From f24e917d9cf2146bdf754feb2c2dee8a12469941 Mon Sep 17 00:00:00 2001
From: Klemens Morgenstern <klemens.morgenstern@gmx.net>
Date: Fri, 27 Jun 2025 14:12:24 +0800
Subject: [PATCH] channel handles close & cancel can occur before
 await_suspend.

---
 include/boost/cobalt/channel.hpp      | 13 ++--
 include/boost/cobalt/impl/channel.hpp | 38 +++++++++++-
 src/channel.cpp                       | 23 ++++++-
 test/channel.cpp                      | 88 +++++++++++++++++++++++++++
 test/test.hpp                         | 43 +++++++++++++
 5 files changed, 196 insertions(+), 9 deletions(-)

diff --git a/include/boost/cobalt/channel.hpp b/include/boost/cobalt/channel.hpp
index 23d779f..768a7fc 100644
--- a/include/boost/cobalt/channel.hpp
+++ b/include/boost/cobalt/channel.hpp
@@ -96,7 +96,7 @@ struct channel
     }
 
     struct cancel_impl;
-    bool await_ready() { return !chn->buffer_.empty(); }
+    bool await_ready() { return !chn->buffer_.empty() || chn->is_closed_; }
     template<typename Promise>
     BOOST_COBALT_MSVC_NOINLINE
     std::coroutine_handle<void> await_suspend(std::coroutine_handle<Promise> h);
@@ -140,7 +140,7 @@ struct channel
 
     struct cancel_impl;
 
-    bool await_ready() { return !chn->buffer_.full(); }
+    bool await_ready() { return !chn->buffer_.full() || chn->is_closed_; }
     template<typename Promise>
     BOOST_COBALT_MSVC_NOINLINE
     std::coroutine_handle<void> await_suspend(std::coroutine_handle<Promise> h);
@@ -257,9 +257,12 @@ struct channel<void>
     }
 
     struct cancel_impl;
-    bool await_ready() { return (chn->n_ > 0); }
-    template<typename Promise>
+    bool await_ready()
+    {
+      return (chn->n_ > 0) || chn->is_closed_;
+    }
 
+    template<typename Promise>
     BOOST_COBALT_MSVC_NOINLINE
     std::coroutine_handle<void> await_suspend(std::coroutine_handle<Promise> h);
     BOOST_COBALT_DECL void await_resume();
@@ -297,7 +300,7 @@ struct channel<void>
     struct cancel_impl;
     bool await_ready()
     {
-      return chn->n_ < chn->limit_;
+      return chn->n_ < chn->limit_ || chn->is_closed_;
     }
 
     template<typename Promise>
diff --git a/include/boost/cobalt/impl/channel.hpp b/include/boost/cobalt/impl/channel.hpp
index caec65f..18ab98b 100644
--- a/include/boost/cobalt/impl/channel.hpp
+++ b/include/boost/cobalt/impl/channel.hpp
@@ -96,6 +96,9 @@ template<typename T>
 template<typename Promise>
 std::coroutine_handle<void> channel<T>::read_op::await_suspend(std::coroutine_handle<Promise> h)
 {
+  if (cancelled)
+    return h; // already interrupted.
+
   if constexpr (requires (Promise p) {p.get_cancellation_slot();})
     if ((cancel_slot = h.promise().get_cancellation_slot()).is_connected())
       cancel_slot.emplace<cancel_impl>(this);
@@ -162,8 +165,17 @@ system::result<T> channel<T>::read_op::await_resume(const struct as_result_tag &
   if (cancel_slot.is_connected())
     cancel_slot.clear();
 
+  if (chn->is_closed_ && chn->buffer_.empty() && !direct)
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::broken_pipe, &loc};
+  }
+
   if (cancelled)
-   return {system::in_place_error, asio::error::operation_aborted};
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::operation_aborted, &loc};
+  }
 
   T value = chn->buffer_.empty() ? std::move(*direct) : std::move(chn->buffer_.front());
   if (!chn->buffer_.empty())
@@ -207,6 +219,10 @@ template<typename T>
 template<typename Promise>
 std::coroutine_handle<void> channel<T>::write_op::await_suspend(std::coroutine_handle<Promise> h)
 {
+  if (cancelled)
+    return h; // already interrupted.
+
+
   if constexpr (requires (Promise p) {p.get_cancellation_slot();})
     if ((cancel_slot = h.promise().get_cancellation_slot()).is_connected())
       cancel_slot.emplace<cancel_impl>(this);
@@ -263,8 +279,19 @@ system::result<void>  channel<T>::write_op::await_resume(const struct as_result_
 {
   if (cancel_slot.is_connected())
     cancel_slot.clear();
+
+  if (chn->is_closed_)
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::broken_pipe, &loc};
+  }
+
+
   if (cancelled)
-    return {system::in_place_error, asio::error::operation_aborted};
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::operation_aborted, &loc};
+  }
 
   if (!direct)
   {
@@ -326,6 +353,10 @@ struct channel<void>::write_op::cancel_impl
 template<typename Promise>
 std::coroutine_handle<void> channel<void>::read_op::await_suspend(std::coroutine_handle<Promise> h)
 {
+
+  if (cancelled)
+    return h; // already interrupted.
+
   if constexpr (requires (Promise p) {p.get_cancellation_slot();})
     if ((cancel_slot = h.promise().get_cancellation_slot()).is_connected())
       cancel_slot.emplace<cancel_impl>(this);
@@ -362,6 +393,9 @@ std::coroutine_handle<void> channel<void>::read_op::await_suspend(std::coroutine
 template<typename Promise>
 std::coroutine_handle<void> channel<void>::write_op::await_suspend(std::coroutine_handle<Promise> h)
 {
+  if (cancelled)
+    return h; // already interrupted.
+
   if constexpr (requires (Promise p) {p.get_cancellation_slot();})
     if ((cancel_slot = h.promise().get_cancellation_slot()).is_connected())
       cancel_slot.emplace<cancel_impl>(this);
diff --git a/src/channel.cpp b/src/channel.cpp
index fa4c8dd..a9974c8 100644
--- a/src/channel.cpp
+++ b/src/channel.cpp
@@ -49,8 +49,17 @@ system::result<void>  channel<void>::read_op::await_resume(const struct as_resul
   if (cancel_slot.is_connected())
     cancel_slot.clear();
 
