Activity

1. pyneda

   added

   3.8 (EOL)end of lifeend of life

   topic-asyncio

   type-featureA feature request or enhancementA feature request or enhancement

   on May 2, 2018
2. pyneda commented on May 16, 2018

   

   pynedamannequin

   on May 16, 2018

   MannequinAuthor

   More actions

   A possible use case (that at least I couldn't find how to solve) is the possibility to cancel a bunch of futures/coroutine objects which are being awaited using asyncio.tasks.wait() by one of the running coroutines when a task succeded or a specific condition happens by just raising an specific exception.

   At the moment this can be done but it will cancel all the coroutines with any exception that is raised and at some occasions this may not be desired.

   A simple example:

   async def example(num):
       if x == 5:
           raise Exception('Exception that does not cancel')
       elif x == 15:
           raise CancelException()
   
   tasks = [asyncio.ensure_future(example(x)) for x in range(20)]
   done, pending = await asyncio.wait(tasks, return_when=FIRST_EXCEPTION, return_on=CancelException)

   This wouldn't cancel everything when a normal exception is raised, instead it will when the exception raised is the one that the user expects to be raised in order to cancel everything that is pending.

   In addition, if the user does not specify the Exception type, it uses default Exception so it would keep working exactly as now.
3. hniksic commented on May 16, 2018

   

   hniksicmannequin

   on May 16, 2018

   Mannequin

   More actions

   """
   At the moment this can be done but it will cancel all the coroutines with any exception that is raised and at some occasions this may not be desired.
   """

   Does wait() really "cancel all the coroutines"? The documentation doesn't mention wait() canceling anything it only returns them in the pending set. It is gather() and wait_for() that cancel automatically.

   If you want to cancel everything on some exception and not on another, you can easily implement the logic yourself, e.g:

   tasks = [asyncio.ensure_future(example(x)) for x in range(20)]
   done, pending = await asyncio.wait(tasks, return_when=FIRST_EXCEPTION)
   for fut in done:
       try:
           fut.result()
       except CancelException:
           for fut in pending:
               fut.cancel()
4. 1st1 commented on May 17, 2018

   

   1st1

   on May 17, 2018

   Member

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   This isn't a priority now, so let's postpone the discussion on this until 3.7 is released.
5. ezio-melotti

   transferred this issue fromon Apr 10, 2022
6. ezio-melotti

   added this to asyncioon Jun 20, 2022
7. ezio-melotti

   moved this to Todo in asyncioon Jul 17, 2022
8. asvetlov commented on Nov 13, 2024

   

   asvetlov

   on Nov 13, 2024

   Contributor

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   Thanks for the proposal, but I'm closing the issue.

   asyncio develops in a slightly different way; task.cancel() accepts an optional msg parameter that could be utilized by user's code.
9. asvetlov

   closed this as completedon Nov 13, 2024
10. github-project-automation

    moved this from Todo to Done in asyncioon Nov 13, 2024