https://github.com/python/cpython/commit/b06dd2233e89715dad546f7b5d4950ad5cd93658
commit: b06dd2233e89715dad546f7b5d4950ad5cd93658
branch: main
author: Timofei Ivankov <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2026-10-03T21:05:39+05:30
summary:
gh-158239: Fix `asyncio.gather()` performance regression (#158240)
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 979f8d2f83eb1e..33284288a7cca7 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -786,7 +786,7 @@ 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)
@@ -852,11 +852,14 @@ 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
@@ -924,10 +927,6 @@ 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 c380dcfec21395..f460029aff839d 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -1250,6 +1250,37 @@ 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 4a3f6482294e08..ad1b1119aa243a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -884,6 +884,7 @@ 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]
