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asyncio.TaskGroup hangs on cancel with eager task factory #155418
Description
Bug report
Bug description:
With eager TF, a child task that calls tg.cancel() before it suspends is never cancelled, and the group hangs forever. This happens if we dont have a suspension point before cancelling the group in the child, abort() happens before the task added to the self._tasks and run on empty list. Then __aexit__ hangs on await self._on_completed_fut that tries to wait task that is not cancelled
Repro:
import asyncio
async def child(tg, done):
tg.cancel()
await done.wait()
async def main():
done = asyncio.Event()
async with asyncio.TaskGroup() as tg:
tg.create_task(child(tg, done))
print("group exited")
loop = asyncio.new_event_loop()
loop.set_task_factory(asyncio.eager_task_factory)
loop.run_until_complete(main())Expected output will be
group exited
But actually there will be no print
Proposed fix - add the check before returning the task
self._tasks.add(task)
task.add_done_callback(self._on_task_done)
if self._aborting and not task.done():
task.cancel()
try:
return task
finally:
# gh-128552: prevent a refcycle of
# task.exception().__traceback__->TaskGroup.create_task->task
del taskI have a fix ready
CPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
Activity
pythongh-155418: Fix TaskGroup hang when a task cancels it before sus…
Merge branch 'main' into pythongh-155418-tg-hang
gh-155418: Fix TaskGroup hang when a task cancels it before suspending (
[3.15] gh-155418: Fix TaskGroup hang when a task cancels it before su…
pythongh-155418: Fix TaskGroup hang when a task cancels it before sus…