PEP 418: Remove duplicate info about clock resolution
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Victor Stinner
parent
03cd4d6a64
commit
61b5e2476c
72
pep-0418.txt
72
pep-0418.txt
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@ -264,23 +264,19 @@ Pseudo-code [#pseudo]_::
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def time():
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if hasattr(time, "clock_gettime"):
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try:
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# resolution = 1 nanosecond
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return time.clock_gettime(time.CLOCK_REALTIME)
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except OSError:
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# CLOCK_REALTIME is not supported (unlikely)
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pass
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if hasattr(_time, "gettimeofday"):
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try:
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# resolution = 1 microsecond
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return _time.gettimeofday()
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except OSError:
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# gettimeofday() should not fail
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pass
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if hasattr(_time, "ftime"):
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# resolution = 1 millisecond
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return _time.ftime()
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else:
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# resolution = 1 second
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return _time.time()
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@ -722,9 +718,9 @@ CLOCK_MONOTONIC OpenBSD 5.0 10 ms
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GetTickCount Windows Seven 15.6 ms
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========================= ================ ===============
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For CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW, the precision of this
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table is the result of ``clock_getres()``. It looks like Linux does
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not implement ``clock_getres()`` and always returns 1 nanosecond.
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For CLOCK_xxx clocks, the precision of this table is the result of
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``clock_getres()``. It looks like Linux does not implement ``clock_getres()``
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and always returns 1 nanosecond.
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mach_absolute_time
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^^^^^^^^^^^^^^^^^^
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@ -743,8 +739,6 @@ mach_absolute_time() stops during a sleep on a PowerPC CPU, but not on
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an Intel CPU: `Different behaviour of mach_absolute_time() on i386/ppc
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<http://lists.apple.com/archives/PerfOptimization-dev/2006/Jul/msg00024.html>`_.
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mach_absolute_time() has a resolution of 1 nanosecond.
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CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW, CLOCK_BOOTTIME
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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@ -792,9 +786,6 @@ CLOCK_MONOTONIC stops while the machine is suspended.
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clock, even if the standard C library supports it. For example,
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CLOCK_MONOTONIC_RAW requires a kernel version 2.6.28 or later.
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``clock_getres()`` gives the clock resolution. It is 1 nanosecond on
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Linux.
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.. note::
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``clock_gettime()`` requires to link the program against the rt
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@ -881,15 +872,14 @@ includes time the system spends in sleep or hibernation.
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GetTickCount64() was added to Windows Vista and Windows Server 2008.
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The clock resolution is 1 millisecond. Its precision is usually
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around 15 ms. It is possible to improve the precision using the
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`undocumented NtSetTimerResolution() function
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It is possible to improve the precision using the `undocumented
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NtSetTimerResolution() function
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<http://undocumented.ntinternals.net/UserMode/Undocumented%20Functions/Time/NtSetTimerResolution.html>`_.
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There are applications using this undocumented function, example:
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`Timer Resolution <http://www.lucashale.com/timer-resolution/>`_.
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There are applications using this undocumented function, example: `Timer
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Resolution <http://www.lucashale.com/timer-resolution/>`_.
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WaitForSingleObject() uses the same timer as GetTickCount() with the
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same resolution.
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same precision.
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GetTickCount() has an precision of 55 ms on Windows 9x.
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@ -990,16 +980,9 @@ and always returns 1 nanosecond.
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Windows: GetSystemTimeAsFileTime
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The system time can be read using GetSystemTimeAsFileTime(), ftime()
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and time().
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The system time resolution can be read using
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GetSystemTimeAdjustment(). The precision is usually between 1
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millisecond and 15 milliseconds. Resolution:
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* GetSystemTimeAsFileTime(): 100 nanoseconds
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* ftime(): 1 millisecond
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* time(): 1 second
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The system time can be read using GetSystemTimeAsFileTime(), ftime() and
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time(). The precision of the system clock can be read using
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GetSystemTimeAdjustment().
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Read the `GetSystemTimeAsFileTime() documentation
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<http://msdn.microsoft.com/en-us/library/windows/desktop/ms724397(v=vs.85).aspx>`_.
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@ -1012,13 +995,6 @@ System time on UNIX
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gettimeofday(), ftime(), time() and clock_gettime(CLOCK_REALTIME)
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return the system clock.
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Resolution:
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* clock_gettime(): clock_getres(CLOCK_REALTIME)
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* gettimeofday(): 1 microsecond
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* ftime(): 1 millisecond
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* time(): 1 second
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The system time can be set using settimeofday() or
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clock_settime(CLOCK_REALTIME).
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@ -1071,7 +1047,8 @@ GetSystemTimeAdjustment().
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Functions
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^^^^^^^^^
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* Windows: GetProcessTimes()
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* Windows: GetProcessTimes(). The precision can be read using
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GetSystemTimeAdjustment().
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* clock_gettime(CLOCK_PROCESS_CPUTIME_ID): High-resolution per-process
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timer from the CPU.
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* clock():
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@ -1085,13 +1062,6 @@ Functions
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* times()
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* getrusage(): ru_utime and ru_stime fields
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Resolution:
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* clock() rate is CLOCKS_PER_SEC. It was called CLK_TCK in Microsoft
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C before 6.0.
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* The clock resolution can be read using clock_getres().
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* GetProcessTimes(): call GetSystemTimeAdjustment().
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Python source code includes a portable library to get the process time (CPU
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time): `Tools/pybench/systimes.py
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<http://hg.python.org/cpython/file/tip/Tools/pybench/systimes.py>`_.
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@ -1128,15 +1098,11 @@ the precision is read using GetSystemTimeAdjustment().
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Functions
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^^^^^^^^^
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* Windows: GetThreadTimes()
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* Windows: GetThreadTimes(). The precision can be read using
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GetSystemTimeAdjustment().
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* clock_gettime(CLOCK_THREAD_CPUTIME_ID): Thread-specific CPU-time
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clock.
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Resolution:
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* CLOCK_THREAD_CPUTIME_ID: call clock_getres().
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* GetThreadTimes(): call GetSystemTimeAdjustment()
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See also pthread_getcpuclockid().
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@ -1273,10 +1239,10 @@ Other functions
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* sem_timedwait(): "If the Timers option is supported, the timeout
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shall be based on the CLOCK_REALTIME clock. If the Timers option is
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not supported, the timeout shall be based on the system clock as
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returned by the time() function. The resolution of the timeout
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shall be the resolution of the clock on which it is based."
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returned by the time() function. The precision of the timeout
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shall be the precision of the clock on which it is based."
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* WaitForSingleObject(): use the same timer than GetTickCount() with
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the same resolution.
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the same precision.
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Alternatives: API design
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@ -1336,7 +1302,7 @@ One function choosing the clock from a list of constraints
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* time.MONOTONIC: clock cannot go backward
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* time.STEADY: clock rate is steady and the clock is not adjusted
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* time.HIGHRES: clock with the highest resolutions
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* time.HIGHRES: clock with the highest precision
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time.get_clock() returns None if the clock is found and so calls can
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be chained using the or operator. Example::
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