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()
         return task
 
     # Since Python 3.8 Tasks propagate all exceptions correctly,

@@ -997,6 +997,31 @@ 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
+
+        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.assertIsInstance(exc, MyError)
+        self.assertTrue(ran)
 
 if __name__ == "__main__":
     unittest.main()
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 an edge case issue in :class:`asyncio.TaskGroup` when an eager task creates another eager task that raises an exception and aborts the group before the former task is added to that group.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix an edge case issue in :class:`asyncio.TaskGroup` when an eager task creates another eager task that raises an exception and aborts the group before the former task is added to that group.
Comment thread graingert marked this conversation as resolved. Outdated