASIO_CONSTEXPR prefer_only(const InnerProperty& p)
+    : detail::prefer_only_property<InnerProperty>(p)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, InnerProperty>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::static_query<T, InnerProperty>::is_noexcept))
+  {
+    return traits::static_query<T, InnerProperty>::value();
+  }
+
+  template <typename E, typename T = decltype(prefer_only::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = prefer_only::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  template <typename Executor, typename Property>
+  friend BOOST_ASIO_CONSTEXPR
+  typename prefer_result_type<const Executor&, const InnerProperty&>::type
+  prefer(const Executor& ex, const prefer_only<Property>& p,
+      typename enable_if<
+        is_same<Property, InnerProperty>::value
+          && can_prefer<const Executor&, const InnerProperty&>::value
+      >::type* = 0)
+#if !defined(BOOST_ASIO_MSVC) \
+  && !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_prefer<const Executor&, const InnerProperty&>::value))
+#endif // !defined(BOOST_ASIO_MSVC)
+       //   && !defined(__clang__)
+  {
+    return boost::asio::prefer(ex, p.property);
+  }
+
+  template <typename Executor, typename Property>
+  friend BOOST_ASIO_CONSTEXPR
+  typename query_result_type<const Executor&, const InnerProperty&>::type
+  query(const Executor& ex, const prefer_only<Property>& p,
+      typename enable_if<
+        is_same<Property, InnerProperty>::value
+          && can_query<const Executor&, const InnerProperty&>::value
+      >::type* = 0)
+#if !defined(BOOST_ASIO_MSVC) \
+  && !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, const InnerProperty&>::value))
+#endif // !defined(BOOST_ASIO_MSVC)
+       //   && !defined(__clang__)
+  {
+    return boost::asio::query(ex, p.property);
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename InnerProperty> template <typename E, typename T>
+const T prefer_only<InnerProperty>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace execution
+
+template <typename T, typename InnerProperty>
+struct is_applicable_property<T, execution::prefer_only<InnerProperty> >
+  : is_applicable_property<T, InnerProperty>
+{
+};
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T, typename InnerProperty>
+struct static_query<T, execution::prefer_only<InnerProperty> > :
+  static_query<T, const InnerProperty&>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename T, typename InnerProperty>
+struct prefer_free_default<T, execution::prefer_only<InnerProperty>,
+    typename enable_if<
+      can_prefer<const T&, const InnerProperty&>::value
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_prefer<const T&, const InnerProperty&>::value));
+
+  typedef typename prefer_result_type<const T&,
+      const InnerProperty&>::type result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T, typename InnerProperty>
+struct query_free<T, execution::prefer_only<InnerProperty>,
+    typename enable_if<
+      can_query<const T&, const InnerProperty&>::value
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<const T&, const InnerProperty&>::value));
+
+  typedef typename query_result_type<const T&,
+      const InnerProperty&>::type result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_PREFER_ONLY_HPP
diff --git a/include/boost/asio/execution/relationship.hpp b/include/boost/asio/execution/relationship.hpp
new file mode 100644
index 00000000..bc45f88b
--- /dev/null
+++ b/include/boost/asio/execution/relationship.hpp
@@ -0,0 +1,699 @@
+//
+// execution/relationship.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_EXECUTION_RELATIONSHIP_HPP
+#define BOOST_ASIO_EXECUTION_RELATIONSHIP_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_static_constexpr_member.hpp>
+#include <boost/asio/traits/static_query.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe whether submitted tasks represent continuations of
+/// the calling context.
+struct relationship_t
+{
+  /// The relationship_t property applies to executors.
+  template <typename T>
+  static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+  /// The top-level relationship_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level relationship_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef relationship_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that the executor does not represent a
+  /// continuation of the calling context.
+  struct fork_t
+  {
+    /// The relationship_t::fork_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The relationship_t::fork_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The relationship_t::fork_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef relationship_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr fork_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns fork_t();
+     */
+    static constexpr relationship_t value();
+  };
+
+  /// A sub-property that indicates that the executor represents a continuation
+  /// of the calling context.
+  struct continuation_t
+  {
+    /// The relationship_t::continuation_t property applies to executors.
+    template <typename T>
+    static constexpr bool is_applicable_property_v = is_executor_v<T>;
+
+    /// The relationship_t::continuation_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The relationship_t::continuation_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef relationship_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr continuation_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns continuation_t();
+     */
+    static constexpr relationship_t value();
+  };
+
+  /// A special value used for accessing the relationship_t::fork_t property.
+  static constexpr fork_t fork;
+
+  /// A special value used for accessing the relationship_t::continuation_t
+  /// property.
+  static constexpr continuation_t continuation;
+
+  /// Default constructor.
+  constexpr relationship_t();
+
+  /// Construct from a sub-property value.
+  constexpr relationship_t(fork_t);
+
+  /// Construct from a sub-property value.
+  constexpr relationship_t(continuation_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const relationship_t& a, const relationship_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const relationship_t& a, const relationship_t& b) noexcept;
+};
+
+/// A special value used for accessing the relationship_t property.
+constexpr relationship_t relationship;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace relationship {
+
+template <int I> struct fork_t;
+template <int I> struct continuation_t;
+
+} // namespace relationship
+
+template <int I = 0>
+struct relationship_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef relationship_t polymorphic_query_result_type;
+
+  typedef detail::relationship::fork_t<I> fork_t;
+  typedef detail::relationship::continuation_t<I> continuation_t;
+
+  BOOST_ASIO_CONSTEXPR relationship_t()
+    : value_(-1)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR relationship_t(fork_t)
+    : value_(0)
+  {
+  }
+
+  BOOST_ASIO_CONSTEXPR relationship_t(continuation_t)
+    : value_(1)
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<
+      T, relationship_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<
+        T, relationship_t
+      >::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<
+        T, relationship_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, fork_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<
+            T, relationship_t>::is_valid
+          && !traits::query_member<T, relationship_t>::is_valid
+          && traits::static_query<T, fork_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, fork_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::static_query<T, continuation_t>::result_type
+  static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<
+            T, relationship_t>::is_valid
+          && !traits::query_member<T, relationship_t>::is_valid
+          && !traits::static_query<T, fork_t>::is_valid
+          && traits::static_query<T, continuation_t>::is_valid
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, continuation_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(relationship_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = relationship_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const relationship_t& a, const relationship_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const relationship_t& a, const relationship_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_relationship_t
+  {
+    BOOST_ASIO_CONSTEXPR convertible_from_relationship_t(relationship_t)
+    {
+    }
+  };
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR relationship_t query(
+      const Executor& ex, convertible_from_relationship_t,
+      typename enable_if<
+        can_query<const Executor&, fork_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, relationship_t<>::fork_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, fork_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, fork_t());
+  }
+
+  template <typename Executor>
+  friend BOOST_ASIO_CONSTEXPR relationship_t query(
+      const Executor& ex, convertible_from_relationship_t,
+      typename enable_if<
+        !can_query<const Executor&, fork_t>::value
+          && can_query<const Executor&, continuation_t>::value
+      >::type* = 0)
+#if defined(_MSC_VER) // Visual C++ wants the type to be qualified.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        relationship_t<>::continuation_t>::value))
+#elif !defined(__clang__) // Clang crashes if noexcept is used here.
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, continuation_t>::value))
+#endif // !defined(__clang__)
+  {
+    return boost::asio::query(ex, continuation_t());
+  }
+
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(fork_t, fork);
+  BOOST_ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(continuation_t, continuation);
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+  static const relationship_t instance;
+#endif // !defined(BOOST_ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T relationship_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_CONSTEXPR)
+template <int I>
+const relationship_t<I> relationship_t<I>::instance;
+#endif
+
+template <int I>
+const typename relationship_t<I>::fork_t
+relationship_t<I>::fork;
+
+template <int I>
+const typename relationship_t<I>::continuation_t
+relationship_t<I>::continuation;
+
+namespace relationship {
+
+template <int I = 0>
+struct fork_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef relationship_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR fork_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, fork_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, fork_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, fork_t>::value();
+  }
+
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR fork_t static_query(
+      typename enable_if<
+        !traits::query_static_constexpr_member<T, fork_t>::is_valid
+          && !traits::query_member<T, fork_t>::is_valid
+          && !traits::query_free<T, fork_t>::is_valid
+          && !can_query<T, continuation_t<I> >::value
+      >::type* = 0) BOOST_ASIO_NOEXCEPT
+  {
+    return fork_t();
+  }
+
+  template <typename E, typename T = decltype(fork_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = fork_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR relationship_t<I> value()
+  {
+    return fork_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const fork_t&, const fork_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const fork_t&, const fork_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T fork_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct continuation_t
+{
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  BOOST_ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = is_executor<T>::value);
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef relationship_t<I> polymorphic_query_result_type;
+
+  BOOST_ASIO_CONSTEXPR continuation_t()
+  {
+  }
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static BOOST_ASIO_CONSTEXPR
+  typename traits::query_static_constexpr_member<T, continuation_t>::result_type
+  static_query()
+    BOOST_ASIO_NOEXCEPT_IF((
+      traits::query_static_constexpr_member<T, continuation_t>::is_noexcept))
+  {
+    return traits::query_static_constexpr_member<T, continuation_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(continuation_t::static_query<E>())>
+  static BOOST_ASIO_CONSTEXPR const T static_query_v
+    = continuation_t::static_query<E>();
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static BOOST_ASIO_CONSTEXPR relationship_t<I> value()
+  {
+    return continuation_t();
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator==(
+      const continuation_t&, const continuation_t&)
+  {
+    return true;
+  }
+
+  friend BOOST_ASIO_CONSTEXPR bool operator!=(
+      const continuation_t&, const continuation_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T continuation_t<I>::static_query_v;
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace relationship
+} // namespace detail
+
+typedef detail::relationship_t<> relationship_t;
+
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr relationship_t relationship;
+#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const relationship_t&
+  relationship = relationship_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::relationship_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::relationship_t::fork_t>
+  : execution::is_executor<T>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::relationship_t::continuation_t>
+  : execution::is_executor<T>
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::relationship_t,
+  typename enable_if<
+    can_query<T, execution::relationship_t::fork_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::relationship_t::fork_t>::value));
+
+  typedef execution::relationship_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::relationship_t,
+  typename enable_if<
+    !can_query<T, execution::relationship_t::fork_t>::value
+      && can_query<T, execution::relationship_t::continuation_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::relationship_t::continuation_t>::value));
+
+  typedef execution::relationship_t result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::relationship_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::relationship_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::relationship_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::relationship_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::relationship_t>::is_valid
+      && !traits::query_member<T,
+        execution::relationship_t>::is_valid
+      && traits::static_query<T,
+        execution::relationship_t::fork_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::relationship_t::fork_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::relationship_t::fork_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::relationship_t>::is_valid
+      && !traits::query_member<T,
+        execution::relationship_t>::is_valid
+      && !traits::static_query<T,
+        execution::relationship_t::fork_t>::is_valid
+      && traits::static_query<T,
+        execution::relationship_t::continuation_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::relationship_t::continuation_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::relationship_t::continuation_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t::fork_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::relationship_t::fork_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::relationship_t::fork_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::relationship_t::fork_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t::fork_t,
+  typename enable_if<
+    !traits::query_static_constexpr_member<T,
+        execution::relationship_t::fork_t>::is_valid
+      && !traits::query_member<T,
+        execution::relationship_t::fork_t>::is_valid
+      && !traits::query_free<T,
+        execution::relationship_t::fork_t>::is_valid
+      && !can_query<T, execution::relationship_t::continuation_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::relationship_t::fork_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t::continuation_t,
+  typename enable_if<
+    traits::query_static_constexpr_member<T,
+      execution::relationship_t::continuation_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::query_static_constexpr_member<T,
+    execution::relationship_t::continuation_t>::result_type result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return traits::query_static_constexpr_member<T,
+      execution::relationship_t::continuation_t>::value();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::relationship_t::fork_t,
+  typename enable_if<
+    static_query<T, execution::relationship_t::fork_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::relationship_t::fork_t>::result_type,
+        execution::relationship_t::fork_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::relationship_t::continuation_t,
+  typename enable_if<
+    static_query<T, execution::relationship_t::continuation_t>::is_valid
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::relationship_t::continuation_t>::result_type,
+        execution::relationship_t::continuation_t>::value));
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_EXECUTION_RELATIONSHIP_HPP
diff --git a/include/boost/asio/executor.hpp b/include/boost/asio/executor.hpp
index a71c8b5a..4f259cef 100644
--- a/include/boost/asio/executor.hpp
+++ b/include/boost/asio/executor.hpp
@@ -16,8 +16,12 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #include <typeinfo>
 #include <boost/asio/detail/cstddef.hpp>
+#include <boost/asio/detail/executor_function.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/throw_exception.hpp>
 #include <boost/asio/execution_context.hpp>
@@ -254,7 +258,7 @@ public:
 
 private:
 #if !defined(GENERATING_DOCUMENTATION)
-  class function;
+  typedef detail::executor_function function;
   template <typename, typename> class impl;
 
 #if !defined(BOOST_ASIO_NO_TYPEID)
@@ -340,4 +344,6 @@ BOOST_ASIO_USES_ALLOCATOR(boost::asio::executor)
 # include <boost/asio/impl/executor.ipp>
 #endif // defined(BOOST_ASIO_HEADER_ONLY)
 
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #endif // BOOST_ASIO_EXECUTOR_HPP
diff --git a/include/boost/asio/executor_work_guard.hpp b/include/boost/asio/executor_work_guard.hpp
index 18f64e02..be78a9ef 100644
--- a/include/boost/asio/executor_work_guard.hpp
+++ b/include/boost/asio/executor_work_guard.hpp
@@ -1,6 +1,6 @@
 //
 // executor_work_guard.hpp
-// ~~~~~~~~~~~~~~~~~
+// ~~~~~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 //
@@ -16,8 +16,12 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution.hpp>
 #include <boost/asio/is_executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -25,9 +29,21 @@
 namespace boost {
 namespace asio {
 
+#if !defined(BOOST_ASIO_EXECUTOR_WORK_GUARD_DECL)
+#define BOOST_ASIO_EXECUTOR_WORK_GUARD_DECL
+
+template <typename Executor, typename = void>
+class executor_work_guard;
+
+#endif // !defined(BOOST_ASIO_EXECUTOR_WORK_GUARD_DECL)
+
 /// An object of type @c executor_work_guard controls ownership of executor work
 /// within a scope.
+#if defined(GENERATING_DOCUMENTATION)
 template <typename Executor>
+#else // defined(GENERATING_DOCUMENTATION)
+template <typename Executor, typename>
+#endif // defined(GENERATING_DOCUMENTATION)
 class executor_work_guard
 {
 public:
@@ -109,10 +125,102 @@ private:
   bool owns_;
 };
 
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Executor>
+class executor_work_guard<Executor,
+    typename enable_if<
+      !is_executor<Executor>::value && execution::is_executor<Executor>::value
+    >::type>
+{
+public:
+  typedef Executor executor_type;
+
+  explicit executor_work_guard(const executor_type& e) BOOST_ASIO_NOEXCEPT
+    : executor_(e),
+      owns_(true)
+  {
+    new (&work_) work_type(boost::asio::prefer(executor_,
+          execution::outstanding_work.tracked));
+  }
+
+  executor_work_guard(const executor_work_guard& other) BOOST_ASIO_NOEXCEPT
+    : executor_(other.executor_),
+      owns_(other.owns_)
+  {
+    if (owns_)
+    {
+      new (&work_) work_type(boost::asio::prefer(executor_,
+            execution::outstanding_work.tracked));
+    }
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  executor_work_guard(executor_work_guard&& other) BOOST_ASIO_NOEXCEPT
+    : executor_(BOOST_ASIO_MOVE_CAST(Executor)(other.executor_)),
+      owns_(other.owns_)
+  {
+    if (owns_)
+    {
+      new (&work_) work_type(
+          BOOST_ASIO_MOVE_CAST(work_type)(
+            *static_cast<work_type*>(
+              static_cast<void*>(&other.work_))));
+      other.owns_ = false;
+    }
+  }
+#endif //  defined(BOOST_ASIO_HAS_MOVE)
+
+  ~executor_work_guard()
+  {
+    if (owns_)
+      static_cast<work_type*>(static_cast<void*>(&work_))->~work_type();
+  }
+
+  executor_type get_executor() const BOOST_ASIO_NOEXCEPT
+  {
+    return executor_;
+  }
+
+  bool owns_work() const BOOST_ASIO_NOEXCEPT
+  {
+    return owns_;
+  }
+
+  void reset() BOOST_ASIO_NOEXCEPT
+  {
+    if (owns_)
+    {
+      static_cast<work_type*>(static_cast<void*>(&work_))->~work_type();
+      owns_ = false;
+    }
+  }
+
+private:
+  // Disallow assignment.
+  executor_work_guard& operator=(const executor_work_guard&);
+
+  typedef typename decay<
+      typename prefer_result_type<
+        const executor_type&,
+        execution::outstanding_work_t::tracked_t
+      >::type
+    >::type work_type;
+
+  executor_type executor_;
+  typename aligned_storage<sizeof(work_type),
+      alignment_of<work_type>::value>::type work_;
+  bool owns_;
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
 /// Create an @ref executor_work_guard object.
 template <typename Executor>
 inline executor_work_guard<Executor> make_work_guard(const Executor& ex,
-    typename enable_if<is_executor<Executor>::value>::type* = 0)
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type* = 0)
 {
   return executor_work_guard<Executor>(ex);
 }
@@ -122,7 +230,8 @@ template <typename ExecutionContext>
 inline executor_work_guard<typename ExecutionContext::executor_type>
 make_work_guard(ExecutionContext& ctx,
     typename enable_if<
-      is_convertible<ExecutionContext&, execution_context&>::value>::type* = 0)
+      is_convertible<ExecutionContext&, execution_context&>::value
+    >::type* = 0)
 {
   return executor_work_guard<typename ExecutionContext::executor_type>(
       ctx.get_executor());
@@ -132,8 +241,10 @@ make_work_guard(ExecutionContext& ctx,
 template <typename T>
 inline executor_work_guard<typename associated_executor<T>::type>
 make_work_guard(const T& t,
-    typename enable_if<!is_executor<T>::value &&
-      !is_convertible<T&, execution_context&>::value>::type* = 0)
+    typename enable_if<
+      !is_executor<T>::value && !execution::is_executor<T>::value
+        && !is_convertible<T&, execution_context&
+    >::value>::type* = 0)
 {
   return executor_work_guard<typename associated_executor<T>::type>(
       associated_executor<T>::get(t));
@@ -143,7 +254,9 @@ make_work_guard(const T& t,
 template <typename T, typename Executor>
 inline executor_work_guard<typename associated_executor<T, Executor>::type>
 make_work_guard(const T& t, const Executor& ex,
-    typename enable_if<is_executor<Executor>::value>::type* = 0)
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type* = 0)
 {
   return executor_work_guard<typename associated_executor<T, Executor>::type>(
       associated_executor<T, Executor>::get(t, ex));
@@ -154,9 +267,11 @@ template <typename T, typename ExecutionContext>
 inline executor_work_guard<typename associated_executor<T,
   typename ExecutionContext::executor_type>::type>
 make_work_guard(const T& t, ExecutionContext& ctx,
-    typename enable_if<!is_executor<T>::value &&
-      !is_convertible<T&, execution_context&>::value &&
-      is_convertible<ExecutionContext&, execution_context&>::value>::type* = 0)
+    typename enable_if<
+      !is_executor<T>::value && !execution::is_executor<T>::value
+        && !is_convertible<T&, execution_context&>::value
+        && is_convertible<ExecutionContext&, execution_context&>::value
+    >::type* = 0)
 {
   return executor_work_guard<typename associated_executor<T,
     typename ExecutionContext::executor_type>::type>(
@@ -169,4 +284,6 @@ make_work_guard(const T& t, ExecutionContext& ctx,
 
 #include <boost/asio/detail/pop_options.hpp>
 
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #endif // BOOST_ASIO_EXECUTOR_WORK_GUARD_HPP
diff --git a/include/boost/asio/handler_alloc_hook.hpp b/include/boost/asio/handler_alloc_hook.hpp
index 1f23a8b1..c1f53b6e 100644
--- a/include/boost/asio/handler_alloc_hook.hpp
+++ b/include/boost/asio/handler_alloc_hook.hpp
@@ -23,7 +23,30 @@
 namespace boost {
 namespace asio {
 
-/// Default allocation function for handlers.
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+
+// Places in asio that would have previously called the allocate or deallocate
+// hooks to manage memory, now call them only to check whether the result types
+// are these types. If the result is not the correct type, it indicates that
+// the user code still has the old hooks in place, and if so we want to trigger
+// a compile error.
+enum asio_handler_allocate_is_no_longer_used {};
+enum asio_handler_deallocate_is_no_longer_used {};
+
+typedef asio_handler_allocate_is_no_longer_used
+  asio_handler_allocate_is_deprecated;
+typedef asio_handler_deallocate_is_no_longer_used
+  asio_handler_deallocate_is_deprecated;
+
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
+
+typedef void* asio_handler_allocate_is_deprecated;
+typedef void asio_handler_deallocate_is_deprecated;
+
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
+
+/// (Deprecated: Use the associated_allocator trait.) Default allocation
+/// function for handlers.
 /**
  * Asynchronous operations may need to allocate temporary objects. Since
  * asynchronous operations have a handler function object, these temporary
@@ -55,8 +78,8 @@ namespace asio {
  * }
  * @endcode
  */
-BOOST_ASIO_DECL void* asio_handler_allocate(
-    std::size_t size, ...);
+BOOST_ASIO_DECL asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size, ...);
 
 /// Default deallocation function for handlers.
 /**
@@ -68,8 +91,8 @@ BOOST_ASIO_DECL void* asio_handler_allocate(
  *
  * @sa asio_handler_allocate.
  */
-BOOST_ASIO_DECL void asio_handler_deallocate(
-    void* pointer, std::size_t size, ...);
+BOOST_ASIO_DECL asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size, ...);
 
 } // namespace asio
 } // namespace boost
diff --git a/include/boost/asio/handler_invoke_hook.hpp b/include/boost/asio/handler_invoke_hook.hpp
index 74139dcb..4b4a4518 100644
--- a/include/boost/asio/handler_invoke_hook.hpp
+++ b/include/boost/asio/handler_invoke_hook.hpp
@@ -24,7 +24,8 @@ namespace asio {
 
 /** @defgroup asio_handler_invoke boost::asio::asio_handler_invoke
  *
- * @brief Default invoke function for handlers.
+ * @brief (Deprecated: Use the associated_executor trait.) Default invoke
+ * function for handlers.
  *
  * Completion handlers for asynchronous operations are invoked by the
  * io_context associated with the corresponding object (e.g. a socket or
@@ -62,19 +63,44 @@ namespace asio {
  */
 /*@{*/
 
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+
+// Places in asio that would have previously called the invocation hook to
+// execute a handler, now call it only to check whether the result type is this
+// type. If the result is not this type, it indicates that the user code still
+// has the old hooks in place, and if so we want to trigger a compile error.
+enum asio_handler_invoke_is_no_longer_used {};
+
+typedef asio_handler_invoke_is_no_longer_used
+  asio_handler_invoke_is_deprecated;
+
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
+
+typedef void asio_handler_invoke_is_deprecated;
+
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
+
 /// Default handler invocation hook used for non-const function objects.
 template <typename Function>
-inline void asio_handler_invoke(Function& function, ...)
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function, ...)
 {
   function();
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 /// Default handler invocation hook used for const function objects.
 template <typename Function>
-inline void asio_handler_invoke(const Function& function, ...)
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function, ...)
 {
   Function tmp(function);
   tmp();
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 /*@}*/
diff --git a/include/boost/asio/impl/awaitable.hpp b/include/boost/asio/impl/awaitable.hpp
index 088d03d1..6f67e608 100644
--- a/include/boost/asio/impl/awaitable.hpp
+++ b/include/boost/asio/impl/awaitable.hpp
@@ -406,6 +406,21 @@ protected:
 } // namespace boost
 
 #if !defined(GENERATING_DOCUMENTATION)
+# if defined(BOOST_ASIO_HAS_STD_COROUTINE)
+
+namespace boost {
+namespace system {
+
+template <typename T, typename Executor, typename... Args>
+struct coroutine_traits<boost::asio::awaitable<T, Executor>, Args...>
+{
+  typedef boost::asio::detail::awaitable_frame<T, Executor> promise_type;
+};
+
+} // namespace system
+} // namespace boost
+
+# else // defined(BOOST_ASIO_HAS_STD_COROUTINE)
 
 namespace std { namespace experimental {
 
@@ -417,6 +432,7 @@ struct coroutine_traits<boost::asio::awaitable<T, Executor>, Args...>
 
 }} // namespace std::experimental
 
+# endif // defined(BOOST_ASIO_HAS_STD_COROUTINE)
 #endif // !defined(GENERATING_DOCUMENTATION)
 
 #include <boost/asio/detail/pop_options.hpp>
diff --git a/include/boost/asio/impl/buffered_read_stream.hpp b/include/boost/asio/impl/buffered_read_stream.hpp
index f94c5111..73f1049b 100644
--- a/include/boost/asio/impl/buffered_read_stream.hpp
+++ b/include/boost/asio/impl/buffered_read_stream.hpp
@@ -102,19 +102,29 @@ namespace detail
   };
 
   template <typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       buffered_fill_handler<ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       buffered_fill_handler<ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename ReadHandler>
@@ -126,19 +136,27 @@ namespace detail
   }
 
   template <typename Function, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       buffered_fill_handler<ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       buffered_fill_handler<ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Stream>
@@ -313,21 +331,31 @@ namespace detail
   };
 
   template <typename MutableBufferSequence, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       buffered_read_some_handler<
         MutableBufferSequence, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename MutableBufferSequence, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       buffered_read_some_handler<
         MutableBufferSequence, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename MutableBufferSequence, typename ReadHandler>
@@ -341,22 +369,30 @@ namespace detail
 
   template <typename Function, typename MutableBufferSequence,
       typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       buffered_read_some_handler<
         MutableBufferSequence, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename MutableBufferSequence,
       typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       buffered_read_some_handler<
         MutableBufferSequence, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Stream>
diff --git a/include/boost/asio/impl/buffered_write_stream.hpp b/include/boost/asio/impl/buffered_write_stream.hpp
index 74095cb3..cf33911f 100644
--- a/include/boost/asio/impl/buffered_write_stream.hpp
+++ b/include/boost/asio/impl/buffered_write_stream.hpp
@@ -87,19 +87,29 @@ namespace detail
   };
 
   template <typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       buffered_flush_handler<WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       buffered_flush_handler<WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename WriteHandler>
@@ -111,19 +121,27 @@ namespace detail
   }
 
   template <typename Function, typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       buffered_flush_handler<WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       buffered_flush_handler<WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Stream>
@@ -299,21 +317,31 @@ namespace detail
   };
 
   template <typename ConstBufferSequence, typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       buffered_write_some_handler<
         ConstBufferSequence, WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename ConstBufferSequence, typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       buffered_write_some_handler<
         ConstBufferSequence, WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename ConstBufferSequence, typename WriteHandler>
@@ -327,22 +355,30 @@ namespace detail
 
   template <typename Function, typename ConstBufferSequence,
       typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       buffered_write_some_handler<
         ConstBufferSequence, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename ConstBufferSequence,
       typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       buffered_write_some_handler<
         ConstBufferSequence, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Stream>
diff --git a/include/boost/asio/impl/co_spawn.hpp b/include/boost/asio/impl/co_spawn.hpp
index 2d71969e..a2f95779 100644
--- a/include/boost/asio/impl/co_spawn.hpp
+++ b/include/boost/asio/impl/co_spawn.hpp
@@ -18,7 +18,9 @@
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/awaitable.hpp>
 #include <boost/asio/dispatch.hpp>
+#include <boost/asio/execution/outstanding_work.hpp>
 #include <boost/asio/post.hpp>
+#include <boost/asio/prefer.hpp>
 #include <boost/asio/use_awaitable.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -27,12 +29,56 @@ namespace boost {
 namespace asio {
 namespace detail {
 
+template <typename Executor, typename = void>
+class co_spawn_work_guard
+{
+public:
+  typedef typename decay<
+      typename prefer_result_type<Executor,
+        execution::outstanding_work_t::tracked_t
+      >::type
+    >::type executor_type;
+
+  co_spawn_work_guard(const Executor& ex)
+    : executor_(boost::asio::prefer(ex, execution::outstanding_work.tracked))
+  {
+  }
+
+  executor_type get_executor() const BOOST_ASIO_NOEXCEPT
+  {
+    return executor_;
+  }
+
+private:
+  executor_type executor_;
+};
+
+template <typename Executor>
+struct co_spawn_work_guard<Executor,
+    typename enable_if<
+      !execution::is_executor<Executor>::value
+    >::type> : executor_work_guard<Executor>
+{
+  co_spawn_work_guard(const Executor& ex)
+    : executor_work_guard<Executor>(ex)
+  {
+  }
+};
+
+template <typename Executor>
+inline co_spawn_work_guard<Executor>
+make_co_spawn_work_guard(const Executor& ex)
+{
+  return co_spawn_work_guard<Executor>(ex);
+}
+
 template <typename T, typename Executor, typename F, typename Handler>
 awaitable<void, Executor> co_spawn_entry_point(
     awaitable<T, Executor>*, Executor ex, F f, Handler handler)
 {
-  auto spawn_work = make_work_guard(ex);
-  auto handler_work = make_work_guard(handler, ex);
+  auto spawn_work = make_co_spawn_work_guard(ex);
+  auto handler_work = make_co_spawn_work_guard(
+      boost::asio::get_associated_executor(handler, ex));
 
   (void) co_await (post)(spawn_work.get_executor(),
       use_awaitable_t<Executor>{});
@@ -67,11 +113,12 @@ template <typename Executor, typename F, typename Handler>
 awaitable<void, Executor> co_spawn_entry_point(
     awaitable<void, Executor>*, Executor ex, F f, Handler handler)
 {
-  auto spawn_work = make_work_guard(ex);
-  auto handler_work = make_work_guard(handler, ex);
+  auto spawn_work = make_co_spawn_work_guard(ex);
+  auto handler_work = make_co_spawn_work_guard(
+      boost::asio::get_associated_executor(handler, ex));
 
   (void) co_await (post)(spawn_work.get_executor(),
-      use_awaitable_t<Executor>{});
+      use_awaitable_t<Executor>{__FILE__, __LINE__, "co_spawn_entry_point"});
 
   std::exception_ptr e = nullptr;
   try
@@ -90,6 +137,24 @@ awaitable<void, Executor> co_spawn_entry_point(
       });
 }
 
+template <typename T, typename Executor>
+class awaitable_as_function
+{
+public:
+  explicit awaitable_as_function(awaitable<T, Executor>&& a)
+    : awaitable_(std::move(a))
+  {
+  }
+
+  awaitable<T, Executor> operator()()
+  {
+    return std::move(awaitable_);
+  }
+
+private:
+  awaitable<T, Executor> awaitable_;
+};
+
 template <typename Executor>
 class initiate_co_spawn
 {
@@ -123,6 +188,75 @@ private:
 
 } // namespace detail
 
+template <typename Executor, typename T, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr, T)) CompletionToken>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr, T))
+co_spawn(const Executor& ex,
+    awaitable<T, AwaitableExecutor> a, CompletionToken&& token,
+    typename enable_if<
+      (is_executor<Executor>::value || execution::is_executor<Executor>::value)
+        && is_convertible<Executor, AwaitableExecutor>::value
+    >::type*)
+{
+  return async_initiate<CompletionToken, void(std::exception_ptr, T)>(
+      detail::initiate_co_spawn<AwaitableExecutor>(AwaitableExecutor(ex)),
+      token, detail::awaitable_as_function<T, AwaitableExecutor>(std::move(a)));
+}
+
+template <typename Executor, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr)) CompletionToken>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr))
+co_spawn(const Executor& ex,
+    awaitable<void, AwaitableExecutor> a, CompletionToken&& token,
+    typename enable_if<
+      (is_executor<Executor>::value || execution::is_executor<Executor>::value)
+        && is_convertible<Executor, AwaitableExecutor>::value
+    >::type*)
+{
+  return async_initiate<CompletionToken, void(std::exception_ptr)>(
+      detail::initiate_co_spawn<AwaitableExecutor>(AwaitableExecutor(ex)),
+      token, detail::awaitable_as_function<
+        void, AwaitableExecutor>(std::move(a)));
+}
+
+template <typename ExecutionContext, typename T, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr, T)) CompletionToken>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr, T))
+co_spawn(ExecutionContext& ctx,
+    awaitable<T, AwaitableExecutor> a, CompletionToken&& token,
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value
+        && is_convertible<typename ExecutionContext::executor_type,
+          AwaitableExecutor>::value
+    >::type*)
+{
+  return (co_spawn)(ctx.get_executor(), std::move(a),
+      std::forward<CompletionToken>(token));
+}
+
+template <typename ExecutionContext, typename AwaitableExecutor,
+    BOOST_ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr)) CompletionToken>
+inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr))
+co_spawn(ExecutionContext& ctx,
+    awaitable<void, AwaitableExecutor> a, CompletionToken&& token,
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value
+        && is_convertible<typename ExecutionContext::executor_type,
+          AwaitableExecutor>::value
+    >::type*)
+{
+  return (co_spawn)(ctx.get_executor(), std::move(a),
+      std::forward<CompletionToken>(token));
+}
+
 template <typename Executor, typename F,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(typename detail::awaitable_signature<
       typename result_of<F()>::type>::type) CompletionToken>
@@ -130,11 +264,11 @@ inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken,
     typename detail::awaitable_signature<typename result_of<F()>::type>::type)
 co_spawn(const Executor& ex, F&& f, CompletionToken&& token,
     typename enable_if<
-      is_executor<Executor>::value
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
     >::type*)
 {
   return async_initiate<CompletionToken,
-    typename detail::awaitable_signature<typename result_of<F()>::type>>(
+    typename detail::awaitable_signature<typename result_of<F()>::type>::type>(
       detail::initiate_co_spawn<
         typename result_of<F()>::type::executor_type>(ex),
       token, std::forward<F>(f));
diff --git a/include/boost/asio/impl/compose.hpp b/include/boost/asio/impl/compose.hpp
index 3c329f03..62ae2a9d 100644
--- a/include/boost/asio/impl/compose.hpp
+++ b/include/boost/asio/impl/compose.hpp
@@ -16,11 +16,14 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <boost/asio/associated_executor.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/detail/variadic_templates.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/execution/outstanding_work.hpp>
 #include <boost/asio/executor_work_guard.hpp>
 #include <boost/asio/is_executor.hpp>
 #include <boost/asio/system_executor.hpp>
@@ -32,6 +35,50 @@ namespace asio {
 
 namespace detail
 {
+  template <typename Executor, typename = void>
+  class composed_work_guard
+  {
+  public:
+    typedef typename decay<
+        typename prefer_result_type<Executor,
+          execution::outstanding_work_t::tracked_t
+        >::type
+      >::type executor_type;
+
+    composed_work_guard(const Executor& ex)
+      : executor_(boost::asio::prefer(ex, execution::outstanding_work.tracked))
+    {
+    }
+
+    void reset()
+    {
+    }
+
+    executor_type get_executor() const BOOST_ASIO_NOEXCEPT
+    {
+      return executor_;
+    }
+
+  private:
+    executor_type executor_;
+  };
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+  template <typename Executor>
+  struct composed_work_guard<Executor,
+      typename enable_if<
+        !execution::is_executor<Executor>::value
+      >::type> : executor_work_guard<Executor>
+  {
+    composed_work_guard(const Executor& ex)
+      : executor_work_guard<Executor>(ex)
+    {
+    }
+  };
+
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
   template <typename>
   struct composed_io_executors;
 
@@ -159,7 +206,7 @@ namespace detail
     }
 
     typedef system_executor head_type;
-    executor_work_guard<system_executor> head_;
+    composed_work_guard<system_executor> head_;
   };
 
   template <typename Head>
@@ -178,7 +225,7 @@ namespace detail
     }
 
     typedef Head head_type;
-    executor_work_guard<Head> head_;
+    composed_work_guard<Head> head_;
   };
 
 #if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
@@ -201,7 +248,7 @@ namespace detail
     }
 
     typedef Head head_type;
-    executor_work_guard<Head> head_;
+    composed_work_guard<Head> head_;
     composed_work<void(Tail...)> tail_;
   };
 
@@ -227,7 +274,7 @@ namespace detail
     } \
   \
     typedef Head head_type; \
-    executor_work_guard<Head> head_; \
+    composed_work_guard<Head> head_; \
     composed_work<void(BOOST_ASIO_VARIADIC_TARGS(n))> tail_; \
   }; \
   /**/
@@ -249,12 +296,13 @@ namespace detail
 #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
   {
   public:
-    composed_op(BOOST_ASIO_MOVE_ARG(Impl) impl,
-        BOOST_ASIO_MOVE_ARG(Work) work,
-        BOOST_ASIO_MOVE_ARG(Handler) handler)
-      : impl_(BOOST_ASIO_MOVE_CAST(Impl)(impl)),
-        work_(BOOST_ASIO_MOVE_CAST(Work)(work)),
-        handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
+    template <typename I, typename W, typename H>
+    composed_op(BOOST_ASIO_MOVE_ARG(I) impl,
+        BOOST_ASIO_MOVE_ARG(W) work,
+        BOOST_ASIO_MOVE_ARG(H) handler)
+      : impl_(BOOST_ASIO_MOVE_CAST(I)(impl)),
+        work_(BOOST_ASIO_MOVE_CAST(W)(work)),
+        handler_(BOOST_ASIO_MOVE_CAST(H)(handler)),
         invocations_(0)
     {
     }
@@ -290,7 +338,7 @@ namespace detail
     template<typename... T>
     void operator()(BOOST_ASIO_MOVE_ARG(T)... t)
     {
-      if (invocations_ < ~unsigned(0))
+      if (invocations_ < ~0u)
         ++invocations_;
       impl_(*this, BOOST_ASIO_MOVE_CAST(T)(t)...);
     }
@@ -305,7 +353,7 @@ namespace detail
 
     void operator()()
     {
-      if (invocations_ < ~unsigned(0))
+      if (invocations_ < ~0u)
         ++invocations_;
       impl_(*this);
     }
@@ -320,7 +368,7 @@ namespace detail
     template<BOOST_ASIO_VARIADIC_TPARAMS(n)> \
     void operator()(BOOST_ASIO_VARIADIC_MOVE_PARAMS(n)) \
     { \
-      if (invocations_ < ~unsigned(0)) \
+      if (invocations_ < ~0u) \
         ++invocations_; \
       impl_(*this, BOOST_ASIO_VARIADIC_MOVE_ARGS(n)); \
     } \
@@ -345,19 +393,29 @@ namespace detail
   };
 
   template <typename Impl, typename Work, typename Handler, typename Signature>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       composed_op<Impl, Work, Handler, Signature>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Impl, typename Work, typename Handler, typename Signature>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       composed_op<Impl, Work, Handler, Signature>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Impl, typename Work, typename Handler, typename Signature>
@@ -371,20 +429,28 @@ namespace detail
 
   template <typename Function, typename Impl,
       typename Work, typename Handler, typename Signature>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       composed_op<Impl, Work, Handler, Signature>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename Impl,
       typename Work, typename Handler, typename Signature>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       composed_op<Impl, Work, Handler, Signature>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Signature, typename Executors>
@@ -498,6 +564,30 @@ async_compose(BOOST_ASIO_MOVE_ARG(Implementation) implementation,
   detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3)), \
   detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T4)(x4)), \
   detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T5)(x5))
+# define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_6 \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T4)(x4)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T5)(x5)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T6)(x6))
+# define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_7 \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T4)(x4)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T5)(x5)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T6)(x6)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T7)(x7))
+# define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_8 \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T4)(x4)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T5)(x5)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T6)(x6)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T7)(x7)), \
+  detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T8)(x8))
 
 #define BOOST_ASIO_PRIVATE_ASYNC_COMPOSE_DEF(n) \
   template <typename CompletionToken, typename Signature, \
@@ -523,6 +613,9 @@ async_compose(BOOST_ASIO_MOVE_ARG(Implementation) implementation,
 #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_3
 #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_4
 #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_5
+#undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_6
+#undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_7
+#undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_8
 
 #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
 #endif // !defined(GENERATING_DOCUMENTATION)
diff --git a/include/boost/asio/impl/connect.hpp b/include/boost/asio/impl/connect.hpp
index 82b17908..421ff2fc 100644
--- a/include/boost/asio/impl/connect.hpp
+++ b/include/boost/asio/impl/connect.hpp
@@ -22,6 +22,7 @@
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/throw_error.hpp>
@@ -358,6 +359,7 @@ namespace detail
           if (iter != end)
           {
             socket_.close(ec);
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
             socket_.async_connect(*iter,
                 BOOST_ASIO_MOVE_CAST(range_connect_op)(*this));
             return;
@@ -366,6 +368,7 @@ namespace detail
           if (start)
           {
             ec = boost::asio::error::not_found;
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
             boost::asio::post(socket_.get_executor(),
                 detail::bind_handler(
                   BOOST_ASIO_MOVE_CAST(range_connect_op)(*this), ec));
@@ -405,22 +408,32 @@ namespace detail
 
   template <typename Protocol, typename Executor, typename EndpointSequence,
       typename ConnectCondition, typename RangeConnectHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       range_connect_op<Protocol, Executor, EndpointSequence,
         ConnectCondition, RangeConnectHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Protocol, typename Executor, typename EndpointSequence,
       typename ConnectCondition, typename RangeConnectHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       range_connect_op<Protocol, Executor, EndpointSequence,
         ConnectCondition, RangeConnectHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Protocol, typename Executor, typename EndpointSequence,
@@ -436,23 +449,31 @@ namespace detail
   template <typename Function, typename Executor, typename Protocol,
       typename EndpointSequence, typename ConnectCondition,
       typename RangeConnectHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       range_connect_op<Protocol, Executor, EndpointSequence,
         ConnectCondition, RangeConnectHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename Executor, typename Protocol,
       typename EndpointSequence, typename ConnectCondition,
       typename RangeConnectHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       range_connect_op<Protocol, Executor, EndpointSequence,
         ConnectCondition, RangeConnectHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Protocol, typename Executor>
@@ -545,6 +566,7 @@ namespace detail
           if (iter_ != end_)
           {
             socket_.close(ec);
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
             socket_.async_connect(*iter_,
                 BOOST_ASIO_MOVE_CAST(iterator_connect_op)(*this));
             return;
@@ -553,6 +575,7 @@ namespace detail
           if (start)
           {
             ec = boost::asio::error::not_found;
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
             boost::asio::post(socket_.get_executor(),
                 detail::bind_handler(
                   BOOST_ASIO_MOVE_CAST(iterator_connect_op)(*this), ec));
@@ -591,22 +614,32 @@ namespace detail
 
   template <typename Protocol, typename Executor, typename Iterator,
       typename ConnectCondition, typename IteratorConnectHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       iterator_connect_op<Protocol, Executor, Iterator,
         ConnectCondition, IteratorConnectHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Protocol, typename Executor, typename Iterator,
       typename ConnectCondition, typename IteratorConnectHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       iterator_connect_op<Protocol, Executor, Iterator,
         ConnectCondition, IteratorConnectHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Protocol, typename Executor, typename Iterator,
@@ -622,23 +655,31 @@ namespace detail
   template <typename Function, typename Executor, typename Protocol,
       typename Iterator, typename ConnectCondition,
       typename IteratorConnectHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       iterator_connect_op<Protocol, Executor, Iterator,
         ConnectCondition, IteratorConnectHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename Executor, typename Protocol,
       typename Iterator, typename ConnectCondition,
       typename IteratorConnectHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       iterator_connect_op<Protocol, Executor, Iterator,
         ConnectCondition, IteratorConnectHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Protocol, typename Executor>
diff --git a/include/boost/asio/impl/defer.hpp b/include/boost/asio/impl/defer.hpp
index 4db26d19..7821bdaf 100644
--- a/include/boost/asio/impl/defer.hpp
+++ b/include/boost/asio/impl/defer.hpp
@@ -19,6 +19,11 @@
 #include <boost/asio/associated_allocator.hpp>
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/detail/work_dispatcher.hpp>
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/relationship.hpp>
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/require.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -30,14 +35,47 @@ class initiate_defer
 {
 public:
   template <typename CompletionHandler>
-  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler) const
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        execution::is_executor<
+          typename associated_executor<
+            typename decay<CompletionHandler>::type
+          >::type
+        >::value
+      >::type* = 0) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_executor<DecayedHandler>::type ex(
+    typename associated_executor<handler_t>::type ex(
         (get_associated_executor)(handler));
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typename associated_allocator<handler_t>::type alloc(
+        (get_associated_allocator)(handler));
+
+    execution::execute(
+        boost::asio::prefer(
+          boost::asio::require(ex, execution::blocking.never),
+          execution::relationship.continuation,
+          execution::allocator(alloc)),
+        BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
+  }
+
+  template <typename CompletionHandler>
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        !execution::is_executor<
+          typename associated_executor<
+            typename decay<CompletionHandler>::type
+          >::type
+        >::value
+      >::type* = 0) const
+  {
+    typedef typename decay<CompletionHandler>::type handler_t;
+
+    typename associated_executor<handler_t>::type ex(
+        (get_associated_executor)(handler));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
     ex.defer(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
@@ -61,18 +99,85 @@ public:
   }
 
   template <typename CompletionHandler>
-  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler) const
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        execution::is_executor<
+          typename conditional<true, executor_type, CompletionHandler>::type
+        >::value
+      >::type* = 0) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
-    ex_.defer(detail::work_dispatcher<DecayedHandler>(
-          BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler)), alloc);
+    if (this->is_same_executor(ex_, handler_ex))
+    {
+      execution::execute(
+          boost::asio::prefer(
+            boost::asio::require(ex_, execution::blocking.never),
+            execution::relationship.continuation,
+            execution::allocator(alloc)),
+          BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
+    }
+    else
+    {
+      execution::execute(
+          boost::asio::prefer(
+            boost::asio::require(ex_, execution::blocking.never),
+            execution::relationship.continuation,
+            execution::allocator(alloc)),
+          detail::work_dispatcher<handler_t, handler_ex_t>(
+            BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), handler_ex));
+    }
+  }
+
+  template <typename CompletionHandler>
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        !execution::is_executor<
+          typename conditional<true, executor_type, CompletionHandler>::type
+        >::value
+      >::type* = 0) const
+  {
+    typedef typename decay<CompletionHandler>::type handler_t;
+
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
+        (get_associated_allocator)(handler));
+
+    if (this->is_same_executor(ex_, handler_ex))
+    {
+      ex_.defer(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
+    }
+    else
+    {
+      ex_.defer(detail::work_dispatcher<handler_t, handler_ex_t>(
+            BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler),
+            handler_ex), alloc);
+    }
   }
 
 private:
+  template <typename T, typename U>
+  bool is_same_executor(const T&, const U&) const BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+
+  template <typename T>
+  bool is_same_executor(const T& a, const T& b) const BOOST_ASIO_NOEXCEPT
+  {
+    return a == b;
+  }
+
   Executor ex_;
 };
 
@@ -90,7 +195,9 @@ template <typename Executor,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void()) CompletionToken>
 BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) defer(
     const Executor& ex, BOOST_ASIO_MOVE_ARG(CompletionToken) token,
-    typename enable_if<is_executor<Executor>::value>::type*)
+    typename enable_if<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    >::type*)
 {
   return async_initiate<CompletionToken, void()>(
       detail::initiate_defer_with_executor<Executor>(ex), token);
@@ -103,8 +210,10 @@ inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) defer(
     typename enable_if<is_convertible<
       ExecutionContext&, execution_context&>::value>::type*)
 {
-  return (defer)(ctx.get_executor(),
-      BOOST_ASIO_MOVE_CAST(CompletionToken)(token));
+  return async_initiate<CompletionToken, void()>(
+      detail::initiate_defer_with_executor<
+        typename ExecutionContext::executor_type>(
+          ctx.get_executor()), token);
 }
 
 } // namespace asio
diff --git a/include/boost/asio/impl/dispatch.hpp b/include/boost/asio/impl/dispatch.hpp
index 8b0df469..e1642c1e 100644
--- a/include/boost/asio/impl/dispatch.hpp
+++ b/include/boost/asio/impl/dispatch.hpp
@@ -19,6 +19,9 @@
 #include <boost/asio/associated_allocator.hpp>
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/detail/work_dispatcher.hpp>
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/prefer.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -30,14 +33,46 @@ class initiate_dispatch
 {
 public:
   template <typename CompletionHandler>
-  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler) const
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        execution::is_executor<
+          typename associated_executor<
+            typename decay<CompletionHandler>::type
+          >::type
+        >::value
+      >::type* = 0) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_executor<DecayedHandler>::type ex(
+    typename associated_executor<handler_t>::type ex(
         (get_associated_executor)(handler));
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typename associated_allocator<handler_t>::type alloc(
+        (get_associated_allocator)(handler));
+
+    execution::execute(
+        boost::asio::prefer(ex,
+          execution::blocking.possibly,
+          execution::allocator(alloc)),
+        BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
+  }
+
+  template <typename CompletionHandler>
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        !execution::is_executor<
+          typename associated_executor<
+            typename decay<CompletionHandler>::type
+          >::type
+        >::value
+      >::type* = 0) const
+  {
+    typedef typename decay<CompletionHandler>::type handler_t;
+
+    typename associated_executor<handler_t>::type ex(
+        (get_associated_executor)(handler));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
     ex.dispatch(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
@@ -61,18 +96,83 @@ public:
   }
 
   template <typename CompletionHandler>
-  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler) const
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        execution::is_executor<
+          typename conditional<true, executor_type, CompletionHandler>::type
+        >::value
+      >::type* = 0) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
-    ex_.dispatch(detail::work_dispatcher<DecayedHandler>(
-          BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler)), alloc);
+    if (this->is_same_executor(ex_, handler_ex))
+    {
+      execution::execute(
+          boost::asio::prefer(ex_,
+            execution::blocking.possibly,
+            execution::allocator(alloc)),
+          BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
+    }
+    else
+    {
+      execution::execute(
+          boost::asio::prefer(ex_,
+            execution::blocking.possibly,
+            execution::allocator(alloc)),
+          detail::work_dispatcher<handler_t, handler_ex_t>(
+            BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), handler_ex));
+    }
+  }
+
+  template <typename CompletionHandler>
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        !execution::is_executor<
+          typename conditional<true, executor_type, CompletionHandler>::type
+        >::value
+      >::type* = 0) const
+  {
+    typedef typename decay<CompletionHandler>::type handler_t;
+
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
+        (get_associated_allocator)(handler));
+
+    if (this->is_same_executor(ex_, handler_ex))
+    {
+      ex_.dispatch(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
+    }
+    else
+    {
+      ex_.dispatch(detail::work_dispatcher<handler_t, handler_ex_t>(
+            BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler),
+            handler_ex), alloc);
+    }
   }
 
 private:
+  template <typename T, typename U>
+  bool is_same_executor(const T&, const U&) const BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+
+  template <typename T>
+  bool is_same_executor(const T& a, const T& b) const BOOST_ASIO_NOEXCEPT
+  {
+    return a == b;
+  }
+
   Executor ex_;
 };
 
@@ -90,7 +190,9 @@ template <typename Executor,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void()) CompletionToken>
 BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) dispatch(
     const Executor& ex, BOOST_ASIO_MOVE_ARG(CompletionToken) token,
-    typename enable_if<is_executor<Executor>::value>::type*)
+    typename enable_if<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    >::type*)
 {
   return async_initiate<CompletionToken, void()>(
       detail::initiate_dispatch_with_executor<Executor>(ex), token);
@@ -103,8 +205,10 @@ inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) dispatch(
     typename enable_if<is_convertible<
       ExecutionContext&, execution_context&>::value>::type*)
 {
-  return (dispatch)(ctx.get_executor(),
-      BOOST_ASIO_MOVE_CAST(CompletionToken)(token));
+  return async_initiate<CompletionToken, void()>(
+      detail::initiate_dispatch_with_executor<
+        typename ExecutionContext::executor_type>(
+          ctx.get_executor()), token);
 }
 
 } // namespace asio
diff --git a/include/boost/asio/impl/executor.hpp b/include/boost/asio/impl/executor.hpp
index 31a1e43b..261ca263 100644
--- a/include/boost/asio/impl/executor.hpp
+++ b/include/boost/asio/impl/executor.hpp
@@ -16,8 +16,10 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #include <boost/asio/detail/atomic_count.hpp>
-#include <boost/asio/detail/executor_function.hpp>
 #include <boost/asio/detail/global.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/recycling_allocator.hpp>
@@ -31,99 +33,7 @@ namespace asio {
 
 #if !defined(GENERATING_DOCUMENTATION)
 
-#if defined(BOOST_ASIO_HAS_MOVE)
-
-// Lightweight, move-only function object wrapper.
-class executor::function
-{
-public:
-  template <typename F, typename Alloc>
-  explicit function(F f, const Alloc& a)
-  {
-    // Allocate and construct an operation to wrap the function.
-    typedef detail::executor_function<F, Alloc> func_type;
-    typename func_type::ptr p = {
-      detail::addressof(a), func_type::ptr::allocate(a), 0 };
-    func_ = new (p.v) func_type(BOOST_ASIO_MOVE_CAST(F)(f), a);
-    p.v = 0;
-  }
-
-  function(function&& other) BOOST_ASIO_NOEXCEPT
-    : func_(other.func_)
-  {
-    other.func_ = 0;
-  }
-
-  ~function()
-  {
-    if (func_)
-      func_->destroy();
-  }
-
-  void operator()()
-  {
-    if (func_)
-    {
-      detail::executor_function_base* func = func_;
-      func_ = 0;
-      func->complete();
-    }
-  }
-
-private:
-  detail::executor_function_base* func_;
-};
-
-#else // defined(BOOST_ASIO_HAS_MOVE)
-
-// Not so lightweight, copyable function object wrapper.
-class executor::function
-{
-public:
-  template <typename F, typename Alloc>
-  explicit function(const F& f, const Alloc&)
-    : impl_(new impl<F>(f))
-  {
-  }
-
-  void operator()()
-  {
-    impl_->invoke_(impl_.get());
-  }
-
-private:
-  // Base class for polymorphic function implementations.
-  struct impl_base
-  {
-    void (*invoke_)(impl_base*);
-  };
-
-  // Polymorphic function implementation.
-  template <typename F>
-  struct impl : impl_base
-  {
-    impl(const F& f)
-      : function_(f)
-    {
-      invoke_ = &function::invoke<F>;
-    }
-
-    F function_;
-  };
-
-  // Helper to invoke a function.
-  template <typename F>
-  static void invoke(impl_base* i)
-  {
-    static_cast<impl<F>*>(i)->function_();
-  }
-
-  detail::shared_ptr<impl_base> impl_;
-};
-
-#endif // defined(BOOST_ASIO_HAS_MOVE)
-
-// Default polymorphic allocator implementation.
+// Default polymorphic executor implementation.
 template <typename Executor, typename Allocator>
 class executor::impl
   : public executor::impl_base
@@ -149,13 +59,13 @@ public:
 
   impl_base* clone() const BOOST_ASIO_NOEXCEPT
   {
-    ++ref_count_;
+    detail::ref_count_up(ref_count_);
     return const_cast<impl_base*>(static_cast<const impl_base*>(this));
   }
 
   void destroy() BOOST_ASIO_NOEXCEPT
   {
-    if (--ref_count_ == 0)
+    if (detail::ref_count_down(ref_count_))
     {
       allocator_type alloc(allocator_);
       impl* p = this;
@@ -247,7 +157,7 @@ private:
   };
 };
 
