https://github.com/python/cpython/commit/a1c48a750cc52332b0ed16ea8ffa07c18ea... commit: a1c48a750cc52332b0ed16ea8ffa07c18eaee201 branch: 3.13 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: kumaraditya303 <kumaraditya@python.org> date: 2025-01-20T17:36:50Z summary: [3.13] gh-128588: gh-128550: remove eager tasks optimization that missed and introduced incorrect cancellations (GH-129063) (#129089) gh-128588: gh-128550: remove eager tasks optimization that missed and introduced incorrect cancellations (GH-129063) (cherry picked from commit ed6934e71e55d398df8263f4697f58e4a3815f69) Co-authored-by: Thomas Grainger <tagrain@gmail.com> Co-authored-by: Kumar Aditya <kumaraditya@python.org> files: A Misc/NEWS.d/next/Library/2025-01-20-13-12-39.gh-issue-128550.AJ5TOL.rst M Lib/asyncio/taskgroups.py M Lib/test/test_asyncio/test_taskgroups.py diff --git a/Lib/asyncio/taskgroups.py b/Lib/asyncio/taskgroups.py index 8af199d6dcc41a..8fda6c8d55e16c 100644 --- a/Lib/asyncio/taskgroups.py +++ b/Lib/asyncio/taskgroups.py @@ -197,14 +197,12 @@ def create_task(self, coro, *, name=None, context=None): else: task = self._loop.create_task(coro, name=name, context=context) - # optimization: Immediately call the done callback if the task is + # Always schedule the done callback even if the task is # already done (e.g. if the coro was able to complete eagerly), - # and skip scheduling a done callback - if task.done(): - self._on_task_done(task) - else: - self._tasks.add(task) - task.add_done_callback(self._on_task_done) + # otherwise if the task completes with an exception then it will cancel + # the current task too early. gh-128550, gh-128588 + self._tasks.add(task) + task.add_done_callback(self._on_task_done) try: return task finally: diff --git a/Lib/test/test_asyncio/test_taskgroups.py b/Lib/test/test_asyncio/test_taskgroups.py index e52061aac923cc..ad61cb46c7c07c 100644 --- a/Lib/test/test_asyncio/test_taskgroups.py +++ b/Lib/test/test_asyncio/test_taskgroups.py @@ -1032,6 +1032,56 @@ class MyKeyboardInterrupt(KeyboardInterrupt): self.assertListEqual(gc.get_referrers(exc), []) + async def test_cancels_task_if_created_during_creation(self): + # regression test for gh-128550 + ran = False + class MyError(Exception): + pass + + exc = None + try: + async with asyncio.TaskGroup() as tg: + async def third_task(): + raise MyError("third task failed") + + async def second_task(): + nonlocal ran + tg.create_task(third_task()) + with self.assertRaises(asyncio.CancelledError): + await asyncio.sleep(0) # eager tasks cancel here + await asyncio.sleep(0) # lazy tasks cancel here + ran = True + + tg.create_task(second_task()) + except* MyError as excs: + exc = excs.exceptions[0] + + self.assertTrue(ran) + self.assertIsInstance(exc, MyError) + + + async def test_cancellation_does_not_leak_out_of_tg(self): + class MyError(Exception): + pass + + async def throw_error(): + raise MyError + + try: + async with asyncio.TaskGroup() as tg: + tg.create_task(throw_error()) + except* MyError: + pass + else: + self.fail("should have raised one MyError in group") + + # if this test fails this current task will be cancelled + # outside the task group and inside unittest internals + # we yield to the event loop with sleep(0) so that + # cancellation happens here and error is more understandable + await asyncio.sleep(0) + + class TestTaskGroup(BaseTestTaskGroup, unittest.IsolatedAsyncioTestCase): loop_factory = asyncio.EventLoop diff --git a/Misc/NEWS.d/next/Library/2025-01-20-13-12-39.gh-issue-128550.AJ5TOL.rst b/Misc/NEWS.d/next/Library/2025-01-20-13-12-39.gh-issue-128550.AJ5TOL.rst new file mode 100644 index 00000000000000..f59feac795ea18 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-01-20-13-12-39.gh-issue-128550.AJ5TOL.rst @@ -0,0 +1 @@ +Removed an incorrect optimization relating to eager tasks in :class:`asyncio.TaskGroup` that resulted in cancellations being missed.