Switch gen.with_timeout to asyncio.wait_for

[jrbourbeau]

There are several instances where gen.with_timeout is used in the codebase. As part of our switch from existing tornado code to asyncio, we should move to using asyncio.wait_for.

However, one important distinction between these functions is that gen.with_timeout does not cancel a task when it's timeout expires, while asyncio.wait_fordoes cancel the task. So we need to be careful and determine on a case by case basis when task cancellation on timeout should happen. From @jcrist's comment (#3365 (comment)):

replacing it isn't always straightforward. Each case needs to be examined to determine what the intent was and if the lack of cancellation was accidental or necessary.

To avoid task cancellation when using asyncio.wait_for, the task should first be wrapped in asyncio.shield

[mrocklin]

My guess is that in most cases we'll be fine with cancellation. I would encourage a PR that tries this, just to see if the test suite passes.

…

On Mon, Jan 13, 2020, 10:32 AM James Bourbeau ***@***.***> wrote: There are several instances where gen.with_timeout <https://www.tornadoweb.org/en/stable/gen.html#tornado.gen.with_timeout> is used in the codebase. As part of our switch from existing tornado code to asyncio, we should move to using asyncio.wait_for <https://docs.python.org/3/library/asyncio-task.html#asyncio.wait_for>. However, one important distinction between these functions is that gen.with_timeout does not cancel a task when it's timeout expires, while asyncio.wait_fordoes cancel the task. So we need to be careful and determine on a case by case basis when task cancellation on timeout should happen. From @jcrist <https://github.com/jcrist>'s comment (#3365 (comment) <#3365 (comment)>): replacing it isn't always straightforward. Each case needs to be examined to determine what the intent was and if the lack of cancellation was accidental or necessary. To avoid task cancellation when using asyncio.wait_for, the task should first be wrapped in asyncio.shield <https://docs.python.org/3/library/asyncio-task.html#asyncio.shield> — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#3367?email_source=notifications&email_token=AACKZTEFBKNDIBV2ZUO65K3Q5SXTNA5CNFSM4KGG2BKKYY3PNVWWK3TUL52HS4DFUVEXG43VMWVGG33NNVSW45C7NFSM4IF2W6HA>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AACKZTHPEQWCG2NW45GDGTLQ5SXTNANCNFSM4KGG2BKA> .

[jrbourbeau]

Closed by #3372