[New-bugs-announce] [issue44328] time.monotonic() should use QueryPerformanceCounter() on Windows

[Ryan Hileman]

New submission from Ryan Hileman <lunixbochs at gmail.com>:

Related to https://bugs.python.org/issue41299#msg395220

Presumably `time.monotonic()` on Windows historically used GetTickCount64() because QueryPerformanceCounter() could fail. However, that hasn't been the case since Windows XP: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter

> On systems that run Windows XP or later, the function will always succeed and will thus never return zero

I've run into issues with this when porting python-based applications to Windows. On other platforms, time.monotonic() was a decent precision so I used it. When I ported to Windows, I had to replace all of my time.monotonic() calls with time.perf_counter(). I would pretty much never knowingly call time.monotonic() if I knew ahead of time it could be quantized to 16ms.

My opinion is that the GetTickCount64() monotonic time code in CPython should be removed entirely and only the QueryPerformanceCounter() path should be used.

I also think some of the failure checks could be removed from QueryPerformanceCounter() / QueryPerformanceFrequency(), as they're documented to never fail in modern Windows and CPython has been dropping support for older versions of Windows, but that's less of a firm opinion.

----------
components: Library (Lib), Windows
messages: 395221
nosy: lunixbochs2, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: time.monotonic() should use QueryPerformanceCounter() on Windows
type: performance
versions: Python 3.10, Python 3.11, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44328>
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