Prevent asyncio.wait_for swallowing task cancellation

[aronhoff]

I've been running up against an issue in a project I'm working on, where I cannot cancel an asyncio task while it is waiting on an asyncua call. The CancelledError simply gets swallowed and the task continues as if nothing happened

I traced it down. It turns out, there is a bug in the implementation of asyncio.wait_for, making it swallow the cancellation if the task was cancelled from the outside. See references below.

The bug is only fixed in Python 3.12, existing in one way or another since 3.7. The library wait_for2 provides a fixed implementation for the affected versions.

This PR adds wait_for2 as a dependency replaces calls to asyncio.wait_for with wait_for2.wait_for pre-3.12.

python/cpython#87555
python/cpython#86296
python/cpython#107547

[aronhoff]

Note that in 3.12, asyncio.wait_for seems to be using an alternative implementation based on asyncio.timeout: python/cpython#96764.

asyncio.timeout was only introduced in 3.11. Backport async-timeout exists for earlier versions, but also seems to have unresolved issues regarding swallowed cancellations:
aio-libs/async-timeout#229
aio-libs/async-timeout#235

In my own project, setting asyncio.wait_for = wait_for2.wait_for at the start of the script, running in 3.11, has fixed the cancellation issues, circumventing asyncua's use of the function.

[oroulet]

Did you really manage to reliably stop a task using CancelledError? My experience over several years is that they are always swallowed somehwere, if not a local error in code base then a bug in Python itself as you found out ;-)