[issue10278] add time.wallclock() method

[STINNER Victor]

STINNER Victor <victor.stinner at haypocalc.com> added the comment:

I think that we should process in two steps:

* Expose low level C functions
* Write a high level reusing the best low level function depending on the OS

Low level functions:

* Expose clock_gettime() into the time module, with CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW constants, if available. The wrapper should be thin, so the result would be a tuple (sec, nsec) (to avoid issues with floating point numbers)
* Windows: GetTickCount, GetTickCount64 and QueryPerformaceCounter are monotonic. GetTickCount wraps after 50 days, so GetTickCount64 should be preferred. GetTickCount(64) returns a number of milliseconds. It looks like QueryPerformaceCounter has a better resolution than GetTickCount(64). I don't know when QueryPerformaceCounter does wrap? QueryPerformaceCounter is already exposed as time.clock().


High level:
* Use clock_gettime(CLOCK_MONOTONIC_RAW) on Linux>=2.6.28
* Use clock_gettime(CLOCK_MONOTONIC) on UNIX
* Use time.clock() (QueryPerformaceCounter) on Windows?
* If none of these functions is available, don't define the function

I propose time.monotonic() because I saw this name in different projects.

Pseudo-code for the time module:

monotonic = None
if hasattr(time, 'clock_gettime'):
  if hasattr(time, 'CLOCK_MONOTONIC_RAW'):
    def monotonic(): return time.clock_gettime(CLOCK_MONOTONIC_RAW)
  else:
    # i don't think that we should expose clock_gettime
    # if CLOCK_MONOTONIC is not available (or the function is useless)
    def monotonic(): return time.clock_gettime(CLOCK_MONOTONIC)
elif os.name == 'nt':
    def monotonic(): return time.clock()
if monotonic is not None:
   monotonic.__doc__ = 'monotonic time'
else:
   del monotonic

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<http://bugs.python.org/issue10278>
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