python · graingert · Jan 6, 2025 · Jan 6, 2025 · Jan 6, 2025 · Jan 6, 2025
@@ -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:

@@ -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

diff --git a/Misc/NEWS.d/next/Library/2025-01-06-18-58-07.gh-issue-128550.lzeWhZ.rst b/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.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix a deadlock in :class:`asyncio.TaskGroup` when using eager tasks that abort the task group too early.