https://github.com/python/cpython/commit/06537bb3b17a1095e129cf388363595f4ab6341b
commit: 06537bb3b17a1095e129cf388363595f4ab6341b
branch: 3.15
author: Timofei Ivankov <[email protected]>
committer: hugovk <[email protected]>
date: 2026-09-05T14:41:53+01:00
summary:
[3.15] gh-155418: Fix TaskGroup hang when a task cancels it before suspending
(#156760)
files:
A Misc/NEWS.d/next/Library/2026-08-09-14-27-23.gh-issue-155418.kCXUIG.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 a431b45a19489d5..1fdffcc81a88655 100644
--- a/Lib/asyncio/taskgroups.py
+++ b/Lib/asyncio/taskgroups.py
@@ -222,6 +222,9 @@ def create_task(self, coro, **kwargs):
# the current task too early. gh-128550, gh-128588
self._tasks.add(task)
task.add_done_callback(self._on_task_done)
+ # gh-155418: an eager task can cancel the group before joining _tasks
+ if self._aborting and not task.done():
+ task.cancel()
try:
return task
finally:
diff --git a/Lib/test/test_asyncio/test_taskgroups.py
b/Lib/test/test_asyncio/test_taskgroups.py
index e34c552fc19ff80..b1bff6b476c5dd0 100644
--- a/Lib/test/test_asyncio/test_taskgroups.py
+++ b/Lib/test/test_asyncio/test_taskgroups.py
@@ -1154,6 +1154,17 @@ async def test_taskgroup_cancel_before_create_task(self):
with self.assertRaises(RuntimeError):
tg.create_task(asyncio.sleep(1))
+ async def test_taskgroup_cancel_from_child_before_first_suspension(self):
+ # gh-155418: an eager task can cancel the group before joining _tasks
+ async def child(tg):
+ tg.cancel()
+ await asyncio.sleep(10)
+ self.fail("the child was not cancelled")
+
+ async with asyncio.TaskGroup() as tg:
+ task = tg.create_task(child(tg))
+ self.assertTrue(task.cancelled())
+
async def test_taskgroup_cancel_before_exception(self):
async def raise_exc(parent_tg: asyncio.TaskGroup):
parent_tg.cancel()
diff --git
a/Misc/NEWS.d/next/Library/2026-08-09-14-27-23.gh-issue-155418.kCXUIG.rst
b/Misc/NEWS.d/next/Library/2026-08-09-14-27-23.gh-issue-155418.kCXUIG.rst
new file mode 100644
index 000000000000000..7fe30ddb1ce8b79
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-09-14-27-23.gh-issue-155418.kCXUIG.rst
@@ -0,0 +1,2 @@
+Fix :class:`asyncio.TaskGroup` hang when a task created by
+:func:`asyncio.eager_task_factory` cancels the group before suspending.
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