Scott wrote:
<< The Boost implementation can be summarized as:
system_clock:
mac = gettimeofday
posix = clock_gettime(CLOCK_REALTIME)
win = GetSystemTimeAsFileTime
steady_clock:
mac = mach_absolute_time
posix = clock_gettime(CLOCK_MONOTONIC)
win = QueryPerformanceCounter
high_resolution_clock:
* = { steady_clock, if available
system_clock, otherwise } >>
I read again the doc of the QElapsedTimer class of the Qt library. So Qt
and Boost agree to say that QueryPerformanceCounter() *is* monotonic.
I was confused because of a bug found in 2006 in Windows XP on multicore
processors. QueryPerformanceCounter() gave a different value on each
core. The bug was fixed in Windows and is known as KB896256 (I already
added a link to the bug in the PEP).
I added a time.hires() clock to the PEP for the benchmarking/profiling
use case (...)
It is this always-having-to-manually-fallback-depending-on-os that I was
hoping your new functionality would avoid. Is time.try_monotonic()
suitable for this usecase?
If QueryPerformanceCounter() is monotonic, the API can be simplified to:
* time.time() = system clock
* time.monotonic() = monotonic clock
* time.hires() = monotonic clock or fallback to system clock
time.hires() definition is exactly what I was trying to implement with
"time.steady(strict=True)" / "time.try_monotonic()".
--
Scott> monotonic_clock = always goes forward but can be adjusted
Scott> steady_clock = always goes forward and cannot be adjusted
I don't know if the monotonic clock should be called time.monotonic() or
time.steady(). The clock speed can be adjusted by NTP, at least on Linux
< 2.6.28.
I don't know if other clocks used by my time.monotonic() proposition can
be adjusted or not.
If I understand correctly, time.steady() cannot be implemented using
CLOCK_MONOTONIC on Linux because CLOCK_MONOTONIC can be adjusted?
Does it really matter if a monotonic speed is adjusted?
Victor
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