-// Polymorphic allocator specialisation for system_executor.
+// Polymorphic executor specialisation for system_executor.
 template <typename Allocator>
 class executor::impl<system_executor, Allocator>
   : public executor::impl_base
@@ -290,17 +200,20 @@ public:
 
   void dispatch(BOOST_ASIO_MOVE_ARG(function) f)
   {
-    executor_.dispatch(BOOST_ASIO_MOVE_CAST(function)(f), allocator_);
+    executor_.dispatch(BOOST_ASIO_MOVE_CAST(function)(f),
+        std::allocator<void>());
   }
 
   void post(BOOST_ASIO_MOVE_ARG(function) f)
   {
-    executor_.post(BOOST_ASIO_MOVE_CAST(function)(f), allocator_);
+    executor_.post(BOOST_ASIO_MOVE_CAST(function)(f),
+        std::allocator<void>());
   }
 
   void defer(BOOST_ASIO_MOVE_ARG(function) f)
   {
-    executor_.defer(BOOST_ASIO_MOVE_CAST(function)(f), allocator_);
+    executor_.defer(BOOST_ASIO_MOVE_CAST(function)(f),
+        std::allocator<void>());
   }
 
   type_id_result_type target_type() const BOOST_ASIO_NOEXCEPT
@@ -325,7 +238,6 @@ public:
 
 private:
   system_executor executor_;
-  Allocator allocator_;
 };
 
 template <typename Executor>
@@ -386,4 +298,6 @@ const Executor* executor::target() const BOOST_ASIO_NOEXCEPT
 
 #include <boost/asio/detail/pop_options.hpp>
 
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #endif // BOOST_ASIO_IMPL_EXECUTOR_HPP
diff --git a/include/boost/asio/impl/executor.ipp b/include/boost/asio/impl/executor.ipp
index 7b02ef2e..340578d6 100644
--- a/include/boost/asio/impl/executor.ipp
+++ b/include/boost/asio/impl/executor.ipp
@@ -16,6 +16,9 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #include <boost/asio/executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -37,4 +40,6 @@ const char* bad_executor::what() const BOOST_ASIO_NOEXCEPT_OR_NOTHROW
 
 #include <boost/asio/detail/pop_options.hpp>
 
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
 #endif // BOOST_ASIO_IMPL_EXECUTOR_IPP
diff --git a/include/boost/asio/impl/handler_alloc_hook.ipp b/include/boost/asio/impl/handler_alloc_hook.ipp
index 2b96e9fd..1e5ca9f8 100644
--- a/include/boost/asio/impl/handler_alloc_hook.ipp
+++ b/include/boost/asio/impl/handler_alloc_hook.ipp
@@ -25,9 +25,13 @@
 namespace boost {
 namespace asio {
 
-void* asio_handler_allocate(std::size_t size, ...)
+asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size, ...)
 {
-#if !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  (void)size;
+  return asio_handler_allocate_is_no_longer_used();
+#elif !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
   return detail::thread_info_base::allocate(
       detail::thread_context::thread_call_stack::top(), size);
 #else // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
@@ -35,9 +39,14 @@ void* asio_handler_allocate(std::size_t size, ...)
 #endif // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
 }
 
-void asio_handler_deallocate(void* pointer, std::size_t size, ...)
+asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size, ...)
 {
-#if !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  (void)pointer;
+  (void)size;
+  return asio_handler_deallocate_is_no_longer_used();
+#elif !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
   detail::thread_info_base::deallocate(
       detail::thread_context::thread_call_stack::top(), pointer, size);
 #else // !defined(BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING)
diff --git a/include/boost/asio/impl/io_context.hpp b/include/boost/asio/impl/io_context.hpp
index 91d2d7b2..553a86d5 100644
--- a/include/boost/asio/impl/io_context.hpp
+++ b/include/boost/asio/impl/io_context.hpp
@@ -157,10 +157,10 @@ struct io_context::initiate_dispatch
     {
       // Allocate and construct an operation to wrap the handler.
       typedef detail::completion_handler<
-        typename decay<LegacyCompletionHandler>::type> op;
+        typename decay<LegacyCompletionHandler>::type, executor_type> op;
       typename op::ptr p = { detail::addressof(handler2.value),
         op::ptr::allocate(handler2.value), 0 };
-      p.p = new (p.v) op(handler2.value);
+      p.p = new (p.v) op(handler2.value, self->get_executor());
 
       BOOST_ASIO_HANDLER_CREATION((*self, *p.p,
             "io_context", self, 0, "dispatch"));
@@ -197,10 +197,10 @@ struct io_context::initiate_post
 
     // Allocate and construct an operation to wrap the handler.
     typedef detail::completion_handler<
-      typename decay<LegacyCompletionHandler>::type> op;
+      typename decay<LegacyCompletionHandler>::type, executor_type> op;
     typename op::ptr p = { detail::addressof(handler2.value),
         op::ptr::allocate(handler2.value), 0 };
-    p.p = new (p.v) op(handler2.value);
+    p.p = new (p.v) op(handler2.value, self->get_executor());
 
     BOOST_ASIO_HANDLER_CREATION((*self, *p.p,
           "io_context", self, 0, "post"));
@@ -231,32 +231,133 @@ io_context::wrap(Handler handler)
 
 #endif // !defined(BOOST_ASIO_NO_DEPRECATED)
 
-inline io_context&
-io_context::executor_type::context() const BOOST_ASIO_NOEXCEPT
+template <typename Allocator, unsigned int Bits>
+io_context::basic_executor_type<Allocator, Bits>&
+io_context::basic_executor_type<Allocator, Bits>::operator=(
+    const basic_executor_type& other) BOOST_ASIO_NOEXCEPT
 {
-  return io_context_;
+  if (this != &other)
+  {
+    io_context* old_io_context = io_context_;
+    io_context_ = other.io_context_;
+    allocator_ = other.allocator_;
+    bits_ = other.bits_;
+    if (Bits & outstanding_work_tracked)
+    {
+      if (io_context_)
+        io_context_->impl_.work_started();
+      if (old_io_context)
+        old_io_context->impl_.work_finished();
+    }
+  }
+  return *this;
 }
 
-inline void
-io_context::executor_type::on_work_started() const BOOST_ASIO_NOEXCEPT
+#if defined(BOOST_ASIO_HAS_MOVE)
+template <typename Allocator, unsigned int Bits>
+io_context::basic_executor_type<Allocator, Bits>&
+io_context::basic_executor_type<Allocator, Bits>::operator=(
+    basic_executor_type&& other) BOOST_ASIO_NOEXCEPT
 {
-  io_context_.impl_.work_started();
+  if (this != &other)
+  {
+    io_context_ = other.io_context_;
+    allocator_ = std::move(other.allocator_);
+    bits_ = other.bits_;
+    if (Bits & outstanding_work_tracked)
+      other.io_context_ = 0;
+  }
+  return *this;
+}
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+template <typename Allocator, unsigned int Bits>
+inline bool io_context::basic_executor_type<Allocator,
+    Bits>::running_in_this_thread() const BOOST_ASIO_NOEXCEPT
+{
+  return io_context_->impl_.can_dispatch();
 }
 
-inline void
-io_context::executor_type::on_work_finished() const BOOST_ASIO_NOEXCEPT
+template <typename Allocator, unsigned int Bits>
+template <typename Function>
+void io_context::basic_executor_type<Allocator, Bits>::execute(
+    BOOST_ASIO_MOVE_ARG(Function) f) const
 {
-  io_context_.impl_.work_finished();
+  typedef typename decay<Function>::type function_type;
+
+  // Invoke immediately if the blocking.possibly property is enabled and we are
+  // already inside the thread pool.
+  if ((bits_ & blocking_never) == 0 && io_context_->impl_.can_dispatch())
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(BOOST_ASIO_MOVE_CAST(Function)(f));
+
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       //   && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+      detail::fenced_block b(detail::fenced_block::full);
+      boost_asio_handler_invoke_helpers::invoke(tmp, tmp);
+      return;
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      io_context_->impl_.capture_current_exception();
+      return;
+    }
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       //   && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, Allocator, detail::operation> op;
+  typename op::ptr p = { detail::addressof(allocator_),
+      op::ptr::allocate(allocator_), 0 };
+  p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), allocator_);
+
+  BOOST_ASIO_HANDLER_CREATION((*io_context_, *p.p,
+        "io_context", io_context_, 0, "execute"));
+
+  io_context_->impl_.post_immediate_completion(p.p,
+      (bits_ & relationship_continuation) != 0);
+  p.v = p.p = 0;
 }
 
-template <typename Function, typename Allocator>
-void io_context::executor_type::dispatch(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+template <typename Allocator, unsigned int Bits>
+inline io_context& io_context::basic_executor_type<
+    Allocator, Bits>::context() const BOOST_ASIO_NOEXCEPT
+{
+  return *io_context_;
+}
+
+template <typename Allocator, unsigned int Bits>
+inline void io_context::basic_executor_type<Allocator,
+    Bits>::on_work_started() const BOOST_ASIO_NOEXCEPT
+{
+  io_context_->impl_.work_started();
+}
+
+template <typename Allocator, unsigned int Bits>
+inline void io_context::basic_executor_type<Allocator,
+    Bits>::on_work_finished() const BOOST_ASIO_NOEXCEPT
+{
+  io_context_->impl_.work_finished();
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void io_context::basic_executor_type<Allocator, Bits>::dispatch(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
   // Invoke immediately if we are already inside the thread pool.
-  if (io_context_.impl_.can_dispatch())
+  if (io_context_->impl_.can_dispatch())
   {
     // Make a local, non-const copy of the function.
     function_type tmp(BOOST_ASIO_MOVE_CAST(Function)(f));
@@ -267,58 +368,58 @@ void io_context::executor_type::dispatch(
   }
 
   // Allocate and construct an operation to wrap the function.
-  typedef detail::executor_op<function_type, Allocator, detail::operation> op;
+  typedef detail::executor_op<function_type,
+      OtherAllocator, detail::operation> op;
   typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
   p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), a);
 
-  BOOST_ASIO_HANDLER_CREATION((this->context(), *p.p,
-        "io_context", &this->context(), 0, "dispatch"));
+  BOOST_ASIO_HANDLER_CREATION((*io_context_, *p.p,
+        "io_context", io_context_, 0, "dispatch"));
 
-  io_context_.impl_.post_immediate_completion(p.p, false);
+  io_context_->impl_.post_immediate_completion(p.p, false);
   p.v = p.p = 0;
 }
 
-template <typename Function, typename Allocator>
-void io_context::executor_type::post(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void io_context::basic_executor_type<Allocator, Bits>::post(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
   // Allocate and construct an operation to wrap the function.
-  typedef detail::executor_op<function_type, Allocator, detail::operation> op;
+  typedef detail::executor_op<function_type,
+      OtherAllocator, detail::operation> op;
   typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
   p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), a);
 
-  BOOST_ASIO_HANDLER_CREATION((this->context(), *p.p,
-        "io_context", &this->context(), 0, "post"));
+  BOOST_ASIO_HANDLER_CREATION((*io_context_, *p.p,
+        "io_context", io_context_, 0, "post"));
 
-  io_context_.impl_.post_immediate_completion(p.p, false);
+  io_context_->impl_.post_immediate_completion(p.p, false);
   p.v = p.p = 0;
 }
 
-template <typename Function, typename Allocator>
-void io_context::executor_type::defer(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void io_context::basic_executor_type<Allocator, Bits>::defer(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
   // Allocate and construct an operation to wrap the function.
-  typedef detail::executor_op<function_type, Allocator, detail::operation> op;
+  typedef detail::executor_op<function_type,
+      OtherAllocator, detail::operation> op;
   typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
   p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), a);
 
-  BOOST_ASIO_HANDLER_CREATION((this->context(), *p.p,
-        "io_context", &this->context(), 0, "defer"));
+  BOOST_ASIO_HANDLER_CREATION((*io_context_, *p.p,
+        "io_context", io_context_, 0, "defer"));
 
-  io_context_.impl_.post_immediate_completion(p.p, true);
+  io_context_->impl_.post_immediate_completion(p.p, true);
   p.v = p.p = 0;
 }
-
-inline bool
-io_context::executor_type::running_in_this_thread() const BOOST_ASIO_NOEXCEPT
-{
-  return io_context_.impl_.can_dispatch();
-}
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 #if !defined(BOOST_ASIO_NO_DEPRECATED)
 inline io_context::work::work(boost::asio::io_context& io_context)
diff --git a/include/boost/asio/impl/multiple_exceptions.ipp b/include/boost/asio/impl/multiple_exceptions.ipp
new file mode 100644
index 00000000..c8530bb9
--- /dev/null
+++ b/include/boost/asio/impl/multiple_exceptions.ipp
@@ -0,0 +1,51 @@
+//
+// impl/multiple_exceptions.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_IMPL_MULTIPLE_EXCEPTIONS_IPP
+#define BOOST_ASIO_IMPL_MULTIPLE_EXCEPTIONS_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/multiple_exceptions.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+
+multiple_exceptions::multiple_exceptions(
+    std::exception_ptr first) BOOST_ASIO_NOEXCEPT
+  : first_(BOOST_ASIO_MOVE_CAST(std::exception_ptr)(first))
+{
+}
+
+const char* multiple_exceptions::what() const BOOST_ASIO_NOEXCEPT_OR_NOTHROW
+{
+  return "multiple exceptions";
+}
+
+std::exception_ptr multiple_exceptions::first_exception() const
+{
+  return first_;
+}
+
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_IMPL_MULTIPLE_EXCEPTIONS_IPP
diff --git a/include/boost/asio/impl/post.hpp b/include/boost/asio/impl/post.hpp
index ef7a739b..3a89a1c6 100644
--- a/include/boost/asio/impl/post.hpp
+++ b/include/boost/asio/impl/post.hpp
@@ -19,6 +19,11 @@
 #include <boost/asio/associated_allocator.hpp>
 #include <boost/asio/associated_executor.hpp>
 #include <boost/asio/detail/work_dispatcher.hpp>
+#include <boost/asio/execution/allocator.hpp>
+#include <boost/asio/execution/blocking.hpp>
+#include <boost/asio/execution/relationship.hpp>
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/require.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -30,14 +35,47 @@ class initiate_post
 {
 public:
   template <typename CompletionHandler>
-  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler) const
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        execution::is_executor<
+          typename associated_executor<
+            typename decay<CompletionHandler>::type
+          >::type
+        >::value
+      >::type* = 0) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_executor<DecayedHandler>::type ex(
+    typename associated_executor<handler_t>::type ex(
         (get_associated_executor)(handler));
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typename associated_allocator<handler_t>::type alloc(
+        (get_associated_allocator)(handler));
+
+    execution::execute(
+        boost::asio::prefer(
+          boost::asio::require(ex, execution::blocking.never),
+          execution::relationship.fork,
+          execution::allocator(alloc)),
+        BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
+  }
+
+  template <typename CompletionHandler>
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        !execution::is_executor<
+          typename associated_executor<
+            typename decay<CompletionHandler>::type
+          >::type
+        >::value
+      >::type* = 0) const
+  {
+    typedef typename decay<CompletionHandler>::type handler_t;
+
+    typename associated_executor<handler_t>::type ex(
+        (get_associated_executor)(handler));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
     ex.post(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
@@ -61,18 +99,85 @@ public:
   }
 
   template <typename CompletionHandler>
-  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler) const
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        execution::is_executor<
+          typename conditional<true, executor_type, CompletionHandler>::type
+        >::value
+      >::type* = 0) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
-    ex_.post(detail::work_dispatcher<DecayedHandler>(
-          BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler)), alloc);
+    if (this->is_same_executor(ex_, handler_ex))
+    {
+      execution::execute(
+          boost::asio::prefer(
+            boost::asio::require(ex_, execution::blocking.never),
+            execution::relationship.fork,
+            execution::allocator(alloc)),
+          BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler));
+    }
+    else
+    {
+      execution::execute(
+          boost::asio::prefer(
+            boost::asio::require(ex_, execution::blocking.never),
+            execution::relationship.fork,
+            execution::allocator(alloc)),
+          detail::work_dispatcher<handler_t, handler_ex_t>(
+            BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), handler_ex));
+    }
+  }
+
+  template <typename CompletionHandler>
+  void operator()(BOOST_ASIO_MOVE_ARG(CompletionHandler) handler,
+      typename enable_if<
+        !execution::is_executor<
+          typename conditional<true, executor_type, CompletionHandler>::type
+        >::value
+      >::type* = 0) const
+  {
+    typedef typename decay<CompletionHandler>::type handler_t;
+
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
+        (get_associated_allocator)(handler));
+
+    if (this->is_same_executor(ex_, handler_ex))
+    {
+      ex_.post(BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
+    }
+    else
+    {
+      ex_.post(detail::work_dispatcher<handler_t, handler_ex_t>(
+            BOOST_ASIO_MOVE_CAST(CompletionHandler)(handler),
+            handler_ex), alloc);
+    }
   }
 
 private:
+  template <typename T, typename U>
+  bool is_same_executor(const T&, const U&) const BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+
+  template <typename T>
+  bool is_same_executor(const T& a, const T& b) const BOOST_ASIO_NOEXCEPT
+  {
+    return a == b;
+  }
+
   Executor ex_;
 };
 
@@ -90,7 +195,9 @@ template <typename Executor,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void()) CompletionToken>
 BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) post(
     const Executor& ex, BOOST_ASIO_MOVE_ARG(CompletionToken) token,
-    typename enable_if<is_executor<Executor>::value>::type*)
+    typename enable_if<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    >::type*)
 {
   return async_initiate<CompletionToken, void()>(
       detail::initiate_post_with_executor<Executor>(ex), token);
@@ -103,8 +210,10 @@ inline BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) post(
     typename enable_if<is_convertible<
       ExecutionContext&, execution_context&>::value>::type*)
 {
-  return (post)(ctx.get_executor(),
-      BOOST_ASIO_MOVE_CAST(CompletionToken)(token));
+  return async_initiate<CompletionToken, void()>(
+      detail::initiate_post_with_executor<
+        typename ExecutionContext::executor_type>(
+          ctx.get_executor()), token);
 }
 
 } // namespace asio
diff --git a/include/boost/asio/impl/read.hpp b/include/boost/asio/impl/read.hpp
index 9889aceb..30919788 100644
--- a/include/boost/asio/impl/read.hpp
+++ b/include/boost/asio/impl/read.hpp
@@ -28,6 +28,7 @@
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/throw_error.hpp>
@@ -361,8 +362,11 @@ namespace detail
         max_size = this->check_for_completion(ec, buffers_.total_consumed());
         do
         {
-          stream_.async_read_some(buffers_.prepare(max_size),
-              BOOST_ASIO_MOVE_CAST(read_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read"));
+            stream_.async_read_some(buffers_.prepare(max_size),
+                BOOST_ASIO_MOVE_CAST(read_op)(*this));
+          }
           return; default:
           buffers_.consume(bytes_transferred);
           if ((!ec && bytes_transferred == 0) || buffers_.empty())
@@ -387,23 +391,33 @@ namespace detail
   template <typename AsyncReadStream, typename MutableBufferSequence,
       typename MutableBufferIterator, typename CompletionCondition,
       typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_op<AsyncReadStream, MutableBufferSequence, MutableBufferIterator,
         CompletionCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename MutableBufferSequence,
       typename MutableBufferIterator, typename CompletionCondition,
       typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_op<AsyncReadStream, MutableBufferSequence, MutableBufferIterator,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename MutableBufferSequence,
@@ -421,23 +435,31 @@ namespace detail
   template <typename Function, typename AsyncReadStream,
       typename MutableBufferSequence, typename MutableBufferIterator,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_op<AsyncReadStream, MutableBufferSequence, MutableBufferIterator,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename MutableBufferSequence, typename MutableBufferIterator,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_op<AsyncReadStream, MutableBufferSequence, MutableBufferIterator,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename MutableBufferSequence,
@@ -632,8 +654,11 @@ namespace detail
                 buffers_.max_size() - buffers_.size()));
         for (;;)
         {
-          stream_.async_read_some(buffers_.prepare(bytes_available),
-              BOOST_ASIO_MOVE_CAST(read_dynbuf_v1_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read"));
+            stream_.async_read_some(buffers_.prepare(bytes_available),
+                BOOST_ASIO_MOVE_CAST(read_dynbuf_v1_op)(*this));
+          }
           return; default:
           total_transferred_ += bytes_transferred;
           buffers_.commit(bytes_transferred);
@@ -661,22 +686,32 @@ namespace detail
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
       typename CompletionCondition, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_dynbuf_v1_op<AsyncReadStream, DynamicBuffer_v1,
         CompletionCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_dynbuf_v1_op<AsyncReadStream, DynamicBuffer_v1,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
@@ -693,23 +728,31 @@ namespace detail
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename CompletionCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_dynbuf_v1_op<AsyncReadStream, DynamicBuffer_v1,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename CompletionCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_dynbuf_v1_op<AsyncReadStream, DynamicBuffer_v1,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -932,8 +975,11 @@ namespace detail
         {
           pos = buffers_.size();
           buffers_.grow(bytes_available_);
-          stream_.async_read_some(buffers_.data(pos, bytes_available_),
-              BOOST_ASIO_MOVE_CAST(read_dynbuf_v2_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read"));
+            stream_.async_read_some(buffers_.data(pos, bytes_available_),
+                BOOST_ASIO_MOVE_CAST(read_dynbuf_v2_op)(*this));
+          }
           return; default:
           total_transferred_ += bytes_transferred;
           buffers_.shrink(bytes_available_ - bytes_transferred);
@@ -962,22 +1008,32 @@ namespace detail
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
       typename CompletionCondition, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_dynbuf_v2_op<AsyncReadStream, DynamicBuffer_v2,
         CompletionCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_dynbuf_v2_op<AsyncReadStream, DynamicBuffer_v2,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
@@ -994,23 +1050,31 @@ namespace detail
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename CompletionCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_dynbuf_v2_op<AsyncReadStream, DynamicBuffer_v2,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename CompletionCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_dynbuf_v2_op<AsyncReadStream, DynamicBuffer_v2,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
diff --git a/include/boost/asio/impl/read_at.hpp b/include/boost/asio/impl/read_at.hpp
index 8edc5e08..e3b710f5 100644
--- a/include/boost/asio/impl/read_at.hpp
+++ b/include/boost/asio/impl/read_at.hpp
@@ -28,6 +28,7 @@
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/throw_error.hpp>
@@ -226,9 +227,12 @@ namespace detail
         max_size = this->check_for_completion(ec, buffers_.total_consumed());
         do
         {
-          device_.async_read_some_at(
-              offset_ + buffers_.total_consumed(), buffers_.prepare(max_size),
-              BOOST_ASIO_MOVE_CAST(read_at_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read_at"));
+            device_.async_read_some_at(
+                offset_ + buffers_.total_consumed(), buffers_.prepare(max_size),
+                BOOST_ASIO_MOVE_CAST(read_at_op)(*this));
+          }
           return; default:
           buffers_.consume(bytes_transferred);
           if ((!ec && bytes_transferred == 0) || buffers_.empty())
@@ -254,23 +258,33 @@ namespace detail
   template <typename AsyncRandomAccessReadDevice,
       typename MutableBufferSequence, typename MutableBufferIterator,
       typename CompletionCondition, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
         MutableBufferIterator, CompletionCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessReadDevice,
       typename MutableBufferSequence, typename MutableBufferIterator,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
         MutableBufferIterator, CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessReadDevice,
@@ -288,23 +302,31 @@ namespace detail
   template <typename Function, typename AsyncRandomAccessReadDevice,
       typename MutableBufferSequence, typename MutableBufferIterator,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
         MutableBufferIterator, CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncRandomAccessReadDevice,
       typename MutableBufferSequence, typename MutableBufferIterator,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
         MutableBufferIterator, CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessReadDevice,
@@ -501,9 +523,12 @@ namespace detail
         bytes_available = read_size_helper(streambuf_, max_size);
         for (;;)
         {
-          device_.async_read_some_at(offset_ + total_transferred_,
-              streambuf_.prepare(bytes_available),
-              BOOST_ASIO_MOVE_CAST(read_at_streambuf_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read_at"));
+            device_.async_read_some_at(offset_ + total_transferred_,
+                streambuf_.prepare(bytes_available),
+                BOOST_ASIO_MOVE_CAST(read_at_streambuf_op)(*this));
+          }
           return; default:
           total_transferred_ += bytes_transferred;
           streambuf_.commit(bytes_transferred);
@@ -528,22 +553,32 @@ namespace detail
 
   template <typename AsyncRandomAccessReadDevice, typename Allocator,
       typename CompletionCondition, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_at_streambuf_op<AsyncRandomAccessReadDevice, Allocator,
         CompletionCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessReadDevice, typename Allocator,
       typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_at_streambuf_op<AsyncRandomAccessReadDevice, Allocator,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessReadDevice, typename Allocator,
@@ -559,22 +594,30 @@ namespace detail
 
   template <typename Function, typename AsyncRandomAccessReadDevice,
       typename Allocator, typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_at_streambuf_op<AsyncRandomAccessReadDevice, Allocator,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncRandomAccessReadDevice,
       typename Allocator, typename CompletionCondition, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_at_streambuf_op<AsyncRandomAccessReadDevice, Allocator,
         CompletionCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessReadDevice>
diff --git a/include/boost/asio/impl/read_until.hpp b/include/boost/asio/impl/read_until.hpp
index 132adfe8..faac5d6d 100644
--- a/include/boost/asio/impl/read_until.hpp
+++ b/include/boost/asio/impl/read_until.hpp
@@ -27,6 +27,7 @@
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/limits.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
@@ -871,9 +872,13 @@ namespace detail
           if (!start && bytes_to_read == 0)
             break;
 
-          // Start a new asynchronous read op_v1eration to obtain more data.
-          stream_.async_read_some(buffers_.prepare(bytes_to_read),
-              BOOST_ASIO_MOVE_CAST(read_until_delim_op_v1)(*this));
+          // Start a new asynchronous read operation to obtain more data.
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.prepare(bytes_to_read),
+                BOOST_ASIO_MOVE_CAST(read_until_delim_op_v1)(*this));
+          }
           return; default:
           buffers_.commit(bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -903,22 +908,32 @@ namespace detail
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_delim_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_delim_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
@@ -934,22 +949,30 @@ namespace detail
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_delim_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_delim_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -1155,9 +1178,13 @@ namespace detail
           if (!start && bytes_to_read == 0)
             break;
 
-          // Start a new asynchronous read op_v1eration to obtain more data.
-          stream_.async_read_some(buffers_.prepare(bytes_to_read),
-              BOOST_ASIO_MOVE_CAST(read_until_delim_string_op_v1)(*this));
+          // Start a new asynchronous read operation to obtain more data.
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.prepare(bytes_to_read),
+                BOOST_ASIO_MOVE_CAST(read_until_delim_string_op_v1)(*this));
+          }
           return; default:
           buffers_.commit(bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -1187,22 +1214,32 @@ namespace detail
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_delim_string_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_delim_string_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
@@ -1218,22 +1255,30 @@ namespace detail
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_delim_string_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_delim_string_op_v1<AsyncReadStream,
         DynamicBuffer_v1, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -1447,9 +1492,13 @@ namespace detail
           if (!start && bytes_to_read == 0)
             break;
 
-          // Start a new asynchronous read op_v1eration to obtain more data.
-          stream_.async_read_some(buffers_.prepare(bytes_to_read),
-              BOOST_ASIO_MOVE_CAST(read_until_expr_op_v1)(*this));
+          // Start a new asynchronous read operation to obtain more data.
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.prepare(bytes_to_read),
+                BOOST_ASIO_MOVE_CAST(read_until_expr_op_v1)(*this));
+          }
           return; default:
           buffers_.commit(bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -1479,22 +1528,32 @@ namespace detail
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
       typename RegEx, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_expr_op_v1<AsyncReadStream,
         DynamicBuffer_v1, RegEx, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
       typename RegEx, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_expr_op_v1<AsyncReadStream,
         DynamicBuffer_v1, RegEx, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
@@ -1510,22 +1569,30 @@ namespace detail
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename RegEx, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_expr_op_v1<AsyncReadStream,
         DynamicBuffer_v1, RegEx, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename RegEx, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_expr_op_v1<AsyncReadStream,
         DynamicBuffer_v1, RegEx, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -1732,9 +1799,13 @@ namespace detail
           if (!start && bytes_to_read == 0)
             break;
 
-          // Start a new asynchronous read op_v1eration to obtain more data.
-          stream_.async_read_some(buffers_.prepare(bytes_to_read),
-              BOOST_ASIO_MOVE_CAST(read_until_match_op_v1)(*this));
+          // Start a new asynchronous read operation to obtain more data.
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.prepare(bytes_to_read),
+                BOOST_ASIO_MOVE_CAST(read_until_match_op_v1)(*this));
+          }
           return; default:
           buffers_.commit(bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -1764,22 +1835,32 @@ namespace detail
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
       typename MatchCondition, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_match_op_v1<AsyncReadStream, DynamicBuffer_v1,
         MatchCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
       typename MatchCondition, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_match_op_v1<AsyncReadStream, DynamicBuffer_v1,
         MatchCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v1,
@@ -1796,23 +1877,31 @@ namespace detail
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename MatchCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_match_op_v1<AsyncReadStream, DynamicBuffer_v1,
         MatchCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v1, typename MatchCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_match_op_v1<AsyncReadStream, DynamicBuffer_v1,
       MatchCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -2079,11 +2168,15 @@ namespace detail
           if (!start && bytes_to_read_ == 0)
             break;
 
-          // Start a new asynchronous read op_v2eration to obtain more data.
+          // Start a new asynchronous read operation to obtain more data.
           pos = buffers_.size();
           buffers_.grow(bytes_to_read_);
-          stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
-              BOOST_ASIO_MOVE_CAST(read_until_delim_op_v2)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
+                BOOST_ASIO_MOVE_CAST(read_until_delim_op_v2)(*this));
+          }
           return; default:
           buffers_.shrink(bytes_to_read_ - bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -2114,22 +2207,32 @@ namespace detail
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_delim_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_delim_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
@@ -2145,22 +2248,30 @@ namespace detail
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_delim_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_delim_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -2368,11 +2479,15 @@ namespace detail
           if (!start && bytes_to_read_ == 0)
             break;
 
-          // Start a new asynchronous read op_v2eration to obtain more data.
+          // Start a new asynchronous read operation to obtain more data.
           pos = buffers_.size();
           buffers_.grow(bytes_to_read_);
-          stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
-              BOOST_ASIO_MOVE_CAST(read_until_delim_string_op_v2)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
+                BOOST_ASIO_MOVE_CAST(read_until_delim_string_op_v2)(*this));
+          }
           return; default:
           buffers_.shrink(bytes_to_read_ - bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -2403,22 +2518,32 @@ namespace detail
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_delim_string_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_delim_string_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream,
@@ -2434,22 +2559,30 @@ namespace detail
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_delim_string_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_delim_string_op_v2<AsyncReadStream,
         DynamicBuffer_v2, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -2667,11 +2800,15 @@ namespace detail
           if (!start && bytes_to_read_ == 0)
             break;
 
-          // Start a new asynchronous read op_v2eration to obtain more data.
+          // Start a new asynchronous read operation to obtain more data.
           pos = buffers_.size();
           buffers_.grow(bytes_to_read_);
-          stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
-              BOOST_ASIO_MOVE_CAST(read_until_expr_op_v2)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
+                BOOST_ASIO_MOVE_CAST(read_until_expr_op_v2)(*this));
+          }
           return; default:
           buffers_.shrink(bytes_to_read_ - bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -2702,22 +2839,32 @@ namespace detail
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
       typename RegEx, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_expr_op_v2<AsyncReadStream,
         DynamicBuffer_v2, RegEx, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
       typename RegEx, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_expr_op_v2<AsyncReadStream,
         DynamicBuffer_v2, RegEx, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
@@ -2733,22 +2880,30 @@ namespace detail
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename RegEx, typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_expr_op_v2<AsyncReadStream,
         DynamicBuffer_v2, RegEx, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename RegEx, typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_expr_op_v2<AsyncReadStream,
         DynamicBuffer_v2, RegEx, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
@@ -2958,11 +3113,15 @@ namespace detail
           if (!start && bytes_to_read_ == 0)
             break;
 
-          // Start a new asynchronous read op_v2eration to obtain more data.
+          // Start a new asynchronous read operation to obtain more data.
           pos = buffers_.size();
           buffers_.grow(bytes_to_read_);
-          stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
-              BOOST_ASIO_MOVE_CAST(read_until_match_op_v2)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, "async_read_until"));
+            stream_.async_read_some(buffers_.data(pos, bytes_to_read_),
+                BOOST_ASIO_MOVE_CAST(read_until_match_op_v2)(*this));
+          }
           return; default:
           buffers_.shrink(bytes_to_read_ - bytes_transferred);
           if (ec || bytes_transferred == 0)
@@ -2993,22 +3152,32 @@ namespace detail
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
       typename MatchCondition, typename ReadHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       read_until_match_op_v2<AsyncReadStream, DynamicBuffer_v2,
         MatchCondition, ReadHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
       typename MatchCondition, typename ReadHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       read_until_match_op_v2<AsyncReadStream, DynamicBuffer_v2,
         MatchCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream, typename DynamicBuffer_v2,
@@ -3025,23 +3194,31 @@ namespace detail
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename MatchCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       read_until_match_op_v2<AsyncReadStream, DynamicBuffer_v2,
         MatchCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncReadStream,
       typename DynamicBuffer_v2, typename MatchCondition,
       typename ReadHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       read_until_match_op_v2<AsyncReadStream, DynamicBuffer_v2,
       MatchCondition, ReadHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncReadStream>
diff --git a/include/boost/asio/impl/redirect_error.hpp b/include/boost/asio/impl/redirect_error.hpp
index eb65e83d..a358b47c 100644
--- a/include/boost/asio/impl/redirect_error.hpp
+++ b/include/boost/asio/impl/redirect_error.hpp
@@ -126,19 +126,29 @@ public:
 };
 
 template <typename Handler>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     redirect_error_handler<Handler>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     redirect_error_handler<Handler>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Handler>
@@ -150,19 +160,27 @@ inline bool asio_handler_is_continuation(
 }
 
 template <typename Function, typename Handler>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     redirect_error_handler<Handler>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Handler>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     redirect_error_handler<Handler>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Signature>
diff --git a/include/boost/asio/impl/spawn.hpp b/include/boost/asio/impl/spawn.hpp
index 3eef52c6..1c5706e7 100644
--- a/include/boost/asio/impl/spawn.hpp
+++ b/include/boost/asio/impl/spawn.hpp
@@ -110,19 +110,29 @@ namespace detail {
   };
 
   template <typename Handler, typename T>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       coro_handler<Handler, T>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Handler, typename T>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       coro_handler<Handler, T>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Handler, typename T>
@@ -132,19 +142,27 @@ namespace detail {
   }
 
   template <typename Function, typename Handler, typename T>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       coro_handler<Handler, T>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename Handler, typename T>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       coro_handler<Handler, T>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Handler, typename T>
@@ -359,19 +377,27 @@ namespace detail {
   };
 
   template <typename Function, typename Handler, typename Function1>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       spawn_helper<Handler, Function1>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->data_->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename Handler, typename Function1>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       spawn_helper<Handler, Function1>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->data_->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   inline void default_spawn_handler() {}
@@ -394,7 +420,9 @@ template <typename Handler, typename Function>
 void spawn(BOOST_ASIO_MOVE_ARG(Handler) handler,
     BOOST_ASIO_MOVE_ARG(Function) function,
     const boost::coroutines::attributes& attributes,
-    typename enable_if<!is_executor<typename decay<Handler>::type>::value &&
+    typename enable_if<
+      !is_executor<typename decay<Handler>::type>::value &&
+      !execution::is_executor<typename decay<Handler>::type>::value &&
       !is_convertible<Handler&, execution_context&>::value>::type*)
 {
   typedef typename decay<Handler>::type handler_type;
@@ -445,7 +473,9 @@ template <typename Function, typename Executor>
 inline void spawn(const Executor& ex,
     BOOST_ASIO_MOVE_ARG(Function) function,
     const boost::coroutines::attributes& attributes,
-    typename enable_if<is_executor<Executor>::value>::type*)
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type*)
 {
   boost::asio::spawn(boost::asio::strand<Executor>(ex),
       BOOST_ASIO_MOVE_CAST(Function)(function), attributes);
diff --git a/include/boost/asio/impl/src.cpp b/include/boost/asio/impl/src.cpp
index a44d3877..0ea3601e 100644
--- a/include/boost/asio/impl/src.cpp
+++ b/include/boost/asio/impl/src.cpp
@@ -9,7 +9,7 @@
 //
 
 #if defined(_MSC_VER) \
-  || defined(__BORLANDC__) \
+  || (defined(__BORLANDC__) && !defined(__clang__)) \
   || defined(__DMC__)
 # pragma message ( \
     "This file is deprecated. " \
diff --git a/include/boost/asio/impl/src.hpp b/include/boost/asio/impl/src.hpp
index 56322b1e..02f44094 100644
--- a/include/boost/asio/impl/src.hpp
+++ b/include/boost/asio/impl/src.hpp
@@ -24,6 +24,7 @@
 #include <boost/asio/impl/executor.ipp>
 #include <boost/asio/impl/handler_alloc_hook.ipp>
 #include <boost/asio/impl/io_context.ipp>
+#include <boost/asio/impl/multiple_exceptions.ipp>
 #include <boost/asio/impl/serial_port_base.ipp>
 #include <boost/asio/impl/system_context.ipp>
 #include <boost/asio/impl/thread_pool.ipp>
@@ -68,6 +69,7 @@
 #include <boost/asio/detail/impl/winrt_ssocket_service_base.ipp>
 #include <boost/asio/detail/impl/winrt_timer_scheduler.ipp>
 #include <boost/asio/detail/impl/winsock_init.ipp>
+#include <boost/asio/execution/impl/bad_executor.ipp>
 #include <boost/asio/generic/detail/impl/endpoint.ipp>
 #include <boost/asio/ip/impl/address.ipp>
 #include <boost/asio/ip/impl/address_v4.ipp>
diff --git a/include/boost/asio/impl/system_context.ipp b/include/boost/asio/impl/system_context.ipp
index 36fadfbb..8eaba70b 100644
--- a/include/boost/asio/impl/system_context.ipp
+++ b/include/boost/asio/impl/system_context.ipp
@@ -29,8 +29,19 @@ struct system_context::thread_function
 
   void operator()()
   {
-    boost::system::error_code ec;
-    scheduler_->run(ec);
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
+      boost::system::error_code ec;
+      scheduler_->run(ec);
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      std::terminate();
+    }
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
   }
 };
 
@@ -40,8 +51,9 @@ system_context::system_context()
   scheduler_.work_started();
 
   thread_function f = { &scheduler_ };
-  std::size_t num_threads = detail::thread::hardware_concurrency() * 2;
-  threads_.create_threads(f, num_threads ? num_threads : 2);
+  num_threads_ = detail::thread::hardware_concurrency() * 2;
+  num_threads_ = num_threads_ ? num_threads_ : 2;
+  threads_.create_threads(f, num_threads_);
 }
 
 system_context::~system_context()
diff --git a/include/boost/asio/impl/system_executor.hpp b/include/boost/asio/impl/system_executor.hpp
index ef4760d8..c14729ee 100644
--- a/include/boost/asio/impl/system_executor.hpp
+++ b/include/boost/asio/impl/system_executor.hpp
@@ -26,22 +26,121 @@
 namespace boost {
 namespace asio {
 
-inline system_context& system_executor::context() const BOOST_ASIO_NOEXCEPT
+template <typename Blocking, typename Relationship, typename Allocator>
+inline system_context&
+basic_system_executor<Blocking, Relationship, Allocator>::query(
+    execution::context_t) BOOST_ASIO_NOEXCEPT
 {
   return detail::global<system_context>();
 }
 
-template <typename Function, typename Allocator>
-void system_executor::dispatch(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator&) const
+template <typename Blocking, typename Relationship, typename Allocator>
+inline std::size_t
+basic_system_executor<Blocking, Relationship, Allocator>::query(
+    execution::occupancy_t) const BOOST_ASIO_NOEXCEPT
+{
+  return detail::global<system_context>().num_threads_;
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function>
+inline void
+basic_system_executor<Blocking, Relationship, Allocator>::do_execute(
+    BOOST_ASIO_MOVE_ARG(Function) f, execution::blocking_t::possibly_t) const
+{
+  // Obtain a non-const instance of the function.
+  detail::non_const_lvalue<Function> f2(f);
+
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  try
+  {
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    detail::fenced_block b(detail::fenced_block::full);
+    boost_asio_handler_invoke_helpers::invoke(f2.value, f2.value);
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+  catch (...)
+  {
+    std::terminate();
+  }
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function>
+inline void
+basic_system_executor<Blocking, Relationship, Allocator>::do_execute(
+    BOOST_ASIO_MOVE_ARG(Function) f, execution::blocking_t::always_t) const
+{
+  // Obtain a non-const instance of the function.
+  detail::non_const_lvalue<Function> f2(f);
+
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  try
+  {
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    detail::fenced_block b(detail::fenced_block::full);
+    boost_asio_handler_invoke_helpers::invoke(f2.value, f2.value);
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+  catch (...)
+  {
+    std::terminate();
+  }
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function>
+void basic_system_executor<Blocking, Relationship, Allocator>::do_execute(
+    BOOST_ASIO_MOVE_ARG(Function) f, execution::blocking_t::never_t) const
+{
+  system_context& ctx = detail::global<system_context>();
+
+  // Allocate and construct an operation to wrap the function.
+  typedef typename decay<Function>::type function_type;
+  typedef detail::executor_op<function_type, Allocator> op;
+  typename op::ptr p = { detail::addressof(allocator_),
+      op::ptr::allocate(allocator_), 0 };
+  p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), allocator_);
+
+  if (is_same<Relationship, execution::relationship_t::continuation_t>::value)
+  {
+    BOOST_ASIO_HANDLER_CREATION((ctx, *p.p,
+          "system_executor", &ctx, 0, "execute(blk=never,rel=cont)"));
+  }
+  else
+  {
+    BOOST_ASIO_HANDLER_CREATION((ctx, *p.p,
+          "system_executor", &ctx, 0, "execute(blk=never,rel=fork)"));
+  }
+
+  ctx.scheduler_.post_immediate_completion(p.p,
+      is_same<Relationship, execution::relationship_t::continuation_t>::value);
+  p.v = p.p = 0;
+}
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+template <typename Blocking, typename Relationship, typename Allocator>
+inline system_context& basic_system_executor<
+    Blocking, Relationship, Allocator>::context() const BOOST_ASIO_NOEXCEPT
+{
+  return detail::global<system_context>();
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function, typename OtherAllocator>
+void basic_system_executor<Blocking, Relationship, Allocator>::dispatch(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator&) const
 {
   typename decay<Function>::type tmp(BOOST_ASIO_MOVE_CAST(Function)(f));
   boost_asio_handler_invoke_helpers::invoke(tmp, tmp);
 }
 
-template <typename Function, typename Allocator>
-void system_executor::post(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function, typename OtherAllocator>
+void basic_system_executor<Blocking, Relationship, Allocator>::post(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
@@ -59,9 +158,10 @@ void system_executor::post(
   p.v = p.p = 0;
 }
 
-template <typename Function, typename Allocator>
-void system_executor::defer(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function, typename OtherAllocator>
+void basic_system_executor<Blocking, Relationship, Allocator>::defer(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
@@ -78,6 +178,7 @@ void system_executor::defer(
   ctx.scheduler_.post_immediate_completion(p.p, true);
   p.v = p.p = 0;
 }
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 } // namespace asio
 } // namespace boost
diff --git a/include/boost/asio/impl/thread_pool.hpp b/include/boost/asio/impl/thread_pool.hpp
index 50484ea5..60788400 100644
--- a/include/boost/asio/impl/thread_pool.hpp
+++ b/include/boost/asio/impl/thread_pool.hpp
@@ -15,8 +15,10 @@
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
+#include <boost/asio/detail/blocking_executor_op.hpp>
 #include <boost/asio/detail/executor_op.hpp>
 #include <boost/asio/detail/fenced_block.hpp>
+#include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/recycling_allocator.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/execution_context.hpp>
@@ -32,32 +34,185 @@ thread_pool::get_executor() BOOST_ASIO_NOEXCEPT
   return executor_type(*this);
 }
 
-inline thread_pool&
-thread_pool::executor_type::context() const BOOST_ASIO_NOEXCEPT
+inline thread_pool::executor_type
+thread_pool::executor() BOOST_ASIO_NOEXCEPT
 {
-  return pool_;
+  return executor_type(*this);
 }
 
-inline void
-thread_pool::executor_type::on_work_started() const BOOST_ASIO_NOEXCEPT
+template <typename Allocator, unsigned int Bits>
+thread_pool::basic_executor_type<Allocator, Bits>&
+thread_pool::basic_executor_type<Allocator, Bits>::operator=(
+    const basic_executor_type& other) BOOST_ASIO_NOEXCEPT
 {
-  pool_.scheduler_.work_started();
+  if (this != &other)
+  {
+    thread_pool* old_thread_pool = pool_;
+    pool_ = other.pool_;
+    allocator_ = other.allocator_;
+    bits_ = other.bits_;
+    if (Bits & outstanding_work_tracked)
+    {
+      if (pool_)
+        pool_->scheduler_.work_started();
+      if (old_thread_pool)
+        old_thread_pool->scheduler_.work_finished();
+    }
+  }
+  return *this;
 }
 
-inline void thread_pool::executor_type::on_work_finished()
-const BOOST_ASIO_NOEXCEPT
+#if defined(BOOST_ASIO_HAS_MOVE)
+template <typename Allocator, unsigned int Bits>
+thread_pool::basic_executor_type<Allocator, Bits>&
+thread_pool::basic_executor_type<Allocator, Bits>::operator=(
+    basic_executor_type&& other) BOOST_ASIO_NOEXCEPT
 {
-  pool_.scheduler_.work_finished();
+  if (this != &other)
+  {
+    pool_ = other.pool_;
+    allocator_ = std::move(other.allocator_);
+    bits_ = other.bits_;
+    if (Bits & outstanding_work_tracked)
+      other.pool_ = 0;
+  }
+  return *this;
+}
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+template <typename Allocator, unsigned int Bits>
+inline bool thread_pool::basic_executor_type<Allocator,
+    Bits>::running_in_this_thread() const BOOST_ASIO_NOEXCEPT
+{
+  return pool_->scheduler_.can_dispatch();
 }
 
-template <typename Function, typename Allocator>
-void thread_pool::executor_type::dispatch(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Allocator, unsigned int Bits>
+template <typename Function>
+void thread_pool::basic_executor_type<Allocator,
+    Bits>::do_execute(BOOST_ASIO_MOVE_ARG(Function) f, false_type) const
+{
+  typedef typename decay<Function>::type function_type;
+
+  // Invoke immediately if the blocking.possibly property is enabled and we are
+  // already inside the thread pool.
+  if ((bits_ & blocking_never) == 0 && pool_->scheduler_.can_dispatch())
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(BOOST_ASIO_MOVE_CAST(Function)(f));
+
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       //   && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+      detail::fenced_block b(detail::fenced_block::full);
+      boost_asio_handler_invoke_helpers::invoke(tmp, tmp);
+      return;
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      pool_->scheduler_.capture_current_exception();
+      return;
+    }
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       //   && !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, Allocator> op;
+  typename op::ptr p = { detail::addressof(allocator_),
+      op::ptr::allocate(allocator_), 0 };
+  p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), allocator_);
+
+  if ((bits_ & relationship_continuation) != 0)
+  {
+    BOOST_ASIO_HANDLER_CREATION((*pool_, *p.p,
+          "thread_pool", pool_, 0, "execute(blk=never,rel=cont)"));
+  }
+  else
+  {
+    BOOST_ASIO_HANDLER_CREATION((*pool_, *p.p,
+          "thread_pool", pool_, 0, "execute(blk=never,rel=fork)"));
+  }
+
+  pool_->scheduler_.post_immediate_completion(p.p,
+      (bits_ & relationship_continuation) != 0);
+  p.v = p.p = 0;
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function>
+void thread_pool::basic_executor_type<Allocator,
+    Bits>::do_execute(BOOST_ASIO_MOVE_ARG(Function) f, true_type) const
+{
+  // Obtain a non-const instance of the function.
+  detail::non_const_lvalue<Function> f2(f);
+
+  // Invoke immediately if we are already inside the thread pool.
+  if (pool_->scheduler_.can_dispatch())
+  {
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
+      detail::fenced_block b(detail::fenced_block::full);
+      boost_asio_handler_invoke_helpers::invoke(f2.value, f2.value);
+      return;
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      std::terminate();
+    }
+#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
+  }
+
+  // Construct an operation to wrap the function.
+  typedef typename decay<Function>::type function_type;
+  detail::blocking_executor_op<function_type> op(f2.value);
+
+  BOOST_ASIO_HANDLER_CREATION((*pool_, op,
+        "thread_pool", pool_, 0, "execute(blk=always)"));
+
+  pool_->scheduler_.post_immediate_completion(&op, false);
+  op.wait();
+}
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+template <typename Allocator, unsigned int Bits>
+inline thread_pool& thread_pool::basic_executor_type<
+    Allocator, Bits>::context() const BOOST_ASIO_NOEXCEPT
+{
+  return *pool_;
+}
+
+template <typename Allocator, unsigned int Bits>
+inline void thread_pool::basic_executor_type<Allocator,
+    Bits>::on_work_started() const BOOST_ASIO_NOEXCEPT
+{
+  pool_->scheduler_.work_started();
+}
+
+template <typename Allocator, unsigned int Bits>
+inline void thread_pool::basic_executor_type<Allocator,
+    Bits>::on_work_finished() const BOOST_ASIO_NOEXCEPT
+{
+  pool_->scheduler_.work_finished();
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void thread_pool::basic_executor_type<Allocator, Bits>::dispatch(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
   // Invoke immediately if we are already inside the thread pool.
-  if (pool_.scheduler_.can_dispatch())
+  if (pool_->scheduler_.can_dispatch())
   {
     // Make a local, non-const copy of the function.
     function_type tmp(BOOST_ASIO_MOVE_CAST(Function)(f));
@@ -68,58 +223,55 @@ void thread_pool::executor_type::dispatch(
   }
 
   // Allocate and construct an operation to wrap the function.
-  typedef detail::executor_op<function_type, Allocator> op;
+  typedef detail::executor_op<function_type, OtherAllocator> op;
   typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
   p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), a);
 
-  BOOST_ASIO_HANDLER_CREATION((pool_, *p.p,
-        "thread_pool", &this->context(), 0, "dispatch"));
+  BOOST_ASIO_HANDLER_CREATION((*pool_, *p.p,
+        "thread_pool", pool_, 0, "dispatch"));
 
-  pool_.scheduler_.post_immediate_completion(p.p, false);
+  pool_->scheduler_.post_immediate_completion(p.p, false);
   p.v = p.p = 0;
 }
 
-template <typename Function, typename Allocator>
-void thread_pool::executor_type::post(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void thread_pool::basic_executor_type<Allocator, Bits>::post(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
   // Allocate and construct an operation to wrap the function.
-  typedef detail::executor_op<function_type, Allocator> op;
+  typedef detail::executor_op<function_type, OtherAllocator> op;
   typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
   p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), a);
 
-  BOOST_ASIO_HANDLER_CREATION((pool_, *p.p,
-        "thread_pool", &this->context(), 0, "post"));
+  BOOST_ASIO_HANDLER_CREATION((*pool_, *p.p,
+        "thread_pool", pool_, 0, "post"));
 
-  pool_.scheduler_.post_immediate_completion(p.p, false);
+  pool_->scheduler_.post_immediate_completion(p.p, false);
   p.v = p.p = 0;
 }
 
-template <typename Function, typename Allocator>
-void thread_pool::executor_type::defer(
-    BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void thread_pool::basic_executor_type<Allocator, Bits>::defer(
+    BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const
 {
   typedef typename decay<Function>::type function_type;
 
   // Allocate and construct an operation to wrap the function.
-  typedef detail::executor_op<function_type, Allocator> op;
+  typedef detail::executor_op<function_type, OtherAllocator> op;
   typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
   p.p = new (p.v) op(BOOST_ASIO_MOVE_CAST(Function)(f), a);
 
-  BOOST_ASIO_HANDLER_CREATION((pool_, *p.p,
-        "thread_pool", &this->context(), 0, "defer"));
+  BOOST_ASIO_HANDLER_CREATION((*pool_, *p.p,
+        "thread_pool", pool_, 0, "defer"));
 
-  pool_.scheduler_.post_immediate_completion(p.p, true);
+  pool_->scheduler_.post_immediate_completion(p.p, true);
   p.v = p.p = 0;
 }
-
-inline bool
-thread_pool::executor_type::running_in_this_thread() const BOOST_ASIO_NOEXCEPT
-{
-  return pool_.scheduler_.can_dispatch();
-}
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 } // namespace asio
 } // namespace boost
diff --git a/include/boost/asio/impl/thread_pool.ipp b/include/boost/asio/impl/thread_pool.ipp
index cf03f8d2..95dc5707 100644
--- a/include/boost/asio/impl/thread_pool.ipp
+++ b/include/boost/asio/impl/thread_pool.ipp
@@ -16,7 +16,9 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <stdexcept>
 #include <boost/asio/thread_pool.hpp>
+#include <boost/asio/detail/throw_exception.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -29,29 +31,68 @@ struct thread_pool::thread_function
 
   void operator()()
   {
-    boost::system::error_code ec;
-    scheduler_->run(ec);
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
+      boost::system::error_code ec;
+      scheduler_->run(ec);
+#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      std::terminate();
+    }
+#endif// !defined(BOOST_ASIO_NO_EXCEPTIONS)
   }
 };
 
