Issue 35599: asyncio windows_events.py IocpProactor bug (original) (raw)

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.debug(f'{self._cache}')

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.