gh-128550: TaskGroup: cancel tasks added to set after aborting

Lib/asyncio/taskgroups.py

@@ -205,6 +205,11 @@ def create_task(self, coro, *, name=None, context=None):
  else:
  self._tasks.add(task)
  task.add_done_callback(self._on_task_done)
+ if self._aborting:
+ # gh-128550: if this task is eager it might have started
+ # another eager task that aborts us, if so we must cancel
+ # this task.
+ task.cancel()
  try:
  return task
  finally:

Lib/test/test_asyncio/test_taskgroups.py

@@ -1040,6 +1040,32 @@ class MyKeyboardInterrupt(KeyboardInterrupt):
  self.assertIsNotNone(exc)
  self.assertListEqual(gc.get_referrers(exc), no_other_refs())
 
+ 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)
 
 class TestTaskGroup(BaseTestTaskGroup, unittest.IsolatedAsyncioTestCase):
  loop_factory = asyncio.EventLoop

Misc/NEWS.d/next/Library/2025-01-06-18-58-07.gh-issue-128550.lzeWhZ.rst

@@ -0,0 +1 @@
+Fix a deadlock in :class:`asyncio.TaskGroup` when using eager tasks that abort the task group too early.