gh-155418: Fix TaskGroup hang when a task cancels it before suspending (#155421)
diff --git a/Lib/asyncio/taskgroups.py b/Lib/asyncio/taskgroups.py
index 955e8e6..2debb4d 100644
--- a/Lib/asyncio/taskgroups.py
+++ b/Lib/asyncio/taskgroups.py
@@ -239,6 +239,9 @@ 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 983e1a7..1515672 100644
--- a/Lib/test/test_asyncio/test_taskgroups.py
+++ b/Lib/test/test_asyncio/test_taskgroups.py
@@ -1187,6 +1187,17 @@ 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_keeps_outer_cancellation(self):
# gh-155433: any cancellation from outside the group must propagate.
async def child():
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 0000000..7fe30dd
--- /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.
