https://github.com/python/cpython/commit/934a82623793e9d52b85f74d5395d65927a... commit: 934a82623793e9d52b85f74d5395d65927a52205 branch: main author: Sam Bull <aa6bs0@sambull.org> committer: asvetlov <andrew.svetlov@gmail.com> date: 2021-11-29T10:12:57+02:00 summary: bpo-37658: Actually return result in race condition (GH-29202) files: A Misc/NEWS.d/next/Library/2021-11-28-15-30-34.bpo-37658.8Hno7d.rst M Lib/asyncio/tasks.py M Lib/test/test_asyncio/test_tasks.py diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py index 9a9d0d6e3cc26..53eef84427be1 100644 --- a/Lib/asyncio/tasks.py +++ b/Lib/asyncio/tasks.py @@ -415,11 +415,9 @@ async def wait_for(fut, timeout): await _cancel_and_wait(fut, loop=loop) try: - fut.result() + return fut.result() except exceptions.CancelledError as exc: raise exceptions.TimeoutError() from exc - else: - raise exceptions.TimeoutError() waiter = loop.create_future() timeout_handle = loop.call_later(timeout, _release_waiter, waiter) @@ -455,11 +453,9 @@ async def wait_for(fut, timeout): # exception, we should re-raise it # See https://bugs.python.org/issue40607 try: - fut.result() + return fut.result() except exceptions.CancelledError as exc: raise exceptions.TimeoutError() from exc - else: - raise exceptions.TimeoutError() finally: timeout_handle.cancel() diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py index 362fbf8df08ca..a88cb89e4e6ee 100644 --- a/Lib/test/test_asyncio/test_tasks.py +++ b/Lib/test/test_asyncio/test_tasks.py @@ -1009,20 +1009,16 @@ def gen(): self.assertEqual(res, "ok") def test_wait_for_cancellation_race_condition(self): - def gen(): - yield 0.1 - yield 0.1 - yield 0.1 - yield 0.1 + async def inner(): + with contextlib.suppress(asyncio.CancelledError): + await asyncio.sleep(1) + return 1 - loop = self.new_test_loop(gen) + async def main(): + result = await asyncio.wait_for(inner(), timeout=.01) + assert result == 1 - fut = self.new_future(loop) - loop.call_later(0.1, fut.set_result, "ok") - task = loop.create_task(asyncio.wait_for(fut, timeout=1)) - loop.call_later(0.1, task.cancel) - res = loop.run_until_complete(task) - self.assertEqual(res, "ok") + asyncio.run(main()) def test_wait_for_waits_for_task_cancellation(self): loop = asyncio.new_event_loop() @@ -1101,24 +1097,6 @@ async def inner(): with self.assertRaises(FooException): loop.run_until_complete(foo()) - def test_wait_for_raises_timeout_error_if_returned_during_cancellation(self): - loop = asyncio.new_event_loop() - self.addCleanup(loop.close) - - async def foo(): - async def inner(): - try: - await asyncio.sleep(0.2) - except asyncio.CancelledError: - return 42 - - inner_task = self.new_task(loop, inner()) - - await asyncio.wait_for(inner_task, timeout=_EPSILON) - - with self.assertRaises(asyncio.TimeoutError): - loop.run_until_complete(foo()) - def test_wait_for_self_cancellation(self): loop = asyncio.new_event_loop() self.addCleanup(loop.close) diff --git a/Misc/NEWS.d/next/Library/2021-11-28-15-30-34.bpo-37658.8Hno7d.rst b/Misc/NEWS.d/next/Library/2021-11-28-15-30-34.bpo-37658.8Hno7d.rst new file mode 100644 index 0000000000000..97d1e961ac2be --- /dev/null +++ b/Misc/NEWS.d/next/Library/2021-11-28-15-30-34.bpo-37658.8Hno7d.rst @@ -0,0 +1,3 @@ +Fix issue when on certain conditions ``asyncio.wait_for()`` may allow a +coroutine to complete successfully, but fail to return the result, +potentially causing memory leaks or other issues.