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clock_getres(CLOCK_REALTIME, .) may return an outdated and too high resolution

clock_getres(CLOCK_REALTIME, &ts) queries the actual resolution through
NtQueryTimerResolution (&coarsest, &finest, &actual) during its first call and returns this value unchanged afterwards.

This returns a global Windows setting which may be temporarily modified by other applications by using e.g. timeBegin/EndPeriod(). For example playing a flash video in browser sets the resolution to 1ms. It is reset to default ~15ms when the browser is closed.

As a consequence the actual resolution might be much lower than reported by clock_getres() when clock_gettime() is used for measurements later. It would IMO be better to return the 'coarsest' instead of the 'actual' value.

If clock_setres() is used, this setting should be returned instead of the 'actual' value at the time of the setting.

BTW: GetSystemTimeAsFileTime() apparently provides the same resolution (at least on Win7 x64). So the more complex use of SharedUserData.InterruptTime may have less benefit than expected.


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