Rather than using a context() member function, query the executor's
execution::context_t property to obtain its associated execution
context:
asio::execution_context& context
= asio::query(my_io_executor, asio::execution::context);
When using standard executors, work is tracked by requiring (or
preferring) an executor with the execution::outstanding_work.tracked
property. This replaces executor_work_guard and make_work_guard() with
code of the form
asio::io_context io_context;
auto work = asio::require(io_context.get_executor(),
asio::execution::outstanding_work.tracked);
To explicitly reset work, store the returned work-tracking executor in
an any_io_executor object:
asio::any_io_executor work
= asio::require(io_context.get_executor(),
asio::execution::outstanding_work.tracked);
and then assign an empty executor into the object when done:
work = asio::any_io_executor();
The BOOST_ASIO_HANDLER_LOCATION((file_name, line, function_name)) macro
may be used to inform the handler tracking mechanism of a source
location. This macro declares an object that is placed on the stack.
When an asynchronous operation is launched with location information, it
outputs lines using the <action> 'n^m', prior to the 'n*m' line that
signifies the beginning of the asynchronous operation. For example:
@asio|1589423304.861944|>7|ec=system:0,bytes_transferred=5
@asio|1589423304.861952|7^8|in 'async_write' (./../../../include/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|
If std::source_location or std::experimental::source_location are
available, the 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.
All I/O objects now have an additional Executor template parameter. This
template parameter defaults to the asio::executor type (the polymorphic
executor wrapper) but can be used to specify a user-defined executor
type.
I/O objects' constructors and functions that previously took an
asio::io_context& now accept either an Executor or a reference to a
concrete ExecutionContext (such as asio::io_context or
asio::thread_pool).
One potential point of breakage in existing user code is when reusing an
I/O object's io_context for constructing another I/O object, as in:
asio::steady_timer my_timer(my_socket.get_executor().context());
To fix this, either construct the second I/O object using the first I/O
object's executor:
asio::steady_timer my_timer(my_socket.get_executor());
or otherwise explicitly pass the io_context:
asio::steady_timer my_timer(my_io_context);
Define BOOST_ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM to enable the
old Boost.Date_Time interface in basic_socket_streambuf and
basic_socket_iostream.
for returning a C++11 std::future from an asynchronous operation's
initiating function.
To use asio::use_future, pass it to an asynchronous operation instead of
a normal completion handler. For example:
std::future<std::size_t> length =
my_socket.async_read_some(my_buffer, asio::use_future);
Where a completion handler signature has the form:
void handler(error_code ec, result_type result);
the initiating function returns a std::future templated on result_type.
In the above example, this is std::size_t. If the asynchronous operation
fails, the error_code is converted into a system_error exception and
passed back to the caller through the future.
Where a completion handler signature has the form:
void handler(error_code ec);
the initiating function returns std::future<void>. As above, an error
is passed back in the future as a system_error exception.
[SVN r84313]
