[Python-Dev] Drop the new time.wallclock() function?

[Michael Foord]

On 13 Mar 2012, at 16:57, Victor Stinner wrote:

> Hi,
> 
> I added two functions to the time module in Python 3.3: wallclock()
> and monotonic(). I'm unable to explain the difference between these
> two functions, even if I wrote them :-) wallclock() is suppose to be
> more accurate than time() but has an unspecified starting point.
> monotonic() is similar except that it is monotonic: it cannot go
> backward. monotonic() may not be available or fail whereas wallclock()
> is available/work, but I think that the two functions are redundant.
> 
> I prefer to keep only monotonic() because it is not affected by system
> clock update and should help to fix issues on NTP update in functions
> implementing a timeout.
> 
> What do you think?
> 


I am in the middle of adding a feature to unittest that involves timing of individual tests. I want the highest resolution cross platform measure of wallclock time - and time.wallclock() looked ideal. If monotonic may not exist or can fail why would that be better?

Michael


> --
> 
> monotonic() has 3 implementations:
> * Windows: QueryPerformanceCounter() with QueryPerformanceFrequency()
> * Mac OS X: mach_absolute_time() with mach_timebase_info()
> * UNIX: clock_gettime(CLOCK_MONOTONIC_RAW) or clock_gettime(CLOCK_MONOTONIC)
> 
> wallclock() has 3 implementations:
> * Windows: QueryPerformanceCounter() with QueryPerformanceFrequency(),
> with a fallback to GetSystemTimeAsFileTime() if
> QueryPerformanceFrequency() failed
> * UNIX: clock_gettime(CLOCK_MONOTONIC_RAW),
> clock_gettime(CLOCK_MONOTONIC) or clock_gettime(CLOCK_REALTIME), with
> a fallback to gettimeofday() if clock_gettime(*) failed
> * Otherwise: gettimeofday()
> 
> (wallclock should also use mach_absolute_time() on Mac OS X)
> 
> 
> Victor
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