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+namespace detail {
+
+inline long default_thread_pool_size()
+{
+  std::size_t num_threads = thread::hardware_concurrency() * 2;
+  num_threads = num_threads == 0 ? 2 : num_threads;
+  return static_cast<long>(num_threads);
+}
+
+} // namespace detail
+
 thread_pool::thread_pool()
-  : scheduler_(add_scheduler(new detail::scheduler(*this, 0, false)))
+  : scheduler_(add_scheduler(new detail::scheduler(*this, 0, false))),
+    num_threads_(detail::default_thread_pool_size())
 {
   scheduler_.work_started();
 
   thread_function f = { &scheduler_ };
-  std::size_t num_threads = detail::thread::hardware_concurrency() * 2;
-  threads_.create_threads(f, num_threads ? num_threads : 2);
+  threads_.create_threads(f, static_cast<std::size_t>(num_threads_));
 }
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
+
+namespace detail {
+
+inline long clamp_thread_pool_size(std::size_t n)
+{
+  if (n > 0x7FFFFFFF)
+  {
+    std::out_of_range ex("thread pool size");
+    boost::asio::detail::throw_exception(ex);
+  }
+  return static_cast<long>(n & 0x7FFFFFFF);
+}
+
+} // namespace detail
 
 thread_pool::thread_pool(std::size_t num_threads)
   : scheduler_(add_scheduler(new detail::scheduler(
-          *this, num_threads == 1 ? 1 : 0, false)))
+          *this, num_threads == 1 ? 1 : 0, false))),
+    num_threads_(detail::clamp_thread_pool_size(num_threads))
 {
   scheduler_.work_started();
 
   thread_function f = { &scheduler_ };
-  threads_.create_threads(f, num_threads);
+  threads_.create_threads(f, static_cast<std::size_t>(num_threads_));
 }
 
 thread_pool::~thread_pool()
@@ -65,6 +106,13 @@ void thread_pool::stop()
   scheduler_.stop();
 }
 
+void thread_pool::attach()
+{
+  ++num_threads_;
+  thread_function f = { &scheduler_ };
+  f();
+}
+
 void thread_pool::join()
 {
   if (!threads_.empty())
@@ -81,6 +129,12 @@ detail::scheduler& thread_pool::add_scheduler(detail::scheduler* s)
   return *scoped_impl.release();
 }
 
+void thread_pool::wait()
+{
+  scheduler_.work_finished();
+  threads_.join();
+}
+
 } // namespace asio
 } // namespace boost
 
diff --git a/include/boost/asio/impl/use_awaitable.hpp b/include/boost/asio/impl/use_awaitable.hpp
index 02a1545a..09025182 100644
--- a/include/boost/asio/impl/use_awaitable.hpp
+++ b/include/boost/asio/impl/use_awaitable.hpp
@@ -55,7 +55,7 @@ template <typename, typename...>
 class awaitable_handler;
 
 template <typename Executor>
-class awaitable_handler<Executor, void>
+class awaitable_handler<Executor>
   : public awaitable_handler_base<Executor, void>
 {
 public:
@@ -252,10 +252,13 @@ public:
 
   template <typename Initiation, typename... InitArgs>
   static return_type initiate(Initiation initiation,
-      use_awaitable_t<Executor>, InitArgs... args)
+      use_awaitable_t<Executor> u, InitArgs... args)
   {
+    (void)u;
+
     co_await [&](auto* frame)
       {
+        BOOST_ASIO_HANDLER_LOCATION((u.file_name_, u.line_, u.function_name_));
         handler_type handler(frame->detach_thread());
         std::move(initiation)(std::move(handler), std::move(args)...);
         return static_cast<handler_type*>(nullptr);
diff --git a/include/boost/asio/impl/use_future.hpp b/include/boost/asio/impl/use_future.hpp
index 59de0b03..73326766 100644
--- a/include/boost/asio/impl/use_future.hpp
+++ b/include/boost/asio/impl/use_future.hpp
@@ -19,7 +19,9 @@
 #include <tuple>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/memory.hpp>
+#include <boost/asio/dispatch.hpp>
 #include <boost/system/error_code.hpp>
+#include <boost/asio/execution.hpp>
 #include <boost/asio/packaged_task.hpp>
 #include <boost/system/system_error.hpp>
 #include <boost/asio/system_executor.hpp>
@@ -201,7 +203,7 @@ private:
 
 // An executor that adapts the system_executor to capture any exeption thrown
 // by a submitted function object and save it into a promise.
-template <typename T>
+template <typename T, typename Blocking = execution::blocking_t::possibly_t>
 class promise_executor
 {
 public:
@@ -210,6 +212,32 @@ public:
   {
   }
 
+  static BOOST_ASIO_CONSTEXPR Blocking query(execution::blocking_t)
+  {
+    return Blocking();
+  }
+
+  promise_executor<T, execution::blocking_t::possibly_t>
+  require(execution::blocking_t::possibly_t) const
+  {
+    return promise_executor<T, execution::blocking_t::possibly_t>(p_);
+  }
+
+  promise_executor<T, execution::blocking_t::never_t>
+  require(execution::blocking_t::never_t) const
+  {
+    return promise_executor<T, execution::blocking_t::never_t>(p_);
+  }
+
+  template <typename F>
+  void execute(BOOST_ASIO_MOVE_ARG(F) f) const
+  {
+    execution::execute(
+        boost::asio::require(system_executor(), Blocking()),
+        promise_invoker<T, F>(p_, BOOST_ASIO_MOVE_CAST(F)(f)));
+  }
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   execution_context& context() const BOOST_ASIO_NOEXCEPT
   {
     return system_executor().context();
@@ -237,6 +265,7 @@ public:
     system_executor().defer(
         promise_invoker<T, F>(p_, BOOST_ASIO_MOVE_CAST(F)(f)), a);
   }
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
   friend bool operator==(const promise_executor& a,
       const promise_executor& b) BOOST_ASIO_NOEXCEPT
@@ -608,13 +637,36 @@ private:
   Allocator allocator_;
 };
 
+template <typename Function>
+struct promise_function_wrapper
+{
+  explicit promise_function_wrapper(Function& f)
+    : function_(BOOST_ASIO_MOVE_CAST(Function)(f))
+  {
+  }
+
+  explicit promise_function_wrapper(const Function& f)
+    : function_(f)
+  {
+  }
+
+  void operator()()
+  {
+    function_();
+  }
+
+  Function function_;
+};
+
+#if !defined(BOOST_ASIO_NO_DEPRECATED)
+
 template <typename Function, typename Signature, typename Allocator>
 inline void asio_handler_invoke(Function& f,
     promise_handler<Signature, Allocator>* h)
 {
   typename promise_handler<Signature, Allocator>::executor_type
     ex(h->get_executor());
-  ex.dispatch(BOOST_ASIO_MOVE_CAST(Function)(f), std::allocator<void>());
+  boost::asio::dispatch(ex, promise_function_wrapper<Function>(f));
 }
 
 template <typename Function, typename Signature, typename Allocator>
@@ -623,9 +675,11 @@ inline void asio_handler_invoke(const Function& f,
 {
   typename promise_handler<Signature, Allocator>::executor_type
     ex(h->get_executor());
-  ex.dispatch(f, std::allocator<void>());
+  boost::asio::dispatch(ex, promise_function_wrapper<Function>(f));
 }
 
+#endif // !defined(BOOST_ASIO_NO_DEPRECATED)
+
 // Helper base class for async_result specialisation.
 template <typename Signature, typename Allocator>
 class promise_async_result
@@ -720,6 +774,8 @@ private:
   Allocator allocator_;
 };
 
+#if !defined(BOOST_ASIO_NO_DEPRECATED)
+
 template <typename Function,
     typename Function1, typename Allocator, typename Result>
 inline void asio_handler_invoke(Function& f,
@@ -727,7 +783,7 @@ inline void asio_handler_invoke(Function& f,
 {
   typename packaged_handler<Function1, Allocator, Result>::executor_type
     ex(h->get_executor());
-  ex.dispatch(BOOST_ASIO_MOVE_CAST(Function)(f), std::allocator<void>());
+  boost::asio::dispatch(ex, promise_function_wrapper<Function>(f));
 }
 
 template <typename Function,
@@ -737,9 +793,11 @@ inline void asio_handler_invoke(const Function& f,
 {
   typename packaged_handler<Function1, Allocator, Result>::executor_type
     ex(h->get_executor());
-  ex.dispatch(f, std::allocator<void>());
+  boost::asio::dispatch(ex, promise_function_wrapper<Function>(f));
 }
 
+#endif // !defined(BOOST_ASIO_NO_DEPRECATED)
+
 // Helper base class for async_result specialisation.
 template <typename Function, typename Allocator, typename Result>
 class packaged_async_result
@@ -879,6 +937,90 @@ public:
 
 #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
 
+namespace execution {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename T, typename Blocking>
+struct is_executor<
+    boost::asio::detail::promise_executor<T, Blocking> > : true_type
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+} // namespace execution
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename T, typename Blocking, typename Function>
+struct execute_member<
+    boost::asio::detail::promise_executor<T, Blocking>, Function>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_TRAIT)
+
+template <typename T, typename Blocking, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::detail::promise_executor<T, Blocking>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::blocking_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Blocking result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
+  {
+    return Blocking();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename T, typename Blocking>
+struct require_member<
+    boost::asio::detail::promise_executor<T, Blocking>,
+    execution::blocking_t::possibly_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::detail::promise_executor<T,
+      execution::blocking_t::possibly_t> result_type;
+};
+
+template <typename T, typename Blocking>
+struct require_member<
+    boost::asio::detail::promise_executor<T, Blocking>,
+    execution::blocking_t::never_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::detail::promise_executor<T,
+      execution::blocking_t::never_t> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+
 #endif // !defined(GENERATING_DOCUMENTATION)
 
 } // namespace asio
diff --git a/include/boost/asio/impl/write.hpp b/include/boost/asio/impl/write.hpp
index cb35613d..d878990d 100644
--- a/include/boost/asio/impl/write.hpp
+++ b/include/boost/asio/impl/write.hpp
@@ -27,6 +27,7 @@
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/throw_error.hpp>
@@ -326,8 +327,11 @@ namespace detail
         max_size = this->check_for_completion(ec, buffers_.total_consumed());
         do
         {
-          stream_.async_write_some(buffers_.prepare(max_size),
-              BOOST_ASIO_MOVE_CAST(write_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_write"));
+            stream_.async_write_some(buffers_.prepare(max_size),
+                BOOST_ASIO_MOVE_CAST(write_op)(*this));
+          }
           return; default:
           buffers_.consume(bytes_transferred);
           if ((!ec && bytes_transferred == 0) || buffers_.empty())
@@ -352,23 +356,33 @@ namespace detail
   template <typename AsyncWriteStream, typename ConstBufferSequence,
       typename ConstBufferIterator, typename CompletionCondition,
       typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       write_op<AsyncWriteStream, ConstBufferSequence, ConstBufferIterator,
         CompletionCondition, WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename ConstBufferSequence,
       typename ConstBufferIterator, typename CompletionCondition,
       typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       write_op<AsyncWriteStream, ConstBufferSequence, ConstBufferIterator,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename ConstBufferSequence,
@@ -386,23 +400,31 @@ namespace detail
   template <typename Function, typename AsyncWriteStream,
       typename ConstBufferSequence, typename ConstBufferIterator,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       write_op<AsyncWriteStream, ConstBufferSequence, ConstBufferIterator,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncWriteStream,
       typename ConstBufferSequence, typename ConstBufferIterator,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       write_op<AsyncWriteStream, ConstBufferSequence, ConstBufferIterator,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename ConstBufferSequence,
@@ -600,22 +622,32 @@ namespace detail
 
   template <typename AsyncWriteStream, typename DynamicBuffer_v1,
       typename CompletionCondition, typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       write_dynbuf_v1_op<AsyncWriteStream, DynamicBuffer_v1,
         CompletionCondition, WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename DynamicBuffer_v1,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       write_dynbuf_v1_op<AsyncWriteStream, DynamicBuffer_v1,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename DynamicBuffer_v1,
@@ -631,23 +663,31 @@ namespace detail
   template <typename Function, typename AsyncWriteStream,
       typename DynamicBuffer_v1, typename CompletionCondition,
       typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       write_dynbuf_v1_op<AsyncWriteStream, DynamicBuffer_v1,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncWriteStream,
       typename DynamicBuffer_v1, typename CompletionCondition,
       typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       write_dynbuf_v1_op<AsyncWriteStream, DynamicBuffer_v1,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream>
@@ -870,22 +910,32 @@ namespace detail
 
   template <typename AsyncWriteStream, typename DynamicBuffer_v2,
       typename CompletionCondition, typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       write_dynbuf_v2_op<AsyncWriteStream, DynamicBuffer_v2,
         CompletionCondition, WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename DynamicBuffer_v2,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       write_dynbuf_v2_op<AsyncWriteStream, DynamicBuffer_v2,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream, typename DynamicBuffer_v2,
@@ -901,23 +951,31 @@ namespace detail
   template <typename Function, typename AsyncWriteStream,
       typename DynamicBuffer_v2, typename CompletionCondition,
       typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       write_dynbuf_v2_op<AsyncWriteStream, DynamicBuffer_v2,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncWriteStream,
       typename DynamicBuffer_v2, typename CompletionCondition,
       typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       write_dynbuf_v2_op<AsyncWriteStream, DynamicBuffer_v2,
         CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncWriteStream>
diff --git a/include/boost/asio/impl/write_at.hpp b/include/boost/asio/impl/write_at.hpp
index bbc6a9da..7748f54f 100644
--- a/include/boost/asio/impl/write_at.hpp
+++ b/include/boost/asio/impl/write_at.hpp
@@ -27,6 +27,7 @@
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/handler_cont_helpers.hpp>
 #include <boost/asio/detail/handler_invoke_helpers.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/throw_error.hpp>
@@ -211,9 +212,12 @@ namespace detail
         max_size = this->check_for_completion(ec, buffers_.total_consumed());
         do
         {
-          device_.async_write_some_at(
-              offset_ + buffers_.total_consumed(), buffers_.prepare(max_size),
-              BOOST_ASIO_MOVE_CAST(write_at_op)(*this));
+          {
+            BOOST_ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_write_at"));
+            device_.async_write_some_at(
+                offset_ + buffers_.total_consumed(), buffers_.prepare(max_size),
+                BOOST_ASIO_MOVE_CAST(write_at_op)(*this));
+          }
           return; default:
           buffers_.consume(bytes_transferred);
           if ((!ec && bytes_transferred == 0) || buffers_.empty())
@@ -239,23 +243,33 @@ namespace detail
   template <typename AsyncRandomAccessWriteDevice,
       typename ConstBufferSequence, typename ConstBufferIterator,
       typename CompletionCondition, typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
         ConstBufferIterator, CompletionCondition, WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessWriteDevice,
       typename ConstBufferSequence, typename ConstBufferIterator,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
         ConstBufferIterator, CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessWriteDevice,
@@ -273,23 +287,31 @@ namespace detail
   template <typename Function, typename AsyncRandomAccessWriteDevice,
       typename ConstBufferSequence, typename ConstBufferIterator,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
         ConstBufferIterator, CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename AsyncRandomAccessWriteDevice,
       typename ConstBufferSequence, typename ConstBufferIterator,
       typename CompletionCondition, typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
         ConstBufferIterator, CompletionCondition, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessWriteDevice,
@@ -468,19 +490,29 @@ namespace detail
   };
 
   template <typename Allocator, typename WriteHandler>
-  inline void* asio_handler_allocate(std::size_t size,
+  inline asio_handler_allocate_is_deprecated
+  asio_handler_allocate(std::size_t size,
       write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
   {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+    return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
     return boost_asio_handler_alloc_helpers::allocate(
         size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Allocator, typename WriteHandler>
-  inline void asio_handler_deallocate(void* pointer, std::size_t size,
+  inline asio_handler_deallocate_is_deprecated
+  asio_handler_deallocate(void* pointer, std::size_t size,
       write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
   {
     boost_asio_handler_alloc_helpers::deallocate(
         pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Allocator, typename WriteHandler>
@@ -492,19 +524,27 @@ namespace detail
   }
 
   template <typename Function, typename Allocator, typename WriteHandler>
-  inline void asio_handler_invoke(Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(Function& function,
       write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename Function, typename Allocator, typename WriteHandler>
-  inline void asio_handler_invoke(const Function& function,
+  inline asio_handler_invoke_is_deprecated
+  asio_handler_invoke(const Function& function,
       write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
   {
     boost_asio_handler_invoke_helpers::invoke(
         function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+    return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
   }
 
   template <typename AsyncRandomAccessWriteDevice>
diff --git a/include/boost/asio/io_context.hpp b/include/boost/asio/io_context.hpp
index 04ba4837..5719014a 100644
--- a/include/boost/asio/io_context.hpp
+++ b/include/boost/asio/io_context.hpp
@@ -20,9 +20,9 @@
 #include <stdexcept>
 #include <typeinfo>
 #include <boost/asio/async_result.hpp>
-#include <boost/asio/detail/noncopyable.hpp>
 #include <boost/asio/detail/wrapped_handler.hpp>
 #include <boost/system/error_code.hpp>
+#include <boost/asio/execution.hpp>
 #include <boost/asio/execution_context.hpp>
 
 #if defined(BOOST_ASIO_HAS_CHRONO)
@@ -48,6 +48,13 @@ namespace detail {
 #else
   typedef class scheduler io_context_impl;
 #endif
+
+  struct io_context_bits
+  {
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, blocking_never = 1);
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, relationship_continuation = 2);
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, outstanding_work_tracked = 4);
+  };
 } // namespace detail
 
 /// Provides core I/O functionality.
@@ -154,12 +161,30 @@ namespace detail {
  * returning when there is no more work to do. For example, the io_context may
  * be being run in a background thread that is launched prior to the
  * application's asynchronous operations. The run() call may be kept running by
- * creating an object of type
- * boost::asio::executor_work_guard<io_context::executor_type>:
+ * creating an executor that tracks work against the io_context:
  *
  * @code boost::asio::io_context io_context;
- * boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
- *   = boost::asio::make_work_guard(io_context);
+ * auto work = boost::asio::require(io_context.get_executor(),
+ *     boost::asio::execution::outstanding_work.tracked);
+ * ... @endcode
+ *
+ * If using C++03, which lacks automatic variable type deduction, you may
+ * compute the return type of the require call:
+ *
+ * @code boost::asio::io_context io_context;
+ * typename boost::asio::require_result_type<
+ *     boost::asio::io_context::executor_type,
+ *     boost::asio::exeution::outstanding_work_t::tracked_t>
+ *   work = boost::asio::require(io_context.get_executor(),
+ *     boost::asio::execution::outstanding_work.tracked);
+ * ... @endcode
+ *
+ * or store the result in the type-erasing executor wrapper, any_io_executor:
+ *
+ * @code boost::asio::io_context io_context;
+ * boost::asio::any_io_executor work
+ *   = boost::asio::require(io_context.get_executor(),
+ *       boost::asio::execution::outstanding_work.tracked);
  * ... @endcode
  *
  * To effect a shutdown, the application will then need to call the io_context
@@ -168,13 +193,15 @@ namespace detail {
  * permitting ready handlers to be dispatched.
  *
  * Alternatively, if the application requires that all operations and handlers
- * be allowed to finish normally, the work object may be explicitly reset.
+ * be allowed to finish normally, store the work-tracking executor in an
+ * any_io_executor object, so that it may be explicitly reset.
  *
  * @code boost::asio::io_context io_context;
- * boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
- *   = boost::asio::make_work_guard(io_context);
+ * boost::asio::any_io_executor work
+ *   = boost::asio::require(io_context.get_executor(),
+ *       boost::asio::execution::outstanding_work.tracked);
  * ...
- * work.reset(); // Allow run() to exit. @endcode
+ * work = boost::asio::any_io_executor(); // Allow run() to exit. @endcode
  */
 class io_context
   : public execution_context
@@ -186,8 +213,14 @@ private:
 #endif
 
 public:
-  class executor_type;
-  friend class executor_type;
+  template <typename Allocator, unsigned int Bits>
+  class basic_executor_type;
+
+  template <typename Allocator, unsigned int Bits>
+  friend class basic_executor_type;
+
+  /// Executor used to submit functions to an io_context.
+  typedef basic_executor_type<std::allocator<void>, 0> executor_type;
 
 #if !defined(BOOST_ASIO_NO_DEPRECATED)
   class work;
@@ -196,9 +229,11 @@ public:
 
   class service;
 
-#if !defined(BOOST_ASIO_NO_EXTENSIONS)
+#if !defined(BOOST_ASIO_NO_EXTENSIONS) \
+  && !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   class strand;
 #endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
+       //   && !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
   /// The type used to count the number of handlers executed by the context.
   typedef std::size_t count_type;
@@ -595,6 +630,9 @@ public:
 #endif // !defined(BOOST_ASIO_NO_DEPRECATED)
 
 private:
+  io_context(const io_context&) BOOST_ASIO_DELETED;
+  io_context& operator=(const io_context&) BOOST_ASIO_DELETED;
+
 #if !defined(BOOST_ASIO_NO_DEPRECATED)
   struct initiate_dispatch;
   struct initiate_post;
@@ -619,10 +657,215 @@ private:
   impl_type& impl_;
 };
 
-/// Executor used to submit functions to an io_context.
-class io_context::executor_type
+namespace detail {
+
+} // namespace detail
+
+/// Executor implementation type used to submit functions to an io_context.
+template <typename Allocator, unsigned int Bits>
+class io_context::basic_executor_type : detail::io_context_bits
 {
 public:
+  /// Copy construtor.
+  basic_executor_type(
+      const basic_executor_type& other) BOOST_ASIO_NOEXCEPT
+    : io_context_(other.io_context_),
+      allocator_(other.allocator_),
+      bits_(other.bits_)
+  {
+    if (Bits & outstanding_work_tracked)
+      if (io_context_)
+        io_context_->impl_.work_started();
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move construtor.
+  basic_executor_type(basic_executor_type&& other) BOOST_ASIO_NOEXCEPT
+    : io_context_(other.io_context_),
+      allocator_(BOOST_ASIO_MOVE_CAST(Allocator)(other.allocator_)),
+      bits_(other.bits_)
+  {
+    if (Bits & outstanding_work_tracked)
+      other.io_context_ = 0;
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
+  /// Destructor.
+  ~basic_executor_type()
+  {
+    if (Bits & outstanding_work_tracked)
+      if (io_context_)
+        io_context_->impl_.work_finished();
+  }
+
+  /// Assignment operator.
+  basic_executor_type& operator=(
+      const basic_executor_type& other) BOOST_ASIO_NOEXCEPT;
+
+#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move assignment operator.
+  basic_executor_type& operator=(
+      basic_executor_type&& other) BOOST_ASIO_NOEXCEPT;
+#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
+  /// Obtain an executor with the @c blocking.possibly property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type require(
+      execution::blocking_t::possibly_t) const
+  {
+    return basic_executor_type(io_context_,
+        allocator_, bits_ & ~blocking_never);
+  }
+
+  /// Obtain an executor with the @c blocking.never property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type require(
+      execution::blocking_t::never_t) const
+  {
+    return basic_executor_type(io_context_,
+        allocator_, bits_ | blocking_never);
+  }
+
+  /// Obtain an executor with the @c relationship.fork property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type require(
+      execution::relationship_t::fork_t) const
+  {
+    return basic_executor_type(io_context_,
+        allocator_, bits_ & ~relationship_continuation);
+  }
+
+  /// Obtain an executor with the @c relationship.continuation property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type require(
+      execution::relationship_t::continuation_t) const
+  {
+    return basic_executor_type(io_context_,
+        allocator_, bits_ | relationship_continuation);
+  }
+
+  /// Obtain an executor with the @c outstanding_work.tracked property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED(Bits | outstanding_work_tracked)>
+  require(execution::outstanding_work_t::tracked_t) const
+  {
+    return basic_executor_type<Allocator, Bits | outstanding_work_tracked>(
+        io_context_, allocator_, bits_);
+  }
+
+  /// Obtain an executor with the @c outstanding_work.untracked property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED(Bits & ~outstanding_work_tracked)>
+  require(execution::outstanding_work_t::untracked_t) const
+  {
+    return basic_executor_type<Allocator, Bits & ~outstanding_work_tracked>(
+        io_context_, allocator_, bits_);
+  }
+
+  /// Obtain an executor with the specified @c allocator property.
+  template <typename OtherAllocator>
+  BOOST_ASIO_CONSTEXPR basic_executor_type<OtherAllocator, Bits>
+  require(execution::allocator_t<OtherAllocator> a) const
+  {
+    return basic_executor_type<OtherAllocator, Bits>(
+        io_context_, a.value(), bits_);
+  }
+
+  /// Obtain an executor with the default @c allocator property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<std::allocator<void>, Bits>
+  require(execution::allocator_t<void>) const
+  {
+    return basic_executor_type<std::allocator<void>, Bits>(
+        io_context_, std::allocator<void>(), bits_);
+  }
+
+  /// Query the current value of the @c mapping property.
+  static BOOST_ASIO_CONSTEXPR execution::mapping_t query(
+      execution::mapping_t) BOOST_ASIO_NOEXCEPT
+  {
+    return execution::mapping.thread;
+  }
+
+  /// Query the current value of the @c context property.
+  io_context& query(execution::context_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return *io_context_;
+  }
+
+  /// Query the current value of the @c blocking property.
+  BOOST_ASIO_CONSTEXPR execution::blocking_t query(
+      execution::blocking_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return (bits_ & blocking_never)
+      ? execution::blocking_t(execution::blocking.never)
+      : execution::blocking_t(execution::blocking.possibly);
+  }
+
+  /// Query the current value of the @c relationship property.
+  BOOST_ASIO_CONSTEXPR execution::relationship_t query(
+      execution::relationship_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return (bits_ & relationship_continuation)
+      ? execution::relationship_t(execution::relationship.continuation)
+      : execution::relationship_t(execution::relationship.fork);
+  }
+
+  /// Query the current value of the @c outstanding_work property.
+  static BOOST_ASIO_CONSTEXPR execution::outstanding_work_t query(
+      execution::outstanding_work_t) BOOST_ASIO_NOEXCEPT
+  {
+    return (Bits & outstanding_work_tracked)
+      ? execution::outstanding_work_t(execution::outstanding_work.tracked)
+      : execution::outstanding_work_t(execution::outstanding_work.untracked);
+  }
+
+  /// Query the current value of the @c allocator property.
+  template <typename OtherAllocator>
+  BOOST_ASIO_CONSTEXPR Allocator query(
+      execution::allocator_t<OtherAllocator>) const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  /// Query the current value of the @c allocator property.
+  BOOST_ASIO_CONSTEXPR Allocator query(
+      execution::allocator_t<void>) const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  /// Determine whether the io_context is running in the current thread.
+  /**
+   * @return @c true if the current thread is running the io_context. Otherwise
+   * returns @c false.
+   */
+  bool running_in_this_thread() const BOOST_ASIO_NOEXCEPT;
+
+  /// Compare two executors for equality.
+  /**
+   * Two executors are equal if they refer to the same underlying io_context.
+   */
+  friend bool operator==(const basic_executor_type& a,
+      const basic_executor_type& b) BOOST_ASIO_NOEXCEPT
+  {
+    return a.io_context_ == b.io_context_
+      && a.allocator_ == b.allocator_
+      && a.bits_ == b.bits_;
+  }
+
+  /// Compare two executors for inequality.
+  /**
+   * Two executors are equal if they refer to the same underlying io_context.
+   */
+  friend bool operator!=(const basic_executor_type& a,
+      const basic_executor_type& b) BOOST_ASIO_NOEXCEPT
+  {
+    return a.io_context_ != b.io_context_
+      || a.allocator_ != b.allocator_
+      || a.bits_ != b.bits_;
+  }
+
+  /// Execution function.
+  template <typename Function>
+  void execute(BOOST_ASIO_MOVE_ARG(Function) f) const;
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   /// Obtain the underlying execution context.
   io_context& context() const BOOST_ASIO_NOEXCEPT;
 
@@ -656,8 +899,9 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f,
+      const OtherAllocator& a) const;
 
   /// Request the io_context to invoke the given function object.
   /**
@@ -672,8 +916,9 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void post(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void post(BOOST_ASIO_MOVE_ARG(Function) f,
+      const OtherAllocator& a) const;
 
   /// Request the io_context to invoke the given function object.
   /**
@@ -692,44 +937,45 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void defer(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
-
-  /// Determine whether the io_context is running in the current thread.
-  /**
-   * @return @c true if the current thread is running the io_context. Otherwise
-   * returns @c false.
-   */
-  bool running_in_this_thread() const BOOST_ASIO_NOEXCEPT;
-
-  /// Compare two executors for equality.
-  /**
-   * Two executors are equal if they refer to the same underlying io_context.
-   */
-  friend bool operator==(const executor_type& a,
-      const executor_type& b) BOOST_ASIO_NOEXCEPT
-  {
-    return &a.io_context_ == &b.io_context_;
-  }
-
-  /// Compare two executors for inequality.
-  /**
-   * Two executors are equal if they refer to the same underlying io_context.
-   */
-  friend bool operator!=(const executor_type& a,
-      const executor_type& b) BOOST_ASIO_NOEXCEPT
-  {
-    return &a.io_context_ != &b.io_context_;
-  }
+  template <typename Function, typename OtherAllocator>
+  void defer(BOOST_ASIO_MOVE_ARG(Function) f,
+      const OtherAllocator& a) const;
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 private:
   friend class io_context;
+  template <typename, unsigned int> friend class basic_executor_type;
 
-  // Constructor.
-  explicit executor_type(io_context& i) : io_context_(i) {}
+  // Constructor used by io_context::get_executor().
+  explicit basic_executor_type(io_context& i) BOOST_ASIO_NOEXCEPT
+    : io_context_(&i),
+      allocator_(),
+      bits_(0)
+  {
+    if (Bits & outstanding_work_tracked)
+      io_context_->impl_.work_started();
+  }
+
+  // Constructor used by require().
+  basic_executor_type(io_context* i,
+      const Allocator& a, unsigned int bits) BOOST_ASIO_NOEXCEPT
+    : io_context_(i),
+      allocator_(a),
+      bits_(bits)
+  {
+    if (Bits & outstanding_work_tracked)
+      if (io_context_)
+        io_context_->impl_.work_started();
+  }
 
   // The underlying io_context.
-  io_context& io_context_;
+  io_context* io_context_;
+
+  // The allocator used for execution functions.
+  Allocator allocator_;
+
+  // The runtime-switched properties of the io_context executor.
+  unsigned int bits_;
 };
 
 #if !defined(BOOST_ASIO_NO_DEPRECATED)
@@ -853,6 +1099,266 @@ template <typename Type>
 boost::asio::detail::service_id<Type> service_base<Type>::id;
 
 } // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename Allocator, unsigned int Bits>
+struct is_executor<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>
+  > : true_type
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+} // namespace execution
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits, typename Function>
+struct execute_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    Function
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::blocking_t::possibly_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      Allocator, Bits> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::blocking_t::never_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      Allocator, Bits> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::relationship_t::fork_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      Allocator, Bits> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::relationship_t::continuation_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      Allocator, Bits> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::outstanding_work_t::tracked_t
+  > : boost::asio::detail::io_context_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      Allocator, Bits | outstanding_work_tracked> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::outstanding_work_t::untracked_t
+  > : boost::asio::detail::io_context_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      Allocator, Bits & ~outstanding_work_tracked> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<void>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      std::allocator<void>, Bits> result_type;
+};
+
+template <unsigned int Bits,
+    typename Allocator, typename OtherAllocator>
+struct require_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<OtherAllocator>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::io_context::basic_executor_type<
+      OtherAllocator, Bits> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::outstanding_work_t
+      >::value
+    >::type
+  > : boost::asio::detail::io_context_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::outstanding_work_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
+  {
+    return (Bits & outstanding_work_tracked)
+      ? execution::outstanding_work_t(execution::outstanding_work.tracked)
+      : execution::outstanding_work_t(execution::outstanding_work.untracked);
+  }
+};
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::mapping_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::mapping_t::thread_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
+  {
+    return result_type();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::blocking_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::blocking_t result_type;
+};
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::relationship_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::relationship_t result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct query_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::context_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::io_context& result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct query_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<void>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Allocator result_type;
+};
+
+template <typename Allocator, unsigned int Bits, typename OtherAllocator>
+struct query_member<
+    boost::asio::io_context::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<OtherAllocator>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Allocator result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
 } // namespace asio
 } // namespace boost
 
diff --git a/include/boost/asio/io_context_strand.hpp b/include/boost/asio/io_context_strand.hpp
index b1725b44..5480919f 100644
--- a/include/boost/asio/io_context_strand.hpp
+++ b/include/boost/asio/io_context_strand.hpp
@@ -17,7 +17,8 @@
 
 #include <boost/asio/detail/config.hpp>
 
-#if !defined(BOOST_ASIO_NO_EXTENSIONS)
+#if !defined(BOOST_ASIO_NO_EXTENSIONS) \
+  && !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
@@ -372,5 +373,6 @@ private:
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
+       //   && !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 #endif // BOOST_ASIO_IO_CONTEXT_STRAND_HPP
diff --git a/include/boost/asio/ip/basic_resolver.hpp b/include/boost/asio/ip/basic_resolver.hpp
index 50f5d56b..ce0f9985 100644
--- a/include/boost/asio/ip/basic_resolver.hpp
+++ b/include/boost/asio/ip/basic_resolver.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <string>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
@@ -25,7 +26,6 @@
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/ip/basic_resolver_iterator.hpp>
 #include <boost/asio/ip/basic_resolver_query.hpp>
 #include <boost/asio/ip/basic_resolver_results.hpp>
@@ -50,7 +50,7 @@ namespace ip {
 #define BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL
 
 // Forward declaration with defaulted arguments.
-template <typename InternetProtocol, typename Executor = executor>
+template <typename InternetProtocol, typename Executor = any_io_executor>
 class basic_resolver;
 
 #endif // !defined(BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL)
@@ -1004,8 +1004,8 @@ private:
 
       boost::asio::detail::non_const_lvalue<ResolveHandler> handler2(handler);
       self_->impl_.get_service().async_resolve(
-          self_->impl_.get_implementation(), q, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), q,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/is_applicable_property.hpp b/include/boost/asio/is_applicable_property.hpp
new file mode 100644
index 00000000..1d38fa72
--- /dev/null
+++ b/include/boost/asio/is_applicable_property.hpp
@@ -0,0 +1,63 @@
+//
+// is_applicable_property.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_IS_APPLICABLE_PROPERTY_HPP
+#define BOOST_ASIO_IS_APPLICABLE_PROPERTY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+namespace boost {
+namespace asio {
+namespace detail {
+
+template <typename T, typename Property, typename = void>
+struct is_applicable_property_trait : false_type
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+struct is_applicable_property_trait<T, Property,
+  typename void_type<
+    typename enable_if<
+      !!Property::template is_applicable_property_v<T>
+    >::type
+  >::type> : true_type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace detail
+
+template <typename T, typename Property, typename = void>
+struct is_applicable_property :
+  detail::is_applicable_property_trait<T, Property>
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+BOOST_ASIO_CONSTEXPR const bool is_applicable_property_v
+  = is_applicable_property<T, Property>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace asio
+} // namespace boost
+
+#endif // BOOST_ASIO_IS_APPLICABLE_PROPERTY_HPP
diff --git a/include/boost/asio/multiple_exceptions.hpp b/include/boost/asio/multiple_exceptions.hpp
new file mode 100644
index 00000000..594cbc87
--- /dev/null
+++ b/include/boost/asio/multiple_exceptions.hpp
@@ -0,0 +1,60 @@
+//
+// multiple_exceptions.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_MULTIPLE_EXCEPTIONS_HPP
+#define BOOST_ASIO_MULTIPLE_EXCEPTIONS_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <exception>
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+#if defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR) \
+  || defined(GENERATING_DOCUMENTATION)
+
+/// Exception thrown when there are multiple pending exceptions to rethrow.
+class multiple_exceptions
+  : public std::exception
+{
+public:
+  /// Constructor.
+  BOOST_ASIO_DECL multiple_exceptions(
+      std::exception_ptr first) BOOST_ASIO_NOEXCEPT;
+
+  /// Obtain message associated with exception.
+  BOOST_ASIO_DECL virtual const char* what() const
+    BOOST_ASIO_NOEXCEPT_OR_NOTHROW;
+
+  /// Obtain a pointer to the first exception.
+  BOOST_ASIO_DECL std::exception_ptr first_exception() const;
+
+private:
+  std::exception_ptr first_;
+};
+
+#endif // defined(BOOST_ASIO_HAS_STD_EXCEPTION_PTR)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#if defined(BOOST_ASIO_HEADER_ONLY)
+# include <boost/asio/impl/multiple_exceptions.ipp>
+#endif // defined(BOOST_ASIO_HEADER_ONLY)
+
+#endif // BOOST_ASIO_MULTIPLE_EXCEPTIONS_HPP
diff --git a/include/boost/asio/posix/basic_descriptor.hpp b/include/boost/asio/posix/basic_descriptor.hpp
index f5b97033..ad71f90a 100644
--- a/include/boost/asio/posix/basic_descriptor.hpp
+++ b/include/boost/asio/posix/basic_descriptor.hpp
@@ -20,6 +20,7 @@
 #if defined(BOOST_ASIO_HAS_POSIX_STREAM_DESCRIPTOR) \
   || defined(GENERATING_DOCUMENTATION)
 
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
@@ -28,7 +29,6 @@
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/posix/descriptor_base.hpp>
 
 #if defined(BOOST_ASIO_HAS_MOVE)
@@ -50,7 +50,7 @@ namespace posix {
  * @e Distinct @e objects: Safe.@n
  * @e Shared @e objects: Unsafe.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_descriptor
   : public descriptor_base
 {
@@ -678,8 +678,8 @@ private:
 
       detail::non_const_lvalue<WaitHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), w, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), w,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/posix/basic_stream_descriptor.hpp b/include/boost/asio/posix/basic_stream_descriptor.hpp
index 7132f3da..cdce1c5d 100644
--- a/include/boost/asio/posix/basic_stream_descriptor.hpp
+++ b/include/boost/asio/posix/basic_stream_descriptor.hpp
@@ -37,7 +37,7 @@ namespace posix {
  * @par Concepts:
  * AsyncReadStream, AsyncWriteStream, Stream, SyncReadStream, SyncWriteStream.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_stream_descriptor
   : public basic_descriptor<Executor>
 {
@@ -420,8 +420,8 @@ private:
 
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_write_some(
-          self_->impl_.get_implementation(), buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -453,8 +453,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_read_some(
-          self_->impl_.get_implementation(), buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/post.hpp b/include/boost/asio/post.hpp
index 8f08a65a..c4094924 100644
--- a/include/boost/asio/post.hpp
+++ b/include/boost/asio/post.hpp
@@ -19,6 +19,7 @@
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/execution_context.hpp>
+#include <boost/asio/execution/executor.hpp>
 #include <boost/asio/is_executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -97,7 +98,9 @@ BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) post(
     const Executor& ex,
     BOOST_ASIO_MOVE_ARG(CompletionToken) token
       BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
-    typename enable_if<is_executor<Executor>::value>::type* = 0);
+    typename enable_if<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    >::type* = 0);
 
