Closes #21886, #21447: Fix a race condition in asyncio when setting the result
of a Future with call_soon(). Add an helper, a private method, to set the
result only if the future was not cancelled.
diff --git a/Lib/asyncio/queues.py b/Lib/asyncio/queues.py
index 57afb05..41551a9 100644
--- a/Lib/asyncio/queues.py
+++ b/Lib/asyncio/queues.py
@@ -173,7 +173,7 @@
# run, we need to defer the put for a tick to ensure that
# getters and putters alternate perfectly. See
# ChannelTest.test_wait.
- self._loop.call_soon(putter.set_result, None)
+ self._loop.call_soon(putter._set_result_unless_cancelled, None)
return self._get()