Description

kumaraditya303

opened on Sep 9, 2022

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Reproducer:

import asyncio
import contextvars

name = contextvars.ContextVar('name', default='foo')


def exc_handler(*args):
    assert name.get() == 'bar'


async def task():
    name.set('bar')
    1/0


async def main():
    loop = asyncio.get_running_loop()
    loop.set_exception_handler(exc_handler)
    asyncio.create_task(task())

asyncio.run(main())

On main:

Unhandled error in exception handler
context: {'message': 'Task exception was never retrieved', 'exception': ZeroDivisionError('division by zero'), 'future': <Task finished name='Task-2' coro=<task() done, defined at /workspaces/cpython/main.py:11> exception=ZeroDivisionError('division by zero')>}
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/asyncio/base_events.py", line 1797, in call_exception_handler
    self._exception_handler(self, context)
  File "/workspaces/cpython/main.py", line 8, in exc_handler
    assert name.get() == 'bar'
AssertionError

The exception handler is called with incorrect context hence the AssertionError. It should called with the same context as the task.
My use case is retrieving the current request id from the context var if there are any unhandled error but because of this bug, I always get the default value.

Activity

1. kumaraditya303

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   topic-asyncio

   3.11only security fixesonly security fixes

   3.10 (EOL)end of lifeend of life

   3.12only security fixesonly security fixes

   on Sep 9, 2022
2. kumaraditya303

   added this to asyncioon Sep 9, 2022
3. kumaraditya303

   moved this to Todo in asyncioon Sep 9, 2022
4. gvanrossum commented on Sep 10, 2022

   

   gvanrossum

   on Sep 10, 2022

   Member

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   Maybe you can retrieve the task from the dict arg to the handler and use its ‘_context’ attribute? Or maybe we need to add a ‘get_context()’ method to Task? That’s a complex API change b/c custom task implementations though. Otherwise the implementation seems far from easy, given how many places call this?
5. kumaraditya303 commented on Sep 11, 2022

   

   kumaraditya303

   on Sep 11, 2022

   ContributorAuthor

   More actions

   I only care about correct context in the task finalizer so that exception handler is called with correct context. I don't want to rely on any private attribute and it can change.
6. gvanrossum

   added a commit that references this issue on Sep 11, 2022

   pythonGH-96704: Add task.get_context(), use it in call_exception_hand…

   36a7adb
7. gvanrossum commented on Sep 11, 2022

   

   gvanrossum

   on Sep 11, 2022

   Member

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   Your wish is my command. :-) (Sorry if you had a PR already, if you did we can compare notes, if you didn't you can review mine. :-)

   Reacted by Kumar Aditya
8. kumaraditya303

   assigned

   gvanrossum

   and

   kumaraditya303

   on Sep 24, 2022
9. gvanrossum

   added 2 commits that reference this issue on Oct 4, 2022

   pythonGH-96704: Add task.get_context(), use it in call_exception_hand…

   1d2d081

   GH-96704: Add {Task,Handle}.get_context(), use it in call_exception_h…

   8079bef
10. gvanrossum

    closed this as completedon Oct 5, 2022
11. Repository owner moved this from Todo to Done in asyncioon Oct 5, 2022
12. carljm

    added a commit that references this issue on Oct 6, 2022

    Merge branch 'main' into dictwatch

    4bb5d9d
13. mpage

    added a commit that references this issue on Oct 11, 2022

    pythonGH-96704: Add {Task,Handle}.get_context(), use it in call_excep…

    681e059

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