 /// Submits a completion token or function object for execution.
 /**
diff --git a/include/boost/asio/prefer.hpp b/include/boost/asio/prefer.hpp
new file mode 100644
index 00000000..d222b349
--- /dev/null
+++ b/include/boost/asio/prefer.hpp
@@ -0,0 +1,660 @@
+//
+// prefer.hpp
+// ~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_PREFER_HPP
+#define BOOST_ASIO_PREFER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/prefer_free.hpp>
+#include <boost/asio/traits/prefer_member.hpp>
+#include <boost/asio/traits/require_free.hpp>
+#include <boost/asio/traits/require_member.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace boost {
+namespace asio {
+
+/// A customisation point that attempts to apply a property to an object.
+/**
+ * The name <tt>prefer</tt> denotes a customisation point object. The
+ * expression <tt>boost::asio::prefer(E, P0, Pn...)</tt> for some subexpressions
+ * <tt>E</tt> and <tt>P0</tt>, and where <tt>Pn...</tt> represents <tt>N</tt>
+ * subexpressions (where <tt>N</tt> is 0 or more, and with types <tt>T =
+ * decay_t<decltype(E)></tt> and <tt>Prop0 = decay_t<decltype(P0)></tt>) is
+ * expression-equivalent to:
+ *
+ * @li If <tt>is_applicable_property_v<T, Prop0> && Prop0::is_preferable</tt> is
+ *   not a well-formed constant expression with value <tt>true</tt>,
+ *   <tt>boost::asio::prefer(E, P0, Pn...)</tt> is ill-formed.
+ *
+ * @li Otherwise, <tt>E</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>Prop0::template static_query_v<T> == Prop0::value()</tt> is a
+ *   well-formed constant expression with value <tt>true</tt>.
+ *
+ * @li Otherwise, <tt>(E).require(P0)</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>(E).require(P0)</tt> is a valid expression.
+ *
+ * @li Otherwise, <tt>require(E, P0)</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>require(E, P0)</tt> is a valid expression with overload resolution
+ *   performed in a context that does not include the declaration of the
+ *   <tt>require</tt> customization point object.
+ *
+ * @li Otherwise, <tt>(E).prefer(P0)</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>(E).prefer(P0)</tt> is a valid expression.
+ *
+ * @li Otherwise, <tt>prefer(E, P0)</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>prefer(E, P0)</tt> is a valid expression with overload resolution
+ *   performed in a context that does not include the declaration of the
+ *   <tt>prefer</tt> customization point object.
+ *
+ * @li Otherwise, <tt>E</tt> if <tt>N == 0</tt>.
+ *
+ * @li Otherwise,
+ *   <tt>boost::asio::prefer(boost::asio::prefer(E, P0), Pn...)</tt>
+ *   if <tt>N > 0</tt> and the expression
+ *   <tt>boost::asio::prefer(boost::asio::prefer(E, P0), Pn...)</tt>
+ *   is a valid expression.
+ *
+ * @li Otherwise, <tt>boost::asio::prefer(E, P0, Pn...)</tt> is ill-formed.
+ */
+inline constexpr unspecified prefer = unspecified;
+
+/// A type trait that determines whether a @c prefer expression is well-formed.
+/**
+ * Class template @c can_prefer is a trait that is derived from
+ * @c true_type if the expression <tt>boost::asio::prefer(std::declval<T>(),
+ * std::declval<Properties>()...)</tt> is well formed; otherwise @c false_type.
+ */
+template <typename T, typename... Properties>
+struct can_prefer :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines whether a @c prefer expression will not throw.
+/**
+ * Class template @c is_nothrow_prefer is a trait that is derived from
+ * @c true_type if the expression <tt>boost::asio::prefer(std::declval<T>(),
+ * std::declval<Properties>()...)</tt> is @c noexcept; otherwise @c false_type.
+ */
+template <typename T, typename... Properties>
+struct is_nothrow_prefer :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines the result type of a @c prefer expression.
+/**
+ * Class template @c prefer_result_type is a trait that determines the result
+ * type of the expression <tt>boost::asio::prefer(std::declval<T>(),
+ * std::declval<Properties>()...)</tt>.
+ */
+template <typename T, typename... Properties>
+struct prefer_result_type
+{
+  /// The result of the @c prefer expression.
+  typedef automatically_determined type;
+};
+
+} // namespace asio
+} // namespace boost
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_prefer_fn {
+
+using boost::asio::decay;
+using boost::asio::declval;
+using boost::asio::enable_if;
+using boost::asio::is_applicable_property;
+using boost::asio::traits::prefer_free;
+using boost::asio::traits::prefer_member;
+using boost::asio::traits::require_free;
+using boost::asio::traits::require_member;
+using boost::asio::traits::static_require;
+
+void prefer();
+void require();
+
+enum overload_type
+{
+  identity,
+  call_require_member,
+  call_require_free,
+  call_prefer_member,
+  call_prefer_free,
+  two_props,
+  n_props,
+  ill_formed
+};
+
+template <typename T, typename Properties, typename = void>
+struct call_traits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_preferable
+      &&
+      static_require<T, Property>::is_valid
+    )
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = identity);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  typedef BOOST_ASIO_MOVE_ARG(T) result_type;
+#else // defined(BOOST_ASIO_HAS_MOVE)
+  typedef BOOST_ASIO_MOVE_ARG(typename decay<T>::type) result_type;
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_preferable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      require_member<T, Property>::is_valid
+    )
+  >::type> :
+  require_member<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_require_member);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_preferable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      !require_member<T, Property>::is_valid
+      &&
+      require_free<T, Property>::is_valid
+    )
+  >::type> :
+  require_free<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_require_free);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_preferable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      !require_member<T, Property>::is_valid
+      &&
+      !require_free<T, Property>::is_valid
+      &&
+      prefer_member<T, Property>::is_valid
+    )
+  >::type> :
+  prefer_member<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_prefer_member);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_preferable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      !require_member<T, Property>::is_valid
+      &&
+      !require_free<T, Property>::is_valid
+      &&
+      !prefer_member<T, Property>::is_valid
+      &&
+      prefer_free<T, Property>::is_valid
+    )
+  >::type> :
+  prefer_free<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_prefer_free);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_preferable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      !require_member<T, Property>::is_valid
+      &&
+      !require_free<T, Property>::is_valid
+      &&
+      !prefer_member<T, Property>::is_valid
+      &&
+      !prefer_free<T, Property>::is_valid
+    )
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = identity);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  typedef BOOST_ASIO_MOVE_ARG(T) result_type;
+#else // defined(BOOST_ASIO_HAS_MOVE)
+  typedef BOOST_ASIO_MOVE_ARG(typename decay<T>::type) result_type;
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+};
+
+template <typename T, typename P0, typename P1>
+struct call_traits<T, void(P0, P1),
+  typename enable_if<
+    call_traits<T, void(P0)>::overload != ill_formed
+    &&
+    call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1)
+    >::overload != ill_formed
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = two_props);
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (
+      call_traits<T, void(P0)>::is_noexcept
+      &&
+      call_traits<
+        typename call_traits<T, void(P0)>::result_type,
+        void(P1)
+      >::is_noexcept
+    ));
+
+  typedef typename decay<
+    typename call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1)
+    >::result_type
+  >::type result_type;
+};
+
+template <typename T, typename P0, typename P1, typename BOOST_ASIO_ELLIPSIS PN>
+struct call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS),
+  typename enable_if<
+    call_traits<T, void(P0)>::overload != ill_formed
+    &&
+    call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1, PN BOOST_ASIO_ELLIPSIS)
+    >::overload != ill_formed
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = n_props);
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (
+      call_traits<T, void(P0)>::is_noexcept
+      &&
+      call_traits<
+        typename call_traits<T, void(P0)>::result_type,
+        void(P1, PN BOOST_ASIO_ELLIPSIS)
+      >::is_noexcept
+    ));
+
+  typedef typename decay<
+    typename call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1, PN BOOST_ASIO_ELLIPSIS)
+    >::result_type
+  >::type result_type;
+};
+
+struct impl
+{
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == identity,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property)) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t);
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_require_member,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t).require(
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_require_free,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return require(
+        BOOST_ASIO_MOVE_CAST(T)(t),
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_prefer_member,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t).prefer(
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_prefer_free,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return prefer(
+        BOOST_ASIO_MOVE_CAST(T)(t),
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename P0, typename P1>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(P0, P1)>::overload == two_props,
+    typename call_traits<T, void(P0, P1)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(P0) p0,
+      BOOST_ASIO_MOVE_ARG(P1) p1) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(P0, P1)>::is_noexcept))
+  {
+    return (*this)(
+        (*this)(
+          BOOST_ASIO_MOVE_CAST(T)(t),
+          BOOST_ASIO_MOVE_CAST(P0)(p0)),
+        BOOST_ASIO_MOVE_CAST(P1)(p1));
+  }
+
+  template <typename T, typename P0, typename P1,
+    typename BOOST_ASIO_ELLIPSIS PN>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS)>::overload == n_props,
+    typename call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(P0) p0,
+      BOOST_ASIO_MOVE_ARG(P1) p1,
+      BOOST_ASIO_MOVE_ARG(PN) BOOST_ASIO_ELLIPSIS pn) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS)>::is_noexcept))
+  {
+    return (*this)(
+        (*this)(
+          BOOST_ASIO_MOVE_CAST(T)(t),
+          BOOST_ASIO_MOVE_CAST(P0)(p0)),
+        BOOST_ASIO_MOVE_CAST(P1)(p1),
+        BOOST_ASIO_MOVE_CAST(PN)(pn) BOOST_ASIO_ELLIPSIS);
+  }
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_prefer_fn
+namespace boost {
+namespace asio {
+namespace {
+
+static BOOST_ASIO_CONSTEXPR const asio_prefer_fn::impl&
+  prefer = asio_prefer_fn::static_instance<>::instance;
+
+} // namespace
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename... Properties>
+struct can_prefer :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(Properties...)>::overload
+      != asio_prefer_fn::ill_formed>
+{
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename P0 = void,
+    typename P1 = void, typename P2 = void>
+struct can_prefer :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(P0, P1, P2)>::overload
+      != asio_prefer_fn::ill_formed>
+{
+};
+
+template <typename T, typename P0, typename P1>
+struct can_prefer<T, P0, P1> :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(P0, P1)>::overload
+      != asio_prefer_fn::ill_formed>
+{
+};
+
+template <typename T, typename P0>
+struct can_prefer<T, P0> :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(P0)>::overload
+      != asio_prefer_fn::ill_formed>
+{
+};
+
+template <typename T>
+struct can_prefer<T> :
+  false_type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename BOOST_ASIO_ELLIPSIS Properties>
+constexpr bool can_prefer_v
+  = can_prefer<T, Properties BOOST_ASIO_ELLIPSIS>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename... Properties>
+struct is_nothrow_prefer :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(Properties...)>::is_noexcept>
+{
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename P0 = void,
+    typename P1 = void, typename P2 = void>
+struct is_nothrow_prefer :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(P0, P1, P2)>::is_noexcept>
+{
+};
+
+template <typename T, typename P0, typename P1>
+struct is_nothrow_prefer<T, P0, P1> :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(P0, P1)>::is_noexcept>
+{
+};
+
+template <typename T, typename P0>
+struct is_nothrow_prefer<T, P0> :
+  integral_constant<bool,
+    asio_prefer_fn::call_traits<T, void(P0)>::is_noexcept>
+{
+};
+
+template <typename T>
+struct is_nothrow_prefer<T> :
+  false_type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename BOOST_ASIO_ELLIPSIS Properties>
+constexpr bool is_nothrow_prefer_v
+  = is_nothrow_prefer<T, Properties BOOST_ASIO_ELLIPSIS>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename... Properties>
+struct prefer_result_type
+{
+  typedef typename asio_prefer_fn::call_traits<
+      T, void(Properties...)>::result_type type;
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename P0 = void,
+    typename P1 = void, typename P2 = void>
+struct prefer_result_type
+{
+  typedef typename asio_prefer_fn::call_traits<
+      T, void(P0, P1, P2)>::result_type type;
+};
+
+template <typename T, typename P0, typename P1>
+struct prefer_result_type<T, P0, P1>
+{
+  typedef typename asio_prefer_fn::call_traits<
+      T, void(P0, P1)>::result_type type;
+};
+
+template <typename T, typename P0>
+struct prefer_result_type<T, P0>
+{
+  typedef typename asio_prefer_fn::call_traits<
+      T, void(P0)>::result_type type;
+};
+
+template <typename T>
+struct prefer_result_type<T>
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+} // namespace asio
+} // namespace boost
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_PREFER_HPP
diff --git a/include/boost/asio/query.hpp b/include/boost/asio/query.hpp
new file mode 100644
index 00000000..db3f0daa
--- /dev/null
+++ b/include/boost/asio/query.hpp
@@ -0,0 +1,300 @@
+//
+// query.hpp
+// ~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_QUERY_HPP
+#define BOOST_ASIO_QUERY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/query_member.hpp>
+#include <boost/asio/traits/query_free.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace boost {
+namespace asio {
+
+/// A customisation point that queries the value of a property.
+/**
+ * The name <tt>query</tt> denotes a customization point object. The
+ * expression <tt>boost::asio::query(E, P)</tt> for some
+ * subexpressions <tt>E</tt> and <tt>P</tt> (with types <tt>T =
+ * decay_t<decltype(E)></tt> and <tt>Prop = decay_t<decltype(P)></tt>) is
+ * expression-equivalent to:
+ *
+ * @li If <tt>is_applicable_property_v<T, Prop></tt> is not a well-formed
+ *   constant expression with value <tt>true</tt>, <tt>boost::asio::query(E,
+ *   P)</tt> is ill-formed.
+ *
+ * @li Otherwise, <tt>Prop::template static_query_v<T></tt> if the expression
+ *   <tt>Prop::template static_query_v<T></tt> is a well-formed constant
+ *   expression.
+ *
+ * @li Otherwise, <tt>(E).query(P)</tt> if the expression
+ *   <tt>(E).query(P)</tt> is well-formed.
+ *
+ * @li Otherwise, <tt>query(E, P)</tt> if the expression
+ *   <tt>query(E, P)</tt> is a valid expression with overload
+ *   resolution performed in a context that does not include the declaration
+ *   of the <tt>query</tt> customization point object.
+ *
+ * @li Otherwise, <tt>boost::asio::query(E, P)</tt> is ill-formed.
+ */
+inline constexpr unspecified query = unspecified;
+
+/// A type trait that determines whether a @c query expression is well-formed.
+/**
+ * Class template @c can_query is a trait that is derived from
+ * @c true_type if the expression <tt>boost::asio::query(std::declval<T>(),
+ * std::declval<Property>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename T, typename Property>
+struct can_query :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines whether a @c query expression will
+/// not throw.
+/**
+ * Class template @c is_nothrow_query is a trait that is derived from
+ * @c true_type if the expression <tt>boost::asio::query(std::declval<T>(),
+ * std::declval<Property>())</tt> is @c noexcept; otherwise @c false_type.
+ */
+template <typename T, typename Property>
+struct is_nothrow_query :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines the result type of a @c query expression.
+/**
+ * Class template @c query_result_type is a trait that determines the
+ * result type of the expression <tt>boost::asio::query(std::declval<T>(),
+ * std::declval<Property>())</tt>.
+ */
+template <typename T, typename Property>
+struct query_result_type
+{
+  /// The result of the @c query expression.
+  typedef automatically_determined type;
+};
+
+} // namespace asio
+} // namespace boost
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_query_fn {
+
+using boost::asio::decay;
+using boost::asio::declval;
+using boost::asio::enable_if;
+using boost::asio::is_applicable_property;
+using boost::asio::traits::query_free;
+using boost::asio::traits::query_member;
+using boost::asio::traits::static_query;
+
+void query();
+
+enum overload_type
+{
+  static_value,
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename T, typename Properties, typename = void>
+struct call_traits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      static_query<T, Property>::is_valid
+    )
+  >::type> :
+  static_query<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = static_value);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      !static_query<T, Property>::is_valid
+      &&
+      query_member<T, Property>::is_valid
+    )
+  >::type> :
+  query_member<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      !static_query<T, Property>::is_valid
+      &&
+      !query_member<T, Property>::is_valid
+      &&
+      query_free<T, Property>::is_valid
+    )
+  >::type> :
+  query_free<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == static_value,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T),
+      BOOST_ASIO_MOVE_ARG(Property)) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return static_query<
+      typename decay<T>::type,
+      typename decay<Property>::type
+    >::value();
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_member,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t).query(BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_free,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return query(BOOST_ASIO_MOVE_CAST(T)(t), BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_query_fn
+namespace boost {
+namespace asio {
+namespace {
+
+static BOOST_ASIO_CONSTEXPR const asio_query_fn::impl&
+  query = asio_query_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename T, typename Property>
+struct can_query :
+  integral_constant<bool,
+    asio_query_fn::call_traits<T, void(Property)>::overload !=
+      asio_query_fn::ill_formed>
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+constexpr bool can_query_v
+  = can_query<T, Property>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+struct is_nothrow_query :
+  integral_constant<bool,
+    asio_query_fn::call_traits<T, void(Property)>::is_noexcept>
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+constexpr bool is_nothrow_query_v
+  = is_nothrow_query<T, Property>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+struct query_result_type
+{
+  typedef typename asio_query_fn::call_traits<
+      T, void(Property)>::result_type type;
+};
+
+} // namespace asio
+} // namespace boost
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_QUERY_HPP
diff --git a/include/boost/asio/read_until.hpp b/include/boost/asio/read_until.hpp
index dec8d4aa..1c204637 100644
--- a/include/boost/asio/read_until.hpp
+++ b/include/boost/asio/read_until.hpp
@@ -115,7 +115,7 @@ struct is_match_condition
  * @par Example
  * To read data into a @c std::string until a newline is encountered:
  * @code std::string data;
- * std::string n = boost::asio::read_until(s,
+ * std::size_t n = boost::asio::read_until(s,
  *     boost::asio::dynamic_buffer(data), '\n');
  * std::string line = data.substr(0, n);
  * data.erase(0, n); @endcode
@@ -217,7 +217,7 @@ std::size_t read_until(SyncReadStream& s,
  * @par Example
  * To read data into a @c std::string until a CR-LF sequence is encountered:
  * @code std::string data;
- * std::string n = boost::asio::read_until(s,
+ * std::size_t n = boost::asio::read_until(s,
  *     boost::asio::dynamic_buffer(data), "\r\n");
  * std::string line = data.substr(0, n);
  * data.erase(0, n); @endcode
@@ -328,7 +328,7 @@ std::size_t read_until(SyncReadStream& s,
  * @par Example
  * To read data into a @c std::string until a CR-LF sequence is encountered:
  * @code std::string data;
- * std::string n = boost::asio::read_until(s,
+ * std::size_t n = boost::asio::read_until(s,
  *     boost::asio::dynamic_buffer(data), boost::regex("\r\n"));
  * std::string line = data.substr(0, n);
  * data.erase(0, n); @endcode
@@ -1056,7 +1056,7 @@ std::size_t read_until(SyncReadStream& s,
  * @par Example
  * To read data into a @c std::string until a newline is encountered:
  * @code std::string data;
- * std::string n = boost::asio::read_until(s,
+ * std::size_t n = boost::asio::read_until(s,
  *     boost::asio::dynamic_buffer(data), '\n');
  * std::string line = data.substr(0, n);
  * data.erase(0, n); @endcode
@@ -1154,7 +1154,7 @@ std::size_t read_until(SyncReadStream& s, DynamicBuffer_v2 buffers,
  * @par Example
  * To read data into a @c std::string until a CR-LF sequence is encountered:
  * @code std::string data;
- * std::string n = boost::asio::read_until(s,
+ * std::size_t n = boost::asio::read_until(s,
  *     boost::asio::dynamic_buffer(data), "\r\n");
  * std::string line = data.substr(0, n);
  * data.erase(0, n); @endcode
@@ -1260,7 +1260,7 @@ std::size_t read_until(SyncReadStream& s, DynamicBuffer_v2 buffers,
  * @par Example
  * To read data into a @c std::string until a CR-LF sequence is encountered:
  * @code std::string data;
- * std::string n = boost::asio::read_until(s,
+ * std::size_t n = boost::asio::read_until(s,
  *     boost::asio::dynamic_buffer(data), boost::regex("\r\n"));
  * std::string line = data.substr(0, n);
  * data.erase(0, n); @endcode
diff --git a/include/boost/asio/require.hpp b/include/boost/asio/require.hpp
new file mode 100644
index 00000000..06920b87
--- /dev/null
+++ b/include/boost/asio/require.hpp
@@ -0,0 +1,528 @@
+//
+// require.hpp
+// ~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_REQUIRE_HPP
+#define BOOST_ASIO_REQUIRE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/require_member.hpp>
+#include <boost/asio/traits/require_free.hpp>
+#include <boost/asio/traits/static_require.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace boost {
+namespace asio {
+
+/// A customisation point that applies a concept-preserving property to an
+/// object.
+/**
+ * The name <tt>require</tt> denotes a customisation point object. The
+ * expression <tt>boost::asio::require(E, P0, Pn...)</tt> for some
+ * subexpressions <tt>E</tt> and <tt>P0</tt>, and where <tt>Pn...</tt>
+ * represents <tt>N</tt> subexpressions (where <tt>N</tt> is 0 or more, and with
+ * types <tt>T = decay_t<decltype(E)></tt> and <tt>Prop0 =
+ * decay_t<decltype(P0)></tt>) is expression-equivalent to:
+ *
+ * @li If <tt>is_applicable_property_v<T, Prop0> && Prop0::is_requirable</tt> is
+ *   not a well-formed constant expression with value <tt>true</tt>,
+ *   <tt>boost::asio::require(E, P0, Pn...)</tt> is ill-formed.
+ *
+ * @li Otherwise, <tt>E</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>Prop0::template static_query_v<T> == Prop0::value()</tt> is a
+ *   well-formed constant expression with value <tt>true</tt>.
+ *
+ * @li Otherwise, <tt>(E).require(P0)</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>(E).require(P0)</tt> is a valid expression.
+ *
+ * @li Otherwise, <tt>require(E, P0)</tt> if <tt>N == 0</tt> and the expression
+ *   <tt>require(E, P0)</tt> is a valid expression with overload resolution
+ *   performed in a context that does not include the declaration of the
+ *   <tt>require</tt> customization point object.
+ *
+ * @li Otherwise,
+ *   <tt>boost::asio::require(boost::asio::require(E, P0), Pn...)</tt>
+ *   if <tt>N > 0</tt> and the expression
+ *   <tt>boost::asio::require(boost::asio::require(E, P0), Pn...)</tt>
+ *   is a valid expression.
+ *
+ * @li Otherwise, <tt>boost::asio::require(E, P0, Pn...)</tt> is ill-formed.
+ */
+inline constexpr unspecified require = unspecified;
+
+/// A type trait that determines whether a @c require expression is well-formed.
+/**
+ * Class template @c can_require is a trait that is derived from
+ * @c true_type if the expression <tt>boost::asio::require(std::declval<T>(),
+ * std::declval<Properties>()...)</tt> is well formed; otherwise @c false_type.
+ */
+template <typename T, typename... Properties>
+struct can_require :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines whether a @c require expression will not throw.
+/**
+ * Class template @c is_nothrow_require is a trait that is derived from
+ * @c true_type if the expression <tt>boost::asio::require(std::declval<T>(),
+ * std::declval<Properties>()...)</tt> is @c noexcept; otherwise @c false_type.
+ */
+template <typename T, typename... Properties>
+struct is_nothrow_require :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines the result type of a @c require expression.
+/**
+ * Class template @c require_result_type is a trait that determines the result
+ * type of the expression <tt>boost::asio::require(std::declval<T>(),
+ * std::declval<Properties>()...)</tt>.
+ */
+template <typename T, typename... Properties>
+struct require_result_type
+{
+  /// The result of the @c require expression.
+  typedef automatically_determined type;
+};
+
+} // namespace asio
+} // namespace boost
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_require_fn {
+
+using boost::asio::decay;
+using boost::asio::declval;
+using boost::asio::enable_if;
+using boost::asio::is_applicable_property;
+using boost::asio::traits::require_free;
+using boost::asio::traits::require_member;
+using boost::asio::traits::static_require;
+
+void require();
+
+enum overload_type
+{
+  identity,
+  call_member,
+  call_free,
+  two_props,
+  n_props,
+  ill_formed
+};
+
+template <typename T, typename Properties, typename = void>
+struct call_traits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_requirable
+      &&
+      static_require<T, Property>::is_valid
+    )
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = identity);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  typedef BOOST_ASIO_MOVE_ARG(T) result_type;
+#else // defined(BOOST_ASIO_HAS_MOVE)
+  typedef BOOST_ASIO_MOVE_ARG(typename decay<T>::type) result_type;
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_requirable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      require_member<T, Property>::is_valid
+    )
+  >::type> :
+  require_member<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_requirable
+      &&
+      !static_require<T, Property>::is_valid
+      &&
+      !require_member<T, Property>::is_valid
+      &&
+      require_free<T, Property>::is_valid
+    )
+  >::type> :
+  require_free<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+template <typename T, typename P0, typename P1>
+struct call_traits<T, void(P0, P1),
+  typename enable_if<
+    call_traits<T, void(P0)>::overload != ill_formed
+    &&
+    call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1)
+    >::overload != ill_formed
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = two_props);
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (
+      call_traits<T, void(P0)>::is_noexcept
+      &&
+      call_traits<
+        typename call_traits<T, void(P0)>::result_type,
+        void(P1)
+      >::is_noexcept
+    ));
+
+  typedef typename decay<
+    typename call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1)
+    >::result_type
+  >::type result_type;
+};
+
+template <typename T, typename P0, typename P1, typename BOOST_ASIO_ELLIPSIS PN>
+struct call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS),
+  typename enable_if<
+    call_traits<T, void(P0)>::overload != ill_formed
+    &&
+    call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1, PN BOOST_ASIO_ELLIPSIS)
+    >::overload != ill_formed
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = n_props);
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (
+      call_traits<T, void(P0)>::is_noexcept
+      &&
+      call_traits<
+        typename call_traits<T, void(P0)>::result_type,
+        void(P1, PN BOOST_ASIO_ELLIPSIS)
+      >::is_noexcept
+    ));
+
+  typedef typename decay<
+    typename call_traits<
+      typename call_traits<T, void(P0)>::result_type,
+      void(P1, PN BOOST_ASIO_ELLIPSIS)
+    >::result_type
+  >::type result_type;
+};
+
+struct impl
+{
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == identity,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property)) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t);
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_member,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t).require(
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_free,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return require(
+        BOOST_ASIO_MOVE_CAST(T)(t),
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename P0, typename P1>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(P0, P1)>::overload == two_props,
+    typename call_traits<T, void(P0, P1)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(P0) p0,
+      BOOST_ASIO_MOVE_ARG(P1) p1) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(P0, P1)>::is_noexcept))
+  {
+    return (*this)(
+        (*this)(
+          BOOST_ASIO_MOVE_CAST(T)(t),
+          BOOST_ASIO_MOVE_CAST(P0)(p0)),
+        BOOST_ASIO_MOVE_CAST(P1)(p1));
+  }
+
+  template <typename T, typename P0, typename P1,
+    typename BOOST_ASIO_ELLIPSIS PN>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS)>::overload == n_props,
+    typename call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(P0) p0,
+      BOOST_ASIO_MOVE_ARG(P1) p1,
+      BOOST_ASIO_MOVE_ARG(PN) BOOST_ASIO_ELLIPSIS pn) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(P0, P1, PN BOOST_ASIO_ELLIPSIS)>::is_noexcept))
+  {
+    return (*this)(
+        (*this)(
+          BOOST_ASIO_MOVE_CAST(T)(t),
+          BOOST_ASIO_MOVE_CAST(P0)(p0)),
+        BOOST_ASIO_MOVE_CAST(P1)(p1),
+        BOOST_ASIO_MOVE_CAST(PN)(pn) BOOST_ASIO_ELLIPSIS);
+  }
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_require_fn
+namespace boost {
+namespace asio {
+namespace {
+
+static BOOST_ASIO_CONSTEXPR const asio_require_fn::impl&
+  require = asio_require_fn::static_instance<>::instance;
+
+} // namespace
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename... Properties>
+struct can_require :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(Properties...)>::overload
+      != asio_require_fn::ill_formed>
+{
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename P0 = void,
+    typename P1 = void, typename P2 = void>
+struct can_require :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(P0, P1, P2)>::overload
+      != asio_require_fn::ill_formed>
+{
+};
+
+template <typename T, typename P0, typename P1>
+struct can_require<T, P0, P1> :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(P0, P1)>::overload
+      != asio_require_fn::ill_formed>
+{
+};
+
+template <typename T, typename P0>
+struct can_require<T, P0> :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(P0)>::overload
+      != asio_require_fn::ill_formed>
+{
+};
+
+template <typename T>
+struct can_require<T> :
+  false_type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename BOOST_ASIO_ELLIPSIS Properties>
+constexpr bool can_require_v
+  = can_require<T, Properties BOOST_ASIO_ELLIPSIS>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename... Properties>
+struct is_nothrow_require :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(Properties...)>::is_noexcept>
+{
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename P0 = void,
+    typename P1 = void, typename P2 = void>
+struct is_nothrow_require :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(P0, P1, P2)>::is_noexcept>
+{
+};
+
+template <typename T, typename P0, typename P1>
+struct is_nothrow_require<T, P0, P1> :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(P0, P1)>::is_noexcept>
+{
+};
+
+template <typename T, typename P0>
+struct is_nothrow_require<T, P0> :
+  integral_constant<bool,
+    asio_require_fn::call_traits<T, void(P0)>::is_noexcept>
+{
+};
+
+template <typename T>
+struct is_nothrow_require<T> :
+  false_type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename BOOST_ASIO_ELLIPSIS Properties>
+constexpr bool is_nothrow_require_v
+  = is_nothrow_require<T, Properties BOOST_ASIO_ELLIPSIS>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename... Properties>
+struct require_result_type
+{
+  typedef typename asio_require_fn::call_traits<
+      T, void(Properties...)>::result_type type;
+};
+
+#else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename T, typename P0 = void,
+    typename P1 = void, typename P2 = void>
+struct require_result_type
+{
+  typedef typename asio_require_fn::call_traits<
+      T, void(P0, P1, P2)>::result_type type;
+};
+
+template <typename T, typename P0, typename P1>
+struct require_result_type<T, P0, P1>
+{
+  typedef typename asio_require_fn::call_traits<
+      T, void(P0, P1)>::result_type type;
+};
+
+template <typename T, typename P0>
+struct require_result_type<T, P0>
+{
+  typedef typename asio_require_fn::call_traits<
+      T, void(P0)>::result_type type;
+};
+
+template <typename T>
+struct require_result_type<T>
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
+
+} // namespace asio
+} // namespace boost
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_REQUIRE_HPP
diff --git a/include/boost/asio/require_concept.hpp b/include/boost/asio/require_concept.hpp
new file mode 100644
index 00000000..d397e24f
--- /dev/null
+++ b/include/boost/asio/require_concept.hpp
@@ -0,0 +1,314 @@
+//
+// require_concept.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_REQUIRE_CONCEPT_HPP
+#define BOOST_ASIO_REQUIRE_CONCEPT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/is_applicable_property.hpp>
+#include <boost/asio/traits/require_concept_member.hpp>
+#include <boost/asio/traits/require_concept_free.hpp>
+#include <boost/asio/traits/static_require_concept.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace boost {
+namespace asio {
+
+/// A customisation point that applies a concept-enforcing property to an
+/// object.
+/**
+ * The name <tt>require_concept</tt> denotes a customization point object. The
+ * expression <tt>boost::asio::require_concept(E, P)</tt> for some
+ * subexpressions <tt>E</tt> and <tt>P</tt> (with types <tt>T =
+ * decay_t<decltype(E)></tt> and <tt>Prop = decay_t<decltype(P)></tt>) is
+ * expression-equivalent to:
+ *
+ * @li If <tt>is_applicable_property_v<T, Prop> &&
+ *   Prop::is_requirable_concept</tt> is not a well-formed constant expression
+ *   with value <tt>true</tt>, <tt>boost::asio::require_concept(E, P)</tt> is
+ *   ill-formed.
+ *
+ * @li Otherwise, <tt>E</tt> if the expression <tt>Prop::template
+ *   static_query_v<T> == Prop::value()</tt> is a well-formed constant
+ *   expression with value <tt>true</tt>.
+ *
+ * @li Otherwise, <tt>(E).require_concept(P)</tt> if the expression
+ *   <tt>(E).require_concept(P)</tt> is well-formed.
+ *
+ * @li Otherwise, <tt>require_concept(E, P)</tt> if the expression
+ *   <tt>require_concept(E, P)</tt> is a valid expression with overload
+ *   resolution performed in a context that does not include the declaration
+ *   of the <tt>require_concept</tt> customization point object.
+ *
+ * @li Otherwise, <tt>boost::asio::require_concept(E, P)</tt> is ill-formed.
+ */
+inline constexpr unspecified require_concept = unspecified;
+
+/// A type trait that determines whether a @c require_concept expression is
+/// well-formed.
+/**
+ * Class template @c can_require_concept is a trait that is derived from
+ * @c true_type if the expression
+ * <tt>boost::asio::require_concept(std::declval<T>(),
+ * std::declval<Property>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename T, typename Property>
+struct can_require_concept :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines whether a @c require_concept expression will
+/// not throw.
+/**
+ * Class template @c is_nothrow_require_concept is a trait that is derived from
+ * @c true_type if the expression
+ * <tt>boost::asio::require_concept(std::declval<T>(),
+ * std::declval<Property>())</tt> is @c noexcept; otherwise @c false_type.
+ */
+template <typename T, typename Property>
+struct is_nothrow_require_concept :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait that determines the result type of a @c require_concept
+/// expression.
+/**
+ * Class template @c require_concept_result_type is a trait that determines the
+ * result type of the expression
+ * <tt>boost::asio::require_concept(std::declval<T>(),
+ * std::declval<Property>())</tt>.
+ */
+template <typename T, typename Property>
+struct require_concept_result_type
+{
+  /// The result of the @c require_concept expression.
+  typedef automatically_determined type;
+};
+
+} // namespace asio
+} // namespace boost
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_require_concept_fn {
+
+using boost::asio::decay;
+using boost::asio::declval;
+using boost::asio::enable_if;
+using boost::asio::is_applicable_property;
+using boost::asio::traits::require_concept_free;
+using boost::asio::traits::require_concept_member;
+using boost::asio::traits::static_require_concept;
+
+void require_concept();
+
+enum overload_type
+{
+  identity,
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename T, typename Properties, typename = void>
+struct call_traits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_requirable_concept
+      &&
+      static_require_concept<T, Property>::is_valid
+    )
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = identity);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef BOOST_ASIO_MOVE_ARG(T) result_type;
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_requirable_concept
+      &&
+      !static_require_concept<T, Property>::is_valid
+      &&
+      require_concept_member<T, Property>::is_valid
+    )
+  >::type> :
+  require_concept_member<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename T, typename Property>
+struct call_traits<T, void(Property),
+  typename enable_if<
+    (
+      is_applicable_property<
+        typename decay<T>::type,
+        typename decay<Property>::type
+      >::value
+      &&
+      decay<Property>::type::is_requirable_concept
+      &&
+      !static_require_concept<T, Property>::is_valid
+      &&
+      !require_concept_member<T, Property>::is_valid
+      &&
+      require_concept_free<T, Property>::is_valid
+    )
+  >::type> :
+  require_concept_free<T, Property>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == identity,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property)) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t);
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_member,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return BOOST_ASIO_MOVE_CAST(T)(t).require_concept(
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+
+  template <typename T, typename Property>
+  BOOST_ASIO_CONSTEXPR typename enable_if<
+    call_traits<T, void(Property)>::overload == call_free,
+    typename call_traits<T, void(Property)>::result_type
+  >::type
+  operator()(
+      BOOST_ASIO_MOVE_ARG(T) t,
+      BOOST_ASIO_MOVE_ARG(Property) p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      call_traits<T, void(Property)>::is_noexcept))
+  {
+    return require_concept(
+        BOOST_ASIO_MOVE_CAST(T)(t),
+        BOOST_ASIO_MOVE_CAST(Property)(p));
+  }
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_require_concept_fn
+namespace boost {
+namespace asio {
+namespace {
+
+static BOOST_ASIO_CONSTEXPR const asio_require_concept_fn::impl&
+  require_concept = asio_require_concept_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename T, typename Property>
+struct can_require_concept :
+  integral_constant<bool,
+    asio_require_concept_fn::call_traits<T, void(Property)>::overload !=
+      asio_require_concept_fn::ill_formed>
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+constexpr bool can_require_concept_v
+  = can_require_concept<T, Property>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+struct is_nothrow_require_concept :
+  integral_constant<bool,
+    asio_require_concept_fn::call_traits<T, void(Property)>::is_noexcept>
+{
+};
+
+#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+constexpr bool is_nothrow_require_concept_v
+  = is_nothrow_require_concept<T, Property>::value;
+
+#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename Property>
+struct require_concept_result_type
+{
+  typedef typename asio_require_concept_fn::call_traits<
+      T, void(Property)>::result_type type;
+};
+
+} // namespace asio
+} // namespace boost
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_REQUIRE_CONCEPT_HPP
diff --git a/include/boost/asio/spawn.hpp b/include/boost/asio/spawn.hpp
index 21cb3cfc..a3064373 100644
--- a/include/boost/asio/spawn.hpp
+++ b/include/boost/asio/spawn.hpp
@@ -17,11 +17,11 @@
 
 #include <boost/asio/detail/config.hpp>
 #include <boost/coroutine/all.hpp>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/bind_executor.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/detail/wrapped_handler.hpp>
-#include <boost/asio/executor.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/is_executor.hpp>
 #include <boost/asio/strand.hpp>
@@ -152,7 +152,7 @@ private:
 typedef basic_yield_context<unspecified> yield_context;
 #else // defined(GENERATING_DOCUMENTATION)
 typedef basic_yield_context<
-  executor_binder<void(*)(), executor> > yield_context;
+  executor_binder<void(*)(), any_io_executor> > yield_context;
 #endif // defined(GENERATING_DOCUMENTATION)
 
 /**
@@ -226,7 +226,9 @@ void spawn(BOOST_ASIO_MOVE_ARG(Handler) handler,
     BOOST_ASIO_MOVE_ARG(Function) function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes(),
-    typename enable_if<!is_executor<typename decay<Handler>::type>::value &&
+    typename enable_if<
+      !is_executor<typename decay<Handler>::type>::value &&
+      !execution::is_executor<typename decay<Handler>::type>::value &&
       !is_convertible<Handler&, execution_context&>::value>::type* = 0);
 
 /// Start a new stackful coroutine, inheriting the execution context of another.
@@ -267,7 +269,9 @@ void spawn(const Executor& ex,
     BOOST_ASIO_MOVE_ARG(Function) function,
     const boost::coroutines::attributes& attributes
       = boost::coroutines::attributes(),
-    typename enable_if<is_executor<Executor>::value>::type* = 0);
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type* = 0);
 
 /// Start a new stackful coroutine that executes on a given strand.
 /**
diff --git a/include/boost/asio/ssl/detail/buffered_handshake_op.hpp b/include/boost/asio/ssl/detail/buffered_handshake_op.hpp
index 4031df63..2cf8d151 100644
--- a/include/boost/asio/ssl/detail/buffered_handshake_op.hpp
+++ b/include/boost/asio/ssl/detail/buffered_handshake_op.hpp
@@ -30,6 +30,11 @@ template <typename ConstBufferSequence>
 class buffered_handshake_op
 {
 public:
+  static BOOST_ASIO_CONSTEXPR const char* tracking_name()
+  {
+    return "ssl::stream<>::async_buffered_handshake";
+  }
+
   buffered_handshake_op(stream_base::handshake_type type,
       const ConstBufferSequence& buffers)
     : type_(type),
diff --git a/include/boost/asio/ssl/detail/engine.hpp b/include/boost/asio/ssl/detail/engine.hpp
index f3c4407a..d84fad97 100644
--- a/include/boost/asio/ssl/detail/engine.hpp
+++ b/include/boost/asio/ssl/detail/engine.hpp
@@ -59,6 +59,11 @@ public:
   // Construct a new engine for the specified context.
   BOOST_ASIO_DECL explicit engine(SSL_CTX* context);
 
+#if defined(BOOST_ASIO_HAS_MOVE)
+  // Move construct from another engine.
+  BOOST_ASIO_DECL engine(engine&& other) BOOST_ASIO_NOEXCEPT;
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
   // Destructor.
   BOOST_ASIO_DECL ~engine();
 
diff --git a/include/boost/asio/ssl/detail/handshake_op.hpp b/include/boost/asio/ssl/detail/handshake_op.hpp
index 58f83124..7904af7b 100644
--- a/include/boost/asio/ssl/detail/handshake_op.hpp
+++ b/include/boost/asio/ssl/detail/handshake_op.hpp
@@ -29,6 +29,11 @@ namespace detail {
 class handshake_op
 {
 public:
+  static BOOST_ASIO_CONSTEXPR const char* tracking_name()
+  {
+    return "ssl::stream<>::async_handshake";
+  }
+
   handshake_op(stream_base::handshake_type type)
     : type_(type)
   {
diff --git a/include/boost/asio/ssl/detail/impl/engine.ipp b/include/boost/asio/ssl/detail/impl/engine.ipp
index cba7e516..c377ab76 100644
--- a/include/boost/asio/ssl/detail/impl/engine.ipp
+++ b/include/boost/asio/ssl/detail/impl/engine.ipp
@@ -56,16 +56,29 @@ engine::engine(SSL_CTX* context)
   ::SSL_set_bio(ssl_, int_bio, int_bio);
 }
 
+#if defined(BOOST_ASIO_HAS_MOVE)
+engine::engine(engine&& other) BOOST_ASIO_NOEXCEPT
+  : ssl_(other.ssl_),
+    ext_bio_(other.ext_bio_)
+{
+  other.ssl_ = 0;
+  other.ext_bio_ = 0;
+}
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
 engine::~engine()
 {
-  if (SSL_get_app_data(ssl_))
+  if (ssl_ && SSL_get_app_data(ssl_))
   {
     delete static_cast<verify_callback_base*>(SSL_get_app_data(ssl_));
     SSL_set_app_data(ssl_, 0);
   }
 
-  ::BIO_free(ext_bio_);
-  ::SSL_free(ssl_);
+  if (ext_bio_)
+    ::BIO_free(ext_bio_);
+
+  if (ssl_)
+    ::SSL_free(ssl_);
 }
 
 SSL* engine::native_handle()
diff --git a/include/boost/asio/ssl/detail/io.hpp b/include/boost/asio/ssl/detail/io.hpp
index 94d4db1b..a59e96fb 100644
--- a/include/boost/asio/ssl/detail/io.hpp
+++ b/include/boost/asio/ssl/detail/io.hpp
@@ -17,6 +17,7 @@
 
 #include <boost/asio/detail/config.hpp>
 
+#include <boost/asio/detail/handler_tracking.hpp>
 #include <boost/asio/ssl/detail/engine.hpp>
 #include <boost/asio/ssl/detail/stream_core.hpp>
 #include <boost/asio/write.hpp>
@@ -163,6 +164,9 @@ public:
             // Prevent other read operations from being started.
             core_.pending_read_.expires_at(core_.pos_infin());
 
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, Operation::tracking_name()));
+
             // Start reading some data from the underlying transport.
             next_layer_.async_read_some(
                 boost::asio::buffer(core_.input_buffer_),
@@ -170,6 +174,9 @@ public:
           }
           else
           {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, Operation::tracking_name()));
+
             // Wait until the current read operation completes.
             core_.pending_read_.async_wait(BOOST_ASIO_MOVE_CAST(io_op)(*this));
           }
@@ -190,6 +197,9 @@ public:
             // Prevent other write operations from being started.
             core_.pending_write_.expires_at(core_.pos_infin());
 
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, Operation::tracking_name()));
+
             // Start writing all the data to the underlying transport.
             boost::asio::async_write(next_layer_,
                 core_.engine_.get_output(core_.output_buffer_),
@@ -197,6 +207,9 @@ public:
           }
           else
           {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, Operation::tracking_name()));
+
             // Wait until the current write operation completes.
             core_.pending_write_.async_wait(BOOST_ASIO_MOVE_CAST(io_op)(*this));
           }
@@ -214,6 +227,9 @@ public:
           // read so the handler runs "as-if" posted using io_context::post().
           if (start)
           {
+            BOOST_ASIO_HANDLER_LOCATION((
+                  __FILE__, __LINE__, Operation::tracking_name()));
+
             next_layer_.async_read_some(
                 boost::asio::buffer(core_.input_buffer_, 0),
                 BOOST_ASIO_MOVE_CAST(io_op)(*this));
@@ -294,19 +310,29 @@ public:
 };
 
 template <typename Stream, typename Operation, typename Handler>
-inline void* asio_handler_allocate(std::size_t size,
+inline asio_handler_allocate_is_deprecated
+asio_handler_allocate(std::size_t size,
     io_op<Stream, Operation, Handler>* this_handler)
 {
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  boost_asio_handler_alloc_helpers::allocate(size, this_handler->handler_);
+  return asio_handler_allocate_is_no_longer_used();
+#else // defined(BOOST_ASIO_NO_DEPRECATED)
   return boost_asio_handler_alloc_helpers::allocate(
       size, this_handler->handler_);
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Stream, typename Operation, typename Handler>
-inline void asio_handler_deallocate(void* pointer, std::size_t size,
+inline asio_handler_deallocate_is_deprecated
+asio_handler_deallocate(void* pointer, std::size_t size,
     io_op<Stream, Operation, Handler>* this_handler)
 {
   boost_asio_handler_alloc_helpers::deallocate(
       pointer, size, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_deallocate_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Stream, typename Operation, typename Handler>
@@ -319,20 +345,28 @@ inline bool asio_handler_is_continuation(
 
 template <typename Function, typename Stream,
     typename Operation, typename Handler>
-inline void asio_handler_invoke(Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(Function& function,
     io_op<Stream, Operation, Handler>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Function, typename Stream,
     typename Operation, typename Handler>
-inline void asio_handler_invoke(const Function& function,
+inline asio_handler_invoke_is_deprecated
+asio_handler_invoke(const Function& function,
     io_op<Stream, Operation, Handler>* this_handler)
 {
   boost_asio_handler_invoke_helpers::invoke(
       function, this_handler->handler_);
+#if defined(BOOST_ASIO_NO_DEPRECATED)
+  return asio_handler_invoke_is_no_longer_used();
+#endif // defined(BOOST_ASIO_NO_DEPRECATED)
 }
 
 template <typename Stream, typename Operation, typename Handler>
diff --git a/include/boost/asio/ssl/detail/read_op.hpp b/include/boost/asio/ssl/detail/read_op.hpp
index d57366e4..ede49f1b 100644
--- a/include/boost/asio/ssl/detail/read_op.hpp
+++ b/include/boost/asio/ssl/detail/read_op.hpp
@@ -31,6 +31,11 @@ template <typename MutableBufferSequence>
 class read_op
 {
 public:
+  static BOOST_ASIO_CONSTEXPR const char* tracking_name()
+  {
+    return "ssl::stream<>::async_read_some";
+  }
+
   read_op(const MutableBufferSequence& buffers)
     : buffers_(buffers)
   {
diff --git a/include/boost/asio/ssl/detail/shutdown_op.hpp b/include/boost/asio/ssl/detail/shutdown_op.hpp
index 3d96fd2e..51e2c787 100644
--- a/include/boost/asio/ssl/detail/shutdown_op.hpp
+++ b/include/boost/asio/ssl/detail/shutdown_op.hpp
@@ -29,6 +29,11 @@ namespace detail {
 class shutdown_op
 {
 public:
+  static BOOST_ASIO_CONSTEXPR const char* tracking_name()
+  {
+    return "ssl::stream<>::async_shutdown";
+  }
+
   engine::want operator()(engine& eng,
       boost::system::error_code& ec,
       std::size_t& bytes_transferred) const
diff --git a/include/boost/asio/ssl/detail/stream_core.hpp b/include/boost/asio/ssl/detail/stream_core.hpp
index b32c682f..88bad784 100644
--- a/include/boost/asio/ssl/detail/stream_core.hpp
+++ b/include/boost/asio/ssl/detail/stream_core.hpp
@@ -52,6 +52,40 @@ struct stream_core
     pending_write_.expires_at(neg_infin());
   }
 
+#if defined(BOOST_ASIO_HAS_MOVE)
+  stream_core(stream_core&& other)
+    : engine_(BOOST_ASIO_MOVE_CAST(engine)(other.engine_)),
+#if defined(BOOST_ASIO_HAS_BOOST_DATE_TIME)
+      pending_read_(
+         BOOST_ASIO_MOVE_CAST(boost::asio::deadline_timer)(
+           other.pending_read_)),
+      pending_write_(
+         BOOST_ASIO_MOVE_CAST(boost::asio::deadline_timer)(
+           other.pending_write_)),
+#else // defined(BOOST_ASIO_HAS_BOOST_DATE_TIME)
+      pending_read_(
+         BOOST_ASIO_MOVE_CAST(boost::asio::steady_timer)(
+           other.pending_read_)),
+      pending_write_(
+         BOOST_ASIO_MOVE_CAST(boost::asio::steady_timer)(
+           other.pending_write_)),
+#endif // defined(BOOST_ASIO_HAS_BOOST_DATE_TIME)
+      output_buffer_space_(
+          BOOST_ASIO_MOVE_CAST(std::vector<unsigned char>)(
+            other.output_buffer_space_)),
+      output_buffer_(other.output_buffer_),
+      input_buffer_space_(
+          BOOST_ASIO_MOVE_CAST(std::vector<unsigned char>)(
+            other.input_buffer_space_)),
+      input_buffer_(other.input_buffer_),
+      input_(other.input_)
+  {
+    other.output_buffer_ = boost::asio::mutable_buffer(0, 0);
+    other.input_buffer_ = boost::asio::mutable_buffer(0, 0);
+    other.input_ = boost::asio::const_buffer(0, 0);
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
   ~stream_core()
   {
   }
@@ -115,13 +149,13 @@ struct stream_core
   std::vector<unsigned char> output_buffer_space_;
 
   // A buffer that may be used to prepare output intended for the transport.
-  const boost::asio::mutable_buffer output_buffer_;
+  boost::asio::mutable_buffer output_buffer_;
 
   // Buffer space used to read input intended for the engine.
   std::vector<unsigned char> input_buffer_space_;
 
   // A buffer that may be used to read input intended for the engine.
-  const boost::asio::mutable_buffer input_buffer_;
+  boost::asio::mutable_buffer input_buffer_;
 
   // The buffer pointing to the engine's unconsumed input.
   boost::asio::const_buffer input_;
diff --git a/include/boost/asio/ssl/detail/write_op.hpp b/include/boost/asio/ssl/detail/write_op.hpp
index f76b662a..292e5fd5 100644
--- a/include/boost/asio/ssl/detail/write_op.hpp
+++ b/include/boost/asio/ssl/detail/write_op.hpp
@@ -31,6 +31,11 @@ template <typename ConstBufferSequence>
 class write_op
 {
 public:
+  static BOOST_ASIO_CONSTEXPR const char* tracking_name()
+  {
+    return "ssl::stream<>::async_write_some";
+  }
+
   write_op(const ConstBufferSequence& buffers)
     : buffers_(buffers)
   {
@@ -40,9 +45,13 @@ public:
       boost::system::error_code& ec,
       std::size_t& bytes_transferred) const
   {
+    unsigned char storage[
+      boost::asio::detail::buffer_sequence_adapter<boost::asio::const_buffer,
+        ConstBufferSequence>::linearisation_storage_size];
+
     boost::asio::const_buffer buffer =
       boost::asio::detail::buffer_sequence_adapter<boost::asio::const_buffer,
-        ConstBufferSequence>::first(buffers_);
+        ConstBufferSequence>::linearise(buffers_, boost::asio::buffer(storage));
 
     return eng.write(buffer, ec, bytes_transferred);
   }
diff --git a/include/boost/asio/ssl/stream.hpp b/include/boost/asio/ssl/stream.hpp
index 3d64ffb8..cc157b89 100644
--- a/include/boost/asio/ssl/stream.hpp
+++ b/include/boost/asio/ssl/stream.hpp
@@ -110,6 +110,21 @@ public:
   }
 #endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
 
+#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move-construct a stream from another.
+  /**
+   * @param other The other stream object from which the move will occur. Must
+   * have no outstanding asynchronous operations associated with it. Following
+   * the move, @c other has a valid but unspecified state where the only safe
+   * operation is destruction.
+   */
+  stream(stream&& other)
+    : next_layer_(BOOST_ASIO_MOVE_CAST(Stream)(other.next_layer_)),
+      core_(BOOST_ASIO_MOVE_CAST(detail::stream_core)(other.core_))
+  {
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
   /// Destructor.
   /**
    * @note A @c stream object must not be destroyed while there are pending
diff --git a/include/boost/asio/static_thread_pool.hpp b/include/boost/asio/static_thread_pool.hpp
new file mode 100644
index 00000000..3ca477a0
--- /dev/null
+++ b/include/boost/asio/static_thread_pool.hpp
@@ -0,0 +1,33 @@
+//
+// static_thread_pool.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_STATIC_THREAD_POOL_HPP
+#define BOOST_ASIO_STATIC_THREAD_POOL_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/thread_pool.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+
+typedef thread_pool static_thread_pool;
+
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_STATIC_THREAD_POOL_HPP
diff --git a/include/boost/asio/strand.hpp b/include/boost/asio/strand.hpp
index 6f4c5370..c2b9ed8b 100644
--- a/include/boost/asio/strand.hpp
+++ b/include/boost/asio/strand.hpp
@@ -18,6 +18,8 @@
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/detail/strand_executor_service.hpp>
 #include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/execution/executor.hpp>
+#include <boost/asio/is_executor.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -39,16 +41,14 @@ public:
    */
   strand()
     : executor_(),
-      impl_(use_service<detail::strand_executor_service>(
-            executor_.context()).create_implementation())
+      impl_(strand::create_implementation(executor_))
   {
   }
 
   /// Construct a strand for the specified executor.
   explicit strand(const Executor& e)
     : executor_(e),
-      impl_(use_service<detail::strand_executor_service>(
-            executor_.context()).create_implementation())
+      impl_(strand::create_implementation(executor_))
   {
   }
 
@@ -147,6 +147,51 @@ public:
     return executor_;
   }
 
+  /// Forward a query to the underlying executor.
+  template <typename Property>
+  typename enable_if<
+    can_query<const Executor&, Property>::value,
+    typename query_result_type<const Executor&, Property>::type
+  >::type query(const Property& p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, Property>::value))
+  {
+    return boost::asio::query(executor_, p);
+  }
+
+  /// Forward a requirement to the underlying executor.
+  template <typename Property>
+  typename enable_if<
+    can_require<const Executor&, Property>::value,
+    strand<typename decay<
+      typename require_result_type<const Executor&, Property>::type
+    >::type>
+  >::type require(const Property& p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_require<const Executor&, Property>::value))
+  {
+    return strand<typename decay<
+      typename require_result_type<const Executor&, Property>::type
+        >::type>(boost::asio::require(executor_, p), impl_);
+  }
+
+  /// Forward a preference to the underlying executor.
+  template <typename Property>
+  typename enable_if<
+    can_prefer<const Executor&, Property>::value,
+    strand<typename decay<
+      typename prefer_result_type<const Executor&, Property>::type
+    >::type>
+  >::type prefer(const Property& p) const
+    BOOST_ASIO_NOEXCEPT_IF((
+      is_nothrow_prefer<const Executor&, Property>::value))
+  {
+    return strand<typename decay<
+      typename prefer_result_type<const Executor&, Property>::type
+        >::type>(boost::asio::prefer(executor_, p), impl_);
+  }
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   /// Obtain the underlying execution context.
   execution_context& context() const BOOST_ASIO_NOEXCEPT
   {
@@ -170,7 +215,28 @@ public:
   {
     executor_.on_work_finished();
   }
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
+  /// Request the strand to invoke the given function object.
+  /**
+   * This function is used to ask the strand to execute the given function
+   * object on its underlying executor. The function object will be executed
+   * according to the properties of the underlying executor.
+   *
+   * @param f The function object to be called. The executor will make
+   * a copy of the handler object as required. The function signature of the
+   * function object must be: @code void function(); @endcode
+   */
+  template <typename Function>
+  typename enable_if<
+    execution::can_execute<const Executor&, Function>::value
+  >::type execute(BOOST_ASIO_MOVE_ARG(Function) f) const
+  {
+    detail::strand_executor_service::execute(impl_,
+        executor_, BOOST_ASIO_MOVE_CAST(Function)(f));
+  }
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   /// Request the strand to invoke the given function object.
   /**
    * This function is used to ask the strand to execute the given function
@@ -232,6 +298,7 @@ public:
     detail::strand_executor_service::defer(impl_,
         executor_, BOOST_ASIO_MOVE_CAST(Function)(f), a);
   }
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
   /// Determine whether the strand is running in the current thread.
   /**
@@ -267,9 +334,36 @@ public:
 #if defined(GENERATING_DOCUMENTATION)
 private:
 #endif // defined(GENERATING_DOCUMENTATION)
-  Executor executor_;
   typedef detail::strand_executor_service::implementation_type
     implementation_type;
+
+  template <typename InnerExecutor>
+  static implementation_type create_implementation(const InnerExecutor& ex,
+      typename enable_if<
+        can_query<InnerExecutor, execution::context_t>::value
+      >::type* = 0)
+  {
+    return use_service<detail::strand_executor_service>(
+        boost::asio::query(ex, execution::context)).create_implementation();
+  }
+
+  template <typename InnerExecutor>
+  static implementation_type create_implementation(const InnerExecutor& ex,
+      typename enable_if<
+        !can_query<InnerExecutor, execution::context_t>::value
+      >::type* = 0)
+  {
+    return use_service<detail::strand_executor_service>(
+        ex.context()).create_implementation();
+  }
+
+  strand(const Executor& ex, const implementation_type& impl)
+    : executor_(ex),
+      impl_(impl)
+  {
+  }
+
+  Executor executor_;
   implementation_type impl_;
 };
 
@@ -283,7 +377,9 @@ private:
 /// Create a @ref strand object for an executor.
 template <typename Executor>
 inline strand<Executor> make_strand(const Executor& ex,
-    typename enable_if<is_executor<Executor>::value>::type* = 0)
+    typename enable_if<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >::type* = 0)
 {
   return strand<Executor>(ex);
 }
@@ -293,13 +389,98 @@ template <typename ExecutionContext>
 inline strand<typename ExecutionContext::executor_type>
 make_strand(ExecutionContext& ctx,
     typename enable_if<
-      is_convertible<ExecutionContext&, execution_context&>::value>::type* = 0)
+      is_convertible<ExecutionContext&, execution_context&>::value
+    >::type* = 0)
 {
   return strand<typename ExecutionContext::executor_type>(ctx.get_executor());
 }
 
 /*@}*/
 
+#if !defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename Executor>
+struct is_executor<strand<Executor> > : true_type
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+} // namespace execution
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename Executor, typename Function>
+struct execute_member<strand<Executor>, Function>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename Executor, typename Property>
+struct query_member<strand<Executor>, Property,
+    typename enable_if<
+      can_query<const Executor&, Property>::value
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+      (is_nothrow_query<Executor, Property>::value));
+  typedef typename query_result_type<Executor, Property>::type result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename Executor, typename Property>
+struct require_member<strand<Executor>, Property,
+    typename enable_if<
+      can_require<const Executor&, Property>::value
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+      (is_nothrow_require<Executor, Property>::value));
+  typedef strand<typename decay<
+    typename require_result_type<Executor, Property>::type
+      >::type> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_MEMBER_TRAIT)
+
+template <typename Executor, typename Property>
+struct prefer_member<strand<Executor>, Property,
+    typename enable_if<
+      can_prefer<const Executor&, Property>::value
+    >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+      (is_nothrow_prefer<Executor, Property>::value));
+  typedef strand<typename decay<
+    typename prefer_result_type<Executor, Property>::type
+      >::type> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_MEMBER_TRAIT)
+
+} // namespace traits
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
 } // namespace asio
 } // namespace boost
 
diff --git a/include/boost/asio/system_context.hpp b/include/boost/asio/system_context.hpp
index 62a0db26..c8c2f321 100644
--- a/include/boost/asio/system_context.hpp
+++ b/include/boost/asio/system_context.hpp
@@ -18,6 +18,7 @@
 #include <boost/asio/detail/config.hpp>
 #include <boost/asio/detail/scheduler.hpp>
 #include <boost/asio/detail/thread_group.hpp>
+#include <boost/asio/execution.hpp>
 #include <boost/asio/execution_context.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
@@ -25,14 +26,19 @@
 namespace boost {
 namespace asio {
 
-class system_executor;
+template <typename Blocking, typename Relationship, typename Allocator>
+class basic_system_executor;
 
 /// The executor context for the system executor.
 class system_context : public execution_context
 {
 public:
   /// The executor type associated with the context.
-  typedef system_executor executor_type;
+  typedef basic_system_executor<
+      execution::blocking_t::possibly_t,
+      execution::relationship_t::fork_t,
+      std::allocator<void>
+    > executor_type;
 
   /// Destructor shuts down all threads in the system thread pool.
   BOOST_ASIO_DECL ~system_context();
@@ -56,7 +62,7 @@ private:
   BOOST_ASIO_DECL system_context();
 
 private:
-  friend class system_executor;
+  template <typename, typename, typename> friend class basic_system_executor;
 
   struct thread_function;
 
@@ -68,6 +74,9 @@ private:
 
   // The threads in the system thread pool.
   detail::thread_group threads_;
+
+  // The number of threads in the pool.
+  std::size_t num_threads_;
 };
 
 } // namespace asio
diff --git a/include/boost/asio/system_executor.hpp b/include/boost/asio/system_executor.hpp
index 718d7b86..8f439bde 100644
--- a/include/boost/asio/system_executor.hpp
+++ b/include/boost/asio/system_executor.hpp
@@ -16,6 +16,8 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/memory.hpp>
+#include <boost/asio/execution.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -27,13 +29,155 @@ class system_context;
 /// An executor that uses arbitrary threads.
 /**
  * The system executor represents an execution context where functions are
- * permitted to run on arbitrary threads. The post() and defer() functions
- * schedule the function to run on an unspecified system thread pool, and
- * dispatch() invokes the function immediately.
+ * permitted to run on arbitrary threads. When the blocking.never property is
+ * established, the system executor will schedule the function to run on an
+ * unspecified system thread pool. When either blocking.possibly or
+ * blocking.always is established, the executor invokes the function
+ * immediately.
  */
-class system_executor
+template <typename Blocking, typename Relationship, typename Allocator>
+class basic_system_executor
 {
 public:
+  /// Default constructor.
+  basic_system_executor() BOOST_ASIO_NOEXCEPT
+    : allocator_(Allocator())
+  {
+  }
+
+  /// Obtain an executor with the @c blocking.possibly property.
+  basic_system_executor<execution::blocking_t::possibly_t,
+      Relationship, Allocator>
+  require(execution::blocking_t::possibly_t) const
+  {
+    return basic_system_executor<execution::blocking_t::possibly_t,
+        Relationship, Allocator>(allocator_);
+  }
+
+  /// Obtain an executor with the @c blocking.always property.
+  basic_system_executor<execution::blocking_t::always_t,
+      Relationship, Allocator>
+  require(execution::blocking_t::always_t) const
+  {
+    return basic_system_executor<execution::blocking_t::always_t,
+        Relationship, Allocator>(allocator_);
+  }
+
+  /// Obtain an executor with the @c blocking.never property.
+  basic_system_executor<execution::blocking_t::never_t,
+      Relationship, Allocator>
+  require(execution::blocking_t::never_t) const
+  {
+    return basic_system_executor<execution::blocking_t::never_t,
+        Relationship, Allocator>(allocator_);
+  }
+
+  /// Obtain an executor with the @c relationship.continuation property.
+  basic_system_executor<Blocking,
+      execution::relationship_t::continuation_t, Allocator>
+  require(execution::relationship_t::continuation_t) const
+  {
+    return basic_system_executor<Blocking,
+        execution::relationship_t::continuation_t, Allocator>(allocator_);
+  }
+
+  /// Obtain an executor with the @c relationship.fork property.
+  basic_system_executor<Blocking,
+      execution::relationship_t::fork_t, Allocator>
+  require(execution::relationship_t::fork_t) const
+  {
+    return basic_system_executor<Blocking,
+        execution::relationship_t::fork_t, Allocator>(allocator_);
+  }
+
+  /// Obtain an executor with the specified @c allocator property.
+  template <typename OtherAllocator>
+  basic_system_executor<Blocking, Relationship, OtherAllocator>
+  require(execution::allocator_t<OtherAllocator> a) const
+  {
+    return basic_system_executor<Blocking,
+        Relationship, OtherAllocator>(a.value());
+  }
+
+  /// Obtain an executor with the default @c allocator property.
+  basic_system_executor<Blocking, Relationship, std::allocator<void> >
+  require(execution::allocator_t<void>) const
+  {
+    return basic_system_executor<Blocking,
+        Relationship, std::allocator<void> >();
+  }
+
+  /// Query the current value of the @c mapping property.
+  static BOOST_ASIO_CONSTEXPR execution::mapping_t query(
+      execution::mapping_t) BOOST_ASIO_NOEXCEPT
+  {
+    return execution::mapping.thread;
+  }
+
+  /// Query the current value of the @c context property.
+  static system_context& query(execution::context_t) BOOST_ASIO_NOEXCEPT;
+
+  /// Query the current value of the @c blocking property.
+  static BOOST_ASIO_CONSTEXPR execution::blocking_t query(
+      execution::blocking_t) BOOST_ASIO_NOEXCEPT
+  {
+    return Blocking();
+  }
+
+  /// Query the current value of the @c relationship property.
+  static BOOST_ASIO_CONSTEXPR execution::relationship_t query(
+      execution::relationship_t) BOOST_ASIO_NOEXCEPT
+  {
+    return Relationship();
+  }
+
+  /// Query the current value of the @c allocator property.
+  template <typename OtherAllocator>
+  BOOST_ASIO_CONSTEXPR Allocator query(
+      execution::allocator_t<OtherAllocator>) const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  /// Query the current value of the @c allocator property.
+  BOOST_ASIO_CONSTEXPR Allocator query(
+      execution::allocator_t<void>) const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  /// Query the occupancy (recommended number of work items) for the system
+  /// context.
+  std::size_t query(execution::occupancy_t) const BOOST_ASIO_NOEXCEPT;
+
+  /// Compare two executors for equality.
+  /**
+   * Two executors are equal if they refer to the same underlying io_context.
+   */
+  friend bool operator==(const basic_system_executor&,
+      const basic_system_executor&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  /// Compare two executors for inequality.
+  /**
+   * Two executors are equal if they refer to the same underlying io_context.
+   */
+  friend bool operator!=(const basic_system_executor&,
+      const basic_system_executor&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+
+  /// Oneway execution function.
+  template <typename Function>
+  void execute(BOOST_ASIO_MOVE_ARG(Function) f) const
+  {
+    this->do_execute(BOOST_ASIO_MOVE_CAST(Function)(f), Blocking());
+  }
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   /// Obtain the underlying execution context.
   system_context& context() const BOOST_ASIO_NOEXCEPT;
 
@@ -65,8 +209,8 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const;
 
   /// Request the system executor to invoke the given function object.
   /**
@@ -81,8 +225,8 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void post(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void post(BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const;
 
   /// Request the system executor to invoke the given function object.
   /**
@@ -97,30 +241,283 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void defer(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void defer(BOOST_ASIO_MOVE_ARG(Function) f, const OtherAllocator& a) const;
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
-  /// Compare two executors for equality.
-  /**
-   * System executors always compare equal.
-   */
-  friend bool operator==(const system_executor&,
-      const system_executor&) BOOST_ASIO_NOEXCEPT
+private:
+  template <typename, typename, typename> friend class basic_system_executor;
+
+  // Constructor used by require().
+  basic_system_executor(const Allocator& a)
+    : allocator_(a)
   {
-    return true;
   }
 
