asyncio - how to stop background task cleanly

Marko Rauhamaa marko at pacujo.net
Sat Feb 6 03:39:37 EST 2016


"Frank Millman" <frank at chagford.com>:

> When shutting the main program down, I want to stop the task, but I
> cannot figure out how to stop it cleanly - i.e. wait until it has
> finished the current task and possibly performed some cleanup, before
> continuing.

Here (and really, only here) is where asyncio shows its superiority over
threads: you can multiplex.

You should

   await asyncio.wait(..., return_when=asyncio.FIRST_COMPLETED)

to deal with multiple alternative stimuli.

In fact, since there is always a minimum of two alternative stimuli to
await, you should only ever await asyncio.wait().

And, while viable, that's what makes every asyncio program ugly as hell.


Marko


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