[Async-sig] asyncio.timeout() is not portable

[Andrew Svetlov]

asyncio.timeout behaves like asyncio.wait_for BTW.
It cancels inner tasks and sends asyncio.TimeoutError to outer.


On Mon, Jun 6, 2016 at 12:37 PM Nathaniel Smith <njs at pobox.com> wrote:

> On Jun 6, 2016 10:19 AM, "Yury Selivanov" <yselivanov at gmail.com> wrote:
> >
> >
> > > On Jun 5, 2016, at 11:56 AM, Ben Darnell <ben at bendarnell.com> wrote:
> > >
> > > It has come to my attention (
> https://github.com/KeepSafe/aiohttp/issues/877) that Python 3.5.2 (!)
> introduced a new context manager asyncio.timeout, which attaches a timeout
> to the current asyncio.Task. Any library or application that uses this
> feature will not be portable to other coroutine runners.
> > >
> > >     with asyncio.timeout(1):
> > >         result = await aiohttp.get('http://www.example.com')
> > >
> > > It's difficult to make this interface portable. We'd need to introduce
> a global thread-specific object that all of the coroutine runners could
> register the current task on, and define an interface that asyncio.timeout
> would call on that object to set the timeout. We could get rid of the
> global if the context manager used `async with` instead of `with`, since
> that would give us a way to communicate with the coroutine runner directly,
> but the net result is still that each runner needs to implement hooks for
> this feature (the hooks may or may not be generalizable to other features
> in the future).
> >
> > We’ve discussed this and decided that we should revert asyncio.Timeout
> from 3.5.2.  I’ll do that later today.
>
> This is tangential and somewhat irrelevant given the above, but since I'm
> not sure where else to put it: having thought about this issue a bit more
> last night, I also think that it's important that the timeout manager
> (if/when it's reintroduced) should inject a meaningful exception like
> TimeoutError, and it should be legal for the coroutine to catch this and
> continue. This is in contrast to the one that's currently being reverted,
> which uses the task cancellation feature and is indistinguishable from any
> other use of the task cancellation feature.
>
> -n
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-- 
Thanks,
Andrew Svetlov
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