-  /// Compare two executors for inequality.
-  /**
-   * System executors always compare equal.
-   */
-  friend bool operator!=(const system_executor&,
-      const system_executor&) BOOST_ASIO_NOEXCEPT
+  /// Execution helper implementation for the possibly blocking property.
+  template <typename Function>
+  void do_execute(BOOST_ASIO_MOVE_ARG(Function) f,
+      execution::blocking_t::possibly_t) const;
+
+  /// Execution helper implementation for the always blocking property.
+  template <typename Function>
+  void do_execute(BOOST_ASIO_MOVE_ARG(Function) f,
+      execution::blocking_t::always_t) const;
+
+  /// Execution helper implementation for the never blocking property.
+  template <typename Function>
+  void do_execute(BOOST_ASIO_MOVE_ARG(Function) f,
+      execution::blocking_t::never_t) const;
+
+  // The allocator used for execution functions.
+  Allocator allocator_;
+};
+
+/// An executor that uses arbitrary threads.
+/**
+ * The system executor represents an execution context where functions are
+ * permitted to run on arbitrary threads. When the blocking.never property is
+ * established, the system executor will schedule the function to run on an
+ * unspecified system thread pool. When either blocking.possibly or
+ * blocking.always is established, the executor invokes the function
+ * immediately.
+ */
+typedef basic_system_executor<execution::blocking_t::possibly_t,
+    execution::relationship_t::fork_t, std::allocator<void> >
+  system_executor;
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct is_executor<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>
+  > : true_type
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+} // namespace execution
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename Blocking, typename Relationship,
+    typename Allocator, typename Function>
+struct execute_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    Function
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::blocking_t::possibly_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<
+      boost::asio::execution::blocking_t::possibly_t,
+      Relationship, Allocator> result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::blocking_t::always_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<
+      boost::asio::execution::blocking_t::always_t,
+      Relationship, Allocator> result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::blocking_t::never_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<
+      boost::asio::execution::blocking_t::never_t,
+      Relationship, Allocator> result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::relationship_t::fork_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<Blocking,
+      boost::asio::execution::relationship_t::fork_t,
+      Allocator> result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::relationship_t::continuation_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<Blocking,
+      boost::asio::execution::relationship_t::continuation_t,
+      Allocator> result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::allocator_t<void>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<Blocking,
+      Relationship, std::allocator<void> > result_type;
+};
+
+template <typename Blocking, typename Relationship,
+    typename Allocator, typename OtherAllocator>
+struct require_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::allocator_t<OtherAllocator>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::basic_system_executor<Blocking,
+      Relationship, OtherAllocator> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename Blocking, typename Relationship,
+    typename Allocator, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::mapping_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::mapping_t::thread_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
   {
-    return false;
+    return result_type();
   }
 };
 
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename Blocking, typename Relationship,
+    typename Allocator, typename Property>
+struct query_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::blocking_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::blocking_t result_type;
+};
+
+template <typename Blocking, typename Relationship,
+    typename Allocator, typename Property>
+struct query_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::relationship_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::relationship_t result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct query_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::context_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::system_context& result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct query_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::allocator_t<void>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Allocator result_type;
+};
+
+template <typename Blocking, typename Relationship, typename Allocator>
+struct query_member<
+    boost::asio::basic_system_executor<Blocking, Relationship, Allocator>,
+    boost::asio::execution::allocator_t<Allocator>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Allocator result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
 } // namespace asio
 } // namespace boost
 
diff --git a/include/boost/asio/thread_pool.hpp b/include/boost/asio/thread_pool.hpp
index d1c585a7..e7c23214 100644
--- a/include/boost/asio/thread_pool.hpp
+++ b/include/boost/asio/thread_pool.hpp
@@ -16,15 +16,26 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
-#include <boost/asio/detail/noncopyable.hpp>
+#include <boost/asio/detail/atomic_count.hpp>
 #include <boost/asio/detail/scheduler.hpp>
 #include <boost/asio/detail/thread_group.hpp>
+#include <boost/asio/execution.hpp>
 #include <boost/asio/execution_context.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
+namespace detail {
+  struct thread_pool_bits
+  {
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, blocking_never = 1);
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, blocking_always = 2);
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, blocking_mask = 3);
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, relationship_continuation = 4);
+    BOOST_ASIO_STATIC_CONSTEXPR(unsigned int, outstanding_work_tracked = 8);
+  };
+} // namespace detail
 
 /// A simple fixed-size thread pool.
 /**
@@ -33,7 +44,7 @@ namespace asio {
  *
  * @par Submitting tasks to the pool
  *
- * To submit functions to the thread_pool, use the @ref boost::asio::dispatch,
+ * To submit functions to the thread pool, use the @ref boost::asio::dispatch,
  * @ref boost::asio::post or @ref boost::asio::defer free functions.
  *
  * For example:
@@ -65,10 +76,19 @@ class thread_pool
   : public execution_context
 {
 public:
-  class executor_type;
+  template <typename Allocator, unsigned int Bits>
+  class basic_executor_type;
 
+  template <typename Allocator, unsigned int Bits>
+  friend class basic_executor_type;
+
+  /// Executor used to submit functions to a thread pool.
+  typedef basic_executor_type<std::allocator<void>, 0> executor_type;
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   /// Constructs a pool with an automatically determined number of threads.
   BOOST_ASIO_DECL thread_pool();
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
   /// Constructs a pool with a specified number of threads.
   BOOST_ASIO_DECL thread_pool(std::size_t num_threads);
@@ -82,6 +102,9 @@ public:
   /// Obtains the executor associated with the pool.
   executor_type get_executor() BOOST_ASIO_NOEXCEPT;
 
+  /// Obtains the executor associated with the pool.
+  executor_type executor() BOOST_ASIO_NOEXCEPT;
+
   /// Stops the threads.
   /**
    * This function stops the threads as soon as possible. As a result of calling
@@ -89,6 +112,14 @@ public:
    */
   BOOST_ASIO_DECL void stop();
 
+  /// Attaches the current thread to the pool.
+  /**
+   * This function attaches the current thread to the pool so that it may be
+   * used for executing submitted function objects. Blocks the calling thread
+   * until the pool is stopped or joined and has no outstanding work.
+   */
+  BOOST_ASIO_DECL void attach();
+
   /// Joins the threads.
   /**
    * This function blocks until the threads in the pool have completed. If @c
@@ -97,8 +128,18 @@ public:
    */
   BOOST_ASIO_DECL void join();
 
+  /// Waits for threads to complete.
+  /**
+   * This function blocks until the threads in the pool have completed. If @c
+   * stop() is not called prior to @c wait(), the @c wait() call will wait
+   * until the pool has no more outstanding work.
+   */
+  BOOST_ASIO_DECL void wait();
+
 private:
-  friend class executor_type;
+  thread_pool(const thread_pool&) BOOST_ASIO_DELETED;
+  thread_pool& operator=(const thread_pool&) BOOST_ASIO_DELETED;
+
   struct thread_function;
 
   // Helper function to create the underlying scheduler.
@@ -109,12 +150,247 @@ private:
 
   // The threads in the pool.
   detail::thread_group threads_;
+
+  // The current number of threads in the pool.
+  detail::atomic_count num_threads_;
 };
 
-/// Executor used to submit functions to a thread pool.
-class thread_pool::executor_type
+/// Executor implementation type used to submit functions to a thread pool.
+template <typename Allocator, unsigned int Bits>
+class thread_pool::basic_executor_type : detail::thread_pool_bits
 {
 public:
+  /// Copy construtor.
+  basic_executor_type(
+      const basic_executor_type& other) BOOST_ASIO_NOEXCEPT
+    : pool_(other.pool_),
+      allocator_(other.allocator_),
+      bits_(other.bits_)
+  {
+    if (Bits & outstanding_work_tracked)
+      if (pool_)
+        pool_->scheduler_.work_started();
+  }
+
+#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move construtor.
+  basic_executor_type(basic_executor_type&& other) BOOST_ASIO_NOEXCEPT
+    : pool_(other.pool_),
+      allocator_(BOOST_ASIO_MOVE_CAST(Allocator)(other.allocator_)),
+      bits_(other.bits_)
+  {
+    if (Bits & outstanding_work_tracked)
+      other.pool_ = 0;
+  }
+#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
+  /// Destructor.
+  ~basic_executor_type()
+  {
+    if (Bits & outstanding_work_tracked)
+      if (pool_)
+        pool_->scheduler_.work_finished();
+  }
+
+  /// Assignment operator.
+  basic_executor_type& operator=(
+      const basic_executor_type& other) BOOST_ASIO_NOEXCEPT;
+
+#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move assignment operator.
+  basic_executor_type& operator=(
+      basic_executor_type&& other) BOOST_ASIO_NOEXCEPT;
+#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
+  /// Obtain an executor with the @c blocking.possibly property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED(Bits & ~blocking_mask)>
+  require(execution::blocking_t::possibly_t) const
+  {
+    return basic_executor_type<Allocator, Bits & ~blocking_mask>(
+        pool_, allocator_, bits_ & ~blocking_mask);
+  }
+
+  /// Obtain an executor with the @c blocking.always property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED((Bits & ~blocking_mask) | blocking_always)>
+  require(execution::blocking_t::always_t) const
+  {
+    return basic_executor_type<Allocator,
+        BOOST_ASIO_UNSPECIFIED((Bits & ~blocking_mask) | blocking_always)>(
+          pool_, allocator_, bits_ & ~blocking_mask);
+  }
+
+  /// Obtain an executor with the @c blocking.never property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED(Bits & ~blocking_mask)>
+  require(execution::blocking_t::never_t) const
+  {
+    return basic_executor_type<Allocator, Bits & ~blocking_mask>(
+        pool_, allocator_, (bits_ & ~blocking_mask) | blocking_never);
+  }
+
+  /// Obtain an executor with the @c relationship.fork property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type require(
+      execution::relationship_t::fork_t) const
+  {
+    return basic_executor_type(pool_,
+        allocator_, bits_ & ~relationship_continuation);
+  }
+
+  /// Obtain an executor with the @c relationship.continuation property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type require(
+      execution::relationship_t::continuation_t) const
+  {
+    return basic_executor_type(pool_,
+        allocator_, bits_ | relationship_continuation);
+  }
+
+  /// Obtain an executor with the @c outstanding_work.tracked property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED(Bits | outstanding_work_tracked)>
+  require(execution::outstanding_work_t::tracked_t) const
+  {
+    return basic_executor_type<Allocator, Bits | outstanding_work_tracked>(
+        pool_, allocator_, bits_);
+  }
+
+  /// Obtain an executor with the @c outstanding_work.untracked property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<Allocator,
+      BOOST_ASIO_UNSPECIFIED(Bits & ~outstanding_work_tracked)>
+  require(execution::outstanding_work_t::untracked_t) const
+  {
+    return basic_executor_type<Allocator, Bits & ~outstanding_work_tracked>(
+        pool_, allocator_, bits_);
+  }
+
+  /// Obtain an executor with the specified @c allocator property.
+  template <typename OtherAllocator>
+  BOOST_ASIO_CONSTEXPR basic_executor_type<OtherAllocator, Bits>
+  require(execution::allocator_t<OtherAllocator> a) const
+  {
+    return basic_executor_type<OtherAllocator, Bits>(
+        pool_, a.value(), bits_);
+  }
+
+  /// Obtain an executor with the default @c allocator property.
+  BOOST_ASIO_CONSTEXPR basic_executor_type<std::allocator<void>, Bits>
+  require(execution::allocator_t<void>) const
+  {
+    return basic_executor_type<std::allocator<void>, Bits>(
+        pool_, std::allocator<void>(), bits_);
+  }
+
+  /// Query the current value of the @c bulk_guarantee property.
+  static BOOST_ASIO_CONSTEXPR execution::bulk_guarantee_t query(
+      execution::bulk_guarantee_t) BOOST_ASIO_NOEXCEPT
+  {
+    return execution::bulk_guarantee.parallel;
+  }
+
+  /// Query the current value of the @c mapping property.
+  static BOOST_ASIO_CONSTEXPR execution::mapping_t query(
+      execution::mapping_t) BOOST_ASIO_NOEXCEPT
+  {
+    return execution::mapping.thread;
+  }
+
+  /// Query the current value of the @c context property.
+  thread_pool& query(execution::context_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return *pool_;
+  }
+
+  /// Query the current value of the @c blocking property.
+  BOOST_ASIO_CONSTEXPR execution::blocking_t query(
+      execution::blocking_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return (bits_ & blocking_never)
+      ? execution::blocking_t(execution::blocking.never)
+      : ((Bits & blocking_always)
+          ? execution::blocking_t(execution::blocking.always)
+          : execution::blocking_t(execution::blocking.possibly));
+  }
+
+  /// Query the current value of the @c relationship property.
+  BOOST_ASIO_CONSTEXPR execution::relationship_t query(
+      execution::relationship_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return (bits_ & relationship_continuation)
+      ? execution::relationship_t(execution::relationship.continuation)
+      : execution::relationship_t(execution::relationship.fork);
+  }
+
+  /// Query the current value of the @c outstanding_work property.
+  static BOOST_ASIO_CONSTEXPR execution::outstanding_work_t query(
+      execution::outstanding_work_t) BOOST_ASIO_NOEXCEPT
+  {
+    return (Bits & outstanding_work_tracked)
+      ? execution::outstanding_work_t(execution::outstanding_work.tracked)
+      : execution::outstanding_work_t(execution::outstanding_work.untracked);
+  }
+
+  /// Query the current value of the @c allocator property.
+  template <typename OtherAllocator>
+  BOOST_ASIO_CONSTEXPR Allocator query(
+      execution::allocator_t<OtherAllocator>) const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  /// Query the current value of the @c allocator property.
+  BOOST_ASIO_CONSTEXPR Allocator query(
+      execution::allocator_t<void>) const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_;
+  }
+
+  /// Query the occupancy (recommended number of work items) for the pool.
+  std::size_t query(execution::occupancy_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return static_cast<std::size_t>(pool_->num_threads_);
+  }
+
+  /// Determine whether the thread pool is running in the current thread.
+  /**
+   * @return @c true if the current thread is running the thread pool. Otherwise
+   * returns @c false.
+   */
+  bool running_in_this_thread() const BOOST_ASIO_NOEXCEPT;
+
+  /// Compare two executors for equality.
+  /**
+   * Two executors are equal if they refer to the same underlying thread pool.
+   */
+  friend bool operator==(const basic_executor_type& a,
+      const basic_executor_type& b) BOOST_ASIO_NOEXCEPT
+  {
+    return a.pool_ == b.pool_
+      && a.allocator_ == b.allocator_
+      && a.bits_ == b.bits_;
+  }
+
+  /// Compare two executors for inequality.
+  /**
+   * Two executors are equal if they refer to the same underlying thread pool.
+   */
+  friend bool operator!=(const basic_executor_type& a,
+      const basic_executor_type& b) BOOST_ASIO_NOEXCEPT
+  {
+    return a.pool_ != b.pool_
+      || a.allocator_ != b.allocator_
+      || a.bits_ != b.bits_;
+  }
+
+  /// Execution function.
+  template <typename Function>
+  void execute(BOOST_ASIO_MOVE_ARG(Function) f) const
+  {
+    this->do_execute(BOOST_ASIO_MOVE_CAST(Function)(f),
+        integral_constant<bool, (Bits & blocking_always) != 0>());
+  }
+
+#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
   /// Obtain the underlying execution context.
   thread_pool& context() const BOOST_ASIO_NOEXCEPT;
 
@@ -148,8 +424,9 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f,
+      const OtherAllocator& a) const;
 
   /// Request the thread pool to invoke the given function object.
   /**
@@ -164,8 +441,9 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void post(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
+  template <typename Function, typename OtherAllocator>
+  void post(BOOST_ASIO_MOVE_ARG(Function) f,
+      const OtherAllocator& a) const;
 
   /// Request the thread pool to invoke the given function object.
   /**
@@ -184,46 +462,359 @@ public:
    * @param a An allocator that may be used by the executor to allocate the
    * internal storage needed for function invocation.
    */
-  template <typename Function, typename Allocator>
-  void defer(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
-
-  /// Determine whether the thread pool is running in the current thread.
-  /**
-   * @return @c true if the current thread belongs to the pool. Otherwise
-   * returns @c false.
-   */
-  bool running_in_this_thread() const BOOST_ASIO_NOEXCEPT;
-
-  /// Compare two executors for equality.
-  /**
-   * Two executors are equal if they refer to the same underlying thread pool.
-   */
-  friend bool operator==(const executor_type& a,
-      const executor_type& b) BOOST_ASIO_NOEXCEPT
-  {
-    return &a.pool_ == &b.pool_;
-  }
-
-  /// Compare two executors for inequality.
-  /**
-   * Two executors are equal if they refer to the same underlying thread pool.
-   */
-  friend bool operator!=(const executor_type& a,
-      const executor_type& b) BOOST_ASIO_NOEXCEPT
-  {
-    return &a.pool_ != &b.pool_;
-  }
+  template <typename Function, typename OtherAllocator>
+  void defer(BOOST_ASIO_MOVE_ARG(Function) f,
+      const OtherAllocator& a) const;
+#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)
 
 private:
   friend class thread_pool;
+  template <typename, unsigned int> friend class basic_executor_type;
 
-  // Constructor.
-  explicit executor_type(thread_pool& p) : pool_(p) {}
+  // Constructor used by thread_pool::get_executor().
+  explicit basic_executor_type(thread_pool& p) BOOST_ASIO_NOEXCEPT
+    : pool_(&p),
+      allocator_(),
+      bits_(0)
+  {
+    if (Bits & outstanding_work_tracked)
+      pool_->scheduler_.work_started();
+  }
+
+  // Constructor used by require().
+  basic_executor_type(thread_pool* p,
+      const Allocator& a, unsigned int bits) BOOST_ASIO_NOEXCEPT
+    : pool_(p),
+      allocator_(a),
+      bits_(bits)
+  {
+    if (Bits & outstanding_work_tracked)
+      if (pool_)
+        pool_->scheduler_.work_started();
+  }
+
+  /// Execution helper implementation for possibly and never blocking.
+  template <typename Function>
+  void do_execute(BOOST_ASIO_MOVE_ARG(Function) f, false_type) const;
+
+  /// Execution helper implementation for always blocking.
+  template <typename Function>
+  void do_execute(BOOST_ASIO_MOVE_ARG(Function) f, true_type) const;
 
   // The underlying thread pool.
-  thread_pool& pool_;
+  thread_pool* pool_;
+
+  // The allocator used for execution functions.
+  Allocator allocator_;
+
+  // The runtime-switched properties of the thread pool executor.
+  unsigned int bits_;
 };
 
+#if !defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename Allocator, unsigned int Bits>
+struct is_executor<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>
+  > : true_type
+{
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+} // namespace execution
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits, typename Function>
+struct execute_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    Function
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::blocking_t::possibly_t
+  > : boost::asio::detail::thread_pool_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      Allocator, Bits & ~blocking_mask> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::blocking_t::always_t
+  > : boost::asio::detail::thread_pool_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<Allocator,
+      (Bits & ~blocking_mask) | blocking_always> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::blocking_t::never_t
+  > : boost::asio::detail::thread_pool_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      Allocator, Bits & ~blocking_mask> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::relationship_t::fork_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      Allocator, Bits> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::relationship_t::continuation_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      Allocator, Bits> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::outstanding_work_t::tracked_t
+  > : boost::asio::detail::thread_pool_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      Allocator, Bits | outstanding_work_tracked> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::outstanding_work_t::untracked_t
+  > : boost::asio::detail::thread_pool_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      Allocator, Bits & ~outstanding_work_tracked> result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<void>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      std::allocator<void>, Bits> result_type;
+};
+
+template <unsigned int Bits,
+    typename Allocator, typename OtherAllocator>
+struct require_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<OtherAllocator>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef boost::asio::thread_pool::basic_executor_type<
+      OtherAllocator, Bits> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::bulk_guarantee_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::bulk_guarantee_t::parallel_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
+  {
+    return result_type();
+  }
+};
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::outstanding_work_t
+      >::value
+    >::type
+  > : boost::asio::detail::thread_pool_bits
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::outstanding_work_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
+  {
+    return (Bits & outstanding_work_tracked)
+      ? execution::outstanding_work_t(execution::outstanding_work.tracked)
+      : execution::outstanding_work_t(execution::outstanding_work.untracked);
+  }
+};
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_static_constexpr_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::mapping_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::mapping_t::thread_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value() BOOST_ASIO_NOEXCEPT
+  {
+    return result_type();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::blocking_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::blocking_t result_type;
+};
+
+template <typename Allocator, unsigned int Bits, typename Property>
+struct query_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    Property,
+    typename boost::asio::enable_if<
+      boost::asio::is_convertible<
+        Property,
+        boost::asio::execution::relationship_t
+      >::value
+    >::type
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::execution::relationship_t result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct query_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::occupancy_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef std::size_t result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct query_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::context_t
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef boost::asio::thread_pool& result_type;
+};
+
+template <typename Allocator, unsigned int Bits>
+struct query_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<void>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Allocator result_type;
+};
+
+template <typename Allocator, unsigned int Bits, typename OtherAllocator>
+struct query_member<
+    boost::asio::thread_pool::basic_executor_type<Allocator, Bits>,
+    boost::asio::execution::allocator_t<OtherAllocator>
+  >
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef Allocator result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
 } // namespace asio
 } // namespace boost
 
diff --git a/include/boost/asio/traits/equality_comparable.hpp b/include/boost/asio/traits/equality_comparable.hpp
new file mode 100644
index 00000000..c49a21f0
--- /dev/null
+++ b/include/boost/asio/traits/equality_comparable.hpp
@@ -0,0 +1,102 @@
+//
+// traits/equality_comparable.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_EQUALITY_COMPARABLE_HPP
+#define BOOST_ASIO_TRAITS_EQUALITY_COMPARABLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename = void>
+struct equality_comparable_default;
+
+template <typename T, typename = void>
+struct equality_comparable;
+
+} // namespace traits
+namespace detail {
+
+struct no_equality_comparable
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+template <typename T, typename = void>
+struct equality_comparable_trait : no_equality_comparable
+{
+};
+
+template <typename T>
+struct equality_comparable_trait<T,
+  typename void_type<
+    decltype(
+      static_cast<bool>(declval<const T>() == declval<const T>()),
+      static_cast<bool>(declval<const T>() != declval<const T>())
+    )
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    noexcept(declval<const T>() == declval<const T>())
+      && noexcept(declval<const T>() != declval<const T>()));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+template <typename T, typename = void>
+struct equality_comparable_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value,
+    no_equality_comparable,
+    traits::equality_comparable<typename decay<T>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename>
+struct equality_comparable_default : detail::equality_comparable_trait<T>
+{
+};
+
+template <typename T, typename>
+struct equality_comparable : equality_comparable_default<T>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // BOOST_ASIO_TRAITS_EQUALITY_COMPARABLE_HPP
diff --git a/include/boost/asio/traits/execute_free.hpp b/include/boost/asio/traits/execute_free.hpp
new file mode 100644
index 00000000..68344598
--- /dev/null
+++ b/include/boost/asio/traits/execute_free.hpp
@@ -0,0 +1,110 @@
+//
+// traits/execute_free.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_EXECUTE_FREE_HPP
+#define BOOST_ASIO_TRAITS_EXECUTE_FREE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename F, typename = void>
+struct execute_free_default;
+
+template <typename T, typename F, typename = void>
+struct execute_free;
+
+} // namespace traits
+namespace detail {
+
+struct no_execute_free
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+template <typename T, typename F, typename = void>
+struct execute_free_trait : no_execute_free
+{
+};
+
+template <typename T, typename F>
+struct execute_free_trait<T, F,
+  typename void_type<
+    decltype(execute(declval<T>(), declval<F>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    execute(declval<T>(), declval<F>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    execute(declval<T>(), declval<F>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+template <typename T, typename F, typename = void>
+struct execute_free_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<F, typename decay<F>::type>::value,
+    no_execute_free,
+    traits::execute_free<
+      typename decay<T>::type,
+      typename decay<F>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename F, typename>
+struct execute_free_default :
+  detail::execute_free_trait<T, F>
+{
+};
+
+template <typename T, typename F, typename>
+struct execute_free :
+  execute_free_default<T, F>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_EXECUTE_FREE_HPP
diff --git a/include/boost/asio/traits/execute_member.hpp b/include/boost/asio/traits/execute_member.hpp
new file mode 100644
index 00000000..87b43ce4
--- /dev/null
+++ b/include/boost/asio/traits/execute_member.hpp
@@ -0,0 +1,110 @@
+//
+// traits/execute_member.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_EXECUTE_MEMBER_HPP
+#define BOOST_ASIO_TRAITS_EXECUTE_MEMBER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename F, typename = void>
+struct execute_member_default;
+
+template <typename T, typename F, typename = void>
+struct execute_member;
+
+} // namespace traits
+namespace detail {
+
+struct no_execute_member
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename T, typename F, typename = void>
+struct execute_member_trait : no_execute_member
+{
+};
+
+template <typename T, typename F>
+struct execute_member_trait<T, F,
+  typename void_type<
+    decltype(declval<T>().execute(declval<F>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    declval<T>().execute(declval<F>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    declval<T>().execute(declval<F>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename T, typename F, typename = void>
+struct execute_member_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<F, typename decay<F>::type>::value,
+    no_execute_member,
+    traits::execute_member<
+      typename decay<T>::type,
+      typename decay<F>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename F, typename>
+struct execute_member_default :
+  detail::execute_member_trait<T, F>
+{
+};
+
+template <typename T, typename F, typename>
+struct execute_member :
+  execute_member_default<T, F>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_EXECUTE_MEMBER_HPP
diff --git a/include/boost/asio/traits/prefer_free.hpp b/include/boost/asio/traits/prefer_free.hpp
new file mode 100644
index 00000000..5f8b73de
--- /dev/null
+++ b/include/boost/asio/traits/prefer_free.hpp
@@ -0,0 +1,110 @@
+//
+// traits/prefer_free.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_PREFER_FREE_HPP
+#define BOOST_ASIO_TRAITS_PREFER_FREE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct prefer_free_default;
+
+template <typename T, typename Property, typename = void>
+struct prefer_free;
+
+} // namespace traits
+namespace detail {
+
+struct no_prefer_free
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct prefer_free_trait : no_prefer_free
+{
+};
+
+template <typename T, typename Property>
+struct prefer_free_trait<T, Property,
+  typename void_type<
+    decltype(prefer(declval<T>(), declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    prefer(declval<T>(), declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    prefer(declval<T>(), declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct prefer_free_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_prefer_free,
+    traits::prefer_free<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct prefer_free_default :
+  detail::prefer_free_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct prefer_free :
+  prefer_free_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_PREFER_FREE_HPP
diff --git a/include/boost/asio/traits/prefer_member.hpp b/include/boost/asio/traits/prefer_member.hpp
new file mode 100644
index 00000000..4c71c439
--- /dev/null
+++ b/include/boost/asio/traits/prefer_member.hpp
@@ -0,0 +1,110 @@
+//
+// traits/prefer_member.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_PREFER_MEMBER_HPP
+#define BOOST_ASIO_TRAITS_PREFER_MEMBER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_PREFER_MEMBER_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct prefer_member_default;
+
+template <typename T, typename Property, typename = void>
+struct prefer_member;
+
+} // namespace traits
+namespace detail {
+
+struct no_prefer_member
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_PREFER_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct prefer_member_trait : no_prefer_member
+{
+};
+
+template <typename T, typename Property>
+struct prefer_member_trait<T, Property,
+  typename void_type<
+    decltype(declval<T>().prefer(declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    declval<T>().prefer(declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    declval<T>().prefer(declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_PREFER_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct prefer_member_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_prefer_member,
+    traits::prefer_member<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_PREFER_MEMBER_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct prefer_member_default :
+  detail::prefer_member_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct prefer_member :
+  prefer_member_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_PREFER_MEMBER_HPP
diff --git a/include/boost/asio/traits/query_free.hpp b/include/boost/asio/traits/query_free.hpp
new file mode 100644
index 00000000..335b12e5
--- /dev/null
+++ b/include/boost/asio/traits/query_free.hpp
@@ -0,0 +1,110 @@
+//
+// traits/query_free.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_QUERY_FREE_HPP
+#define BOOST_ASIO_TRAITS_QUERY_FREE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct query_free_default;
+
+template <typename T, typename Property, typename = void>
+struct query_free;
+
+} // namespace traits
+namespace detail {
+
+struct no_query_free
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct query_free_trait : no_query_free
+{
+};
+
+template <typename T, typename Property>
+struct query_free_trait<T, Property,
+  typename void_type<
+    decltype(query(declval<T>(), declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    query(declval<T>(), declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    query(declval<T>(), declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct query_free_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_query_free,
+    traits::query_free<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct query_free_default :
+  detail::query_free_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct query_free :
+  query_free_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_QUERY_FREE_HPP
diff --git a/include/boost/asio/traits/query_member.hpp b/include/boost/asio/traits/query_member.hpp
new file mode 100644
index 00000000..aa175934
--- /dev/null
+++ b/include/boost/asio/traits/query_member.hpp
@@ -0,0 +1,110 @@
+//
+// traits/query_member.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_QUERY_MEMBER_HPP
+#define BOOST_ASIO_TRAITS_QUERY_MEMBER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct query_member_default;
+
+template <typename T, typename Property, typename = void>
+struct query_member;
+
+} // namespace traits
+namespace detail {
+
+struct no_query_member
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct query_member_trait : no_query_member
+{
+};
+
+template <typename T, typename Property>
+struct query_member_trait<T, Property,
+  typename void_type<
+    decltype(declval<T>().query(declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    declval<T>().query(declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    declval<T>().query(declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct query_member_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_query_member,
+    traits::query_member<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct query_member_default :
+  detail::query_member_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct query_member :
+  query_member_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_QUERY_MEMBER_HPP
diff --git a/include/boost/asio/traits/query_static_constexpr_member.hpp b/include/boost/asio/traits/query_static_constexpr_member.hpp
new file mode 100644
index 00000000..582e7f9a
--- /dev/null
+++ b/include/boost/asio/traits/query_static_constexpr_member.hpp
@@ -0,0 +1,110 @@
+//
+// traits/query_static_constexpr_member.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_QUERY_STATIC_CONSTEXPR_MEMBER_HPP
+#define BOOST_ASIO_TRAITS_QUERY_STATIC_CONSTEXPR_MEMBER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_CONSTEXPR) \
+  && defined(BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_CONSTEXPR)
+       //   && defined(BOOST_ASIO_HAS_CONSTANT_EXPRESSION_SFINAE)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct query_static_constexpr_member_default;
+
+template <typename T, typename Property, typename = void>
+struct query_static_constexpr_member;
+
+} // namespace traits
+namespace detail {
+
+struct no_query_static_constexpr_member
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+};
+
+template <typename T, typename Property, typename = void>
+struct query_static_constexpr_member_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_query_static_constexpr_member,
+    traits::query_static_constexpr_member<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename T, typename Property>
+struct query_static_constexpr_member_trait<T, Property,
+  typename enable_if<
+    (static_cast<void>(T::query(Property{})), true)
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(T::query(Property{}));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    noexcept(T::query(Property{})));
+
+  static BOOST_ASIO_CONSTEXPR result_type value() noexcept(is_noexcept)
+  {
+    return T::query(Property{});
+  }
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct query_static_constexpr_member_default :
+  detail::query_static_constexpr_member_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct query_static_constexpr_member :
+  query_static_constexpr_member_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_QUERY_STATIC_CONSTEXPR_MEMBER_HPP
diff --git a/include/boost/asio/traits/require_concept_free.hpp b/include/boost/asio/traits/require_concept_free.hpp
new file mode 100644
index 00000000..4b27af43
--- /dev/null
+++ b/include/boost/asio/traits/require_concept_free.hpp
@@ -0,0 +1,110 @@
+//
+// traits/require_concept_free.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_REQUIRE_CONCEPT_FREE_HPP
+#define BOOST_ASIO_TRAITS_REQUIRE_CONCEPT_FREE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_FREE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct require_concept_free_default;
+
+template <typename T, typename Property, typename = void>
+struct require_concept_free;
+
+} // namespace traits
+namespace detail {
+
+struct no_require_concept_free
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_concept_free_trait : no_require_concept_free
+{
+};
+
+template <typename T, typename Property>
+struct require_concept_free_trait<T, Property,
+  typename void_type<
+    decltype(require_concept(declval<T>(), declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    require_concept(declval<T>(), declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    require_concept(declval<T>(), declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_concept_free_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_require_concept_free,
+    traits::require_concept_free<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_FREE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct require_concept_free_default :
+  detail::require_concept_free_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct require_concept_free :
+  require_concept_free_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_REQUIRE_CONCEPT_FREE_HPP
diff --git a/include/boost/asio/traits/require_concept_member.hpp b/include/boost/asio/traits/require_concept_member.hpp
new file mode 100644
index 00000000..c8084a84
--- /dev/null
+++ b/include/boost/asio/traits/require_concept_member.hpp
@@ -0,0 +1,110 @@
+//
+// traits/require_concept_member.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_REQUIRE_CONCEPT_MEMBER_HPP
+#define BOOST_ASIO_TRAITS_REQUIRE_CONCEPT_MEMBER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_MEMBER_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct require_concept_member_default;
+
+template <typename T, typename Property, typename = void>
+struct require_concept_member;
+
+} // namespace traits
+namespace detail {
+
+struct no_require_concept_member
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_concept_member_trait : no_require_concept_member
+{
+};
+
+template <typename T, typename Property>
+struct require_concept_member_trait<T, Property,
+  typename void_type<
+    decltype(declval<T>().require_concept(declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    declval<T>().require_concept(declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    declval<T>().require_concept(declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_concept_member_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_require_concept_member,
+    traits::require_concept_member<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_CONCEPT_MEMBER_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct require_concept_member_default :
+  detail::require_concept_member_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct require_concept_member :
+  require_concept_member_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_REQUIRE_CONCEPT_MEMBER_HPP
diff --git a/include/boost/asio/traits/require_free.hpp b/include/boost/asio/traits/require_free.hpp
new file mode 100644
index 00000000..10a8ed07
--- /dev/null
+++ b/include/boost/asio/traits/require_free.hpp
@@ -0,0 +1,110 @@
+//
+// traits/require_free.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_REQUIRE_FREE_HPP
+#define BOOST_ASIO_TRAITS_REQUIRE_FREE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct require_free_default;
+
+template <typename T, typename Property, typename = void>
+struct require_free;
+
+} // namespace traits
+namespace detail {
+
+struct no_require_free
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_free_trait : no_require_free
+{
+};
+
+template <typename T, typename Property>
+struct require_free_trait<T, Property,
+  typename void_type<
+    decltype(require(declval<T>(), declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    require(declval<T>(), declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    require(declval<T>(), declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_free_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_require_free,
+    traits::require_free<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct require_free_default :
+  detail::require_free_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct require_free :
+  require_free_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_REQUIRE_FREE_HPP
diff --git a/include/boost/asio/traits/require_member.hpp b/include/boost/asio/traits/require_member.hpp
new file mode 100644
index 00000000..63bb7564
--- /dev/null
+++ b/include/boost/asio/traits/require_member.hpp
@@ -0,0 +1,110 @@
+//
+// traits/require_member.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_REQUIRE_MEMBER_HPP
+#define BOOST_ASIO_TRAITS_REQUIRE_MEMBER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct require_member_default;
+
+template <typename T, typename Property, typename = void>
+struct require_member;
+
+} // namespace traits
+namespace detail {
+
+struct no_require_member
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_member_trait : no_require_member
+{
+};
+
+template <typename T, typename Property>
+struct require_member_trait<T, Property,
+  typename void_type<
+    decltype(declval<T>().require(declval<Property>()))
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+    declval<T>().require(declval<Property>()));
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = noexcept(
+    declval<T>().require(declval<Property>())));
+};
+
+#else // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct require_member_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_require_member,
+    traits::require_member<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct require_member_default :
+  detail::require_member_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct require_member :
+  require_member_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_REQUIRE_MEMBER_HPP
diff --git a/include/boost/asio/traits/static_query.hpp b/include/boost/asio/traits/static_query.hpp
new file mode 100644
index 00000000..2cc8fbe6
--- /dev/null
+++ b/include/boost/asio/traits/static_query.hpp
@@ -0,0 +1,110 @@
+//
+// traits/static_query.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_STATIC_QUERY_HPP
+#define BOOST_ASIO_TRAITS_STATIC_QUERY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT) \
+  && defined(BOOST_ASIO_HAS_CONSTEXPR) \
+  && defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES) \
+  && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+       //   && defined(BOOST_ASIO_HAS_CONSTEXPR)
+       //   && defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
+       //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct static_query_default;
+
+template <typename T, typename Property, typename = void>
+struct static_query;
+
+} // namespace traits
+namespace detail {
+
+struct no_static_query
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+};
+
+template <typename T, typename Property, typename = void>
+struct static_query_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_static_query,
+    traits::static_query<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+
+template <typename T, typename Property>
+struct static_query_trait<T, Property,
+  typename void_type<
+    decltype(decay<Property>::type::template static_query_v<T>)
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+
+  using result_type = decltype(
+      decay<Property>::type::template static_query_v<T>);
+
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    noexcept(decay<Property>::type::template static_query_v<T>));
+
+  static BOOST_ASIO_CONSTEXPR result_type value() noexcept(is_noexcept)
+  {
+    return decay<Property>::type::template static_query_v<T>;
+  }
+};
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct static_query_default : detail::static_query_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct static_query : static_query_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_STATIC_QUERY_HPP
diff --git a/include/boost/asio/traits/static_require.hpp b/include/boost/asio/traits/static_require.hpp
new file mode 100644
index 00000000..c0bdbbea
--- /dev/null
+++ b/include/boost/asio/traits/static_require.hpp
@@ -0,0 +1,125 @@
+//
+// traits/static_require.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_STATIC_REQUIRE_HPP
+#define BOOST_ASIO_TRAITS_STATIC_REQUIRE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT)
+# define BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct static_require_default;
+
+template <typename T, typename Property, typename = void>
+struct static_require;
+
+} // namespace traits
+namespace detail {
+
+struct no_static_require
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+};
+
+template <typename T, typename Property, typename = void>
+struct static_require_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_static_require,
+    traits::static_require<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+#if defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+template <typename T, typename Property>
+struct static_require_trait<T, Property,
+  typename enable_if<
+    decay<Property>::type::value() == traits::static_query<T, Property>::value()
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+};
+
+#else // defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+false_type static_require_test(...);
+
+template <typename T, typename Property>
+true_type static_require_test(T*, Property*,
+    typename enable_if<
+      Property::value() == traits::static_query<T, Property>::value()
+    >::type* = 0);
+
+template <typename T, typename Property>
+struct has_static_require
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, value =
+    decltype((static_require_test)(
+      static_cast<T*>(0), static_cast<Property*>(0)))::value);
+};
+
+template <typename T, typename Property>
+struct static_require_trait<T, Property,
+  typename enable_if<
+    has_static_require<typename decay<T>::type,
+      typename decay<Property>::type>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+};
+
+#endif // defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct static_require_default : detail::static_require_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct static_require : static_require_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_STATIC_REQUIRE_HPP
diff --git a/include/boost/asio/traits/static_require_concept.hpp b/include/boost/asio/traits/static_require_concept.hpp
new file mode 100644
index 00000000..97ee2285
--- /dev/null
+++ b/include/boost/asio/traits/static_require_concept.hpp
@@ -0,0 +1,125 @@
+//
+// traits/static_require_concept.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BOOST_ASIO_TRAITS_STATIC_REQUIRE_CONCEPT_HPP
+#define BOOST_ASIO_TRAITS_STATIC_REQUIRE_CONCEPT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+#include <boost/asio/traits/static_query.hpp>
+
+#if defined(BOOST_ASIO_HAS_DECLTYPE) \
+  && defined(BOOST_ASIO_HAS_NOEXCEPT)
+# define BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_CONCEPT_TRAIT 1
+#endif // defined(BOOST_ASIO_HAS_DECLTYPE)
+       //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct static_require_concept_default;
+
+template <typename T, typename Property, typename = void>
+struct static_require_concept;
+
+} // namespace traits
+namespace detail {
+
+struct no_static_require_concept
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+};
+
+template <typename T, typename Property, typename = void>
+struct static_require_concept_trait :
+  conditional<
+    is_same<T, typename decay<T>::type>::value
+      && is_same<Property, typename decay<Property>::type>::value,
+    no_static_require_concept,
+    traits::static_require_concept<
+      typename decay<T>::type,
+      typename decay<Property>::type>
+  >::type
+{
+};
+
+#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_CONCEPT_TRAIT)
+
+#if defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+template <typename T, typename Property>
+struct static_require_concept_trait<T, Property,
+  typename enable_if<
+    decay<Property>::type::value() == traits::static_query<T, Property>::value()
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+};
+
+#else // defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+false_type static_require_concept_test(...);
+
+template <typename T, typename Property>
+true_type static_require_concept_test(T*, Property*,
+    typename enable_if<
+      Property::value() == traits::static_query<T, Property>::value()
+    >::type* = 0);
+
+template <typename T, typename Property>
+struct has_static_require_concept
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, value =
+    decltype((static_require_concept_test)(
+      static_cast<T*>(0), static_cast<Property*>(0)))::value);
+};
+
+template <typename T, typename Property>
+struct static_require_concept_trait<T, Property,
+  typename enable_if<
+    has_static_require_concept<T, typename decay<Property>::type>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+};
+
+#endif // defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_REQUIRE_CONCEPT_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct static_require_concept_default :
+  detail::static_require_concept_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct static_require_concept : static_require_concept_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_TRAITS_STATIC_REQUIRE_CONCEPT_HPP
diff --git a/include/boost/asio/ts/netfwd.hpp b/include/boost/asio/ts/netfwd.hpp
index 2a7d5a85..309f9e33 100644
--- a/include/boost/asio/ts/netfwd.hpp
+++ b/include/boost/asio/ts/netfwd.hpp
@@ -37,13 +37,23 @@ class execution_context;
 template <typename T, typename Executor>
 class executor_binder;
 
-template <typename Executor>
+#if !defined(BOOST_ASIO_EXECUTOR_WORK_GUARD_DECL)
+#define BOOST_ASIO_EXECUTOR_WORK_GUARD_DECL
+
+template <typename Executor, typename = void>
 class executor_work_guard;
 
-class system_executor;
+#endif // !defined(BOOST_ASIO_EXECUTOR_WORK_GUARD_DECL)
+
+template <typename Blocking, typename Relationship, typename Allocator>
+class basic_system_executor;
+
+#if defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
 
 class executor;
 
+#endif // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
 template <typename Executor>
 class strand;
 
@@ -59,6 +69,8 @@ struct time_traits;
 
 #endif // defined(BOOST_ASIO_HAS_BOOST_DATE_TIME)
 
+#if defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
 #if !defined(BOOST_ASIO_BASIC_WAITABLE_TIMER_FWD_DECL)
 #define BOOST_ASIO_BASIC_WAITABLE_TIMER_FWD_DECL
 
@@ -69,8 +81,6 @@ class basic_waitable_timer;
 
 #endif // !defined(BOOST_ASIO_BASIC_WAITABLE_TIMER_FWD_DECL)
 
-#if defined(BOOST_ASIO_HAS_CHRONO)
-
 typedef basic_waitable_timer<chrono::system_clock> system_timer;
 
 typedef basic_waitable_timer<chrono::steady_clock> steady_timer;
@@ -78,8 +88,19 @@ typedef basic_waitable_timer<chrono::steady_clock> steady_timer;
 typedef basic_waitable_timer<chrono::high_resolution_clock>
   high_resolution_timer;
 
+#else // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+template <typename Clock, typename WaitTraits, typename Executor>
+class basic_waitable_timer;
+
+#endif // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+#if defined(BOOST_ASIO_HAS_CHRONO)
+
 #endif // defined(BOOST_ASIO_HAS_CHRONO)
 
+#if defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
 #if !defined(BOOST_ASIO_BASIC_SOCKET_FWD_DECL)
 #define BOOST_ASIO_BASIC_SOCKET_FWD_DECL
 
@@ -113,6 +134,23 @@ class basic_socket_acceptor;
 
 #endif // !defined(BOOST_ASIO_BASIC_SOCKET_ACCEPTOR_FWD_DECL)
 
+#else // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+template <typename Protocol, typename Executor>
+class basic_socket;
+
+template <typename Protocol, typename Executor>
+class basic_datagram_socket;
+
+// Forward declaration with defaulted arguments.
+template <typename Protocol, typename Executor>
+class basic_stream_socket;
+
+template <typename Protocol, typename Executor>
+class basic_socket_acceptor;
+
+#endif // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
 #if !defined(BOOST_ASIO_BASIC_SOCKET_STREAMBUF_FWD_DECL)
 #define BOOST_ASIO_BASIC_SOCKET_STREAMBUF_FWD_DECL
 
@@ -182,6 +220,8 @@ class basic_resolver_entry;
 template <typename InternetProtocol>
 class basic_resolver_results;
 
+#if defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
 #if !defined(BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL)
 #define BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL
 
@@ -190,6 +230,13 @@ class basic_resolver;
 
 #endif // !defined(BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL)
 
+#else // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+template <typename InternetProtocol, typename Executor>
+class basic_resolver;
+
+#endif // defined(BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
 class tcp;
 
 class udp;
diff --git a/include/boost/asio/use_awaitable.hpp b/include/boost/asio/use_awaitable.hpp
index 152e3286..724f42b2 100644
--- a/include/boost/asio/use_awaitable.hpp
+++ b/include/boost/asio/use_awaitable.hpp
@@ -20,6 +20,13 @@
 #if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
 
 #include <boost/asio/awaitable.hpp>
+#include <boost/asio/detail/handler_tracking.hpp>
+
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+# if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+#  include <boost/asio/detail/source_location.hpp>
+# endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+#endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -43,14 +50,47 @@ namespace asio {
  * the asynchronous operation completes, and the result of the operation is
  * returned.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 struct use_awaitable_t
 {
   /// Default constructor.
-  BOOST_ASIO_CONSTEXPR use_awaitable_t()
+  BOOST_ASIO_CONSTEXPR use_awaitable_t(
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+# if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+      detail::source_location location = detail::source_location::current()
+# endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+#endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+    )
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+# if defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+    : file_name_(location.file_name()),
+      line_(location.line()),
+      function_name_(location.function_name())
+# else // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+    : file_name_(0),
+      line_(0),
+      function_name_(0)
+# endif // defined(BOOST_ASIO_HAS_SOURCE_LOCATION)
+#endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
   {
   }
 
+  /// Constructor used to specify file name, line, and function name.
+  BOOST_ASIO_CONSTEXPR use_awaitable_t(const char* file_name,
+      int line, const char* function_name)
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+    : file_name_(file_name),
+      line_(line),
+      function_name_(function_name)
+#endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+  {
+#if !defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+    (void)file_name;
+    (void)line;
+    (void)function_name;
+#endif // !defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+  }
+
   /// Adapts an executor to add the @c use_awaitable_t completion token as the
   /// default.
   template <typename InnerExecutor>
@@ -64,6 +104,17 @@ struct use_awaitable_t
       : InnerExecutor(ex)
     {
     }
+
+    /// Convert the specified executor to the inner executor type, then use
+    /// that to construct the adapted executor.
+    template <typename OtherExecutor>
+    executor_with_default(const OtherExecutor& ex,
+        typename enable_if<
+          is_convertible<OtherExecutor, InnerExecutor>::value
+        >::type* = 0) BOOST_ASIO_NOEXCEPT
+      : InnerExecutor(ex)
+    {
+    }
   };
 
   /// Type alias to adapt an I/O object to use @c use_awaitable_t as its
@@ -88,16 +139,24 @@ struct use_awaitable_t
         executor_with_default<typename decay<T>::type::executor_type>
       >::other(BOOST_ASIO_MOVE_CAST(T)(object));
   }
+
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+  const char* file_name_;
+  int line_;
+  const char* function_name_;
+#endif // defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
 };
 
 /// A completion token object that represents the currently executing coroutine.
 /**
  * See the documentation for boost::asio::use_awaitable_t for a usage example.
  */
-#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+#if defined(GENERATING_DOCUMENTATION)
 constexpr use_awaitable_t<> use_awaitable;
+#elif defined(BOOST_ASIO_HAS_CONSTEXPR)
+constexpr use_awaitable_t<> use_awaitable(0, 0, 0);
 #elif defined(BOOST_ASIO_MSVC)
-__declspec(selectany) use_awaitable_t<> use_awaitable;
+__declspec(selectany) use_awaitable_t<> use_awaitable(0, 0, 0);
 #endif
 
 } // namespace asio
diff --git a/include/boost/asio/windows/basic_object_handle.hpp b/include/boost/asio/windows/basic_object_handle.hpp
index 283dbb04..6c3d9309 100644
--- a/include/boost/asio/windows/basic_object_handle.hpp
+++ b/include/boost/asio/windows/basic_object_handle.hpp
@@ -21,13 +21,13 @@
 #if defined(BOOST_ASIO_HAS_WINDOWS_OBJECT_HANDLE) \
   || defined(GENERATING_DOCUMENTATION)
 
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/detail/win_object_handle_service.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 
 #if defined(BOOST_ASIO_HAS_MOVE)
 # include <utility>
@@ -48,7 +48,7 @@ namespace windows {
  * @e Distinct @e objects: Safe.@n
  * @e Shared @e objects: Unsafe.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_object_handle
 {
 public:
@@ -413,8 +413,8 @@ private:
 
       detail::non_const_lvalue<WaitHandler> handler2(handler);
       self_->impl_.get_service().async_wait(
-          self_->impl_.get_implementation(), handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(),
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/windows/basic_overlapped_handle.hpp b/include/boost/asio/windows/basic_overlapped_handle.hpp
index 78d27aae..928c4855 100644
--- a/include/boost/asio/windows/basic_overlapped_handle.hpp
+++ b/include/boost/asio/windows/basic_overlapped_handle.hpp
@@ -22,13 +22,13 @@
   || defined(GENERATING_DOCUMENTATION)
 
 #include <cstddef>
+#include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/detail/win_iocp_handle_service.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
-#include <boost/asio/executor.hpp>
 
 #if defined(BOOST_ASIO_HAS_MOVE)
 # include <utility>
@@ -51,7 +51,7 @@ namespace windows {
  * @e Distinct @e objects: Safe.@n
  * @e Shared @e objects: Unsafe.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_overlapped_handle
 {
 public:
diff --git a/include/boost/asio/windows/basic_random_access_handle.hpp b/include/boost/asio/windows/basic_random_access_handle.hpp
index e1d04c78..2afa0bdd 100644
--- a/include/boost/asio/windows/basic_random_access_handle.hpp
+++ b/include/boost/asio/windows/basic_random_access_handle.hpp
@@ -36,7 +36,7 @@ namespace windows {
  * @e Distinct @e objects: Safe.@n
  * @e Shared @e objects: Unsafe.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_random_access_handle
   : public basic_overlapped_handle<Executor>
 {
@@ -438,8 +438,8 @@ private:
 
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_write_some_at(
-          self_->impl_.get_implementation(), offset, buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), offset, buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -471,8 +471,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_read_some_at(
-          self_->impl_.get_implementation(), offset, buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), offset, buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/windows/basic_stream_handle.hpp b/include/boost/asio/windows/basic_stream_handle.hpp
index c0323dc2..9ed81a62 100644
--- a/include/boost/asio/windows/basic_stream_handle.hpp
+++ b/include/boost/asio/windows/basic_stream_handle.hpp
@@ -39,7 +39,7 @@ namespace windows {
  * @par Concepts:
  * AsyncReadStream, AsyncWriteStream, Stream, SyncReadStream, SyncWriteStream.
  */
-template <typename Executor = executor>
+template <typename Executor = any_io_executor>
 class basic_stream_handle
   : public basic_overlapped_handle<Executor>
 {
@@ -422,8 +422,8 @@ private:
 
       detail::non_const_lvalue<WriteHandler> handler2(handler);
       self_->impl_.get_service().async_write_some(
-          self_->impl_.get_implementation(), buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
@@ -455,8 +455,8 @@ private:
 
       detail::non_const_lvalue<ReadHandler> handler2(handler);
       self_->impl_.get_service().async_read_some(
-          self_->impl_.get_implementation(), buffers, handler2.value,
-          self_->impl_.get_implementation_executor());
+          self_->impl_.get_implementation(), buffers,
+          handler2.value, self_->impl_.get_executor());
     }
 
   private:
diff --git a/include/boost/asio/windows/overlapped_ptr.hpp b/include/boost/asio/windows/overlapped_ptr.hpp
index f8e6407e..4dd487c6 100644
--- a/include/boost/asio/windows/overlapped_ptr.hpp
+++ b/include/boost/asio/windows/overlapped_ptr.hpp
@@ -65,7 +65,8 @@ public:
   explicit overlapped_ptr(const Executor& ex,
       BOOST_ASIO_MOVE_ARG(Handler) handler,
       typename enable_if<
-        is_executor<Executor>::value
+        execution::is_executor<Executor>::value
+          || is_executor<Executor>::value
       >::type* = 0)
     : impl_(ex, BOOST_ASIO_MOVE_CAST(Handler)(handler))
   {
@@ -98,7 +99,8 @@ public:
   template <typename Executor, typename Handler>
   void reset(const Executor& ex, BOOST_ASIO_MOVE_ARG(Handler) handler,
       typename enable_if<
-        is_executor<Executor>::value
+        execution::is_executor<Executor>::value
+          || is_executor<Executor>::value
       >::type* = 0)
   {
     impl_.reset(ex, BOOST_ASIO_MOVE_CAST(Handler)(handler));
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index a9835751..fd02ed27 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -176,6 +176,8 @@ test-suite "asio" :
   [ run signal_set.cpp : : : $(USE_SELECT) : signal_set_select ]
   [ run socket_base.cpp ]
   [ run socket_base.cpp : : : $(USE_SELECT) : socket_base_select ]
+  [ run static_thread_pool.cpp ]
+  [ run static_thread_pool.cpp : : : $(USE_SELECT) : static_thread_pool_select ]
   [ link steady_timer.cpp ]
   [ link steady_timer.cpp : $(USE_SELECT) : steady_timer_select ]
   [ run strand.cpp ]
@@ -190,6 +192,8 @@ test-suite "asio" :
   [ link system_executor.cpp : $(USE_SELECT) : system_executor_select ]
   [ link this_coro.cpp ]
   [ link this_coro.cpp : $(USE_SELECT) : this_coro_select ]
+  [ run thread_pool.cpp ]
+  [ run thread_pool.cpp : : : $(USE_SELECT) : thread_pool_select ]
   [ link time_traits.cpp ]
   [ link time_traits.cpp : $(USE_SELECT) : time_traits_select ]
   [ link ts/buffer.cpp : : ts_buffer ]
diff --git a/test/compose.cpp b/test/compose.cpp
index 3255ef82..8282b10c 100644
--- a/test/compose.cpp
+++ b/test/compose.cpp
@@ -74,6 +74,16 @@ void compose_0_args_handler(int* count)
   ++(*count);
 }
 
+struct compose_0_args_lvalue_handler
+{
+  int* count_;
+
+  void operator()()
+  {
+    ++(*count_);
+  }
+};
+
 void compose_0_completion_args_test()
 {
 #if defined(BOOST_ASIO_HAS_BOOST_BIND)
@@ -96,6 +106,22 @@ void compose_0_completion_args_test()
   // The run() call will not return until all work has finished.
   BOOST_ASIO_CHECK(ioc.stopped());
   BOOST_ASIO_CHECK(count == 1);
+
+  ioc.restart();
+  count = 0;
+
+  compose_0_args_lvalue_handler lvalue_handler = { &count };
+  async_0_completion_args(ioc, lvalue_handler);
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
 }
 
