Re: [boost] Low-level precision timer proposal

From: John Maddock (john_at_[hidden])
Date: 2006-05-15 12:36:02

Silex wrote:
> I found out that there's already
> <boost/date_time/microsec_time_clock.hpp>, but on windows it uses
> GetSystemTimeAsFileTime().
>
> This raises a potential issue: I don't know if
> GetSystemTimeAsFileTime() works at millisecond resolution like
> QueryPerformanceCounter() does, and I don't know if
> QueryPerformanceCounter() returns some kind of epoch.. the docs are
> rather lowly-documented on this.

Ah, I suspect there may be problems with the CPU clock changing speed with 
some of these timers, I'm not sure though...

>
> I also noticed that getimeofday() wasn't checked for failure in the
> current boost headers.
>
> I also fell on a page which stated that "On Windows, clock() returns
> the nearest approximation to wall-clock time since the first call to
> this function, based on the Win32 function QueryPerformanceCounter().
> The resolution is typically better than one microsecond.". While I
> doubt it it might be interesting for our problem if it happen to be
> true.
>
> After the suggestions & having read the wiki I think we should indeed
> modifiy parts of date_time and template the timer class like
> mentionned. Should I try to give it a go ?

I guess it depends what the class is supposed to do: whether it measures 
real-world time, or some performance metric that isn't really time related.

John.