[issue39010] ProactorEventLoop raises unhandled ConnectionResetError

[Ben Darnell]

Ben Darnell <ben.darnell at gmail.com> added the comment:

I just spent some time digging into this. Each call to `run_forever` starts a call to `_loop_self_reading`, then attempts to cancel it before returning:

https://github.com/python/cpython/blob/1ed61617a4a6632905ad6a0b440cd2cafb8b6414/Lib/asyncio/windows_events.py#L312-L325

The comment at line 321 is not entirely accurate: the future will not resolve in the future, but it may have *already* resolved, and added its callback to the call_soon queue. This callback will run if the event loop is restarted again. Since `_loop_self_reading` calls itself, this results in two copies of the "loop" running concurrently and stepping on each other's `_self_reading_futures`. 

This appears to be fairly harmless except for noise in the logs when only one of the loops is stopped cleanly.

I believe the simplest fix is for `_loop_self_reading` to compare its argument to `self._self_reading_future` to determine if it is the "current" loop and if not, don't reschedule anything.

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nosy: +Ben.Darnell

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39010>
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