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[Python-Dev] asyncio: how to interrupt an async def w/ finally: ( e.g. Condition.wait() )

Matthias Urlichs matthias at urlichs.de
Sat Dec 19 16:40:58 EST 2015 
On 19.12.2015 20:25, Guido van Rossum wrote:
> Perhaps you can add a check for a simple boolean 'stop' flag to your
> condition check, and when you want to stop the loop you set that flag
> and then call notify() on the condition. Then you can follow the
> standard condition variable protocol instead of all this nonsense. :-)
Your example does not work.

>    def stop_it(self):
>        self.stopped = True
>        self.uptodate.notify()

self.uptodate needs to be locked before I can call .notify() on it.
Creating a new task just for that seems like overkill, and I'd have to
add a generation counter to prevent a race condition. Doable, but ugly.

However, this doesn't fix the generic problem; Condition.wait() was just
what bit me today.
When a non-async generator goes out of scope, its finally: blocks will
execute. An async procedure call whose refcount reaches zero without
completing simply goes away; finally: blocks are *not* called and there
is *no* warning.
I consider that to be a bug.

-- 
-- Matthias Urlichs
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