[issue35580] Windows IocpProactor: CreateIoCompletionPort 4th arg 0xffffffff -- why is this value the default?

[Jeff Robbins]

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

By default, the __init__ function of IocpProactor in windows_events.py calls CreateIoCompletionPort with a 4th argument of 0xffffffff, yet MSDN doesn't document this as a valid argument.    https://docs.microsoft.com/en-us/windows/desktop/fileio/createiocompletionport

It looks like the 4th arg (NumberOfConcurrentThreads) is meant to be either a positive integer or 0.  0 is a special value meaning "If this parameter is zero, the system allows as many concurrently running threads as there are processors in the system."

Why does asyncio use 0xffffffff instead as the default value?

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components: asyncio
messages: 332498
nosy: asvetlov, jeffr at livedata.com, yselivanov
priority: normal
severity: normal
status: open
title: Windows IocpProactor: CreateIoCompletionPort 4th arg 0xffffffff -- why is this value the default?
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35580>
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