spawn race condition fix, closes #167.

include/boost/cobalt/detail/forward_cancellation.hpp

@@ -39,18 +39,6 @@ struct forward_cancellation
   }
 };
 
-struct forward_dispatch_cancellation
-{
-  asio::cancellation_signal &cancel_signal;
-  executor exec;
-
-  forward_dispatch_cancellation(asio::cancellation_signal &cancel_signal,
-                            executor exec) : cancel_signal(cancel_signal), exec(exec) {}
-  void operator()(asio::cancellation_type ct) const
-  {
-    asio::dispatch(exec, [this, ct]{cancel_signal.emit(ct);});
-  }
-};
 
 }
 

include/boost/cobalt/detail/spawn.hpp

@@ -39,11 +39,15 @@ struct async_initiate_spawn
 #else
     auto alloc = asio::get_associated_allocator(h);
 #endif
-    auto recs = allocate_unique<detail::task_receiver<T>>(alloc, std::move(rec));
+    auto recs = std::allocate_shared<detail::task_receiver<T>>(alloc, std::move(rec));
 
     auto sl = asio::get_associated_cancellation_slot(h);
     if (sl.is_connected())
-      sl.template emplace<detail::forward_dispatch_cancellation>(recs->promise->signal, exec);
+      sl.assign(
+          [exec, recs](asio::cancellation_type ct)
+          {
+            asio::dispatch(exec, [recs, ct] {recs->cancel(ct);});
+          });
 
     auto p = recs.get();
 
@@ -97,15 +101,19 @@ struct async_initiate_spawn
 #else
     auto alloc = asio::get_associated_allocator(h);
 #endif
-    auto recs = allocate_unique<detail::task_receiver<void>>(alloc, std::move(a.receiver_));
+    auto recs = std::allocate_shared<detail::task_receiver<void>>(alloc, std::move(a.receiver_));
 
     if (recs->done)
       return asio::dispatch(asio::get_associated_immediate_executor(h, exec),
                             asio::append(std::forward<Handler>(h), recs->exception));
 
     auto sl = asio::get_associated_cancellation_slot(h);
     if (sl.is_connected())
-      sl.template emplace<detail::forward_dispatch_cancellation>(recs->promise->signal, exec);
+      sl.assign(
+          [exec, recs](asio::cancellation_type ct)
+          {
+            asio::dispatch(exec, [recs, ct] {recs->cancel(ct);});
+          });
 
     auto p = recs.get();
 

include/boost/cobalt/detail/task.hpp

@@ -108,6 +108,12 @@ struct task_receiver : task_value_holder<T>
     done = true;
   }
 
+  void cancel(asio::cancellation_type ct) const
+  {
+    if (!done)
+      promise->signal.emit(ct);
+  }
+
   task_receiver() = default;
   task_receiver(task_receiver && lhs)
       : task_value_holder<T>(std::move(lhs)),

test/task.cpp

@@ -312,5 +312,16 @@ CO_TEST_CASE(move_only)
   co_await task_move_only_test();
 }
 
+BOOST_AUTO_TEST_CASE(cancel_task_)
+{
+  asio::thread_pool ctx{1};
+  asio::cancellation_signal sig;
+  cobalt::spawn(ctx, test0(), asio::bind_cancellation_slot(sig.slot(), asio::detached));
+  sig.emit(asio::cancellation_type::all);
+  ctx.join();
+}
+
+
+
 
 BOOST_AUTO_TEST_SUITE_END();