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shield() documentation should mention user needs to keep reference to the task #94972
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[-]sheild() documentation should mention user needs to keep reference to the task[/-][+]shield() documentation should mention user needs to keep reference to the task[/+]on Jul 18, 2022 Can you provide reproducible code where this happens?
@kumaraditya303 here's the repro on python3.10:
import weakref import asyncio import gc import logging logger = logging.getLogger(__name__) async def async_fn(): try: await asyncio.get_running_loop().create_future() except BaseException: logger.exception("closed!") raise async def amain(): weak_task = weakref.ref(asyncio.create_task(async_fn())) await asyncio.sleep(0.01) gc.collect() print(weak_task()) async def sheild_gc(): strong_shielded_fut = asyncio.shield(async_fn()) await asyncio.sleep(0) asyncio.current_task().cancel() try: await strong_shielded_fut except asyncio.CancelledError: pass gc.collect() asyncio.run(amain()) print("======================") asyncio.run(sheild_gc())
output:
closed! Traceback (most recent call last): File "/home/graingert/projects/foo.py", line 14, in async_fn await asyncio.get_running_loop().create_future() GeneratorExit Task was destroyed but it is pending! task: <Task pending name='Task-2' coro=<async_fn() done, defined at /home/graingert/projects/foo.py:12> wait_for=<Future pending cb=[Task.task_wakeup()]>> None ====================== closed! Traceback (most recent call last): File "/home/graingert/projects/foo.py", line 14, in async_fn await asyncio.get_running_loop().create_future() GeneratorExit Task was destroyed but it is pending! task: <Task pending name='Task-6' coro=<async_fn() done, defined at /home/graingert/projects/foo.py:12> wait_for=<Future pending cb=[Task.task_wakeup()]>>Are you too busy to submit a PR that updates the docs?
I think I get the same output on 3.11. Question, is
import objgraphneeded in the repro? (I had to delete it, no idea what it is.)- added a commit that references this issue
on Sep 10, 2022 - added 4 commits that reference this issue
on Sep 10, 2022 I think I get the same output on 3.11. Question, is
import objgraphneeded in the repro? (I had to delete it, no idea what it is.)Left in by accident. It's not needed to cause the error but I used it to help build it
- added a commit that references this issue
on Dec 28, 2024
Documentation
asyncio will only keep weak references to alive tasks (in _all_tasks). If a user does not keep a reference to a task and the task is not currently executing or sleeping, the user may get "Task was destroyed but it is pending!".
see also #88831
shield has the same issue and the documentation currently recommends the incorrect usage