+  if (chn->is_closed_)
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::broken_pipe, &loc};
+  }
+
   if (cancelled)
-    return {system::in_place_error, asio::error::operation_aborted};
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::operation_aborted, &loc};
+  }
 
   if (!direct)
     chn->n_--;
@@ -83,8 +92,18 @@ system::result<void> channel<void>::write_op::await_resume(const struct as_resul
 {
   if (cancel_slot.is_connected())
     cancel_slot.clear();
+
+  if (chn->is_closed_)
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::broken_pipe, &loc};
+  }
+
   if (cancelled)
-    return {system::in_place_error, asio::error::operation_aborted};
+  {
+    constexpr static boost::source_location loc{BOOST_CURRENT_LOCATION};
+    return {system::in_place_error, asio::error::operation_aborted, &loc};
+  }
   if (!direct)
     chn->n_++;
 
diff --git a/test/channel.cpp b/test/channel.cpp
index d8b2156..4486125 100644
--- a/test/channel.cpp
+++ b/test/channel.cpp
@@ -393,4 +393,92 @@ CO_TEST_CASE(interrupt_void_1)
   BOOST_CHECK(rl == 1);
 }
 
+
+
+cobalt::promise<void> do_write(cobalt::channel<void> & c, int times = 1)
+{
+  while (times --> 0)
+    co_await c.write();
+};
+
+CO_TEST_CASE(interrupt_0_void)
+{
+  cobalt::channel<void> c{0};
+  auto w = do_write(c);
+
+  BOOST_CHECK(!w.ready());
+  auto [ec] = co_await cobalt::as_tuple(test_interrupt(c.read()));
+  BOOST_CHECK_MESSAGE(ec == asio::error::operation_aborted, ec.to_string());
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(!w.ready());
+  co_await c.read();
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(w.ready());
+}
+
+
+CO_TEST_CASE(interrupt_1_void)
+{
+  cobalt::channel<void> c{1};
+  auto w = do_write(c, 2);
+
+  BOOST_CHECK(!w.ready());
+  auto [ec] = co_await cobalt::as_tuple(test_interrupt(c.read()));
+  BOOST_CHECK_MESSAGE(ec == asio::error::operation_aborted, ec.to_string());
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(!w.ready());
+  co_await c.read();
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(w.ready());
+  co_await c.read();
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(w.ready());
+}
+
+cobalt::promise<void> do_write(cobalt::channel<int> & c, int times = 1)
+{
+  int i = 0;
+  while (times --> 0)
+    co_await c.write(i++);
+};
+
+
+CO_TEST_CASE(interrupt_0_int)
+{
+  cobalt::channel<int> c{0};
+  auto w = do_write(c);
+
+  BOOST_CHECK(!w.ready());
+  auto [ec, i] = co_await cobalt::as_tuple(test_interrupt(c.read()));
+
+  BOOST_CHECK_MESSAGE(ec == asio::error::operation_aborted, ec.to_string());
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(!w.ready());
+  i = co_await c.read();
+  BOOST_CHECK_EQUAL(i, 0);
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(w.ready());
+}
+
+
+CO_TEST_CASE(interrupt_1_int)
+{
+  cobalt::channel<int> c{1};
+  auto w = do_write(c, 2);
+
+  BOOST_CHECK(!w.ready());
+  auto [ec, i] = co_await cobalt::as_tuple(test_interrupt(c.read()));
+  BOOST_CHECK_MESSAGE(ec == asio::error::operation_aborted, ec.to_string());
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(!w.ready());
+  i = co_await c.read();
+  BOOST_CHECK_EQUAL(i, 0);
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(w.ready());
+  i = co_await c.read();
+  BOOST_CHECK_EQUAL(i, 1);
+  co_await asio::post(co_await this_coro::executor);
+  BOOST_CHECK(w.ready());
+}
+
 }
diff --git a/test/test.hpp b/test/test.hpp
index 8ff006d..69f17b5 100644
--- a/test/test.hpp
+++ b/test/test.hpp
@@ -173,4 +173,47 @@ struct posted_handle
   }
 };
 
+template<boost::cobalt::awaitable_type Aw>
+struct test_interrupt
+{
+  Aw aw;
+
+  test_interrupt(Aw && aw) : aw(std::move(aw)) {}
+
+  bool await_ready()
+  {
+    auto res = aw.await_ready();
+    aw.interrupt_await();
+    return res;
+  }
+
+  template<typename T>
+  auto await_suspend(std::coroutine_handle<T> h)
+  {
+    using type = decltype(aw.await_suspend(h));
+    if constexpr (std::is_void_v<type>)
+    {
+      aw.await_suspend(h);
+      aw.interrupt_await();
+    }
+    else
+    {
+      auto r = aw.await_suspend(h);
+      aw.interrupt_await();
+      return r;
+    }
+  }
+
+  template<typename T>
+  auto await_resume(const T & tag)
+  {
+    return aw.await_resume(tag);
+  }
+
+  auto await_resume()
+  {
+    return aw.await_resume();
+  }
+};
+
 #endif //BOOST_COBALT_TEST2_HPP