 //------------------------------------------------------------------------------
@@ -140,12 +166,24 @@ async_1_completion_arg(boost::asio::io_context& ioc,
       impl_1_completion_arg(ioc), token);
 }
 
-void compose_1_args_handler(int* count, int* result_out, int result)
+void compose_1_arg_handler(int* count, int* result_out, int result)
 {
   ++(*count);
   *result_out = result;
 }
 
+struct compose_1_arg_lvalue_handler
+{
+  int* count_;
+  int* result_out_;
+
+  void operator()(int result)
+  {
+    ++(*count_);
+    *result_out_ = result;
+  }
+};
+
 void compose_1_completion_arg_test()
 {
 #if defined(BOOST_ASIO_HAS_BOOST_BIND)
@@ -160,7 +198,26 @@ void compose_1_completion_arg_test()
   int result = 0;
 
   async_1_completion_arg(ioc,
-      bindns::bind(&compose_1_args_handler, &count, &result, _1));
+      bindns::bind(&compose_1_arg_handler, &count, &result, _1));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+  BOOST_ASIO_CHECK(result == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+  BOOST_ASIO_CHECK(result == 42);
+
+  ioc.restart();
+  count = 0;
+  result = 0;
+
+  compose_1_arg_lvalue_handler lvalue_handler = { &count, &result };
+  async_1_completion_arg(ioc, lvalue_handler);
 
   // No handlers can be called until run() is called.
   BOOST_ASIO_CHECK(!ioc.stopped());
diff --git a/test/deadline_timer.cpp b/test/deadline_timer.cpp
index 0ff0d9bd..c6ce397b 100644
--- a/test/deadline_timer.cpp
+++ b/test/deadline_timer.cpp
@@ -250,22 +250,78 @@ struct custom_allocation_timer_handler
   custom_allocation_timer_handler(int* count) : count_(count) {}
   void operator()(const boost::system::error_code&) {}
   int* count_;
+
+  template <typename T>
+  struct allocator
+  {
+    typedef size_t size_type;
+    typedef ptrdiff_t difference_type;
+    typedef T* pointer;
+    typedef const T* const_pointer;
+    typedef T& reference;
+    typedef const T& const_reference;
+    typedef T value_type;
+
+    template <typename U>
+    struct rebind
+    {
+      typedef allocator<U> other;
+    };
+
+    explicit allocator(int* count) BOOST_ASIO_NOEXCEPT
+      : count_(count)
+    {
+    }
+
+    allocator(const allocator& other) BOOST_ASIO_NOEXCEPT
+      : count_(other.count_)
+    {
+    }
+
+    template <typename U>
+    allocator(const allocator<U>& other) BOOST_ASIO_NOEXCEPT
+      : count_(other.count_)
+    {
+    }
+
+    pointer allocate(size_type n, const void* = 0)
+    {
+      ++(*count_);
+      return static_cast<T*>(::operator new(sizeof(T) * n));
+    }
+
+    void deallocate(pointer p, size_type)
+    {
+      --(*count_);
+      ::operator delete(p);
+    }
+
+    size_type max_size() const
+    {
+      return ~size_type(0);
+    }
+
+    void construct(pointer p, const T& v)
+    {
+      new (p) T(v);
+    }
+
+    void destroy(pointer p)
+    {
+      p->~T();
+    }
+
+    int* count_;
+  };
+
+  typedef allocator<int> allocator_type;
+
+  allocator_type get_allocator() const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_type(count_);
+  }
 };
 
-void* asio_handler_allocate(std::size_t size,
-    custom_allocation_timer_handler* handler)
-{
-  ++(*handler->count_);
-  return ::operator new(size);
-}
-
-void asio_handler_deallocate(void* pointer, std::size_t,
-    custom_allocation_timer_handler* handler)
-{
-  --(*handler->count_);
-  ::operator delete(pointer);
-}
-
 void deadline_timer_custom_allocation_test()
 {
   static boost::asio::io_context io_context;
diff --git a/test/execution/Jamfile.v2 b/test/execution/Jamfile.v2
new file mode 100644
index 00000000..eee590b0
--- /dev/null
+++ b/test/execution/Jamfile.v2
@@ -0,0 +1,55 @@
+#
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+
+import feature ;
+
+lib socket ; # SOLARIS, QNXNTO
+lib nsl ; # SOLARIS
+lib ws2_32 ; # NT
+lib mswsock ; # NT
+lib ipv6 ; # HPUX
+lib network ; # HAIKU
+
+project
+  : requirements
+    <library>/boost/date_time//boost_date_time
+    <library>/boost/system//boost_system
+    <library>/boost/chrono//boost_chrono
+    <library>/boost/regex//boost_regex
+    <define>BOOST_ALL_NO_LIB=1
+    <threading>multi
+    <target-os>linux:<define>_XOPEN_SOURCE=600
+    <target-os>linux:<define>_GNU_SOURCE=1
+    <target-os>solaris:<define>_XOPEN_SOURCE=500
+    <target-os>solaris:<define>__EXTENSIONS__
+    <target-os>solaris:<library>socket
+    <target-os>solaris:<library>nsl
+    <target-os>windows:<define>_WIN32_WINNT=0x0501
+    <target-os>windows,<toolset>cw:<library>ws2_32
+    <target-os>windows,<toolset>cw:<library>mswsock
+    <target-os>windows,<toolset>gcc:<library>ws2_32
+    <target-os>windows,<toolset>gcc:<library>mswsock
+    <target-os>windows,<toolset>gcc-cygwin:<define>__USE_W32_SOCKETS
+    <target-os>hpux,<toolset>gcc:<define>_XOPEN_SOURCE_EXTENDED
+    <target-os>hpux:<library>ipv6
+    <target-os>qnxnto:<library>socket
+    <target-os>haiku:<library>network
+  ;
+
+test-suite "asio" :
+  [ run any_executor.cpp ]
+  [ run blocking.cpp ]
+  [ run blocking_adaptation.cpp ]
+  [ run bulk_guarantee.cpp ]
+  [ run context_as.cpp ]
+  [ run execute.cpp ]
+  [ run invocable_archetype.cpp ]
+  [ run mapping.cpp ]
+  [ run outstanding_work.cpp ]
+  [ run prefer_only.cpp ]
+  [ run relationship.cpp ]
+  ;
diff --git a/test/execution/any_executor.cpp b/test/execution/any_executor.cpp
new file mode 100644
index 00000000..69d15f57
--- /dev/null
+++ b/test/execution/any_executor.cpp
@@ -0,0 +1,139 @@
+//
+// any_executor.cpp
+// ~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/any_executor.hpp>
+
+#include <boost/asio/thread_pool.hpp>
+#include "../unit_test.hpp"
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <boost/bind/bind.hpp>
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <functional>
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+using namespace boost::asio;
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = boost;
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = std;
+#endif
+
+void increment(int* count)
+{
+  ++(*count);
+}
+
+void any_executor_executor_query_test()
+{
+  thread_pool pool(1);
+  execution::any_executor<
+      execution::blocking_t,
+      execution::outstanding_work_t,
+      execution::relationship_t,
+      execution::mapping_t::thread_t,
+      execution::occupancy_t>
+    ex(pool.executor());
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::blocking)
+        == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::blocking.possibly)
+        == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::outstanding_work)
+        == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::outstanding_work.untracked)
+        == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::relationship)
+        == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::relationship.fork)
+        == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::mapping)
+        == boost::asio::execution::mapping.thread);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex, boost::asio::execution::occupancy)
+        == 1);
+}
+
+void any_executor_executor_execute_test()
+{
+  int count = 0;
+  thread_pool pool(1);
+  execution::any_executor<
+      execution::blocking_t::possibly_t,
+      execution::blocking_t::never_t,
+      execution::outstanding_work_t::untracked_t,
+      execution::outstanding_work_t::tracked_t,
+      execution::relationship_t::continuation_t>
+    ex(pool.executor());
+
+  boost::asio::execution::execute(pool.executor(),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.possibly),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.tracked),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.continuation),
+      bindns::bind(increment, &count));
+
+  pool.wait();
+
+  BOOST_ASIO_CHECK(count == 6);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "any_executor",
+  BOOST_ASIO_TEST_CASE(any_executor_executor_query_test)
+  BOOST_ASIO_TEST_CASE(any_executor_executor_execute_test)
+)
diff --git a/test/execution/blocking.cpp b/test/execution/blocking.cpp
new file mode 100644
index 00000000..d9bbbd4f
--- /dev/null
+++ b/test/execution/blocking.cpp
@@ -0,0 +1,2000 @@
+//
+// blocking.cpp
+// ~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/blocking.hpp>
+
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+#include "../unit_test.hpp"
+
+namespace exec = boost::asio::execution;
+
+typedef exec::blocking_t s;
+typedef exec::blocking_t::possibly_t n1;
+typedef exec::blocking_t::always_t n2;
+typedef exec::blocking_t::never_t n3;
+
+struct ex_nq_nr
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<ex_nq_nr> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_cq_nr
+{
+  static BOOST_ASIO_CONSTEXPR ResultType query(ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_cq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_static_constexpr_member<
+  ex_cq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef Result result_type; // Must return raw result type.
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return Result();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_mq_nr
+{
+  ResultType query(ParamType) const BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_mq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_member<
+  ex_mq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_fq_nr
+{
+  friend ResultType query(const ex_fq_nr&, ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_fq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_free<
+  ex_fq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_mq_mr
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  CurrentType query(OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, OtherType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, OtherType>();
+  }
+
+  ex_mq_mr<OtherType, CurrentType> require(
+      OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_mq_mr<CurrentType, CurrentType>
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, CurrentType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_mq_mr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_fq_fr
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend CurrentType query(const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> require(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> prefer(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_fq_fr<CurrentType, CurrentType>
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_fq_fr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_query()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_query<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_query<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_query<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_query<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_query()
+{
+  exec::blocking_t result1 = boost::asio::query(Executor(), Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+
+  Executor ex1 = {};
+  exec::blocking_t result2 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result2 == ExpectedResult());
+
+  const Executor ex2 = {};
+  exec::blocking_t result3 = boost::asio::query(ex2, Param());
+  BOOST_ASIO_CHECK(result3 == ExpectedResult());
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_constexpr_query()
+{
+#if defined(BOOST_ASIO_HAS_CONSTEXPR)
+  constexpr Executor ex1 = {};
+  constexpr exec::blocking_t result1 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+#endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_require()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_require<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_require<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_require<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_require<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_require()
+{
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(Executor(), Param()),
+        Param()) == ExpectedResult());
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex1, Param()),
+        Param()) == ExpectedResult());
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex2, Param()),
+        Param()) == ExpectedResult());
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_prefer()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_prefer<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_prefer<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_prefer<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_prefer<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_prefer()
+{
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(Executor(), Param()),
+          s())) == s(ExpectedResult()));
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex1, Param()),
+          s())) == s(ExpectedResult()));
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex2, Param()),
+          s())) == s(ExpectedResult()));
+}
+
+void test_vars()
+{
+  BOOST_ASIO_CHECK(s() == exec::blocking);
+  BOOST_ASIO_CHECK(n1() == exec::blocking.possibly);
+  BOOST_ASIO_CHECK(n2() == exec::blocking.always);
+  BOOST_ASIO_CHECK(n3() == exec::blocking.never);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "blocking",
+
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, s, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n2, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n3, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n2, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n3, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_require<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n2, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n3, true>)
+
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n1, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n2, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n3, n1>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n3, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n3, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n3>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n3>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n1>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n2>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n3>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n3>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n1>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n2>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE(test_vars)
+)
diff --git a/test/execution/blocking_adaptation.cpp b/test/execution/blocking_adaptation.cpp
new file mode 100644
index 00000000..ccdeeb8a
--- /dev/null
+++ b/test/execution/blocking_adaptation.cpp
@@ -0,0 +1,1272 @@
+//
+// blocking_adaptation.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/blocking_adaptation.hpp>
+
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+#include "../unit_test.hpp"
+
+namespace exec = boost::asio::execution;
+
+typedef exec::blocking_adaptation_t s;
+typedef exec::blocking_adaptation_t::disallowed_t n1;
+typedef exec::blocking_adaptation_t::allowed_t n2;
+
+struct ex_nq_nr
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<ex_nq_nr> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_cq_nr
+{
+  static BOOST_ASIO_CONSTEXPR ResultType query(ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_cq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_static_constexpr_member<
+  ex_cq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef Result result_type; // Must return raw result type.
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return Result();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_mq_nr
+{
+  ResultType query(ParamType) const BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_mq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_member<
+  ex_mq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_fq_nr
+{
+  friend ResultType query(const ex_fq_nr&, ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_fq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_free<
+  ex_fq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_mq_mr
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  CurrentType query(OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, OtherType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, OtherType>();
+  }
+
+  ex_mq_mr<OtherType, CurrentType> require(
+      OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_mq_mr<CurrentType, CurrentType>
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, CurrentType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_mq_mr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_fq_fr
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend CurrentType query(const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> require(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> prefer(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_fq_fr<CurrentType, CurrentType>
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_fq_fr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_query()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_query<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_query<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_query<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_query<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_query()
+{
+  exec::blocking_adaptation_t result1 = boost::asio::query(Executor(), Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+
+  Executor ex1 = {};
+  exec::blocking_adaptation_t result2 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result2 == ExpectedResult());
+
+  const Executor ex2 = {};
+  exec::blocking_adaptation_t result3 = boost::asio::query(ex2, Param());
+  BOOST_ASIO_CHECK(result3 == ExpectedResult());
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_constexpr_query()
+{
+#if defined(BOOST_ASIO_HAS_CONSTEXPR)
+  constexpr Executor ex1 = {};
+  constexpr exec::blocking_adaptation_t result1 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+#endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_require()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_require<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_require<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_require<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_require<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_require()
+{
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(Executor(), Param()),
+        Param()) == ExpectedResult());
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex1, Param()),
+        Param()) == ExpectedResult());
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex2, Param()),
+        Param()) == ExpectedResult());
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_prefer()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_prefer<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_prefer<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_prefer<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_prefer<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_prefer()
+{
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(Executor(), Param()),
+          s())) == s(ExpectedResult()));
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex1, Param()),
+          s())) == s(ExpectedResult()));
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex2, Param()),
+          s())) == s(ExpectedResult()));
+}
+
+void test_vars()
+{
+  BOOST_ASIO_CHECK(s() == exec::blocking_adaptation);
+  BOOST_ASIO_CHECK(n1() == exec::blocking_adaptation.disallowed);
+  BOOST_ASIO_CHECK(n2() == exec::blocking_adaptation.allowed);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "blocking_adaptation",
+
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, s, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n2, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n2, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_require<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n2, true>)
+
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n1, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n2, n1>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n2, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n2, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE(test_vars)
+)
diff --git a/test/execution/bulk_guarantee.cpp b/test/execution/bulk_guarantee.cpp
new file mode 100644
index 00000000..af4c9cd5
--- /dev/null
+++ b/test/execution/bulk_guarantee.cpp
@@ -0,0 +1,2000 @@
+//
+// bulk_guarantee.cpp
+// ~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/bulk_guarantee.hpp>
+
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+#include "../unit_test.hpp"
+
+namespace exec = boost::asio::execution;
+
+typedef exec::bulk_guarantee_t s;
+typedef exec::bulk_guarantee_t::unsequenced_t n1;
+typedef exec::bulk_guarantee_t::sequenced_t n2;
+typedef exec::bulk_guarantee_t::parallel_t n3;
+
+struct ex_nq_nr
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<ex_nq_nr> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_cq_nr
+{
+  static BOOST_ASIO_CONSTEXPR ResultType query(ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_cq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_static_constexpr_member<
+  ex_cq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef Result result_type; // Must return raw result type.
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return Result();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_mq_nr
+{
+  ResultType query(ParamType) const BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_mq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_member<
+  ex_mq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_fq_nr
+{
+  friend ResultType query(const ex_fq_nr&, ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_fq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_free<
+  ex_fq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_mq_mr
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  CurrentType query(OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, OtherType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, OtherType>();
+  }
+
+  ex_mq_mr<OtherType, CurrentType> require(
+      OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_mq_mr<CurrentType, CurrentType>
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, CurrentType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_mq_mr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_fq_fr
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend CurrentType query(const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> require(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> prefer(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_fq_fr<CurrentType, CurrentType>
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_fq_fr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_query()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_query<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_query<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_query<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_query<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_query()
+{
+  exec::bulk_guarantee_t result1 = boost::asio::query(Executor(), Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+
+  Executor ex1 = {};
+  exec::bulk_guarantee_t result2 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result2 == ExpectedResult());
+
+  const Executor ex2 = {};
+  exec::bulk_guarantee_t result3 = boost::asio::query(ex2, Param());
+  BOOST_ASIO_CHECK(result3 == ExpectedResult());
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_constexpr_query()
+{
+#if defined(BOOST_ASIO_HAS_CONSTEXPR)
+  constexpr Executor ex1 = {};
+  constexpr exec::bulk_guarantee_t result1 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+#endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_require()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_require<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_require<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_require<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_require<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_require()
+{
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(Executor(), Param()),
+        Param()) == ExpectedResult());
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex1, Param()),
+        Param()) == ExpectedResult());
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex2, Param()),
+        Param()) == ExpectedResult());
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_prefer()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_prefer<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_prefer<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_prefer<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_prefer<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_prefer()
+{
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(Executor(), Param()),
+          s())) == s(ExpectedResult()));
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex1, Param()),
+          s())) == s(ExpectedResult()));
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex2, Param()),
+          s())) == s(ExpectedResult()));
+}
+
+void test_vars()
+{
+  BOOST_ASIO_CHECK(s() == exec::bulk_guarantee);
+  BOOST_ASIO_CHECK(n1() == exec::bulk_guarantee.unsequenced);
+  BOOST_ASIO_CHECK(n2() == exec::bulk_guarantee.sequenced);
+  BOOST_ASIO_CHECK(n3() == exec::bulk_guarantee.parallel);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "bulk_guarantee",
+
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, s, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n2, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n3, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n2, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n3, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_require<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n2, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n3, true>)
+
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n1, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n2, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n3, n1>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n3, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n3, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n3>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n3>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n1>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n2>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n3>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n3>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n1>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n2>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE(test_vars)
+)
diff --git a/test/execution/context_as.cpp b/test/execution/context_as.cpp
new file mode 100644
index 00000000..480bccb3
--- /dev/null
+++ b/test/execution/context_as.cpp
@@ -0,0 +1,157 @@
+//
+// context_as.cpp
+// ~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/context_as.hpp>
+
+#include <boost/asio/execution/any_executor.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/static_thread_pool.hpp>
+#include "../unit_test.hpp"
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <boost/bind/bind.hpp>
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <functional>
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+using namespace boost::asio;
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = boost;
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = std;
+#endif
+
+void context_as_executor_query_test()
+{
+  static_thread_pool pool(1);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(pool.executor(),
+        execution::context_as_t<static_thread_pool&>())
+        == &pool);
+
+  execution::any_executor<
+      execution::context_as_t<static_thread_pool&>
+    > ex1 = pool.executor();
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex1,
+        execution::context_as_t<static_thread_pool&>())
+        == &pool);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex1, execution::context)
+        == &pool);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(pool.executor(),
+        execution::context_as_t<const static_thread_pool&>())
+        == &pool);
+
+  execution::any_executor<
+      execution::context_as_t<const static_thread_pool&>
+    > ex2 = pool.executor();
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex2,
+        execution::context_as_t<const static_thread_pool&>())
+        == &pool);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex2, execution::context)
+        == &pool);
+
+  io_context io_ctx;
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(io_ctx.get_executor(),
+        execution::context_as_t<io_context&>())
+        == &io_ctx);
+
+  execution::any_executor<
+      execution::context_as_t<io_context&>
+    > ex3 = io_ctx.get_executor();
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex3,
+        execution::context_as_t<io_context&>())
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex3, execution::context)
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(io_ctx.get_executor(),
+        execution::context_as_t<const io_context&>())
+        == &io_ctx);
+
+  execution::any_executor<
+      execution::context_as_t<const io_context&>
+    > ex4 = io_ctx.get_executor();
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex4,
+        execution::context_as_t<const io_context&>())
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex4, execution::context)
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(io_ctx.get_executor(),
+        execution::context_as_t<execution_context&>())
+        == &io_ctx);
+
+  execution::any_executor<
+      execution::context_as_t<execution_context&>
+    > ex5 = io_ctx.get_executor();
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex5,
+        execution::context_as_t<execution_context&>())
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex5, execution::context)
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(io_ctx.get_executor(),
+        execution::context_as_t<const execution_context&>())
+        == &io_ctx);
+
+  execution::any_executor<
+      execution::context_as_t<const execution_context&>
+    > ex6 = io_ctx.get_executor();
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex6,
+        execution::context_as_t<const execution_context&>())
+        == &io_ctx);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ex6, execution::context)
+        == &io_ctx);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "context_as",
+  BOOST_ASIO_TEST_CASE(context_as_executor_query_test)
+)
diff --git a/test/execution/execute.cpp b/test/execution/execute.cpp
new file mode 100644
index 00000000..d411f7f2
--- /dev/null
+++ b/test/execution/execute.cpp
@@ -0,0 +1,301 @@
+//
+// execute.cpp
+// ~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/execute.hpp>
+
+#include <boost/asio/execution/invocable_archetype.hpp>
+#include "../unit_test.hpp"
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <boost/bind/bind.hpp>
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <functional>
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+namespace exec = boost::asio::execution;
+
+struct no_execute
+{
+};
+
+struct const_member_execute
+{
+  template <typename F>
+  void execute(BOOST_ASIO_MOVE_ARG(F) f) const
+  {
+    typename boost::asio::decay<F>::type tmp(BOOST_ASIO_MOVE_CAST(F)(f));
+    tmp();
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename F>
+struct execute_member<const_member_execute, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+struct free_execute_const_executor
+{
+  template <typename F>
+  friend void execute(const free_execute_const_executor&,
+      BOOST_ASIO_MOVE_ARG(F) f)
+  {
+    typename boost::asio::decay<F>::type tmp(BOOST_ASIO_MOVE_CAST(F)(f));
+    tmp();
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename F>
+struct execute_free<free_execute_const_executor, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+
+// Support for rvalue references is required in order to use the execute
+// customisation point with non-const member functions and free functions
+// taking non-const arguments.
+
+struct non_const_member_execute
+{
+  template <typename F>
+  void execute(BOOST_ASIO_MOVE_ARG(F) f)
+  {
+    typename boost::asio::decay<F>::type tmp(BOOST_ASIO_MOVE_CAST(F)(f));
+    tmp();
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename F>
+struct execute_member<non_const_member_execute, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename F>
+struct execute_member<const non_const_member_execute, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename F>
+struct execute_member<const non_const_member_execute&, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+struct free_execute_non_const_executor
+{
+  template <typename F>
+  friend void execute(free_execute_non_const_executor&,
+      BOOST_ASIO_MOVE_ARG(F) f)
+  {
+    typename boost::asio::decay<F>::type tmp(BOOST_ASIO_MOVE_CAST(F)(f));
+    tmp();
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename F>
+struct execute_free<free_execute_non_const_executor, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename F>
+struct execute_free<const free_execute_non_const_executor, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename F>
+struct execute_free<const free_execute_non_const_executor&, F>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
+void test_can_execute()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 = exec::can_execute<
+      no_execute&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b1 == false);
+
+  BOOST_ASIO_CONSTEXPR bool b2 = exec::can_execute<
+      const no_execute&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b2 == false);
+
+  BOOST_ASIO_CONSTEXPR bool b3 = exec::can_execute<
+      const_member_execute&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b3 == true);
+
+  BOOST_ASIO_CONSTEXPR bool b4 = exec::can_execute<
+      const const_member_execute&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b4 == true);
+
+  BOOST_ASIO_CONSTEXPR bool b5 = exec::can_execute<
+      free_execute_const_executor&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b5 == true);
+
+  BOOST_ASIO_CONSTEXPR bool b6 = exec::can_execute<
+      const free_execute_const_executor&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b6 == true);
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  BOOST_ASIO_CONSTEXPR bool b7 = exec::can_execute<
+      non_const_member_execute&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b7 == true);
+
+  BOOST_ASIO_CONSTEXPR bool b8 = exec::can_execute<
+      const non_const_member_execute&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b8 == false);
+
+  BOOST_ASIO_CONSTEXPR bool b9 = exec::can_execute<
+      free_execute_non_const_executor&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b9 == true);
+
+  BOOST_ASIO_CONSTEXPR bool b10 = exec::can_execute<
+      const free_execute_non_const_executor&, exec::invocable_archetype>::value;
+  BOOST_ASIO_CHECK(b10 == false);
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+}
+
+void increment(int* count)
+{
+  ++(*count);
+}
+
+void test_execute()
+{
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+  namespace bindns = boost;
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+  namespace bindns = std;
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+  int count = 0;
+  const_member_execute ex1 = {};
+  exec::execute(ex1, bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  const const_member_execute ex2 = {};
+  exec::execute(ex2, bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  exec::execute(const_member_execute(), bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  free_execute_const_executor ex3 = {};
+  exec::execute(ex3, bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  const free_execute_const_executor ex4 = {};
+  exec::execute(ex4, bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  exec::execute(free_execute_const_executor(),
+      bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+#if defined(BOOST_ASIO_HAS_MOVE)
+  count = 0;
+  non_const_member_execute ex5 = {};
+  exec::execute(ex5, bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  free_execute_non_const_executor ex6 = {};
+  exec::execute(ex6, bindns::bind(&increment, &count));
+  BOOST_ASIO_CHECK(count == 1);
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "blocking",
+  BOOST_ASIO_TEST_CASE(test_can_execute)
+  BOOST_ASIO_TEST_CASE(test_execute)
+)
diff --git a/test/execution/invocable_archetype.cpp b/test/execution/invocable_archetype.cpp
new file mode 100644
index 00000000..629bea52
--- /dev/null
+++ b/test/execution/invocable_archetype.cpp
@@ -0,0 +1,25 @@
+//
+// invocable_archetype.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/invocable_archetype.hpp>
+
+#include "../unit_test.hpp"
+
+BOOST_ASIO_TEST_SUITE
+(
+  "invocable_archetype",
+  BOOST_ASIO_TEST_CASE(null_test)
+)
diff --git a/test/execution/mapping.cpp b/test/execution/mapping.cpp
new file mode 100644
index 00000000..39bfa5aa
--- /dev/null
+++ b/test/execution/mapping.cpp
@@ -0,0 +1,2000 @@
+//
+// mapping.cpp
+// ~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/mapping.hpp>
+
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+#include "../unit_test.hpp"
+
+namespace exec = boost::asio::execution;
+
+typedef exec::mapping_t s;
+typedef exec::mapping_t::thread_t n1;
+typedef exec::mapping_t::new_thread_t n2;
+typedef exec::mapping_t::other_t n3;
+
+struct ex_nq_nr
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<ex_nq_nr> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_cq_nr
+{
+  static BOOST_ASIO_CONSTEXPR ResultType query(ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_cq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_static_constexpr_member<
+  ex_cq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef Result result_type; // Must return raw result type.
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return Result();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_mq_nr
+{
+  ResultType query(ParamType) const BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_mq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_member<
+  ex_mq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_fq_nr
+{
+  friend ResultType query(const ex_fq_nr&, ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_fq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_free<
+  ex_fq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_mq_mr
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  CurrentType query(OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, OtherType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, OtherType>();
+  }
+
+  ex_mq_mr<OtherType, CurrentType> require(
+      OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_mq_mr<CurrentType, CurrentType>
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, CurrentType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_mq_mr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_fq_fr
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend CurrentType query(const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> require(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> prefer(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_fq_fr<CurrentType, CurrentType>
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_fq_fr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_query()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_query<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_query<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_query<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_query<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_query()
+{
+  exec::mapping_t result1 = boost::asio::query(Executor(), Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+
+  Executor ex1 = {};
+  exec::mapping_t result2 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result2 == ExpectedResult());
+
+  const Executor ex2 = {};
+  exec::mapping_t result3 = boost::asio::query(ex2, Param());
+  BOOST_ASIO_CHECK(result3 == ExpectedResult());
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_constexpr_query()
+{
+#if defined(BOOST_ASIO_HAS_CONSTEXPR)
+  constexpr Executor ex1 = {};
+  constexpr exec::mapping_t result1 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+#endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_require()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_require<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_require<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_require<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_require<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_require()
+{
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(Executor(), Param()),
+        Param()) == ExpectedResult());
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex1, Param()),
+        Param()) == ExpectedResult());
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex2, Param()),
+        Param()) == ExpectedResult());
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_prefer()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_prefer<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_prefer<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_prefer<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_prefer<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_prefer()
+{
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(Executor(), Param()),
+          s())) == s(ExpectedResult()));
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex1, Param()),
+          s())) == s(ExpectedResult()));
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex2, Param()),
+          s())) == s(ExpectedResult()));
+}
+
+void test_vars()
+{
+  BOOST_ASIO_CHECK(s() == exec::mapping);
+  BOOST_ASIO_CHECK(n1() == exec::mapping.thread);
+  BOOST_ASIO_CHECK(n2() == exec::mapping.new_thread);
+  BOOST_ASIO_CHECK(n3() == exec::mapping.other);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "mapping",
+
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, s, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n2, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n3, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n2, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n3, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_require<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n2, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n3, true>)
+
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n1, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n2, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n3, n1>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n3, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n3, s, n3>, n3, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n3, n3>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n3, s, n3>, n3, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n3, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n3, s, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n3, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n3, s, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n3>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n3>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n1>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n2>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n3>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n3>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n1>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n2>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n3>, s, n3>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n3, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n3>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n1>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n2>, n3, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n3, n3>, n3, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n3, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n3, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n3>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n1>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n2>, n3, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n1, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n2, n3>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n3, n3>, n3, n3>)
+
+  BOOST_ASIO_TEST_CASE(test_vars)
+)
diff --git a/test/execution/outstanding_work.cpp b/test/execution/outstanding_work.cpp
new file mode 100644
index 00000000..076297af
--- /dev/null
+++ b/test/execution/outstanding_work.cpp
@@ -0,0 +1,1272 @@
+//
+// outstanding_work.cpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/outstanding_work.hpp>
+
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+#include "../unit_test.hpp"
+
+namespace exec = boost::asio::execution;
+
+typedef exec::outstanding_work_t s;
+typedef exec::outstanding_work_t::untracked_t n1;
+typedef exec::outstanding_work_t::tracked_t n2;
+
+struct ex_nq_nr
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<ex_nq_nr> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_cq_nr
+{
+  static BOOST_ASIO_CONSTEXPR ResultType query(ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_cq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_static_constexpr_member<
+  ex_cq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef Result result_type; // Must return raw result type.
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return Result();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_mq_nr
+{
+  ResultType query(ParamType) const BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_mq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_member<
+  ex_mq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_fq_nr
+{
+  friend ResultType query(const ex_fq_nr&, ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_fq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_free<
+  ex_fq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_mq_mr
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  CurrentType query(OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, OtherType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, OtherType>();
+  }
+
+  ex_mq_mr<OtherType, CurrentType> require(
+      OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_mq_mr<CurrentType, CurrentType>
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, CurrentType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_mq_mr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_fq_fr
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend CurrentType query(const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> require(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> prefer(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_fq_fr<CurrentType, CurrentType>
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_fq_fr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_query()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_query<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_query<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_query<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_query<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_query()
+{
+  exec::outstanding_work_t result1 = boost::asio::query(Executor(), Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+
+  Executor ex1 = {};
+  exec::outstanding_work_t result2 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result2 == ExpectedResult());
+
+  const Executor ex2 = {};
+  exec::outstanding_work_t result3 = boost::asio::query(ex2, Param());
+  BOOST_ASIO_CHECK(result3 == ExpectedResult());
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_constexpr_query()
+{
+#if defined(BOOST_ASIO_HAS_CONSTEXPR)
+  constexpr Executor ex1 = {};
+  constexpr exec::outstanding_work_t result1 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+#endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_require()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_require<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_require<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_require<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_require<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_require()
+{
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(Executor(), Param()),
+        Param()) == ExpectedResult());
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex1, Param()),
+        Param()) == ExpectedResult());
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex2, Param()),
+        Param()) == ExpectedResult());
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_prefer()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_prefer<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_prefer<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_prefer<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_prefer<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_prefer()
+{
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(Executor(), Param()),
+          s())) == s(ExpectedResult()));
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex1, Param()),
+          s())) == s(ExpectedResult()));
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex2, Param()),
+          s())) == s(ExpectedResult()));
+}
+
+void test_vars()
+{
+  BOOST_ASIO_CHECK(s() == exec::outstanding_work);
+  BOOST_ASIO_CHECK(n1() == exec::outstanding_work.untracked);
+  BOOST_ASIO_CHECK(n2() == exec::outstanding_work.tracked);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "outstanding_work",
+
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, s, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n2, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n2, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_require<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n2, true>)
+
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n1, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n2, n1>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n2, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n2, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE(test_vars)
+)
diff --git a/test/execution/prefer_only.cpp b/test/execution/prefer_only.cpp
new file mode 100644
index 00000000..6f04ddfb
--- /dev/null
+++ b/test/execution/prefer_only.cpp
@@ -0,0 +1,531 @@
+//
+// prefer_only.cpp
+// ~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/prefer_only.hpp>
+
+#include <boost/asio/execution/any_executor.hpp>
+#include "../unit_test.hpp"
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <boost/bind/bind.hpp>
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <functional>
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+using namespace boost::asio;
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = boost;
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = std;
+#endif
+
+static int possibly_blocking_count = 0;
+static int never_blocking_count = 0;
+
+struct possibly_blocking_executor
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+    ++possibly_blocking_count;
+  }
+
+  friend bool operator==(const possibly_blocking_executor&,
+      const possibly_blocking_executor&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const possibly_blocking_executor&,
+      const possibly_blocking_executor&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<possibly_blocking_executor> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+struct never_blocking_executor
+{
+  static BOOST_ASIO_CONSTEXPR execution::blocking_t::never_t
+    query(execution::blocking_t) BOOST_ASIO_NOEXCEPT
+  {
+    return execution::blocking_t::never_t();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+    ++never_blocking_count;
+  }
+
+  friend bool operator==(const never_blocking_executor&,
+      const never_blocking_executor&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const never_blocking_executor&,
+      const never_blocking_executor&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<never_blocking_executor> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename Param>
+struct query_static_constexpr_member<
+  never_blocking_executor, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, execution::blocking_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::blocking_t::never_t result_type;
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+struct either_blocking_executor
+{
+  execution::blocking_t blocking_;
+
+  explicit either_blocking_executor(execution::blocking_t b)
+    : blocking_(b)
+  {
+  }
+
+  execution::blocking_t query(execution::blocking_t) const BOOST_ASIO_NOEXCEPT
+  {
+    return blocking_;
+  }
+
+  either_blocking_executor require(execution::blocking_t::possibly_t) const
+  {
+    return either_blocking_executor(execution::blocking.possibly);
+  }
+
+  either_blocking_executor require(execution::blocking_t::never_t) const
+  {
+    return either_blocking_executor(execution::blocking.never);
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+    if (blocking_ == execution::blocking.never)
+      ++never_blocking_count;
+    else
+      ++possibly_blocking_count;
+  }
+
+  friend bool operator==(const either_blocking_executor& a,
+      const either_blocking_executor& b) BOOST_ASIO_NOEXCEPT
+  {
+    return a.blocking_ == b.blocking_;
+  }
+
+  friend bool operator!=(const either_blocking_executor& a,
+      const either_blocking_executor& b) BOOST_ASIO_NOEXCEPT
+  {
+    return a.blocking_ != b.blocking_;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<either_blocking_executor> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename Param>
+struct query_member<
+  either_blocking_executor, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, execution::blocking_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::blocking_t result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template <typename Param>
+struct require_member<
+  either_blocking_executor, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, execution::blocking_t>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+
+  typedef either_blocking_executor result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+void prefer_only_executor_query_test()
+{
+  typedef execution::any_executor<
+      execution::blocking_t,
+      execution::prefer_only<execution::blocking_t::possibly_t>,
+      execution::prefer_only<execution::blocking_t::never_t>
+    > executor_type;
+
+  executor_type ex1 = possibly_blocking_executor();
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex1, execution::blocking)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex1, execution::blocking.possibly)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex1, execution::blocking.never)
+        == execution::blocking.possibly);
+
+  executor_type ex2 = boost::asio::prefer(ex1, execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex2, execution::blocking)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex2, execution::blocking.possibly)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex2, execution::blocking.never)
+        == execution::blocking.possibly);
+
+  executor_type ex3 = boost::asio::prefer(ex1, execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex3, execution::blocking)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex3, execution::blocking.possibly)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex3, execution::blocking.never)
+        == execution::blocking.possibly);
+
+  executor_type ex4 = never_blocking_executor();
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex4, execution::blocking)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex4, execution::blocking.possibly)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex4, execution::blocking.never)
+        == execution::blocking.never);
+
+  executor_type ex5 = boost::asio::prefer(ex4, execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex5, execution::blocking)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex5, execution::blocking.possibly)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex5, execution::blocking.never)
+        == execution::blocking.never);
+
+  executor_type ex6 = boost::asio::prefer(ex4, execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex6, execution::blocking)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex6, execution::blocking.possibly)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex6, execution::blocking.never)
+        == execution::blocking.never);
+
+  executor_type ex7 = either_blocking_executor(execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex7, execution::blocking)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex7, execution::blocking.possibly)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex7, execution::blocking.never)
+        == execution::blocking.possibly);
+
+  executor_type ex8 = boost::asio::prefer(ex7, execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex8, execution::blocking)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex8, execution::blocking.possibly)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex8, execution::blocking.never)
+        == execution::blocking.possibly);
+
+  executor_type ex9 = boost::asio::prefer(ex7, execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex9, execution::blocking)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex9, execution::blocking.possibly)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex9, execution::blocking.never)
+        == execution::blocking.never);
+
+  executor_type ex10 = either_blocking_executor(execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex10, execution::blocking)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex10, execution::blocking.possibly)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex10, execution::blocking.never)
+        == execution::blocking.never);
+
+  executor_type ex11 = boost::asio::prefer(ex7, execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex11, execution::blocking)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex11, execution::blocking.possibly)
+        == execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex11, execution::blocking.never)
+        == execution::blocking.possibly);
+
+  executor_type ex12 = boost::asio::prefer(ex7, execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex12, execution::blocking)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex12, execution::blocking.possibly)
+        == execution::blocking.never);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ex12, execution::blocking.never)
+        == execution::blocking.never);
+}
+
+void do_nothing()
+{
+}
+
+void prefer_only_executor_execute_test()
+{
+  typedef execution::any_executor<
+      execution::blocking_t,
+      execution::prefer_only<execution::blocking_t::possibly_t>,
+      execution::prefer_only<execution::blocking_t::never_t>
+    > executor_type;
+
+  executor_type ex1 = possibly_blocking_executor();
+
+  execution::execute(ex1, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 1);
+  BOOST_ASIO_CHECK(never_blocking_count == 0);
+
+  executor_type ex2 = boost::asio::prefer(ex1, execution::blocking.possibly);
+
+  execution::execute(ex2, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 2);
+  BOOST_ASIO_CHECK(never_blocking_count == 0);
+
+  executor_type ex3 = boost::asio::prefer(ex1, execution::blocking.never);
+
+  execution::execute(ex3, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 3);
+  BOOST_ASIO_CHECK(never_blocking_count == 0);
+
+  executor_type ex4 = never_blocking_executor();
+
+  execution::execute(ex4, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 3);
+  BOOST_ASIO_CHECK(never_blocking_count == 1);
+
+  executor_type ex5 = boost::asio::prefer(ex4, execution::blocking.possibly);
+
+  execution::execute(ex5, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 3);
+  BOOST_ASIO_CHECK(never_blocking_count == 2);
+
+  executor_type ex6 = boost::asio::prefer(ex4, execution::blocking.never);
+
+  execution::execute(ex6, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 3);
+  BOOST_ASIO_CHECK(never_blocking_count == 3);
+
+  executor_type ex7 = either_blocking_executor(execution::blocking.possibly);
+
+  execution::execute(ex7, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 4);
+  BOOST_ASIO_CHECK(never_blocking_count == 3);
+
+  executor_type ex8 = boost::asio::prefer(ex7, execution::blocking.possibly);
+
+  execution::execute(ex8, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 5);
+  BOOST_ASIO_CHECK(never_blocking_count == 3);
+
+  executor_type ex9 = boost::asio::prefer(ex7, execution::blocking.never);
+
+  execution::execute(ex9, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 5);
+  BOOST_ASIO_CHECK(never_blocking_count == 4);
+
+  executor_type ex10 = either_blocking_executor(execution::blocking.never);
+
+  execution::execute(ex10, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 5);
+  BOOST_ASIO_CHECK(never_blocking_count == 5);
+
+  executor_type ex11 = boost::asio::prefer(ex7, execution::blocking.possibly);
+
+  execution::execute(ex11, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 6);
+  BOOST_ASIO_CHECK(never_blocking_count == 5);
+
+  executor_type ex12 = boost::asio::prefer(ex7, execution::blocking.never);
+
+  execution::execute(ex12, &do_nothing);
+  BOOST_ASIO_CHECK(possibly_blocking_count == 6);
+  BOOST_ASIO_CHECK(never_blocking_count == 6);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "prefer_only",
+  BOOST_ASIO_TEST_CASE(prefer_only_executor_query_test)
+  BOOST_ASIO_TEST_CASE(prefer_only_executor_execute_test)
+)
diff --git a/test/execution/relationship.cpp b/test/execution/relationship.cpp
new file mode 100644
index 00000000..109a96d9
--- /dev/null
+++ b/test/execution/relationship.cpp
@@ -0,0 +1,1272 @@
+//
+// relationship.cpp
+// ~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/execution/relationship.hpp>
+
+#include <boost/asio/prefer.hpp>
+#include <boost/asio/query.hpp>
+#include <boost/asio/require.hpp>
+#include "../unit_test.hpp"
+
+namespace exec = boost::asio::execution;
+
+typedef exec::relationship_t s;
+typedef exec::relationship_t::fork_t n1;
+typedef exec::relationship_t::continuation_t n2;
+
+struct ex_nq_nr
+{
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_nq_nr&, const ex_nq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <>
+struct is_executor<ex_nq_nr> : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_cq_nr
+{
+  static BOOST_ASIO_CONSTEXPR ResultType query(ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_cq_nr&, const ex_cq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_cq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_static_constexpr_member<
+  ex_cq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef Result result_type; // Must return raw result type.
+
+  static BOOST_ASIO_CONSTEXPR result_type value()
+  {
+    return Result();
+  }
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_mq_nr
+{
+  ResultType query(ParamType) const BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_nr&, const ex_mq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_mq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_member<
+  ex_mq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename ResultType, typename ParamType, typename Result>
+struct ex_fq_nr
+{
+  friend ResultType query(const ex_fq_nr&, ParamType) BOOST_ASIO_NOEXCEPT
+  {
+    return Result();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_nr&, const ex_fq_nr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename ResultType, typename ParamType, typename Result>
+struct is_executor<ex_fq_nr<ResultType, ParamType, Result> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename ResultType, typename ParamType,
+  typename Result, typename Param>
+struct query_free<
+  ex_fq_nr<ResultType, ParamType, Result>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, ParamType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ResultType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_mq_mr
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  CurrentType query(OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, OtherType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, OtherType>();
+  }
+
+  ex_mq_mr<OtherType, CurrentType> require(
+      OtherType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_mq_mr<CurrentType, CurrentType>
+{
+  CurrentType query(CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  ex_mq_mr<CurrentType, CurrentType> require(
+      CurrentType) const BOOST_ASIO_NOEXCEPT
+  {
+    return ex_mq_mr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_mq_mr&, const ex_mq_mr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_mq_mr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_member<
+  ex_mq_mr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_mq_mr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename CurrentType, typename OtherType>
+struct ex_fq_fr
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend CurrentType query(const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> require(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, OtherType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, OtherType>();
+  }
+
+  friend ex_fq_fr<OtherType, CurrentType> prefer(
+      const ex_fq_fr&, OtherType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<OtherType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+template <typename CurrentType>
+struct ex_fq_fr<CurrentType, CurrentType>
+{
+  friend CurrentType query(const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return CurrentType();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> require(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  friend ex_fq_fr<CurrentType, CurrentType> prefer(
+      const ex_fq_fr&, CurrentType) BOOST_ASIO_NOEXCEPT
+  {
+    return ex_fq_fr<CurrentType, CurrentType>();
+  }
+
+  template <typename F>
+  void execute(const F&) const
+  {
+  }
+
+  friend bool operator==(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return true;
+  }
+
+  friend bool operator!=(const ex_fq_fr&, const ex_fq_fr&) BOOST_ASIO_NOEXCEPT
+  {
+    return false;
+  }
+};
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace execution {
+
+template <typename CurrentType, typename OtherType>
+struct is_executor<ex_fq_fr<CurrentType, OtherType> >
+  : boost::asio::true_type
+{
+};
+
+} // namespace execution
+} // namespace asio
+} // namespace boost
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT)
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct query_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+      || boost::asio::is_convertible<Param, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef CurrentType result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct require_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_FREE_TRAIT)
+
+#if !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, CurrentType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<CurrentType, OtherType> result_type;
+};
+
+template <typename CurrentType, typename OtherType, typename Param>
+struct prefer_free<
+  ex_fq_fr<CurrentType, OtherType>, Param,
+  typename boost::asio::enable_if<
+    boost::asio::is_convertible<Param, OtherType>::value
+      && !boost::asio::is_same<CurrentType, OtherType>::value
+  >::type>
+{
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef ex_fq_fr<OtherType, CurrentType> result_type;
+};
+
+#endif // !defined(BOOST_ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_query()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_query<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_query<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_query<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_query<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_query()
+{
+  exec::relationship_t result1 = boost::asio::query(Executor(), Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+
+  Executor ex1 = {};
+  exec::relationship_t result2 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result2 == ExpectedResult());
+
+  const Executor ex2 = {};
+  exec::relationship_t result3 = boost::asio::query(ex2, Param());
+  BOOST_ASIO_CHECK(result3 == ExpectedResult());
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_constexpr_query()
+{
+#if defined(BOOST_ASIO_HAS_CONSTEXPR)
+  constexpr Executor ex1 = {};
+  constexpr exec::relationship_t result1 = boost::asio::query(ex1, Param());
+  BOOST_ASIO_CHECK(result1 == ExpectedResult());
+#endif // defined(BOOST_ASIO_HAS_CONSTEXPR)
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_require()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_require<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_require<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_require<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_require<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_require()
+{
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(Executor(), Param()),
+        Param()) == ExpectedResult());
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex1, Param()),
+        Param()) == ExpectedResult());
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      boost::asio::query(
+        boost::asio::require(ex2, Param()),
+        Param()) == ExpectedResult());
+}
+
+template <typename Executor, typename Param, bool ExpectedResult>
+void test_can_prefer()
+{
+  BOOST_ASIO_CONSTEXPR bool b1 =
+    boost::asio::can_prefer<Executor, Param>::value;
+  BOOST_ASIO_CHECK(b1 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b2 =
+    boost::asio::can_prefer<const Executor, Param>::value;
+  BOOST_ASIO_CHECK(b2 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b3 =
+    boost::asio::can_prefer<Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b3 == ExpectedResult);
+
+  BOOST_ASIO_CONSTEXPR bool b4 =
+    boost::asio::can_prefer<const Executor&, Param>::value;
+  BOOST_ASIO_CHECK(b4 == ExpectedResult);
+}
+
+template <typename Executor, typename Param, typename ExpectedResult>
+void test_prefer()
+{
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(Executor(), Param()),
+          s())) == s(ExpectedResult()));
+
+  Executor ex1 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex1, Param()),
+          s())) == s(ExpectedResult()));
+
+  const Executor ex2 = {};
+  BOOST_ASIO_CHECK(
+      s(boost::asio::query(
+        boost::asio::prefer(ex2, Param()),
+          s())) == s(ExpectedResult()));
+}
+
+void test_vars()
+{
+  BOOST_ASIO_CHECK(s() == exec::relationship);
+  BOOST_ASIO_CHECK(n1() == exec::relationship.fork);
+  BOOST_ASIO_CHECK(n2() == exec::relationship.continuation);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "relationship",
+
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, s, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_query<ex_nq_nr, n2, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, s, n1>)
+  BOOST_ASIO_TEST_CASE3(test_constexpr_query<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_require<ex_nq_nr, n2, false>)
+
+  BOOST_ASIO_TEST_CASE3(test_require<ex_nq_nr, n1, n1>)
+
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, s, false>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n1, true>)
+  BOOST_ASIO_TEST_CASE3(test_can_prefer<ex_nq_nr, n2, true>)
+
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n1, n1>)
+  BOOST_ASIO_TEST_CASE3(test_prefer<ex_nq_nr, n2, n1>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_constexpr_query<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_require<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_cq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_cq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_mq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_mq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_mq_nr<n2, s, n2>, n2, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_mq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_mq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_query<ex_fq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_query<ex_fq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, s, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n1, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<s, n2, n2>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n1, s, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_require<ex_fq_nr<n2, s, n2>, n2, false>)
+
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, s, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<s, n2, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n1, s, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE5(test_can_prefer<ex_fq_nr<n2, s, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, s, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<s, n2, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n1, s, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE5(test_prefer<ex_fq_nr<n2, s, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_mq_mr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_mq_mr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, s, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_query<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, s, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, s, n2>)
+  BOOST_ASIO_TEST_CASE4(test_query<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n1>, n2, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n1, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_require<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_require<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n1, n2>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n1>, n2, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, s, false>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n1, true>)
+  BOOST_ASIO_TEST_CASE4(test_can_prefer<ex_fq_fr<n2, n2>, n2, true>)
+
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n1>, n2, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n1, n2>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n1, n1>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n1>, n2, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n1, n2>)
+  BOOST_ASIO_TEST_CASE4(test_prefer<ex_fq_fr<n2, n2>, n2, n2>)
+
+  BOOST_ASIO_TEST_CASE(test_vars)
+)
diff --git a/test/io_context.cpp b/test/io_context.cpp
index 7b2ff982..83f8b6a8 100644
--- a/test/io_context.cpp
+++ b/test/io_context.cpp
@@ -354,9 +354,232 @@ void io_context_service_test()
   BOOST_ASIO_CHECK(!boost::asio::has_service<test_service>(ioc3));
 }
 
