[Python-ideas] PEP 3156 / Tulip: stopping the loop while in run_until_complete

[Guido van Rossum]

On Mon, Feb 11, 2013 at 10:18 AM, Saúl Ibarra Corretgé <saghul at gmail.com>wrote:

> Guido van Rossum wrote:
>
>> Yeah, I think the base implementation of run_until_complete is wrong.
>> I think I didn't have stop() when I coded that.
>>
>> Could you change it to something that just registers a lambda calling
>> stop() on the Future, and see if that makes your test case behave
>> better? (If so, please add a unit test and submit for code review.)
>>
>>
> Hum, I guess I'm missing something, but futures don't have a stop()
> method. The code already calls loop.stop() when the future is done.
>

Oops, I read your post (and the code) too fast.


> What I had in mind was to add a _called to Handler and expose it with a
> readonly property, so then we could check if handler.called and raise
> TimeoutError or not. As for raising another exception, maybe it's not such
> a good idea, since caller can always check future.done() later anyway.
>

I'm not so keen on that.

But you were probably calling run_until_complete() without an explicit
timeout. In that case, it should not call run() but run_forever(), and it
should never raise TimeoutError.

You could still get a TimeoutError if a timeout was given; in that case, I
think you can fix this case by passing call_later() a helper function that
sets a nonlocal variable which you then inspect.

You could also use a different mechanism, e.g. call cancel() on a Future
when the timeout occurs. (But I think that might be less reliable, since I
think Tasks can catch cancellations.)

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