[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Yury Selivanov added the comment: Note, that this will not be backported to 3.6, as it behaves in a slightly incompatible way. I consider this patch as an enhancement that makes 'asyncio.wait_for' semantics easier to reason about and more practical. --

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Change by Yury Selivanov : -- resolution: -> fixed stage: patch review -> resolved status: open -> closed type: -> behavior ___ Python tracker

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Viktor Kovtun added the comment: Actually provided example without patch will print 1, which is not expected -- ___ Python tracker ___

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Yury Selivanov added the comment: You're right! Let's work on the PR then, I've left a review comment. -- ___ Python tracker ___

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Viktor Kovtun added the comment: asyncio.wait_for is coroutine itself, to start executing code, no matter with this PR or not it needs to be awaited/yield from import asyncio @asyncio.coroutine def foo(): print(1) loop = asyncio.get_event_loop() fut = asyncio.wait_for(foo(), 0)

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Yury Selivanov added the comment: I think this is a backwards incompatible change and thus will be rejected. Currently there's a guarantee that "wait_for" can throw a TimeoutError *only* when when you await it. fut = wait_for(something, 0) # some important code try: await

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Viktor Kovtun added the comment: If coroutine function has some blocking calls before first await/yield from statement maybe makes sense do no let them be executed, if timeout equals 0 -- ___ Python tracker

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Yury Selivanov added the comment: Do you have a use case where this optimization is important? -- ___ Python tracker ___

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

Changes by Viktor Kovtun : -- keywords: +patch pull_requests: +3687 stage: -> patch review ___ Python tracker ___

[issue31556] asyncio.wait_for can cancel futures faster with timeout==0

New submission from Viktor Kovtun: There is no need to create extra future and use loop.call_later to cancel base future from asyncio.wait_for when timeout==0. If loop is heavy loaded it can be cancelled simnifically later then 0 seconds later. -- components: asyncio messages: 302770