https://github.com/python/cpython/commit/08671e782d13cdff779cf5b5deb9dbab5cdbd50f commit: 08671e782d13cdff779cf5b5deb9dbab5cdbd50f branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: kumaraditya303 <[email protected]> date: 2026-10-19T12:46:28+05:30 summary:
[3.14] gh-158239: Fix `asyncio.gather()` performance regression (GH-158240) (#158656) gh-158239: Fix `asyncio.gather()` performance regression (GH-158240) (cherry picked from commit b06dd2233e89715dad546f7b5d4950ad5cd93658) Co-authored-by: Timofei Ivankov <[email protected]> files: M Lib/asyncio/tasks.py M Lib/test/test_asyncio/test_tasks.py M Misc/ACKS diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py index 7819286577d895e..43f425622305b6e 100644 --- a/Lib/asyncio/tasks.py +++ b/Lib/asyncio/tasks.py @@ -775,7 +775,7 @@ def cancel(self, msg=None): return ret -def _discard_awaited_by(children, waiter, outer): +def _discard_awaited_by(children, waiter): for fut in children: futures.future_discard_from_awaited_by(fut, waiter) @@ -841,11 +841,14 @@ def _done_callback(fut, cur_task=cur_task): # 'fut.exception()' will *raise* a CancelledError # instead of returning it. exc = fut._make_cancelled_error() + # gh-157213: children outliving gather() must lose the edge + _discard_awaited_by(children, cur_task) outer.set_exception(exc) return else: exc = fut.exception() if exc is not None: + _discard_awaited_by(children, cur_task) outer.set_exception(exc) return @@ -913,10 +916,6 @@ def _done_callback(fut, cur_task=cur_task): children.append(fut) outer = _GatheringFuture(children, loop=loop) - if cur_task is not None: - # gh-157213: a child outliving gather() must lose the awaited-by edge - outer.add_done_callback( - functools.partial(_discard_awaited_by, children, cur_task)) # Run done callbacks after GatheringFuture created so any post-processing # can be performed at this point # optimization: in the special case that *all* futures finished eagerly, diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py index e0a397186db9fd2..f6b84fac880b048 100644 --- a/Lib/test/test_asyncio/test_tasks.py +++ b/Lib/test/test_asyncio/test_tasks.py @@ -1252,6 +1252,37 @@ async def coro(): self.loop.run_until_complete(self.new_task(self.loop, coro())) + def test_gather_discards_awaited_by_for_cancelled_sibling(self): + # gh-157213: same, when gather() is ended by a cancelled child + async def survivor(): + await asyncio.Future() + + async def coro(): + t = self.new_task(self.loop, survivor()) + victim = self.new_task(self.loop, asyncio.sleep(10)) + victim.cancel() + with self.assertRaises(asyncio.CancelledError): + await asyncio.gather(t, victim) + self.assertFalse(t._asyncio_awaited_by) + t.cancel() + with self.assertRaises(asyncio.CancelledError): + await t + + self.loop.run_until_complete(self.new_task(self.loop, coro())) + + def test_gather_does_not_add_callback_to_outer(self): + # gh-158239: gather() must not add an internal done callback to + # the outer future just to maintain the await graph. + async def child(): + await asyncio.sleep(0) + + async def coro(): + outer = asyncio.gather(child(), child()) + self.assertFalse(outer._callbacks) + await outer + + self.loop.run_until_complete(self.new_task(self.loop, coro())) + def test_wait_really_done(self): # there is possibility that some tasks in the pending list # became done but their callbacks haven't all been called yet diff --git a/Misc/ACKS b/Misc/ACKS index 04401cf87ca6e47..2a8246ce71f6ebe 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -870,6 +870,7 @@ Dean Inwood Bob Ippolito Roger Irwin Atsuo Ishimoto +Timofei Ivankov Alexey Izbyshev Kasia Jachim Adam Jackson _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