+void io_context_executor_query_test()
+{
+  io_context ioc;
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::context)
+      == &ioc);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::blocking)
+      == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::blocking.possibly)
+      == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::outstanding_work)
+      == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::outstanding_work.untracked)
+      == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::relationship)
+      == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::relationship.fork)
+      == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::mapping)
+      == boost::asio::execution::mapping.thread);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(ioc.get_executor(),
+        boost::asio::execution::allocator)
+      == std::allocator<void>());
+}
+
+void io_context_executor_execute_test()
+{
+  io_context ioc;
+  int count = 0;
+
+  boost::asio::execution::execute(ioc.get_executor(),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(ioc.get_executor(),
+        boost::asio::execution::blocking.possibly),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(ioc.get_executor(),
+        boost::asio::execution::blocking.never),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  BOOST_ASIO_CHECK(!ioc.stopped());
+
+  boost::asio::execution::execute(
+      boost::asio::require(ioc.get_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.tracked),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(ioc.get_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(ioc.get_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.fork),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(ioc.get_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.continuation),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(ioc.get_executor(),
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator(std::allocator<void>())),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(ioc.get_executor(),
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+}
+
 BOOST_ASIO_TEST_SUITE
 (
   "io_context",
   BOOST_ASIO_TEST_CASE(io_context_test)
   BOOST_ASIO_TEST_CASE(io_context_service_test)
+  BOOST_ASIO_TEST_CASE(io_context_executor_query_test)
+  BOOST_ASIO_TEST_CASE(io_context_executor_execute_test)
 )
diff --git a/test/properties/cpp03/Jamfile.v2 b/test/properties/cpp03/Jamfile.v2
new file mode 100644
index 00000000..f2264864
--- /dev/null
+++ b/test/properties/cpp03/Jamfile.v2
@@ -0,0 +1,101 @@
+#
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+
+import feature ;
+
+lib socket ; # SOLARIS, QNXNTO
+lib nsl ; # SOLARIS
+lib ws2_32 ; # NT
+lib mswsock ; # NT
+lib ipv6 ; # HPUX
+lib network ; # HAIKU
+
+project
+  : requirements
+    <library>/boost/date_time//boost_date_time
+    <library>/boost/system//boost_system
+    <library>/boost/chrono//boost_chrono
+    <library>/boost/regex//boost_regex
+    <define>BOOST_ALL_NO_LIB=1
+    <threading>multi
+    <target-os>linux:<define>_XOPEN_SOURCE=600
+    <target-os>linux:<define>_GNU_SOURCE=1
+    <target-os>solaris:<define>_XOPEN_SOURCE=500
+    <target-os>solaris:<define>__EXTENSIONS__
+    <target-os>solaris:<library>socket
+    <target-os>solaris:<library>nsl
+    <target-os>windows:<define>_WIN32_WINNT=0x0501
+    <target-os>windows,<toolset>cw:<library>ws2_32
+    <target-os>windows,<toolset>cw:<library>mswsock
+    <target-os>windows,<toolset>gcc:<library>ws2_32
+    <target-os>windows,<toolset>gcc:<library>mswsock
+    <target-os>windows,<toolset>gcc-cygwin:<define>__USE_W32_SOCKETS
+    <target-os>hpux,<toolset>gcc:<define>_XOPEN_SOURCE_EXTENDED
+    <target-os>hpux:<library>ipv6
+    <target-os>qnxnto:<library>socket
+    <target-os>haiku:<library>network
+  ;
+
+test-suite "asio" :
+  [ run can_prefer_free_prefer.cpp ]
+  [ run can_prefer_free_require.cpp ]
+  [ run can_prefer_member_prefer.cpp ]
+  [ run can_prefer_member_require.cpp ]
+  [ run can_prefer_not_applicable_free_prefer.cpp ]
+  [ run can_prefer_not_applicable_free_require.cpp ]
+  [ run can_prefer_not_applicable_member_prefer.cpp ]
+  [ run can_prefer_not_applicable_member_require.cpp ]
+  [ run can_prefer_not_applicable_static.cpp ]
+  [ run can_prefer_not_applicable_unsupported.cpp ]
+  [ run can_prefer_not_preferable_free_prefer.cpp ]
+  [ run can_prefer_not_preferable_free_require.cpp ]
+  [ run can_prefer_not_preferable_member_prefer.cpp ]
+  [ run can_prefer_not_preferable_member_require.cpp ]
+  [ run can_prefer_not_preferable_static.cpp ]
+  [ run can_prefer_not_preferable_unsupported.cpp ]
+  [ run can_prefer_static.cpp ]
+  [ run can_prefer_unsupported.cpp ]
+  [ run can_query_free.cpp ]
+  [ run can_query_member.cpp ]
+  [ run can_query_not_applicable_free.cpp ]
+  [ run can_query_not_applicable_member.cpp ]
+  [ run can_query_not_applicable_static.cpp ]
+  [ run can_query_not_applicable_unsupported.cpp ]
+  [ run can_query_static.cpp ]
+  [ run can_query_unsupported.cpp ]
+  [ run can_require_concept_free.cpp ]
+  [ run can_require_concept_member.cpp ]
+  [ run can_require_concept_not_applicable_free.cpp ]
+  [ run can_require_concept_not_applicable_member.cpp ]
+  [ run can_require_concept_not_applicable_static.cpp ]
+  [ run can_require_concept_not_applicable_unsupported.cpp ]
+  [ run can_require_concept_static.cpp ]
+  [ run can_require_concept_unsupported.cpp ]
+  [ run can_require_free.cpp ]
+  [ run can_require_member.cpp ]
+  [ run can_require_not_applicable_free.cpp ]
+  [ run can_require_not_applicable_member.cpp ]
+  [ run can_require_not_applicable_static.cpp ]
+  [ run can_require_not_applicable_unsupported.cpp ]
+  [ run can_require_static.cpp ]
+  [ run can_require_unsupported.cpp ]
+  [ run prefer_free_prefer.cpp ]
+  [ run prefer_free_require.cpp ]
+  [ run prefer_member_prefer.cpp ]
+  [ run prefer_member_require.cpp ]
+  [ run prefer_static.cpp ]
+  [ run prefer_unsupported.cpp ]
+  [ run query_free.cpp ]
+  [ run query_member.cpp ]
+  [ run query_static.cpp ]
+  [ run require_concept_free.cpp ]
+  [ run require_concept_member.cpp ]
+  [ run require_concept_static.cpp ]
+  [ run require_free.cpp ]
+  [ run require_member.cpp ]
+  [ run require_static.cpp ]
+  ;
diff --git a/test/properties/cpp03/can_prefer_free_prefer.cpp b/test/properties/cpp03/can_prefer_free_prefer.cpp
new file mode 100644
index 00000000..b2f3de93
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_free_prefer.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct prefer_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_free_require.cpp b/test/properties/cpp03/can_prefer_free_require.cpp
new file mode 100644
index 00000000..0afc5b7c
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_free_require.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_member_prefer.cpp b/test/properties/cpp03/can_prefer_member_prefer.cpp
new file mode 100644
index 00000000..86ea5844
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_member_prefer.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct prefer_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_member_require.cpp b/test/properties/cpp03/can_prefer_member_require.cpp
new file mode 100644
index 00000000..ebc4230d
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_member_require.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_applicable_free_prefer.cpp b/test/properties/cpp03/can_prefer_not_applicable_free_prefer.cpp
new file mode 100644
index 00000000..9a090f68
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_applicable_free_prefer.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_prefer_not_applicable_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct prefer_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_applicable_free_require.cpp b/test/properties/cpp03/can_prefer_not_applicable_free_require.cpp
new file mode 100644
index 00000000..d996a685
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_applicable_free_require.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_prefer_not_applicable_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_applicable_member_prefer.cpp b/test/properties/cpp03/can_prefer_not_applicable_member_prefer.cpp
new file mode 100644
index 00000000..9ec96df2
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_applicable_member_prefer.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_prefer_not_applicable_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct prefer_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_applicable_member_require.cpp b/test/properties/cpp03/can_prefer_not_applicable_member_require.cpp
new file mode 100644
index 00000000..ab83a293
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_applicable_member_require.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_prefer_not_applicable_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_applicable_static.cpp b/test/properties/cpp03/can_prefer_not_applicable_static.cpp
new file mode 100644
index 00000000..039bf6bb
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_applicable_static.cpp
@@ -0,0 +1,47 @@
+//
+// cpp03/can_prefer_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<1>, prop<1>, prop<1> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_applicable_unsupported.cpp b/test/properties/cpp03/can_prefer_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..8e8b4697
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_applicable_unsupported.cpp
@@ -0,0 +1,33 @@
+//
+// cpp03/can_prefer_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_preferable_free_prefer.cpp b/test/properties/cpp03/can_prefer_not_preferable_free_prefer.cpp
new file mode 100644
index 00000000..87a1df41
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_preferable_free_prefer.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_not_preferable_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct prefer_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_preferable_free_require.cpp b/test/properties/cpp03/can_prefer_not_preferable_free_require.cpp
new file mode 100644
index 00000000..722ff36e
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_preferable_free_require.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_not_preferable_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_preferable_member_prefer.cpp b/test/properties/cpp03/can_prefer_not_preferable_member_prefer.cpp
new file mode 100644
index 00000000..a3fd6378
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_preferable_member_prefer.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_not_preferable_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct prefer_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_preferable_member_require.cpp b/test/properties/cpp03/can_prefer_not_preferable_member_require.cpp
new file mode 100644
index 00000000..660baead
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_preferable_member_require.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_prefer_not_preferable_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_preferable_static.cpp b/test/properties/cpp03/can_prefer_not_preferable_static.cpp
new file mode 100644
index 00000000..fa886e4b
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_preferable_static.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_prefer_not_preferable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<1>, prop<1>, prop<1> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_not_preferable_unsupported.cpp b/test/properties/cpp03/can_prefer_not_preferable_unsupported.cpp
new file mode 100644
index 00000000..a1dd3cdb
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_not_preferable_unsupported.cpp
@@ -0,0 +1,45 @@
+//
+// cpp03/can_prefer_not_preferable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_static.cpp b/test/properties/cpp03/can_prefer_static.cpp
new file mode 100644
index 00000000..da0b5f8e
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_static.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_prefer_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_prefer<object<1>, prop<1> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<1>, prop<1> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<1>, prop<1>, prop<1> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<1> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<1>, prop<1> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<1>, prop<1>, prop<1> >::value));
+}
diff --git a/test/properties/cpp03/can_prefer_unsupported.cpp b/test/properties/cpp03/can_prefer_unsupported.cpp
new file mode 100644
index 00000000..3006539a
--- /dev/null
+++ b/test/properties/cpp03/can_prefer_unsupported.cpp
@@ -0,0 +1,45 @@
+//
+// cpp03/can_prefer_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_prefer<object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_query_free.cpp b/test/properties/cpp03/can_query_free.cpp
new file mode 100644
index 00000000..d641d8f7
--- /dev/null
+++ b/test/properties/cpp03/can_query_free.cpp
@@ -0,0 +1,50 @@
+//
+// cpp03/can_query_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend int query(const object&, prop) { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct query_free<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_query<object, prop>::value));
+  assert((boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_member.cpp b/test/properties/cpp03/can_query_member.cpp
new file mode 100644
index 00000000..3dd67cc9
--- /dev/null
+++ b/test/properties/cpp03/can_query_member.cpp
@@ -0,0 +1,50 @@
+//
+// cpp03/can_query_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  int query(prop) const { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct query_member<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_query<object, prop>::value));
+  assert((boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_not_applicable_free.cpp b/test/properties/cpp03/can_query_not_applicable_free.cpp
new file mode 100644
index 00000000..7a9f68c8
--- /dev/null
+++ b/test/properties/cpp03/can_query_not_applicable_free.cpp
@@ -0,0 +1,43 @@
+//
+// cpp03/can_query_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend int query(const object&, prop) { return 123; }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<>
+struct query_free<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_query<object, prop>::value));
+  assert((!boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_not_applicable_member.cpp b/test/properties/cpp03/can_query_not_applicable_member.cpp
new file mode 100644
index 00000000..ab70b5f0
--- /dev/null
+++ b/test/properties/cpp03/can_query_not_applicable_member.cpp
@@ -0,0 +1,43 @@
+//
+// cpp03/can_query_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  int query(prop) const { return 123; }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<>
+struct query_member<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_query<object, prop>::value));
+  assert((!boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_not_applicable_static.cpp b/test/properties/cpp03/can_query_not_applicable_static.cpp
new file mode 100644
index 00000000..2d6f0a3f
--- /dev/null
+++ b/test/properties/cpp03/can_query_not_applicable_static.cpp
@@ -0,0 +1,43 @@
+//
+// cpp03/can_query_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<>
+struct static_query<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+  static int value() { return 123; }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_query<object, prop>::value));
+  assert((!boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_not_applicable_unsupported.cpp b/test/properties/cpp03/can_query_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..61158b43
--- /dev/null
+++ b/test/properties/cpp03/can_query_not_applicable_unsupported.cpp
@@ -0,0 +1,26 @@
+//
+// cpp03/can_query_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+int main()
+{
+  assert((!boost::asio::can_query<object, prop>::value));
+  assert((!boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_static.cpp b/test/properties/cpp03/can_query_static.cpp
new file mode 100644
index 00000000..a48384ef
--- /dev/null
+++ b/test/properties/cpp03/can_query_static.cpp
@@ -0,0 +1,50 @@
+//
+// cpp03/can_query_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct static_query<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+  static int value() { return 123; }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_query<object, prop>::value));
+  assert((boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_query_unsupported.cpp b/test/properties/cpp03/can_query_unsupported.cpp
new file mode 100644
index 00000000..1d3c9257
--- /dev/null
+++ b/test/properties/cpp03/can_query_unsupported.cpp
@@ -0,0 +1,38 @@
+//
+// cpp03/can_query_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template <>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_query<object, prop>::value));
+  assert((!boost::asio::can_query<const object, prop>::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_free.cpp b/test/properties/cpp03/can_require_concept_free.cpp
new file mode 100644
index 00000000..b356a371
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_free.cpp
@@ -0,0 +1,57 @@
+//
+// cpp03/can_require_concept_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_concept_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_member.cpp b/test/properties/cpp03/can_require_concept_member.cpp
new file mode 100644
index 00000000..8f54ce2e
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_member.cpp
@@ -0,0 +1,57 @@
+//
+// cpp03/can_require_concept_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_concept_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_not_applicable_free.cpp b/test/properties/cpp03/can_require_concept_not_applicable_free.cpp
new file mode 100644
index 00000000..fdd76b9e
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_not_applicable_free.cpp
@@ -0,0 +1,50 @@
+//
+// cpp03/can_require_concept_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct require_concept_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_not_applicable_member.cpp b/test/properties/cpp03/can_require_concept_not_applicable_member.cpp
new file mode 100644
index 00000000..caf3c6e2
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_not_applicable_member.cpp
@@ -0,0 +1,50 @@
+//
+// cpp03/can_require_concept_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct require_concept_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_not_applicable_static.cpp b/test/properties/cpp03/can_require_concept_not_applicable_static.cpp
new file mode 100644
index 00000000..5340a633
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_not_applicable_static.cpp
@@ -0,0 +1,43 @@
+//
+// cpp03/can_require_concept_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N>
+struct static_require_concept<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_not_applicable_unsupported.cpp b/test/properties/cpp03/can_require_concept_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..f318d38c
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_not_applicable_unsupported.cpp
@@ -0,0 +1,28 @@
+//
+// cpp03/can_require_concept_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  assert((!boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_static.cpp b/test/properties/cpp03/can_require_concept_static.cpp
new file mode 100644
index 00000000..f34187bd
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_static.cpp
@@ -0,0 +1,50 @@
+//
+// cpp03/can_require_concept_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require_concept<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_require_concept<object<1>, prop<1> >::value));
+  assert((boost::asio::can_require_concept<const object<1>, prop<1> >::value));
+}
diff --git a/test/properties/cpp03/can_require_concept_unsupported.cpp b/test/properties/cpp03/can_require_concept_unsupported.cpp
new file mode 100644
index 00000000..1b176189
--- /dev/null
+++ b/test/properties/cpp03/can_require_concept_unsupported.cpp
@@ -0,0 +1,40 @@
+//
+// cpp03/can_require_concept_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require_concept<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require_concept<const object<1>, prop<2> >::value));
+}
diff --git a/test/properties/cpp03/can_require_free.cpp b/test/properties/cpp03/can_require_free.cpp
new file mode 100644
index 00000000..a438ccf8
--- /dev/null
+++ b/test/properties/cpp03/can_require_free.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_require_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_require<object<1>, prop<2> >::value));
+  assert((boost::asio::can_require<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_require_member.cpp b/test/properties/cpp03/can_require_member.cpp
new file mode 100644
index 00000000..64ebe40c
--- /dev/null
+++ b/test/properties/cpp03/can_require_member.cpp
@@ -0,0 +1,61 @@
+//
+// cpp03/can_require_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_require<object<1>, prop<2> >::value));
+  assert((boost::asio::can_require<object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<2> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<2>, prop<3> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_require_not_applicable_free.cpp b/test/properties/cpp03/can_require_not_applicable_free.cpp
new file mode 100644
index 00000000..0ad767c9
--- /dev/null
+++ b/test/properties/cpp03/can_require_not_applicable_free.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_require_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_require_not_applicable_member.cpp b/test/properties/cpp03/can_require_not_applicable_member.cpp
new file mode 100644
index 00000000..6d697e42
--- /dev/null
+++ b/test/properties/cpp03/can_require_not_applicable_member.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_require_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_require_not_applicable_static.cpp b/test/properties/cpp03/can_require_not_applicable_static.cpp
new file mode 100644
index 00000000..13db94d8
--- /dev/null
+++ b/test/properties/cpp03/can_require_not_applicable_static.cpp
@@ -0,0 +1,47 @@
+//
+// cpp03/can_require_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require<object<1>, prop<1> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<1> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<1>, prop<1> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<1>, prop<1>, prop<1> >::value));
+}
diff --git a/test/properties/cpp03/can_require_not_applicable_unsupported.cpp b/test/properties/cpp03/can_require_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..d5de3fc3
--- /dev/null
+++ b/test/properties/cpp03/can_require_not_applicable_unsupported.cpp
@@ -0,0 +1,32 @@
+//
+// cpp03/can_require_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  assert((!boost::asio::can_require<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/can_require_static.cpp b/test/properties/cpp03/can_require_static.cpp
new file mode 100644
index 00000000..fb7d1781
--- /dev/null
+++ b/test/properties/cpp03/can_require_static.cpp
@@ -0,0 +1,54 @@
+//
+// cpp03/can_require_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((boost::asio::can_require<object<1>, prop<1> >::value));
+  assert((boost::asio::can_require<object<1>, prop<1>, prop<1> >::value));
+  assert((boost::asio::can_require<object<1>, prop<1>, prop<1>, prop<1> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<1> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<1>, prop<1> >::value));
+  assert((boost::asio::can_require<const object<1>, prop<1>, prop<1>, prop<1> >::value));
+}
diff --git a/test/properties/cpp03/can_require_unsupported.cpp b/test/properties/cpp03/can_require_unsupported.cpp
new file mode 100644
index 00000000..38f6a977
--- /dev/null
+++ b/test/properties/cpp03/can_require_unsupported.cpp
@@ -0,0 +1,44 @@
+//
+// cpp03/can_require_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  assert((!boost::asio::can_require<object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3> >::value));
+  assert((!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4> >::value));
+}
diff --git a/test/properties/cpp03/prefer_free_prefer.cpp b/test/properties/cpp03/prefer_free_prefer.cpp
new file mode 100644
index 00000000..0e189792
--- /dev/null
+++ b/test/properties/cpp03/prefer_free_prefer.cpp
@@ -0,0 +1,70 @@
+//
+// cpp03/prefer_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct prefer_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/prefer_free_require.cpp b/test/properties/cpp03/prefer_free_require.cpp
new file mode 100644
index 00000000..0c0a4d48
--- /dev/null
+++ b/test/properties/cpp03/prefer_free_require.cpp
@@ -0,0 +1,70 @@
+//
+// cpp03/prefer_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/prefer_member_prefer.cpp b/test/properties/cpp03/prefer_member_prefer.cpp
new file mode 100644
index 00000000..4892bcd6
--- /dev/null
+++ b/test/properties/cpp03/prefer_member_prefer.cpp
@@ -0,0 +1,70 @@
+//
+// cpp03/prefer_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct prefer_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/prefer_member_require.cpp b/test/properties/cpp03/prefer_member_require.cpp
new file mode 100644
index 00000000..7d623ce8
--- /dev/null
+++ b/test/properties/cpp03/prefer_member_require.cpp
@@ -0,0 +1,70 @@
+//
+// cpp03/prefer_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/prefer_static.cpp b/test/properties/cpp03/prefer_static.cpp
new file mode 100644
index 00000000..a3cb6ef2
--- /dev/null
+++ b/test/properties/cpp03/prefer_static.cpp
@@ -0,0 +1,63 @@
+//
+// cpp03/prefer_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::prefer(o1, prop<1>());
+  object<1> o3 = boost::asio::prefer(o1, prop<1>(), prop<1>());
+  object<1> o4 = boost::asio::prefer(o1, prop<1>(), prop<1>(), prop<1>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::prefer(o5, prop<1>());
+  object<1> o7 = boost::asio::prefer(o5, prop<1>(), prop<1>());
+  object<1> o8 = boost::asio::prefer(o5, prop<1>(), prop<1>(), prop<1>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/prefer_unsupported.cpp b/test/properties/cpp03/prefer_unsupported.cpp
new file mode 100644
index 00000000..2c72e7a9
--- /dev/null
+++ b/test/properties/cpp03/prefer_unsupported.cpp
@@ -0,0 +1,48 @@
+//
+// cpp03/prefer_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  const object<1>& o2 = boost::asio::prefer(o1, prop<1>());
+  assert(&o1 == &o2);
+  (void)o2;
+
+  const object<1> o3 = {};
+  const object<1>& o4 = boost::asio::prefer(o3, prop<1>());
+  assert(&o3 == &o4);
+  (void)o4;
+}
diff --git a/test/properties/cpp03/query_free.cpp b/test/properties/cpp03/query_free.cpp
new file mode 100644
index 00000000..03eb8fe5
--- /dev/null
+++ b/test/properties/cpp03/query_free.cpp
@@ -0,0 +1,57 @@
+//
+// cpp03/query_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend int query(const object&, prop) { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct query_free<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+}
diff --git a/test/properties/cpp03/query_member.cpp b/test/properties/cpp03/query_member.cpp
new file mode 100644
index 00000000..3d9e1d18
--- /dev/null
+++ b/test/properties/cpp03/query_member.cpp
@@ -0,0 +1,57 @@
+//
+// cpp03/query_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  int query(prop) const { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct query_member<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+}
diff --git a/test/properties/cpp03/query_static.cpp b/test/properties/cpp03/query_static.cpp
new file mode 100644
index 00000000..d431098f
--- /dev/null
+++ b/test/properties/cpp03/query_static.cpp
@@ -0,0 +1,57 @@
+//
+// cpp03/query_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct static_query<object, prop>
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef int result_type;
+  static int value() { return 123; }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+}
diff --git a/test/properties/cpp03/require_concept_free.cpp b/test/properties/cpp03/require_concept_free.cpp
new file mode 100644
index 00000000..3d75e71e
--- /dev/null
+++ b/test/properties/cpp03/require_concept_free.cpp
@@ -0,0 +1,62 @@
+//
+// cpp03/require_concept_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_concept_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require_concept(o1, prop<2>());
+  (void)o2;
+
+  const object<1> o3 = {};
+  object<2> o4 = boost::asio::require_concept(o3, prop<2>());
+  (void)o4;
+}
diff --git a/test/properties/cpp03/require_concept_member.cpp b/test/properties/cpp03/require_concept_member.cpp
new file mode 100644
index 00000000..e9bc424b
--- /dev/null
+++ b/test/properties/cpp03/require_concept_member.cpp
@@ -0,0 +1,62 @@
+//
+// cpp03/require_concept_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_concept_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require_concept(o1, prop<2>());
+  (void)o2;
+
+  const object<1> o3 = {};
+  object<2> o4 = boost::asio::require_concept(o3, prop<2>());
+  (void)o4;
+}
diff --git a/test/properties/cpp03/require_concept_static.cpp b/test/properties/cpp03/require_concept_static.cpp
new file mode 100644
index 00000000..b80f6724
--- /dev/null
+++ b/test/properties/cpp03/require_concept_static.cpp
@@ -0,0 +1,57 @@
+//
+// cpp03/require_concept_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require_concept<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  const object<1>& o2 = boost::asio::require_concept(o1, prop<1>());
+  assert(&o1 == &o2);
+  (void)o2;
+
+  const object<1> o3 = {};
+  const object<1>& o4 = boost::asio::require_concept(o3, prop<1>());
+  assert(&o3 == &o4);
+  (void)o4;
+}
diff --git a/test/properties/cpp03/require_free.cpp b/test/properties/cpp03/require_free.cpp
new file mode 100644
index 00000000..f97130a5
--- /dev/null
+++ b/test/properties/cpp03/require_free.cpp
@@ -0,0 +1,70 @@
+//
+// cpp03/require_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_free<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require(o1, prop<2>());
+  object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::require(o5, prop<2>());
+  object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/require_member.cpp b/test/properties/cpp03/require_member.cpp
new file mode 100644
index 00000000..fb27d27f
--- /dev/null
+++ b/test/properties/cpp03/require_member.cpp
@@ -0,0 +1,70 @@
+//
+// cpp03/require_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N, int M>
+struct require_member<object<N>, prop<M> >
+{
+  static const bool is_valid = true;
+  static const bool is_noexcept = true;
+  typedef object<M> result_type;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require(o1, prop<2>());
+  object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::require(o5, prop<2>());
+  object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp03/require_static.cpp b/test/properties/cpp03/require_static.cpp
new file mode 100644
index 00000000..54bd896b
--- /dev/null
+++ b/test/properties/cpp03/require_static.cpp
@@ -0,0 +1,63 @@
+//
+// cpp03/require_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static const bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static const bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static const bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::require(o1, prop<1>());
+  object<1> o3 = boost::asio::require(o1, prop<1>(), prop<1>());
+  object<1> o4 = boost::asio::require(o1, prop<1>(), prop<1>(), prop<1>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::require(o5, prop<1>());
+  object<1> o7 = boost::asio::require(o5, prop<1>(), prop<1>());
+  object<1> o8 = boost::asio::require(o5, prop<1>(), prop<1>(), prop<1>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+}
diff --git a/test/properties/cpp11/Jamfile.v2 b/test/properties/cpp11/Jamfile.v2
new file mode 100644
index 00000000..f2264864
--- /dev/null
+++ b/test/properties/cpp11/Jamfile.v2
@@ -0,0 +1,101 @@
+#
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+
+import feature ;
+
+lib socket ; # SOLARIS, QNXNTO
+lib nsl ; # SOLARIS
+lib ws2_32 ; # NT
+lib mswsock ; # NT
+lib ipv6 ; # HPUX
+lib network ; # HAIKU
+
+project
+  : requirements
+    <library>/boost/date_time//boost_date_time
+    <library>/boost/system//boost_system
+    <library>/boost/chrono//boost_chrono
+    <library>/boost/regex//boost_regex
+    <define>BOOST_ALL_NO_LIB=1
+    <threading>multi
+    <target-os>linux:<define>_XOPEN_SOURCE=600
+    <target-os>linux:<define>_GNU_SOURCE=1
+    <target-os>solaris:<define>_XOPEN_SOURCE=500
+    <target-os>solaris:<define>__EXTENSIONS__
+    <target-os>solaris:<library>socket
+    <target-os>solaris:<library>nsl
+    <target-os>windows:<define>_WIN32_WINNT=0x0501
+    <target-os>windows,<toolset>cw:<library>ws2_32
+    <target-os>windows,<toolset>cw:<library>mswsock
+    <target-os>windows,<toolset>gcc:<library>ws2_32
+    <target-os>windows,<toolset>gcc:<library>mswsock
+    <target-os>windows,<toolset>gcc-cygwin:<define>__USE_W32_SOCKETS
+    <target-os>hpux,<toolset>gcc:<define>_XOPEN_SOURCE_EXTENDED
+    <target-os>hpux:<library>ipv6
+    <target-os>qnxnto:<library>socket
+    <target-os>haiku:<library>network
+  ;
+
+test-suite "asio" :
+  [ run can_prefer_free_prefer.cpp ]
+  [ run can_prefer_free_require.cpp ]
+  [ run can_prefer_member_prefer.cpp ]
+  [ run can_prefer_member_require.cpp ]
+  [ run can_prefer_not_applicable_free_prefer.cpp ]
+  [ run can_prefer_not_applicable_free_require.cpp ]
+  [ run can_prefer_not_applicable_member_prefer.cpp ]
+  [ run can_prefer_not_applicable_member_require.cpp ]
+  [ run can_prefer_not_applicable_static.cpp ]
+  [ run can_prefer_not_applicable_unsupported.cpp ]
+  [ run can_prefer_not_preferable_free_prefer.cpp ]
+  [ run can_prefer_not_preferable_free_require.cpp ]
+  [ run can_prefer_not_preferable_member_prefer.cpp ]
+  [ run can_prefer_not_preferable_member_require.cpp ]
+  [ run can_prefer_not_preferable_static.cpp ]
+  [ run can_prefer_not_preferable_unsupported.cpp ]
+  [ run can_prefer_static.cpp ]
+  [ run can_prefer_unsupported.cpp ]
+  [ run can_query_free.cpp ]
+  [ run can_query_member.cpp ]
+  [ run can_query_not_applicable_free.cpp ]
+  [ run can_query_not_applicable_member.cpp ]
+  [ run can_query_not_applicable_static.cpp ]
+  [ run can_query_not_applicable_unsupported.cpp ]
+  [ run can_query_static.cpp ]
+  [ run can_query_unsupported.cpp ]
+  [ run can_require_concept_free.cpp ]
+  [ run can_require_concept_member.cpp ]
+  [ run can_require_concept_not_applicable_free.cpp ]
+  [ run can_require_concept_not_applicable_member.cpp ]
+  [ run can_require_concept_not_applicable_static.cpp ]
+  [ run can_require_concept_not_applicable_unsupported.cpp ]
+  [ run can_require_concept_static.cpp ]
+  [ run can_require_concept_unsupported.cpp ]
+  [ run can_require_free.cpp ]
+  [ run can_require_member.cpp ]
+  [ run can_require_not_applicable_free.cpp ]
+  [ run can_require_not_applicable_member.cpp ]
+  [ run can_require_not_applicable_static.cpp ]
+  [ run can_require_not_applicable_unsupported.cpp ]
+  [ run can_require_static.cpp ]
+  [ run can_require_unsupported.cpp ]
+  [ run prefer_free_prefer.cpp ]
+  [ run prefer_free_require.cpp ]
+  [ run prefer_member_prefer.cpp ]
+  [ run prefer_member_require.cpp ]
+  [ run prefer_static.cpp ]
+  [ run prefer_unsupported.cpp ]
+  [ run query_free.cpp ]
+  [ run query_member.cpp ]
+  [ run query_static.cpp ]
+  [ run require_concept_free.cpp ]
+  [ run require_concept_member.cpp ]
+  [ run require_concept_static.cpp ]
+  [ run require_free.cpp ]
+  [ run require_member.cpp ]
+  [ run require_static.cpp ]
+  ;
diff --git a/test/properties/cpp11/can_prefer_free_prefer.cpp b/test/properties/cpp11/can_prefer_free_prefer.cpp
new file mode 100644
index 00000000..25b5faa5
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_free_prefer.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_free_require.cpp b/test/properties/cpp11/can_prefer_free_require.cpp
new file mode 100644
index 00000000..beceeaa0
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_free_require.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_member_prefer.cpp b/test/properties/cpp11/can_prefer_member_prefer.cpp
new file mode 100644
index 00000000..577da655
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_member_prefer.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_member_require.cpp b/test/properties/cpp11/can_prefer_member_require.cpp
new file mode 100644
index 00000000..94b70b09
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_member_require.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_applicable_free_prefer.cpp b/test/properties/cpp11/can_prefer_not_applicable_free_prefer.cpp
new file mode 100644
index 00000000..85a70b1f
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_applicable_free_prefer.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_prefer_not_applicable_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_applicable_free_require.cpp b/test/properties/cpp11/can_prefer_not_applicable_free_require.cpp
new file mode 100644
index 00000000..91e39100
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_applicable_free_require.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_prefer_not_applicable_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_applicable_member_prefer.cpp b/test/properties/cpp11/can_prefer_not_applicable_member_prefer.cpp
new file mode 100644
index 00000000..2f7b4c80
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_applicable_member_prefer.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_prefer_not_applicable_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_applicable_member_require.cpp b/test/properties/cpp11/can_prefer_not_applicable_member_require.cpp
new file mode 100644
index 00000000..a002e5d0
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_applicable_member_require.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_prefer_not_applicable_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_applicable_static.cpp b/test/properties/cpp11/can_prefer_not_applicable_static.cpp
new file mode 100644
index 00000000..a79303d7
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_applicable_static.cpp
@@ -0,0 +1,47 @@
+//
+// cpp11/can_prefer_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_applicable_unsupported.cpp b/test/properties/cpp11/can_prefer_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..01737c1d
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_applicable_unsupported.cpp
@@ -0,0 +1,33 @@
+//
+// cpp11/can_prefer_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_preferable_free_prefer.cpp b/test/properties/cpp11/can_prefer_not_preferable_free_prefer.cpp
new file mode 100644
index 00000000..e763b246
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_preferable_free_prefer.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_not_preferable_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_preferable_free_require.cpp b/test/properties/cpp11/can_prefer_not_preferable_free_require.cpp
new file mode 100644
index 00000000..e019cf6c
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_preferable_free_require.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_not_preferable_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_preferable_member_prefer.cpp b/test/properties/cpp11/can_prefer_not_preferable_member_prefer.cpp
new file mode 100644
index 00000000..14e3c248
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_preferable_member_prefer.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_not_preferable_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_preferable_member_require.cpp b/test/properties/cpp11/can_prefer_not_preferable_member_require.cpp
new file mode 100644
index 00000000..a0c1af1a
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_preferable_member_require.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_prefer_not_preferable_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_preferable_static.cpp b/test/properties/cpp11/can_prefer_not_preferable_static.cpp
new file mode 100644
index 00000000..4291e8e3
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_preferable_static.cpp
@@ -0,0 +1,45 @@
+//
+// cpp11/can_prefer_not_preferable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_not_preferable_unsupported.cpp b/test/properties/cpp11/can_prefer_not_preferable_unsupported.cpp
new file mode 100644
index 00000000..45e624ab
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_not_preferable_unsupported.cpp
@@ -0,0 +1,45 @@
+//
+// cpp11/can_prefer_not_preferable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_static.cpp b/test/properties/cpp11/can_prefer_static.cpp
new file mode 100644
index 00000000..a17290f7
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_static.cpp
@@ -0,0 +1,54 @@
+//
+// cpp11/can_prefer_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_prefer<object<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+}
diff --git a/test/properties/cpp11/can_prefer_unsupported.cpp b/test/properties/cpp11/can_prefer_unsupported.cpp
new file mode 100644
index 00000000..7fb97323
--- /dev/null
+++ b/test/properties/cpp11/can_prefer_unsupported.cpp
@@ -0,0 +1,45 @@
+//
+// cpp11/can_prefer_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_free.cpp b/test/properties/cpp11/can_query_free.cpp
new file mode 100644
index 00000000..5e9411f6
--- /dev/null
+++ b/test/properties/cpp11/can_query_free.cpp
@@ -0,0 +1,39 @@
+//
+// cpp11/can_query_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend constexpr int query(const object&, prop) { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_query<object, prop>::value, "");
+  static_assert(boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_member.cpp b/test/properties/cpp11/can_query_member.cpp
new file mode 100644
index 00000000..9f530361
--- /dev/null
+++ b/test/properties/cpp11/can_query_member.cpp
@@ -0,0 +1,39 @@
+//
+// cpp11/can_query_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  constexpr int query(prop) const { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_query<object, prop>::value, "");
+  static_assert(boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_not_applicable_free.cpp b/test/properties/cpp11/can_query_not_applicable_free.cpp
new file mode 100644
index 00000000..2641bc7e
--- /dev/null
+++ b/test/properties/cpp11/can_query_not_applicable_free.cpp
@@ -0,0 +1,27 @@
+//
+// cpp11/can_query_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend constexpr int query(const object&, prop) { return 123; }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query<object, prop>::value, "");
+  static_assert(!boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_not_applicable_member.cpp b/test/properties/cpp11/can_query_not_applicable_member.cpp
new file mode 100644
index 00000000..d68af6dd
--- /dev/null
+++ b/test/properties/cpp11/can_query_not_applicable_member.cpp
@@ -0,0 +1,27 @@
+//
+// cpp11/can_query_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  constexpr int query(prop) const { return 123; }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query<object, prop>::value, "");
+  static_assert(!boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_not_applicable_static.cpp b/test/properties/cpp11/can_query_not_applicable_static.cpp
new file mode 100644
index 00000000..a45e0672
--- /dev/null
+++ b/test/properties/cpp11/can_query_not_applicable_static.cpp
@@ -0,0 +1,43 @@
+//
+// cpp11/can_query_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<>
+struct static_query<object, prop>
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef int result_type;
+  static constexpr int value() { return 123; }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_query<object, prop>::value, "");
+  static_assert(!boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_not_applicable_unsupported.cpp b/test/properties/cpp11/can_query_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..cc81dd4b
--- /dev/null
+++ b/test/properties/cpp11/can_query_not_applicable_unsupported.cpp
@@ -0,0 +1,26 @@
+//
+// cpp11/can_query_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query<object, prop>::value, "");
+  static_assert(!boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_static.cpp b/test/properties/cpp11/can_query_static.cpp
new file mode 100644
index 00000000..9502b5a7
--- /dev/null
+++ b/test/properties/cpp11/can_query_static.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_query_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct static_query<object, prop>
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef int result_type;
+  static constexpr int value() { return 123; }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_query<object, prop>::value, "");
+  static_assert(boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_query_unsupported.cpp b/test/properties/cpp11/can_query_unsupported.cpp
new file mode 100644
index 00000000..29332cc0
--- /dev/null
+++ b/test/properties/cpp11/can_query_unsupported.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_query_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_query<object, prop>::value, "");
+  static_assert(!boost::asio::can_query<const object, prop>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_free.cpp b/test/properties/cpp11/can_require_concept_free.cpp
new file mode 100644
index 00000000..8b79219d
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_free.cpp
@@ -0,0 +1,46 @@
+//
+// cpp11/can_require_concept_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_member.cpp b/test/properties/cpp11/can_require_concept_member.cpp
new file mode 100644
index 00000000..2838ae2a
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_member.cpp
@@ -0,0 +1,46 @@
+//
+// cpp11/can_require_concept_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_not_applicable_free.cpp b/test/properties/cpp11/can_require_concept_not_applicable_free.cpp
new file mode 100644
index 00000000..672d55c1
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_not_applicable_free.cpp
@@ -0,0 +1,34 @@
+//
+// cpp11/can_require_concept_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_not_applicable_member.cpp b/test/properties/cpp11/can_require_concept_not_applicable_member.cpp
new file mode 100644
index 00000000..1c80cd9d
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_not_applicable_member.cpp
@@ -0,0 +1,34 @@
+//
+// cpp11/can_require_concept_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_not_applicable_static.cpp b/test/properties/cpp11/can_require_concept_not_applicable_static.cpp
new file mode 100644
index 00000000..9d07aabc
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_not_applicable_static.cpp
@@ -0,0 +1,43 @@
+//
+// cpp11/can_require_concept_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N>
+struct static_require_concept<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_not_applicable_unsupported.cpp b/test/properties/cpp11/can_require_concept_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..ff730995
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_not_applicable_unsupported.cpp
@@ -0,0 +1,28 @@
+//
+// cpp11/can_require_concept_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_static.cpp b/test/properties/cpp11/can_require_concept_static.cpp
new file mode 100644
index 00000000..42843c57
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_static.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_require_concept_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require_concept<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_require_concept<object<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_require_concept<const object<1>, prop<1>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_concept_unsupported.cpp b/test/properties/cpp11/can_require_concept_unsupported.cpp
new file mode 100644
index 00000000..edbca6dd
--- /dev/null
+++ b/test/properties/cpp11/can_require_concept_unsupported.cpp
@@ -0,0 +1,40 @@
+//
+// cpp11/can_require_concept_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_free.cpp b/test/properties/cpp11/can_require_free.cpp
new file mode 100644
index 00000000..2c15a469
--- /dev/null
+++ b/test/properties/cpp11/can_require_free.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_require_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_require<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_require<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_member.cpp b/test/properties/cpp11/can_require_member.cpp
new file mode 100644
index 00000000..efa531a3
--- /dev/null
+++ b/test/properties/cpp11/can_require_member.cpp
@@ -0,0 +1,50 @@
+//
+// cpp11/can_require_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_require<object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_require<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<2>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_not_applicable_free.cpp b/test/properties/cpp11/can_require_not_applicable_free.cpp
new file mode 100644
index 00000000..9dee75bf
--- /dev/null
+++ b/test/properties/cpp11/can_require_not_applicable_free.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_require_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_not_applicable_member.cpp b/test/properties/cpp11/can_require_not_applicable_member.cpp
new file mode 100644
index 00000000..e05e561f
--- /dev/null
+++ b/test/properties/cpp11/can_require_not_applicable_member.cpp
@@ -0,0 +1,38 @@
+//
+// cpp11/can_require_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_not_applicable_static.cpp b/test/properties/cpp11/can_require_not_applicable_static.cpp
new file mode 100644
index 00000000..3c4dc8df
--- /dev/null
+++ b/test/properties/cpp11/can_require_not_applicable_static.cpp
@@ -0,0 +1,47 @@
+//
+// cpp11/can_require_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_require<object<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_not_applicable_unsupported.cpp b/test/properties/cpp11/can_require_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..36fc9f11
--- /dev/null
+++ b/test/properties/cpp11/can_require_not_applicable_unsupported.cpp
@@ -0,0 +1,32 @@
+//
+// cpp11/can_require_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_static.cpp b/test/properties/cpp11/can_require_static.cpp
new file mode 100644
index 00000000..646eeb15
--- /dev/null
+++ b/test/properties/cpp11/can_require_static.cpp
@@ -0,0 +1,54 @@
+//
+// cpp11/can_require_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(boost::asio::can_require<object<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_require<object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_require<object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<1>, prop<1>>::value, "");
+  static_assert(boost::asio::can_require<const object<1>, prop<1>, prop<1>, prop<1>>::value, "");
+}
diff --git a/test/properties/cpp11/can_require_unsupported.cpp b/test/properties/cpp11/can_require_unsupported.cpp
new file mode 100644
index 00000000..e0b4613d
--- /dev/null
+++ b/test/properties/cpp11/can_require_unsupported.cpp
@@ -0,0 +1,44 @@
+//
+// cpp11/can_require_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_require<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>>::value, "");
+  static_assert(!boost::asio::can_require<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
+}
diff --git a/test/properties/cpp11/prefer_free_prefer.cpp b/test/properties/cpp11/prefer_free_prefer.cpp
new file mode 100644
index 00000000..1378a7ce
--- /dev/null
+++ b/test/properties/cpp11/prefer_free_prefer.cpp
@@ -0,0 +1,66 @@
+//
+// cpp11/prefer_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/prefer_free_require.cpp b/test/properties/cpp11/prefer_free_require.cpp
new file mode 100644
index 00000000..a6d2e0f2
--- /dev/null
+++ b/test/properties/cpp11/prefer_free_require.cpp
@@ -0,0 +1,66 @@
+//
+// cpp11/prefer_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/prefer_member_prefer.cpp b/test/properties/cpp11/prefer_member_prefer.cpp
new file mode 100644
index 00000000..11c566e4
--- /dev/null
+++ b/test/properties/cpp11/prefer_member_prefer.cpp
@@ -0,0 +1,66 @@
+//
+// cpp11/prefer_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/prefer_member_require.cpp b/test/properties/cpp11/prefer_member_require.cpp
new file mode 100644
index 00000000..f028406c
--- /dev/null
+++ b/test/properties/cpp11/prefer_member_require.cpp
@@ -0,0 +1,66 @@
+//
+// cpp11/prefer_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/prefer_static.cpp b/test/properties/cpp11/prefer_static.cpp
new file mode 100644
index 00000000..6a685486
--- /dev/null
+++ b/test/properties/cpp11/prefer_static.cpp
@@ -0,0 +1,70 @@
+//
+// cpp11/prefer_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::prefer(o1, prop<1>());
+  object<1> o3 = boost::asio::prefer(o1, prop<1>(), prop<1>());
+  object<1> o4 = boost::asio::prefer(o1, prop<1>(), prop<1>(), prop<1>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::prefer(o5, prop<1>());
+  object<1> o7 = boost::asio::prefer(o5, prop<1>(), prop<1>());
+  object<1> o8 = boost::asio::prefer(o5, prop<1>(), prop<1>(), prop<1>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<1> o9 = boost::asio::prefer(object<1>(), prop<1>());
+  constexpr object<1> o10 = boost::asio::prefer(object<1>(), prop<1>(), prop<1>());
+  constexpr object<1> o11 = boost::asio::prefer(object<1>(), prop<1>(), prop<1>(), prop<1>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/prefer_unsupported.cpp b/test/properties/cpp11/prefer_unsupported.cpp
new file mode 100644
index 00000000..b44b38e6
--- /dev/null
+++ b/test/properties/cpp11/prefer_unsupported.cpp
@@ -0,0 +1,61 @@
+//
+// cpp11/prefer_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::prefer(o1, prop<2>());
+  object<1> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<1> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::prefer(o5, prop<2>());
+  object<1> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<1> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<1> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<1> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<1> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/query_free.cpp b/test/properties/cpp11/query_free.cpp
new file mode 100644
index 00000000..2f831c4e
--- /dev/null
+++ b/test/properties/cpp11/query_free.cpp
@@ -0,0 +1,51 @@
+//
+// cpp11/query_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend constexpr int query(const object&, prop) { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+
+  constexpr object o3 = {};
+  constexpr int result3 = boost::asio::query(o3, prop());
+  assert(result3 == 123);
+  (void)result3;
+}
diff --git a/test/properties/cpp11/query_member.cpp b/test/properties/cpp11/query_member.cpp
new file mode 100644
index 00000000..bb91efe6
--- /dev/null
+++ b/test/properties/cpp11/query_member.cpp
@@ -0,0 +1,51 @@
+//
+// cpp11/query_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  constexpr int query(prop) const { return 123; }
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+
+  constexpr object o3 = {};
+  constexpr int result3 = boost::asio::query(o3, prop());
+  assert(result3 == 123);
+  (void)result3;
+}
diff --git a/test/properties/cpp11/query_static.cpp b/test/properties/cpp11/query_static.cpp
new file mode 100644
index 00000000..8b8f2122
--- /dev/null
+++ b/test/properties/cpp11/query_static.cpp
@@ -0,0 +1,62 @@
+//
+// cpp11/query_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<>
+struct is_applicable_property<object, prop>
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<>
+struct static_query<object, prop>
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef int result_type;
+  static constexpr int value() { return 123; }
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+
+  constexpr object o3 = {};
+  constexpr int result3 = boost::asio::query(o3, prop());
+  assert(result3 == 123);
+  (void)result3;
+}
diff --git a/test/properties/cpp11/require_concept_free.cpp b/test/properties/cpp11/require_concept_free.cpp
new file mode 100644
index 00000000..76d8a2ef
--- /dev/null
+++ b/test/properties/cpp11/require_concept_free.cpp
@@ -0,0 +1,54 @@
+//
+// cpp11/require_concept_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require_concept(o1, prop<2>());
+  (void)o2;
+
+  const object<1> o3 = {};
+  object<2> o4 = boost::asio::require_concept(o3, prop<2>());
+  (void)o4;
+
+  constexpr object<2> o5 = boost::asio::require_concept(object<1>(), prop<2>());
+  (void)o5;
+}
diff --git a/test/properties/cpp11/require_concept_member.cpp b/test/properties/cpp11/require_concept_member.cpp
new file mode 100644
index 00000000..86404e93
--- /dev/null
+++ b/test/properties/cpp11/require_concept_member.cpp
@@ -0,0 +1,54 @@
+//
+// cpp11/require_concept_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require_concept(o1, prop<2>());
+  (void)o2;
+
+  const object<1> o3 = {};
+  object<2> o4 = boost::asio::require_concept(o3, prop<2>());
+  (void)o4;
+
+  constexpr object<2> o5 = boost::asio::require_concept(object<1>(), prop<2>());
+  (void)o5;
+}
diff --git a/test/properties/cpp11/require_concept_static.cpp b/test/properties/cpp11/require_concept_static.cpp
new file mode 100644
index 00000000..cfd29524
--- /dev/null
+++ b/test/properties/cpp11/require_concept_static.cpp
@@ -0,0 +1,60 @@
+//
+// cpp11/require_concept_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require_concept<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  const object<1>& o2 = boost::asio::require_concept(o1, prop<1>());
+  assert(&o1 == &o2);
+  (void)o2;
+
+  const object<1> o3 = {};
+  const object<1>& o4 = boost::asio::require_concept(o3, prop<1>());
+  assert(&o3 == &o4);
+  (void)o4;
+
+  constexpr object<1> o5 = boost::asio::require_concept(object<1>(), prop<1>());
+  (void)o5;
+}
diff --git a/test/properties/cpp11/require_free.cpp b/test/properties/cpp11/require_free.cpp
new file mode 100644
index 00000000..6b99350f
--- /dev/null
+++ b/test/properties/cpp11/require_free.cpp
@@ -0,0 +1,66 @@
+//
+// cpp11/require_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require(o1, prop<2>());
+  object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::require(o5, prop<2>());
+  object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::require(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::require(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::require(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/require_member.cpp b/test/properties/cpp11/require_member.cpp
new file mode 100644
index 00000000..87886133
--- /dev/null
+++ b/test/properties/cpp11/require_member.cpp
@@ -0,0 +1,66 @@
+//
+// cpp11/require_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require(o1, prop<2>());
+  object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::require(o5, prop<2>());
+  object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::require(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::require(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::require(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp11/require_static.cpp b/test/properties/cpp11/require_static.cpp
new file mode 100644
index 00000000..a74b13ec
--- /dev/null
+++ b/test/properties/cpp11/require_static.cpp
@@ -0,0 +1,70 @@
+//
+// cpp11/require_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+namespace traits {
+
+template<int N>
+struct static_require<object<N>, prop<N> >
+{
+  static constexpr bool is_valid = true;
+};
+
+} // namespace traits
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::require(o1, prop<1>());
+  object<1> o3 = boost::asio::require(o1, prop<1>(), prop<1>());
+  object<1> o4 = boost::asio::require(o1, prop<1>(), prop<1>(), prop<1>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::require(o5, prop<1>());
+  object<1> o7 = boost::asio::require(o5, prop<1>(), prop<1>());
+  object<1> o8 = boost::asio::require(o5, prop<1>(), prop<1>(), prop<1>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<1> o9 = boost::asio::require(object<1>(), prop<1>());
+  constexpr object<1> o10 = boost::asio::require(object<1>(), prop<1>(), prop<1>());
+  constexpr object<1> o11 = boost::asio::require(object<1>(), prop<1>(), prop<1>(), prop<1>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/Jamfile.v2 b/test/properties/cpp14/Jamfile.v2
new file mode 100644
index 00000000..f2264864
--- /dev/null
+++ b/test/properties/cpp14/Jamfile.v2
@@ -0,0 +1,101 @@
+#
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+
+import feature ;
+
+lib socket ; # SOLARIS, QNXNTO
+lib nsl ; # SOLARIS
+lib ws2_32 ; # NT
+lib mswsock ; # NT
+lib ipv6 ; # HPUX
+lib network ; # HAIKU
+
+project
+  : requirements
+    <library>/boost/date_time//boost_date_time
+    <library>/boost/system//boost_system
+    <library>/boost/chrono//boost_chrono
+    <library>/boost/regex//boost_regex
+    <define>BOOST_ALL_NO_LIB=1
+    <threading>multi
+    <target-os>linux:<define>_XOPEN_SOURCE=600
+    <target-os>linux:<define>_GNU_SOURCE=1
+    <target-os>solaris:<define>_XOPEN_SOURCE=500
+    <target-os>solaris:<define>__EXTENSIONS__
+    <target-os>solaris:<library>socket
+    <target-os>solaris:<library>nsl
+    <target-os>windows:<define>_WIN32_WINNT=0x0501
+    <target-os>windows,<toolset>cw:<library>ws2_32
+    <target-os>windows,<toolset>cw:<library>mswsock
+    <target-os>windows,<toolset>gcc:<library>ws2_32
+    <target-os>windows,<toolset>gcc:<library>mswsock
+    <target-os>windows,<toolset>gcc-cygwin:<define>__USE_W32_SOCKETS
+    <target-os>hpux,<toolset>gcc:<define>_XOPEN_SOURCE_EXTENDED
+    <target-os>hpux:<library>ipv6
+    <target-os>qnxnto:<library>socket
+    <target-os>haiku:<library>network
+  ;
+
+test-suite "asio" :
+  [ run can_prefer_free_prefer.cpp ]
+  [ run can_prefer_free_require.cpp ]
+  [ run can_prefer_member_prefer.cpp ]
+  [ run can_prefer_member_require.cpp ]
+  [ run can_prefer_not_applicable_free_prefer.cpp ]
+  [ run can_prefer_not_applicable_free_require.cpp ]
+  [ run can_prefer_not_applicable_member_prefer.cpp ]
+  [ run can_prefer_not_applicable_member_require.cpp ]
+  [ run can_prefer_not_applicable_static.cpp ]
+  [ run can_prefer_not_applicable_unsupported.cpp ]
+  [ run can_prefer_not_preferable_free_prefer.cpp ]
+  [ run can_prefer_not_preferable_free_require.cpp ]
+  [ run can_prefer_not_preferable_member_prefer.cpp ]
+  [ run can_prefer_not_preferable_member_require.cpp ]
+  [ run can_prefer_not_preferable_static.cpp ]
+  [ run can_prefer_not_preferable_unsupported.cpp ]
+  [ run can_prefer_static.cpp ]
+  [ run can_prefer_unsupported.cpp ]
+  [ run can_query_free.cpp ]
+  [ run can_query_member.cpp ]
+  [ run can_query_not_applicable_free.cpp ]
+  [ run can_query_not_applicable_member.cpp ]
+  [ run can_query_not_applicable_static.cpp ]
+  [ run can_query_not_applicable_unsupported.cpp ]
+  [ run can_query_static.cpp ]
+  [ run can_query_unsupported.cpp ]
+  [ run can_require_concept_free.cpp ]
+  [ run can_require_concept_member.cpp ]
+  [ run can_require_concept_not_applicable_free.cpp ]
+  [ run can_require_concept_not_applicable_member.cpp ]
+  [ run can_require_concept_not_applicable_static.cpp ]
+  [ run can_require_concept_not_applicable_unsupported.cpp ]
+  [ run can_require_concept_static.cpp ]
+  [ run can_require_concept_unsupported.cpp ]
+  [ run can_require_free.cpp ]
+  [ run can_require_member.cpp ]
+  [ run can_require_not_applicable_free.cpp ]
+  [ run can_require_not_applicable_member.cpp ]
+  [ run can_require_not_applicable_static.cpp ]
+  [ run can_require_not_applicable_unsupported.cpp ]
+  [ run can_require_static.cpp ]
+  [ run can_require_unsupported.cpp ]
+  [ run prefer_free_prefer.cpp ]
+  [ run prefer_free_require.cpp ]
+  [ run prefer_member_prefer.cpp ]
+  [ run prefer_member_require.cpp ]
+  [ run prefer_static.cpp ]
+  [ run prefer_unsupported.cpp ]
+  [ run query_free.cpp ]
+  [ run query_member.cpp ]
+  [ run query_static.cpp ]
+  [ run require_concept_free.cpp ]
+  [ run require_concept_member.cpp ]
+  [ run require_concept_static.cpp ]
+  [ run require_free.cpp ]
+  [ run require_member.cpp ]
+  [ run require_static.cpp ]
+  ;
diff --git a/test/properties/cpp14/can_prefer_free_prefer.cpp b/test/properties/cpp14/can_prefer_free_prefer.cpp
new file mode 100644
index 00000000..c1283fc9
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_free_prefer.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_free_require.cpp b/test/properties/cpp14/can_prefer_free_require.cpp
new file mode 100644
index 00000000..55b742ff
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_free_require.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_member_prefer.cpp b/test/properties/cpp14/can_prefer_member_prefer.cpp
new file mode 100644
index 00000000..e4e085a1
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_member_prefer.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_member_require.cpp b/test/properties/cpp14/can_prefer_member_require.cpp
new file mode 100644
index 00000000..98125970
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_member_require.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_applicable_free_prefer.cpp b/test/properties/cpp14/can_prefer_not_applicable_free_prefer.cpp
new file mode 100644
index 00000000..cde1a188
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_applicable_free_prefer.cpp
@@ -0,0 +1,38 @@
+//
+// cpp14/can_prefer_not_applicable_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_applicable_free_require.cpp b/test/properties/cpp14/can_prefer_not_applicable_free_require.cpp
new file mode 100644
index 00000000..9f1c5496
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_applicable_free_require.cpp
@@ -0,0 +1,38 @@
+//
+// cpp14/can_prefer_not_applicable_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_applicable_member_prefer.cpp b/test/properties/cpp14/can_prefer_not_applicable_member_prefer.cpp
new file mode 100644
index 00000000..2fd97fc7
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_applicable_member_prefer.cpp
@@ -0,0 +1,38 @@
+//
+// cpp14/can_prefer_not_applicable_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_applicable_member_require.cpp b/test/properties/cpp14/can_prefer_not_applicable_member_require.cpp
new file mode 100644
index 00000000..bebe2d3b
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_applicable_member_require.cpp
@@ -0,0 +1,38 @@
+//
+// cpp14/can_prefer_not_applicable_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_applicable_static.cpp b/test/properties/cpp14/can_prefer_not_applicable_static.cpp
new file mode 100644
index 00000000..ebaa1346
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_applicable_static.cpp
@@ -0,0 +1,35 @@
+//
+// cpp14/can_prefer_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_preferable = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<1>, prop<1>, prop<1>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_applicable_unsupported.cpp b/test/properties/cpp14/can_prefer_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..fec98434
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_applicable_unsupported.cpp
@@ -0,0 +1,32 @@
+//
+// cpp14/can_prefer_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_preferable_free_prefer.cpp b/test/properties/cpp14/can_prefer_not_preferable_free_prefer.cpp
new file mode 100644
index 00000000..3a1d156b
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_preferable_free_prefer.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_not_preferable_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_preferable_free_require.cpp b/test/properties/cpp14/can_prefer_not_preferable_free_require.cpp
new file mode 100644
index 00000000..02a7a25f
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_preferable_free_require.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_not_preferable_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_preferable_member_prefer.cpp b/test/properties/cpp14/can_prefer_not_preferable_member_prefer.cpp
new file mode 100644
index 00000000..f87dacbb
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_preferable_member_prefer.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_not_preferable_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_preferable_member_require.cpp b/test/properties/cpp14/can_prefer_not_preferable_member_require.cpp
new file mode 100644
index 00000000..5793d6cc
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_preferable_member_require.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_prefer_not_preferable_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_preferable_static.cpp b/test/properties/cpp14/can_prefer_not_preferable_static.cpp
new file mode 100644
index 00000000..18c59b3e
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_preferable_static.cpp
@@ -0,0 +1,34 @@
+//
+// cpp14/can_prefer_not_preferable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<1>, prop<1>, prop<1>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_not_preferable_unsupported.cpp b/test/properties/cpp14/can_prefer_not_preferable_unsupported.cpp
new file mode 100644
index 00000000..5d1f28a5
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_not_preferable_unsupported.cpp
@@ -0,0 +1,34 @@
+//
+// cpp14/can_prefer_not_preferable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = false;
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_static.cpp b/test/properties/cpp14/can_prefer_static.cpp
new file mode 100644
index 00000000..b4ff8cec
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_static.cpp
@@ -0,0 +1,36 @@
+//
+// cpp14/can_prefer_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<1>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<1>, prop<1>>, "");
+  static_assert(boost::asio::can_prefer_v<object<1>, prop<1>, prop<1>, prop<1>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<1>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<1>, prop<1>>, "");
+  static_assert(boost::asio::can_prefer_v<const object<1>, prop<1>, prop<1>, prop<1>>, "");
+}
diff --git a/test/properties/cpp14/can_prefer_unsupported.cpp b/test/properties/cpp14/can_prefer_unsupported.cpp
new file mode 100644
index 00000000..0d603f00
--- /dev/null
+++ b/test/properties/cpp14/can_prefer_unsupported.cpp
@@ -0,0 +1,44 @@
+//
+// cpp14/can_prefer_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_prefer_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_query_free.cpp b/test/properties/cpp14/can_query_free.cpp
new file mode 100644
index 00000000..ddd5a153
--- /dev/null
+++ b/test/properties/cpp14/can_query_free.cpp
@@ -0,0 +1,28 @@
+//
+// cpp14/can_query_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+};
+
+struct object
+{
+  friend constexpr int query(const object&, prop) { return 123; }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_query_v<object, prop>, "");
+  static_assert(boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_member.cpp b/test/properties/cpp14/can_query_member.cpp
new file mode 100644
index 00000000..05fe40e5
--- /dev/null
+++ b/test/properties/cpp14/can_query_member.cpp
@@ -0,0 +1,28 @@
+//
+// cpp14/can_query_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+};
+
+struct object
+{
+  constexpr int query(prop) const { return 123; }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_query_v<object, prop>, "");
+  static_assert(boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_not_applicable_free.cpp b/test/properties/cpp14/can_query_not_applicable_free.cpp
new file mode 100644
index 00000000..ad2416e7
--- /dev/null
+++ b/test/properties/cpp14/can_query_not_applicable_free.cpp
@@ -0,0 +1,27 @@
+//
+// cpp14/can_query_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  friend constexpr int query(const object&, prop) { return 123; }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query_v<object, prop>, "");
+  static_assert(!boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_not_applicable_member.cpp b/test/properties/cpp14/can_query_not_applicable_member.cpp
new file mode 100644
index 00000000..f4386cc2
--- /dev/null
+++ b/test/properties/cpp14/can_query_not_applicable_member.cpp
@@ -0,0 +1,27 @@
+//
+// cpp14/can_query_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+  constexpr int query(prop) const { return 123; }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query_v<object, prop>, "");
+  static_assert(!boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_not_applicable_static.cpp b/test/properties/cpp14/can_query_not_applicable_static.cpp
new file mode 100644
index 00000000..ea300381
--- /dev/null
+++ b/test/properties/cpp14/can_query_not_applicable_static.cpp
@@ -0,0 +1,27 @@
+//
+// cpp14/can_query_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr int static_query_v = 123;
+};
+
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query_v<object, prop>, "");
+  static_assert(!boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_not_applicable_unsupported.cpp b/test/properties/cpp14/can_query_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..0fcb8757
--- /dev/null
+++ b/test/properties/cpp14/can_query_not_applicable_unsupported.cpp
@@ -0,0 +1,26 @@
+//
+// cpp14/can_query_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+};
+
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query_v<object, prop>, "");
+  static_assert(!boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_static.cpp b/test/properties/cpp14/can_query_static.cpp
new file mode 100644
index 00000000..83d5d302
--- /dev/null
+++ b/test/properties/cpp14/can_query_static.cpp
@@ -0,0 +1,28 @@
+//
+// cpp14/can_query_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  template <typename> static constexpr int static_query_v = 123;
+};
+
+struct object
+{
+};
+
+int main()
+{
+  static_assert(boost::asio::can_query_v<object, prop>, "");
+  static_assert(boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_query_unsupported.cpp b/test/properties/cpp14/can_query_unsupported.cpp
new file mode 100644
index 00000000..4faee2e9
--- /dev/null
+++ b/test/properties/cpp14/can_query_unsupported.cpp
@@ -0,0 +1,27 @@
+//
+// cpp14/can_query_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+};
+
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_query_v<object, prop>, "");
+  static_assert(!boost::asio::can_query_v<const object, prop>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_free.cpp b/test/properties/cpp14/can_require_concept_free.cpp
new file mode 100644
index 00000000..f5c7ad28
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_free.cpp
@@ -0,0 +1,35 @@
+//
+// cpp14/can_require_concept_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_require_concept_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_require_concept_v<const object<1>, prop<2>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_member.cpp b/test/properties/cpp14/can_require_concept_member.cpp
new file mode 100644
index 00000000..e009754c
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_member.cpp
@@ -0,0 +1,35 @@
+//
+// cpp14/can_require_concept_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_require_concept_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_require_concept_v<const object<1>, prop<2>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_not_applicable_free.cpp b/test/properties/cpp14/can_require_concept_not_applicable_free.cpp
new file mode 100644
index 00000000..b0eec76d
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_not_applicable_free.cpp
@@ -0,0 +1,34 @@
+//
+// cpp14/can_require_concept_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_concept_v<const object<1>, prop<2>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_not_applicable_member.cpp b/test/properties/cpp14/can_require_concept_not_applicable_member.cpp
new file mode 100644
index 00000000..78ea50d4
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_not_applicable_member.cpp
@@ -0,0 +1,34 @@
+//
+// cpp14/can_require_concept_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_concept_v<const object<1>, prop<2>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_not_applicable_static.cpp b/test/properties/cpp14/can_require_concept_not_applicable_static.cpp
new file mode 100644
index 00000000..8ebbe174
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_not_applicable_static.cpp
@@ -0,0 +1,31 @@
+//
+// cpp14/can_require_concept_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable_concept = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_concept_v<const object<1>, prop<2>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_not_applicable_unsupported.cpp b/test/properties/cpp14/can_require_concept_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..ebba75a9
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_not_applicable_unsupported.cpp
@@ -0,0 +1,28 @@
+//
+// cpp14/can_require_concept_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_concept_v<const object<1>, prop<2>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_static.cpp b/test/properties/cpp14/can_require_concept_static.cpp
new file mode 100644
index 00000000..994ecdb7
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_static.cpp
@@ -0,0 +1,32 @@
+//
+// cpp14/can_require_concept_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable_concept = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(boost::asio::can_require_concept_v<object<1>, prop<1>>, "");
+  static_assert(boost::asio::can_require_concept_v<const object<1>, prop<1>>, "");
+}
diff --git a/test/properties/cpp14/can_require_concept_unsupported.cpp b/test/properties/cpp14/can_require_concept_unsupported.cpp
new file mode 100644
index 00000000..edda4ed2
--- /dev/null
+++ b/test/properties/cpp14/can_require_concept_unsupported.cpp
@@ -0,0 +1,40 @@
+//
+// cpp14/can_require_concept_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_require_concept<object<1>, prop<2>>::value, "");
+  static_assert(!boost::asio::can_require_concept<const object<1>, prop<2>>::value, "");
+}
diff --git a/test/properties/cpp14/can_require_free.cpp b/test/properties/cpp14/can_require_free.cpp
new file mode 100644
index 00000000..5420e7fd
--- /dev/null
+++ b/test/properties/cpp14/can_require_free.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_require_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_require_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_require_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_require_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_require_member.cpp b/test/properties/cpp14/can_require_member.cpp
new file mode 100644
index 00000000..cd4ce542
--- /dev/null
+++ b/test/properties/cpp14/can_require_member.cpp
@@ -0,0 +1,39 @@
+//
+// cpp14/can_require_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(boost::asio::can_require_v<object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_require_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_require_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<2>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_require_not_applicable_free.cpp b/test/properties/cpp14/can_require_not_applicable_free.cpp
new file mode 100644
index 00000000..9e590ea9
--- /dev/null
+++ b/test/properties/cpp14/can_require_not_applicable_free.cpp
@@ -0,0 +1,38 @@
+//
+// cpp14/can_require_not_applicable_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_require_not_applicable_member.cpp b/test/properties/cpp14/can_require_not_applicable_member.cpp
new file mode 100644
index 00000000..b7a295c1
--- /dev/null
+++ b/test/properties/cpp14/can_require_not_applicable_member.cpp
@@ -0,0 +1,38 @@
+//
+// cpp14/can_require_not_applicable_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_require_not_applicable_static.cpp b/test/properties/cpp14/can_require_not_applicable_static.cpp
new file mode 100644
index 00000000..38037f13
--- /dev/null
+++ b/test/properties/cpp14/can_require_not_applicable_static.cpp
@@ -0,0 +1,35 @@
+//
+// cpp14/can_require_not_applicable_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  static constexpr bool is_requirable = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_v<object<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<1>, prop<1>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<1>, prop<1>, prop<1>>, "");
+}
diff --git a/test/properties/cpp14/can_require_not_applicable_unsupported.cpp b/test/properties/cpp14/can_require_not_applicable_unsupported.cpp
new file mode 100644
index 00000000..ab48b1db
--- /dev/null
+++ b/test/properties/cpp14/can_require_not_applicable_unsupported.cpp
@@ -0,0 +1,32 @@
+//
+// cpp14/can_require_not_applicable_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/can_require_static.cpp b/test/properties/cpp14/can_require_static.cpp
new file mode 100644
index 00000000..bbb00bad
--- /dev/null
+++ b/test/properties/cpp14/can_require_static.cpp
@@ -0,0 +1,36 @@
+//
+// cpp14/can_require_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  static_assert(boost::asio::can_require_v<object<1>, prop<1>>, "");
+  static_assert(boost::asio::can_require_v<object<1>, prop<1>, prop<1>>, "");
+  static_assert(boost::asio::can_require_v<object<1>, prop<1>, prop<1>, prop<1>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<1>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<1>, prop<1>>, "");
+  static_assert(boost::asio::can_require_v<const object<1>, prop<1>, prop<1>, prop<1>>, "");
+}
diff --git a/test/properties/cpp14/can_require_unsupported.cpp b/test/properties/cpp14/can_require_unsupported.cpp
new file mode 100644
index 00000000..e000d700
--- /dev/null
+++ b/test/properties/cpp14/can_require_unsupported.cpp
@@ -0,0 +1,44 @@
+//
+// cpp14/can_require_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+};
+
+template <int>
+struct object
+{
+};
+
+namespace boost {
+namespace asio {
+
+template<int N, int M>
+struct is_applicable_property<object<N>, prop<M> >
+{
+  static constexpr bool value = true;
+};
+
+} // namespace asio
+} // namespace boost
+
+int main()
+{
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<object<1>, prop<2>, prop<3>, prop<4>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>>, "");
+  static_assert(!boost::asio::can_require_v<const object<1>, prop<2>, prop<3>, prop<4>>, "");
+}
diff --git a/test/properties/cpp14/prefer_free_prefer.cpp b/test/properties/cpp14/prefer_free_prefer.cpp
new file mode 100644
index 00000000..e83520c7
--- /dev/null
+++ b/test/properties/cpp14/prefer_free_prefer.cpp
@@ -0,0 +1,55 @@
+//
+// cpp14/prefer_free_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> prefer(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/prefer_free_require.cpp b/test/properties/cpp14/prefer_free_require.cpp
new file mode 100644
index 00000000..19001c52
--- /dev/null
+++ b/test/properties/cpp14/prefer_free_require.cpp
@@ -0,0 +1,55 @@
+//
+// cpp14/prefer_free_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/prefer_member_prefer.cpp b/test/properties/cpp14/prefer_member_prefer.cpp
new file mode 100644
index 00000000..4eba547b
--- /dev/null
+++ b/test/properties/cpp14/prefer_member_prefer.cpp
@@ -0,0 +1,55 @@
+//
+// cpp14/prefer_member_prefer.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> prefer(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/prefer_member_require.cpp b/test/properties/cpp14/prefer_member_require.cpp
new file mode 100644
index 00000000..52f71713
--- /dev/null
+++ b/test/properties/cpp14/prefer_member_require.cpp
@@ -0,0 +1,55 @@
+//
+// cpp14/prefer_member_require.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::prefer(o1, prop<2>());
+  object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::prefer(o5, prop<2>());
+  object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/prefer_static.cpp b/test/properties/cpp14/prefer_static.cpp
new file mode 100644
index 00000000..2e4b56cf
--- /dev/null
+++ b/test/properties/cpp14/prefer_static.cpp
@@ -0,0 +1,52 @@
+//
+// cpp14/prefer_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::prefer(o1, prop<1>());
+  object<1> o3 = boost::asio::prefer(o1, prop<1>(), prop<1>());
+  object<1> o4 = boost::asio::prefer(o1, prop<1>(), prop<1>(), prop<1>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::prefer(o5, prop<1>());
+  object<1> o7 = boost::asio::prefer(o5, prop<1>(), prop<1>());
+  object<1> o8 = boost::asio::prefer(o5, prop<1>(), prop<1>(), prop<1>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<1> o9 = boost::asio::prefer(object<1>(), prop<1>());
+  constexpr object<1> o10 = boost::asio::prefer(object<1>(), prop<1>(), prop<1>());
+  constexpr object<1> o11 = boost::asio::prefer(object<1>(), prop<1>(), prop<1>(), prop<1>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/prefer_unsupported.cpp b/test/properties/cpp14/prefer_unsupported.cpp
new file mode 100644
index 00000000..425144ab
--- /dev/null
+++ b/test/properties/cpp14/prefer_unsupported.cpp
@@ -0,0 +1,50 @@
+//
+// cpp14/prefer_unsupported.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/prefer.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_preferable = true;
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::prefer(o1, prop<2>());
+  object<1> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>());
+  object<1> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::prefer(o5, prop<2>());
+  object<1> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>());
+  object<1> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<1> o9 = boost::asio::prefer(object<1>(), prop<2>());
+  constexpr object<1> o10 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>());
+  constexpr object<1> o11 = boost::asio::prefer(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/query_free.cpp b/test/properties/cpp14/query_free.cpp
new file mode 100644
index 00000000..131f9125
--- /dev/null
+++ b/test/properties/cpp14/query_free.cpp
@@ -0,0 +1,40 @@
+//
+// cpp14/query_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+};
+
+struct object
+{
+  friend constexpr int query(const object&, prop) { return 123; }
+};
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+
+  constexpr object o3 = {};
+  constexpr int result3 = boost::asio::query(o3, prop());
+  assert(result3 == 123);
+  (void)result3;
+}
diff --git a/test/properties/cpp14/query_member.cpp b/test/properties/cpp14/query_member.cpp
new file mode 100644
index 00000000..f0faa02f
--- /dev/null
+++ b/test/properties/cpp14/query_member.cpp
@@ -0,0 +1,40 @@
+//
+// cpp14/query_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+};
+
+struct object
+{
+  constexpr int query(prop) const { return 123; }
+};
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+
+  constexpr object o3 = {};
+  constexpr int result3 = boost::asio::query(o3, prop());
+  assert(result3 == 123);
+  (void)result3;
+}
diff --git a/test/properties/cpp14/query_static.cpp b/test/properties/cpp14/query_static.cpp
new file mode 100644
index 00000000..0254d3c3
--- /dev/null
+++ b/test/properties/cpp14/query_static.cpp
@@ -0,0 +1,40 @@
+//
+// cpp14/query_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/query.hpp>
+#include <cassert>
+
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  template <typename> static constexpr int static_query_v = 123;
+};
+
+struct object
+{
+};
+
+int main()
+{
+  object o1 = {};
+  int result1 = boost::asio::query(o1, prop());
+  assert(result1 == 123);
+  (void)result1;
+
+  const object o2 = {};
+  int result2 = boost::asio::query(o2, prop());
+  assert(result2 == 123);
+  (void)result2;
+
+  constexpr object o3 = {};
+  constexpr int result3 = boost::asio::query(o3, prop());
+  assert(result3 == 123);
+  (void)result3;
+}
diff --git a/test/properties/cpp14/require_concept_free.cpp b/test/properties/cpp14/require_concept_free.cpp
new file mode 100644
index 00000000..4e7752c7
--- /dev/null
+++ b/test/properties/cpp14/require_concept_free.cpp
@@ -0,0 +1,43 @@
+//
+// cpp14/require_concept_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require_concept(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require_concept(o1, prop<2>());
+  (void)o2;
+
+  const object<1> o3 = {};
+  object<2> o4 = boost::asio::require_concept(o3, prop<2>());
+  (void)o4;
+
+  constexpr object<2> o5 = boost::asio::require_concept(object<1>(), prop<2>());
+  (void)o5;
+}
diff --git a/test/properties/cpp14/require_concept_member.cpp b/test/properties/cpp14/require_concept_member.cpp
new file mode 100644
index 00000000..155c1b87
--- /dev/null
+++ b/test/properties/cpp14/require_concept_member.cpp
@@ -0,0 +1,43 @@
+//
+// cpp14/require_concept_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable_concept = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require_concept(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require_concept(o1, prop<2>());
+  (void)o2;
+
+  const object<1> o3 = {};
+  object<2> o4 = boost::asio::require_concept(o3, prop<2>());
+  (void)o4;
+
+  constexpr object<2> o5 = boost::asio::require_concept(object<1>(), prop<2>());
+  (void)o5;
+}
diff --git a/test/properties/cpp14/require_concept_static.cpp b/test/properties/cpp14/require_concept_static.cpp
new file mode 100644
index 00000000..68eba17f
--- /dev/null
+++ b/test/properties/cpp14/require_concept_static.cpp
@@ -0,0 +1,42 @@
+//
+// cpp14/require_concept_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require_concept.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable_concept = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  object<1> o1 = {};
+  const object<1>& o2 = boost::asio::require_concept(o1, prop<1>());
+  assert(&o1 == &o2);
+  (void)o2;
+
+  const object<1> o3 = {};
+  const object<1>& o4 = boost::asio::require_concept(o3, prop<1>());
+  assert(&o3 == &o4);
+  (void)o4;
+
+  constexpr object<1> o5 = boost::asio::require_concept(object<1>(), prop<1>());
+  (void)o5;
+}
diff --git a/test/properties/cpp14/require_free.cpp b/test/properties/cpp14/require_free.cpp
new file mode 100644
index 00000000..8c459267
--- /dev/null
+++ b/test/properties/cpp14/require_free.cpp
@@ -0,0 +1,55 @@
+//
+// cpp14/require_free.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  friend constexpr object<N> require(const object&, prop<N>)
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require(o1, prop<2>());
+  object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::require(o5, prop<2>());
+  object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::require(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::require(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::require(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/require_member.cpp b/test/properties/cpp14/require_member.cpp
new file mode 100644
index 00000000..c433ee94
--- /dev/null
+++ b/test/properties/cpp14/require_member.cpp
@@ -0,0 +1,55 @@
+//
+// cpp14/require_member.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable = true;
+};
+
+template <int>
+struct object
+{
+  template <int N>
+  constexpr object<N> require(prop<N>) const
+  {
+    return object<N>();
+  }
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<2> o2 = boost::asio::require(o1, prop<2>());
+  object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
+  object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<2> o6 = boost::asio::require(o5, prop<2>());
+  object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
+  object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<2> o9 = boost::asio::require(object<1>(), prop<2>());
+  constexpr object<3> o10 = boost::asio::require(object<1>(), prop<2>(), prop<3>());
+  constexpr object<4> o11 = boost::asio::require(object<1>(), prop<2>(), prop<3>(), prop<4>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/properties/cpp14/require_static.cpp b/test/properties/cpp14/require_static.cpp
new file mode 100644
index 00000000..126cb3a6
--- /dev/null
+++ b/test/properties/cpp14/require_static.cpp
@@ -0,0 +1,52 @@
+//
+// cpp14/require_static.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/require.hpp>
+#include <cassert>
+
+template <int>
+struct prop
+{
+  template <typename> static constexpr bool is_applicable_property_v = true;
+  static constexpr bool is_requirable = true;
+  template <typename> static constexpr bool static_query_v = true;
+  static constexpr bool value() { return true; }
+};
+
+template <int>
+struct object
+{
+};
+
+int main()
+{
+  object<1> o1 = {};
+  object<1> o2 = boost::asio::require(o1, prop<1>());
+  object<1> o3 = boost::asio::require(o1, prop<1>(), prop<1>());
+  object<1> o4 = boost::asio::require(o1, prop<1>(), prop<1>(), prop<1>());
+  (void)o2;
+  (void)o3;
+  (void)o4;
+
+  const object<1> o5 = {};
+  object<1> o6 = boost::asio::require(o5, prop<1>());
+  object<1> o7 = boost::asio::require(o5, prop<1>(), prop<1>());
+  object<1> o8 = boost::asio::require(o5, prop<1>(), prop<1>(), prop<1>());
+  (void)o6;
+  (void)o7;
+  (void)o8;
+
+  constexpr object<1> o9 = boost::asio::require(object<1>(), prop<1>());
+  constexpr object<1> o10 = boost::asio::require(object<1>(), prop<1>(), prop<1>());
+  constexpr object<1> o11 = boost::asio::require(object<1>(), prop<1>(), prop<1>(), prop<1>());
+  (void)o9;
+  (void)o10;
+  (void)o11;
+}
diff --git a/test/ssl/stream.cpp b/test/ssl/stream.cpp
index 007dd5f4..24f86acf 100644
--- a/test/ssl/stream.cpp
+++ b/test/ssl/stream.cpp
@@ -75,6 +75,12 @@ void test()
     ip::tcp::socket socket1(ioc, ip::tcp::v4());
     ssl::stream<ip::tcp::socket&> stream2(socket1, context);
 
