[New-bugs-announce] [issue35599] asyncio windows_events.py IocpProactor bug

Jeff Robbins report at bugs.python.org
Thu Dec 27 20:22:04 EST 2018

New submission from Jeff Robbins <jeffr at livedata.com>:

The close() method of IocpProactor in windows_events.py has this code in its close() method:

        while self._cache:
            if not self._poll(1):
                logger.debug('taking long time to close proactor')

The bug is that self._poll() has *no* return statements in it, and so returns None no matter what.  Which makes the "if not" part confusing, at best.  At worst, it might reflect a disconnect with the author's intent.

I added a bit more logging and re-ran my test:

        while self._cache:
            logger.debug('before self._poll(1)')
            if not self._poll(1):
                logger.debug('taking long time to close proactor')

logger output:

20:16:30.247 (D)   MainThread                      asyncio: before self._poll(1)
20:16:30.248 (D)   MainThread                      asyncio: taking long time to close proactor
20:16:30.249 (D)   MainThread                      asyncio: {}

Obviously 1 millisecond isn't "taking a long time to close proactor".  Also of interest, the _cache is now empty.  

I think the intent of the author must have been to check if the call to ._poll() cleared out any possible pending futures, or waited the full 1 second.  Since ._poll() doesn't return any value to differentiate if it waited the full wait period or not, the "if" is wrong, and, I think, the intent of the author isn't met by this code.

But, separate from speculating on "intent", the debug output of "taking a long time to close proactor" seems wrong, and the .close() code seems disassociated with the implementation of ._poll() in the same class IocpProactor in windows_events.py.

components: asyncio
messages: 332632
nosy: asvetlov, jeffr at livedata.com, yselivanov
priority: normal
severity: normal
status: open
title: asyncio windows_events.py IocpProactor bug
versions: Python 3.7

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