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

Guido van Rossum guido at python.org
Sat Dec 19 20:00:00 EST 2015 
On Sat, Dec 19, 2015 at 1:40 PM, Matthias Urlichs <matthias at urlichs.de>
wrote:

> 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.
>

Fair enough.


> 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.
>

I guess that's due to some application logic, but whatever. You don't
really seem to care about finding a solution for this problem anyways:


> 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.
>

If that's so, can you demonstrate that without invoking all these other
things? Other traffic in this thread seems to indicate it may be not as
simple as that.

-- 
--Guido van Rossum (python.org/~guido)
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