+#if defined(BOOST_ASIO_HAS_MOVE)
+    ssl::stream<ip::tcp::socket> stream3
+      = ssl::stream<ip::tcp::socket>(ioc, context);
+    ssl::stream<ip::tcp::socket> stream4(std::move(stream3));
+#endif // defined(BOOST_ASIO_HAS_MOVE)
+
     // basic_io_object functions.
 
     ssl::stream<ip::tcp::socket>::executor_type ex = stream1.get_executor();
@@ -89,9 +95,9 @@ void test()
       = stream1.lowest_layer();
     (void)lowest_layer;
 
-    const ssl::stream<ip::tcp::socket>& stream3 = stream1;
+    const ssl::stream<ip::tcp::socket>& stream5 = stream1;
     const ssl::stream<ip::tcp::socket>::lowest_layer_type& lowest_layer2
-      = stream3.lowest_layer();
+      = stream5.lowest_layer();
     (void)lowest_layer2;
 
     stream1.set_verify_mode(ssl::verify_none);
diff --git a/test/static_thread_pool.cpp b/test/static_thread_pool.cpp
new file mode 100644
index 00000000..145e5ba4
--- /dev/null
+++ b/test/static_thread_pool.cpp
@@ -0,0 +1,30 @@
+//
+// static_thread_pool.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Prevent link dependency on the Boost.System library.
+#if !defined(BOOST_SYSTEM_NO_DEPRECATED)
+#define BOOST_SYSTEM_NO_DEPRECATED
+#endif // !defined(BOOST_SYSTEM_NO_DEPRECATED)
+
+// Test that header file is self-contained.
+#include <boost/asio/static_thread_pool.hpp>
+
+#include "unit_test.hpp"
+
+BOOST_ASIO_TEST_SUITE
+(
+  "static_thread_pool",
+  BOOST_ASIO_TEST_CASE(null_test)
+)
diff --git a/test/strand.cpp b/test/strand.cpp
index 66e97b90..4bfc9b2b 100644
--- a/test/strand.cpp
+++ b/test/strand.cpp
@@ -255,9 +255,222 @@ void strand_conversion_test()
   s3 = strand<io_context::executor_type>(s1);
 }
 
+void strand_query_test()
+{
+  io_context ioc;
+  strand<io_context::executor_type> s1 = make_strand(ioc);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(s1, boost::asio::execution::context)
+        == &ioc);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::blocking)
+        == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::blocking.possibly)
+        == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::outstanding_work)
+        == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::outstanding_work.untracked)
+        == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::relationship)
+        == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::relationship.fork)
+        == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::mapping)
+        == boost::asio::execution::mapping.thread);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(s1, boost::asio::execution::allocator)
+        == std::allocator<void>());
+}
+
+void strand_execute_test()
+{
+  io_context ioc;
+  strand<io_context::executor_type> s1 = make_strand(ioc);
+  int count = 0;
+
+  boost::asio::execution::execute(s1, bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(s1, boost::asio::execution::blocking.possibly),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(s1, boost::asio::execution::blocking.never),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  BOOST_ASIO_CHECK(!ioc.stopped());
+
+  boost::asio::execution::execute(
+      boost::asio::require(s1,
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.tracked),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(s1,
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(s1,
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.fork),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::require(s1,
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.continuation),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(s1,
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator(std::allocator<void>())),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+
+  count = 0;
+  ioc.restart();
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(s1,
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator),
+      bindns::bind(increment, &count));
+
+  // No handlers can be called until run() is called.
+  BOOST_ASIO_CHECK(!ioc.stopped());
+  BOOST_ASIO_CHECK(count == 0);
+
+  ioc.run();
+
+  // The run() call will not return until all work has finished.
+  BOOST_ASIO_CHECK(ioc.stopped());
+  BOOST_ASIO_CHECK(count == 1);
+}
+
 BOOST_ASIO_TEST_SUITE
 (
   "strand",
   BOOST_ASIO_TEST_CASE(strand_test)
   BOOST_ASIO_COMPILE_TEST_CASE(strand_conversion_test)
+  BOOST_ASIO_TEST_CASE(strand_query_test)
+  BOOST_ASIO_TEST_CASE(strand_execute_test)
 )
diff --git a/test/system_executor.cpp b/test/system_executor.cpp
index 2f286f43..a8f4f706 100644
--- a/test/system_executor.cpp
+++ b/test/system_executor.cpp
@@ -21,10 +21,150 @@
 // Test that header file is self-contained.
 #include <boost/asio/system_executor.hpp>
 
+#include <boost/asio/dispatch.hpp>
+#include <boost/asio/post.hpp>
 #include "unit_test.hpp"
 
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <boost/bind/bind.hpp>
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <functional>
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+using namespace boost::asio;
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = boost;
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = std;
+#endif
+
+void increment(boost::asio::detail::atomic_count* count)
+{
+  ++(*count);
+}
+
+void system_executor_query_test()
+{
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(system_executor(),
+        boost::asio::execution::context)
+      != static_cast<const system_context*>(0));
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::blocking)
+      == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::blocking.possibly)
+      == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::outstanding_work)
+      == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::outstanding_work.untracked)
+      == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::relationship)
+      == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::relationship.fork)
+      == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::bulk_guarantee)
+      == boost::asio::execution::bulk_guarantee.unsequenced);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::mapping)
+      == boost::asio::execution::mapping.thread);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(system_executor(),
+        boost::asio::execution::allocator)
+      == std::allocator<void>());
+}
+
+void system_executor_execute_test()
+{
+  boost::asio::detail::atomic_count count(0);
+
+  boost::asio::execution::execute(system_executor(),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(system_executor(),
+        boost::asio::execution::blocking.possibly),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(system_executor(),
+        boost::asio::execution::blocking.always),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(system_executor(),
+        boost::asio::execution::blocking.never),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(system_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(system_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.fork),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(system_executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.continuation),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(system_executor(),
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator(std::allocator<void>())),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(system_executor(),
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator),
+      bindns::bind(increment, &count));
+
+  boost::asio::query(system_executor(), execution::context).join();
+
+  BOOST_ASIO_CHECK(count == 9);
+}
+
 BOOST_ASIO_TEST_SUITE
 (
   "system_executor",
-  BOOST_ASIO_TEST_CASE(null_test)
+  BOOST_ASIO_TEST_CASE(system_executor_query_test)
+  BOOST_ASIO_TEST_CASE(system_executor_execute_test)
 )
diff --git a/test/system_timer.cpp b/test/system_timer.cpp
index 88755bff..e9aadd3f 100644
--- a/test/system_timer.cpp
+++ b/test/system_timer.cpp
@@ -270,22 +270,78 @@ struct custom_allocation_timer_handler
   custom_allocation_timer_handler(int* count) : count_(count) {}
   void operator()(const boost::system::error_code&) {}
   int* count_;
+
+  template <typename T>
+  struct allocator
+  {
+    typedef size_t size_type;
+    typedef ptrdiff_t difference_type;
+    typedef T* pointer;
+    typedef const T* const_pointer;
+    typedef T& reference;
+    typedef const T& const_reference;
+    typedef T value_type;
+
+    template <typename U>
+    struct rebind
+    {
+      typedef allocator<U> other;
+    };
+
+    explicit allocator(int* count) BOOST_ASIO_NOEXCEPT
+      : count_(count)
+    {
+    }
+
+    allocator(const allocator& other) BOOST_ASIO_NOEXCEPT
+      : count_(other.count_)
+    {
+    }
+
+    template <typename U>
+    allocator(const allocator<U>& other) BOOST_ASIO_NOEXCEPT
+      : count_(other.count_)
+    {
+    }
+
+    pointer allocate(size_type n, const void* = 0)
+    {
+      ++(*count_);
+      return static_cast<T*>(::operator new(sizeof(T) * n));
+    }
+
+    void deallocate(pointer p, size_type)
+    {
+      --(*count_);
+      ::operator delete(p);
+    }
+
+    size_type max_size() const
+    {
+      return ~size_type(0);
+    }
+
+    void construct(pointer p, const T& v)
+    {
+      new (p) T(v);
+    }
+
+    void destroy(pointer p)
+    {
+      p->~T();
+    }
+
+    int* count_;
+  };
+
+  typedef allocator<int> allocator_type;
+
+  allocator_type get_allocator() const BOOST_ASIO_NOEXCEPT
+  {
+    return allocator_type(count_);
+  }
 };
 
-void* asio_handler_allocate(std::size_t size,
-    custom_allocation_timer_handler* handler)
-{
-  ++(*handler->count_);
-  return ::operator new(size);
-}
-
-void asio_handler_deallocate(void* pointer, std::size_t,
-    custom_allocation_timer_handler* handler)
-{
-  --(*handler->count_);
-  ::operator delete(pointer);
-}
-
 void system_timer_custom_allocation_test()
 {
   static boost::asio::io_context io_context;
@@ -356,6 +412,19 @@ boost::asio::system_timer make_timer(boost::asio::io_context& ioc, int* count)
   t.async_wait(bindns::bind(increment, count));
   return t;
 }
+
+typedef boost::asio::basic_waitable_timer<
+    boost::asio::system_timer::clock_type,
+    boost::asio::system_timer::traits_type,
+    boost::asio::io_context::executor_type> io_context_system_timer;
+
+io_context_system_timer make_convertible_timer(boost::asio::io_context& ioc, int* count)
+{
+  io_context_system_timer t(ioc);
+  t.expires_after(boost::asio::chrono::seconds(1));
+  t.async_wait(bindns::bind(increment, count));
+  return t;
+}
 #endif
 
 void system_timer_move_test()
@@ -378,6 +447,22 @@ void system_timer_move_test()
   io_context1.run();
 
   BOOST_ASIO_CHECK(count == 2);
+
+  boost::asio::system_timer t4 = make_convertible_timer(io_context1, &count);
+  boost::asio::system_timer t5 = make_convertible_timer(io_context2, &count);
+  boost::asio::system_timer t6 = std::move(t4);
+
+  t2 = std::move(t4);
+
+  io_context2.restart();
+  io_context2.run();
+
+  BOOST_ASIO_CHECK(count == 3);
+
+  io_context1.restart();
+  io_context1.run();
+
+  BOOST_ASIO_CHECK(count == 4);
 #endif // defined(BOOST_ASIO_HAS_MOVE)
 }
 
diff --git a/test/thread_pool.cpp b/test/thread_pool.cpp
new file mode 100644
index 00000000..8cc50907
--- /dev/null
+++ b/test/thread_pool.cpp
@@ -0,0 +1,300 @@
+//
+// thread_pool.cpp
+// ~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Disable autolinking for unit tests.
+#if !defined(BOOST_ALL_NO_LIB)
+#define BOOST_ALL_NO_LIB 1
+#endif // !defined(BOOST_ALL_NO_LIB)
+
+// Test that header file is self-contained.
+#include <boost/asio/thread_pool.hpp>
+
+#include <boost/asio/dispatch.hpp>
+#include <boost/asio/post.hpp>
+#include "unit_test.hpp"
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <boost/bind/bind.hpp>
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+# include <functional>
+#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+
+using namespace boost::asio;
+
+#if defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = boost;
+#else // defined(BOOST_ASIO_HAS_BOOST_BIND)
+namespace bindns = std;
+#endif
+
+void increment(int* count)
+{
+  ++(*count);
+}
+
+void decrement_to_zero(thread_pool* pool, int* count)
+{
+  if (*count > 0)
+  {
+    --(*count);
+
+    int before_value = *count;
+    boost::asio::post(*pool, bindns::bind(decrement_to_zero, pool, count));
+
+    // Handler execution cannot nest, so count value should remain unchanged.
+    BOOST_ASIO_CHECK(*count == before_value);
+  }
+}
+
+void nested_decrement_to_zero(thread_pool* pool, int* count)
+{
+  if (*count > 0)
+  {
+    --(*count);
+
+    boost::asio::dispatch(*pool,
+        bindns::bind(nested_decrement_to_zero, pool, count));
+
+    // Handler execution is nested, so count value should now be zero.
+    BOOST_ASIO_CHECK(*count == 0);
+  }
+}
+
+void thread_pool_test()
+{
+  thread_pool pool(1);
+
+  int count1 = 0;
+  boost::asio::post(pool, bindns::bind(increment, &count1));
+
+  int count2 = 10;
+  boost::asio::post(pool, bindns::bind(decrement_to_zero, &pool, &count2));
+
+  int count3 = 10;
+  boost::asio::post(pool, bindns::bind(nested_decrement_to_zero, &pool, &count3));
+
+  pool.wait();
+
+  BOOST_ASIO_CHECK(count1 == 1);
+  BOOST_ASIO_CHECK(count2 == 0);
+  BOOST_ASIO_CHECK(count3 == 0);
+}
+
+class test_service : public boost::asio::execution_context::service
+{
+public:
+  typedef test_service key_type;
+
+  test_service(boost::asio::execution_context& ctx)
+    : boost::asio::execution_context::service(ctx)
+  {
+  }
+
+private:
+  virtual void shutdown() {}
+};
+
+void thread_pool_service_test()
+{
+  boost::asio::thread_pool pool1(1);
+  boost::asio::thread_pool pool2(1);
+  boost::asio::thread_pool pool3(1);
+
+  // Implicit service registration.
+
+  boost::asio::use_service<test_service>(pool1);
+
+  BOOST_ASIO_CHECK(boost::asio::has_service<test_service>(pool1));
+
+  test_service* svc1 = new test_service(pool1);
+  try
+  {
+    boost::asio::add_service(pool1, svc1);
+    BOOST_ASIO_ERROR("add_service did not throw");
+  }
+  catch (boost::asio::service_already_exists&)
+  {
+  }
+  delete svc1;
+
+  // Explicit service registration.
+
+  test_service& svc2 = boost::asio::make_service<test_service>(pool2);
+
+  BOOST_ASIO_CHECK(boost::asio::has_service<test_service>(pool2));
+  BOOST_ASIO_CHECK(&boost::asio::use_service<test_service>(pool2) == &svc2);
+
+  test_service* svc3 = new test_service(pool2);
+  try
+  {
+    boost::asio::add_service(pool2, svc3);
+    BOOST_ASIO_ERROR("add_service did not throw");
+  }
+  catch (boost::asio::service_already_exists&)
+  {
+  }
+  delete svc3;
+
+  // Explicit registration with invalid owner.
+
+  test_service* svc4 = new test_service(pool2);
+  try
+  {
+    boost::asio::add_service(pool3, svc4);
+    BOOST_ASIO_ERROR("add_service did not throw");
+  }
+  catch (boost::asio::invalid_service_owner&)
+  {
+  }
+  delete svc4;
+
+  BOOST_ASIO_CHECK(!boost::asio::has_service<test_service>(pool3));
+}
+
+void thread_pool_executor_query_test()
+{
+  thread_pool pool(1);
+
+  BOOST_ASIO_CHECK(
+      &boost::asio::query(pool.executor(),
+        boost::asio::execution::context)
+      == &pool);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::blocking)
+      == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::blocking.possibly)
+      == boost::asio::execution::blocking.possibly);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::outstanding_work)
+      == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::outstanding_work.untracked)
+      == boost::asio::execution::outstanding_work.untracked);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::relationship)
+      == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::relationship.fork)
+      == boost::asio::execution::relationship.fork);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::bulk_guarantee)
+      == boost::asio::execution::bulk_guarantee.parallel);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::mapping)
+      == boost::asio::execution::mapping.thread);
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::allocator)
+      == std::allocator<void>());
+
+  BOOST_ASIO_CHECK(
+      boost::asio::query(pool.executor(),
+        boost::asio::execution::occupancy)
+      == 1);
+}
+
+void thread_pool_executor_execute_test()
+{
+  int count = 0;
+  thread_pool pool(1);
+
+  boost::asio::execution::execute(pool.executor(),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.possibly),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.always),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.tracked),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.fork),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::require(pool.executor(),
+        boost::asio::execution::blocking.never,
+        boost::asio::execution::outstanding_work.untracked,
+        boost::asio::execution::relationship.continuation),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(pool.executor(),
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator(std::allocator<void>())),
+      bindns::bind(increment, &count));
+
+  boost::asio::execution::execute(
+      boost::asio::prefer(
+        boost::asio::require(pool.executor(),
+          boost::asio::execution::blocking.never,
+          boost::asio::execution::outstanding_work.untracked,
+          boost::asio::execution::relationship.continuation),
+        boost::asio::execution::allocator),
+      bindns::bind(increment, &count));
+
+  pool.wait();
+
+  BOOST_ASIO_CHECK(count == 10);
+}
+
+BOOST_ASIO_TEST_SUITE
+(
+  "thread_pool",
+  BOOST_ASIO_TEST_CASE(thread_pool_test)
+  BOOST_ASIO_TEST_CASE(thread_pool_service_test)
+  BOOST_ASIO_TEST_CASE(thread_pool_executor_query_test)
+  BOOST_ASIO_TEST_CASE(thread_pool_executor_execute_test)
+)
diff --git a/test/unit_test.hpp b/test/unit_test.hpp
index 6d5a7847..de1f55d5 100644
--- a/test/unit_test.hpp
+++ b/test/unit_test.hpp
@@ -19,7 +19,7 @@
 # include <stdlib.h> // Needed for lrand48.
 #endif // defined(__sun)
 
-#if defined(__BORLANDC__)
+#if defined(__BORLANDC__) && !defined(__clang__)
 
 // Prevent use of intrinsic for strcmp.
 # include <cstring>
@@ -28,7 +28,7 @@
 // Suppress error about condition always being true.
 # pragma option -w-ccc
 
-#endif // defined(__BORLANDC__)
+#endif // defined(__BORLANDC__) && !defined(__clang__)
 
 #if defined(BOOST_ASIO_MSVC)
 # pragma warning (disable:4127)
@@ -154,6 +154,21 @@ void throw_exception(const T& t)
 #define BOOST_ASIO_TEST_CASE(test) \
   boost::asio::detail::run_test<&test>(#test);
 
+#define BOOST_ASIO_TEST_CASE2(test1, test2) \
+  boost::asio::detail::run_test<&test1, test2>(#test1 "," #test2);
+
+#define BOOST_ASIO_TEST_CASE3(test1, test2, test3) \
+  boost::asio::detail::run_test<&test1, test2, test3>( \
+    #test1 "," #test2 "," #test3);
+
+#define BOOST_ASIO_TEST_CASE4(test1, test2, test3, test4) \
+  boost::asio::detail::run_test<&test1, test2, test3, test4>( \
+    #test1 "," #test2 "," #test3 "," #test4);
+
+#define BOOST_ASIO_TEST_CASE5(test1, test2, test3, test4, test5) \
+  boost::asio::detail::run_test<&test1, test2, test3, test4, test5>( \
+    #test1 "," #test2 "," #test3 "," #test4 "," #test5);
+
 #define BOOST_ASIO_COMPILE_TEST_CASE(test) \
   boost::asio::detail::compile_test<&test>(#test);
 
diff --git a/tools/handlerlive.pl b/tools/handlerlive.pl
new file mode 100644
index 00000000..b7a5b8cf
--- /dev/null
+++ b/tools/handlerlive.pl
@@ -0,0 +1,89 @@
+#!/usr/bin/perl -w
+#
+# handlerlive.pl
+# ~~~~~~~~~~~~~~
+#
+# A tool for post-processing the debug output generated by Asio-based programs
+# to print a list of "live" handlers. These are handlers that are associated
+# with operations that have not yet completed, or running handlers that have
+# not yet finished their execution. Programs write this output to the standard
+# error stream when compiled with the define `BOOST_ASIO_ENABLE_HANDLER_TRACKING'.
+#
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+
+use strict;
+
+my %pending_handlers = ();
+my %running_handlers = ();
+
+#-------------------------------------------------------------------------------
+# Parse the debugging output and update the set of pending handlers.
+
+sub parse_debug_output()
+{
+  while (my $line = <>)
+  {
+    chomp($line);
+
+    if ($line =~ /\@asio\|([^|]*)\|([^|]*)\|(.*)$/)
+    {
+      my $action = $2;
+
+      # Handler creation.
+      if ($action =~ /^([0-9]+)\*([0-9]+)$/)
+      {
+        $pending_handlers{$2} = 1;
+      }
+
+      # Begin handler invocation. 
+      elsif ($action =~ /^>([0-9]+)$/)
+      {
+        delete($pending_handlers{$1});
+        $running_handlers{$1} = 1;
+      }
+
+      # End handler invocation.
+      elsif ($action =~ /^<([0-9]+)$/)
+      {
+        delete($running_handlers{$1});
+      }
+
+      # Handler threw exception.
+      elsif ($action =~ /^!([0-9]+)$/)
+      {
+        delete($running_handlers{$1});
+      }
+
+      # Handler was destroyed without being invoked.
+      elsif ($action =~ /^~([0-9]+)$/)
+      {
+        delete($pending_handlers{$1});
+      }
+    }
+  }
+}
+
+#-------------------------------------------------------------------------------
+# Print a list of incompleted handers, on a single line delimited by spaces.
+
+sub print_handlers($)
+{
+  my $handlers = shift;
+  my $prefix = "";
+  foreach my $handler (sort { $a <=> $b } keys %{$handlers})
+  {
+    print("$prefix$handler");
+    $prefix = " ";
+  }
+  print("\n") if ($prefix ne "");
+}
+
+#-------------------------------------------------------------------------------
+
+parse_debug_output();
+print_handlers(\%running_handlers);
+print_handlers(\%pending_handlers);
diff --git a/tools/handlertree.pl b/tools/handlertree.pl
new file mode 100644
index 00000000..ff5c06b1
--- /dev/null
+++ b/tools/handlertree.pl
@@ -0,0 +1,140 @@
+#!/usr/bin/perl -w
+#
+# handlertree.pl
+# ~~~~~~~~~~~~~~
+# A tool for post-processing the debug output generated by Asio-based programs
+# to print the tree of handlers that resulted in some specified handler ids.
+# Programs write this output to the standard error stream when compiled with
+# the define `BOOST_ASIO_ENABLE_HANDLER_TRACKING'.
+#
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+
+use strict;
+
+my %target_handlers = ();
+my @cached_output = ();
+my %outstanding_handlers = ();
+my %running_handlers = ();
+
+#-------------------------------------------------------------------------------
+# Build the initial list of target handlers from the command line arguments.
+
+sub build_initial_target_handlers()
+{
+  for my $handler (@ARGV)
+  {
+    $target_handlers{$handler} = 1;
+  }
+}
+
+#-------------------------------------------------------------------------------
+# Parse the debugging output and cache the handler tracking lines.
+
+sub parse_debug_output()
+{
+  while (my $line = <STDIN>)
+  {
+    chomp($line);
+
+    if ($line =~ /\@asio\|([^|]*)\|([^|]*)\|(.*)$/)
+    {
+      push(@cached_output, $line);
+    }
+  }
+}
+
+#-------------------------------------------------------------------------------
+# Iterate over the cached output in revese and build a hash of all target
+# handlers' ancestors.
+
+sub build_target_handler_tree()
+{
+  my $i = scalar(@cached_output) - 1;
+  while ($i >= 0)
+  {
+    my $line = $cached_output[$i];
+
+    if ($line =~ /\@asio\|([^|]*)\|([^|]*)\|(.*)$/)
+    {
+      my $action = $2;
+
+      # Handler creation.
+      if ($action =~ /^([0-9]+)\*([0-9]+)$/)
+      {
+        if ($1 ne "0" and exists($target_handlers{$2}))
+        {
+          $target_handlers{$1} = 1;
+        }
+      }
+    }
+
+    --$i;
+  }
+}
+
+#-------------------------------------------------------------------------------
+# Print out all handler tracking records associated with the target handlers.
+
+sub print_target_handler_records()
+{
+  for my $line (@cached_output)
+  {
+    if ($line =~ /\@asio\|([^|]*)\|([^|]*)\|(.*)$/)
+    {
+      my $action = $2;
+
+      # Handler location.
+      if ($action =~ /^([0-9]+)\^([0-9]+)$/)
+      {
+        print("$line\n") if ($1 eq "0" or exists($target_handlers{$1})) and exists($target_handlers{$2});
+      }
+
+      # Handler creation.
+      if ($action =~ /^([0-9]+)\*([0-9]+)$/)
+      {
+        print("$1, $2, $line\n") if ($1 eq "0" or exists($target_handlers{$1})) and exists($target_handlers{$2});
+      }
+
+      # Begin handler invocation. 
+      elsif ($action =~ /^>([0-9]+)$/)
+      {
+        print("$line\n") if (exists($target_handlers{$1}));
+      }
+
+      # End handler invocation.
+      elsif ($action =~ /^<([0-9]+)$/)
+      {
+        print("$line\n") if (exists($target_handlers{$1}));
+      }
+
+      # Handler threw exception.
+      elsif ($action =~ /^!([0-9]+)$/)
+      {
+        print("$line\n") if (exists($target_handlers{$1}));
+      }
+
+      # Handler was destroyed without being invoked.
+      elsif ($action =~ /^~([0-9]+)$/)
+      {
+        print("$line\n") if (exists($target_handlers{$1}));
+      }
+
+      # Operation associated with a handler.
+      elsif ($action =~ /^\.([0-9]+)$/)
+      {
+        print("$line\n") if (exists($target_handlers{$1}));
+      }
+    }
+  }
+}
+
+#-------------------------------------------------------------------------------
+
+build_initial_target_handlers();
+parse_debug_output();
+build_target_handler_tree();
+print_target_handler_records();
diff --git a/tools/handlerviz.pl b/tools/handlerviz.pl
index 7e8de3df..7c1ff13c 100755
--- a/tools/handlerviz.pl
+++ b/tools/handlerviz.pl
@@ -16,7 +16,7 @@
 #
 #   perl handlerviz.pl < output.txt | dot -Tpdf > output.pdf
 #
-# Copyright (c) 2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+# Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 #
 # Distributed under the Boost Software License, Version 1.0. (See accompanying
 # file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -26,9 +26,11 @@ use strict;
 
 my %nodes = ();
 my @edges = ();
+my %locations = ();
 my %anon_nodes = ();
 my $anon_id = 0;
 my %all_nodes = ();
+my %pending_nodes = ();
 
 #-------------------------------------------------------------------------------
 # Parse the debugging output and populate the nodes and edges.
@@ -62,6 +64,21 @@ sub parse_debug_output()
 
         my %edge = ( begin=>$begin, end=>$end, label=>$label );
         push(@edges, \%edge);
+
+        $pending_nodes{$end} = 1;
+      }
+
+      # Handler location.
+      elsif ($action =~ /^([0-9]+)\^([0-9]+)$/)
+      {
+        if ($1 ne "0")
+        {
+          if (not exists($locations{($1,$2)}))
+          {
+            $locations{($1,$2)} = ();
+          }
+          push(@{$locations{($1,$2)}}, $description);
+        }
       }
 
       # Begin handler invocation. 
@@ -71,6 +88,7 @@ sub parse_debug_output()
         $new_node{content} = ();
         $nodes{$1} = \%new_node;
         $all_nodes{"$timestamp-$1"} = $1;
+        delete($pending_nodes{$1});
       }
 
       # End handler invocation.
@@ -92,6 +110,7 @@ sub parse_debug_output()
         $new_node{content} = ();
         $nodes{$1} = \%new_node;
         $all_nodes{"$timestamp-$1"} = $1;
+        delete($pending_nodes{$1});
       }
 
       # Handler performed some operation.
@@ -129,8 +148,8 @@ sub escape($)
 # Templates for dot output.
 
 my $graph_header = <<"EOF";
-/* Generated by asioviz.pl */
-digraph G
+/* Generated by handlerviz.pl */
+digraph "handlerviz output"
 {
 graph [ nodesep="1" ];
 node [ shape="box", fontsize="9" ];
@@ -172,9 +191,23 @@ my $anon_node = <<"EOF";
 "%name%" [ label="%label%", color="gray" ];
 EOF
 
+my $pending_nodes_header = <<"EOF";
+{
+node [ shape="record", color="red" ];
+rank = "max";
+EOF
+
+my $pending_nodes_footer = <<"EOF";
+}
+EOF
+
+my $pending_node = <<"EOF";
+"%name%";
+EOF
+
 my $edges_header = <<"EOF";
 {
-edge [ style="dashed", arrowhead="open", weight="100" ];
+edge [ style="dashed", arrowhead="open" ];
 EOF
 
 my $edges_footer = <<"EOF";
@@ -182,12 +215,13 @@ my $edges_footer = <<"EOF";
 EOF
 
 my $edge = <<"EOF";
-"%begin%" -> "%end%" [ label="%label%" ]
+"%begin%" -> "%end%" [ label="%label%", labeltooltip="%tooltip%" ]
 EOF
 
 my $node_order_header = <<"EOF";
 {
-edge [ style="invis", weight="1" ];
+node [ style="invisible" ];
+edge [ style="invis", weight="100" ];
 EOF
 
 my $node_order_footer = <<"EOF";
@@ -195,7 +229,12 @@ my $node_order_footer = <<"EOF";
 EOF
 
 my $node_order = <<"EOF";
-"%begin%" -> "%end%"
+{
+rank="same"
+"%begin%";
+"o%begin%";
+}
+"o%begin%" -> "o%end%";
 EOF
 
 #-------------------------------------------------------------------------------
@@ -214,10 +253,13 @@ sub print_nodes()
     $header =~ s/%label%/$label/g;
     print($header);
 
-    my $line = $node_content;
-    my $content = $entry . " + " . sprintf("%.6f", $exit - $entry) . "s";
-    $line =~ s/%content%/$content/g;
-    print($line);
+    if (defined($exit) and defined($entry))
+    {
+      my $line = $node_content;
+      my $content = $entry . " + " . sprintf("%.6f", $exit - $entry) . "s";
+      $line =~ s/%content%/$content/g;
+      print($line);
+    }
 
     foreach my $content (@{$node->{content}})
     {
@@ -243,7 +285,19 @@ sub print_anon_nodes()
     $line =~ s/%label%/$label/g;
     print($line);
   }
-  print($edges_footer);
+  print($anon_nodes_footer);
+}
+
+sub print_pending_nodes()
+{
+  print($pending_nodes_header);
+  foreach my $name (sort keys %pending_nodes)
+  {
+    my $line = $pending_node;
+    $line =~ s/%name%/$name/g;
+    print($line);
+  }
+  print($pending_nodes_footer);
 }
 
 sub print_edges()
@@ -254,10 +308,19 @@ sub print_edges()
     my $begin = $e->{begin};
     my $end = $e->{end};
     my $label = $e->{label};
+    my $tooltip = "";
+    if (exists($locations{($begin,$end)}))
+    {
+      for my $line (@{$locations{($begin,$end)}})
+      {
+        $tooltip = $tooltip . escape($line) . "\n";
+      }
+    }
     my $line = $edge;
     $line =~ s/%begin%/$begin/g;
     $line =~ s/%end%/$end/g;
     $line =~ s/%label%/$label/g;
+    $line =~ s/%tooltip%/$tooltip/g;
     print($line);
   }
   print($edges_footer);
@@ -280,6 +343,18 @@ sub print_node_order()
     }
     $prev = $all_nodes{$name};
   }
+  foreach my $name (sort keys %pending_nodes)
+  {
+    if ($prev ne "")
+    {
+      my $begin = $prev;
+      my $line = $node_order;
+      $line =~ s/%begin%/$begin/g;
+      $line =~ s/%end%/$name/g;
+      print($line);
+    }
+    last;
+  }
   print($node_order_footer);
 }
 
@@ -288,6 +363,7 @@ sub generate_dot()
   print($graph_header);
   print_nodes();
   print_anon_nodes();
+  print_pending_nodes();
   print_edges();
   print_node_order();
   print($graph_footer);