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[Python-ideas] Asynchronous exception handling around with/try statement borders

Erik Bray erik.m.bray at gmail.com
Wed Jun 28 09:09:13 EDT 2017 
On Wed, Jun 28, 2017 at 2:26 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 28 June 2017 at 21:40, Erik Bray <erik.m.bray at gmail.com> wrote:
>> My colleague's contention is that given
>>
>> lock = threading.Lock()
>>
>> this is simply *wrong*:
>>
>> lock.acquire()
>> try:
>>     do_something()
>> finally:
>>     lock.release()
>>
>> whereas this is okay:
>>
>> with lock:
>>     do_something()
>
> Technically both are slightly racy with respect to async signals (e.g.
> KeyboardInterrupt), but the with statement form is less exposed to the
> problem (since it does more of its work in single opcodes).
>
> Nathaniel Smith posted a good write-up of the technical details to the
> issue tracker based on his work with trio:
> https://bugs.python.org/issue29988

Interesting; thanks for pointing this out.  Part of me felt like this
has to have come up before but my searching didn't bring this up
somehow (and even then it's only a couple months old itself).

I didn't think about the possible race condition before
WITH_CLEANUP_START, but obviously that's a possibility as well.
Anyways since this is already acknowledged as a real bug I guess any
further followup can happen on the issue tracker.

Thanks,
Erik
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