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Date: Tue, 27 Feb 2007 09:22:16 +0800
From: Carlo Florendo <subscribermail AT gmail DOT com>
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Subject: [SOLVED] Re: does usleep() sleep more than it's supposed to?
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Brian Ford wrote:
> Put this in its own (separate from all Cygwin code) object file, call
> it before any timing calls in your application, and link it with -lwinmm:
> 
> #include "windows.h"
> 
> void
> SetSchedulerMaxRes(void)
> {
>     TIMECAPS tc;
> 
>     /* Set the system scheduler resolution to its maximum.
>      * Needed for Cygwin >= 1.5.20, broken in 1.5.19, and unnecessary
>      * <= 1.5.18 because it was always done by Cygwin.  Required for */
>     if (timeGetDevCaps(&tc, sizeof(tc)) != TIMERR_NOERROR)
>     {
>         printf("timeGetDevCaps error %d\n", GetLastError());
>         tc.wPeriodMin = 1; /* Try 1 ms and hope for the best */
>     }
> 
>     if (timeBeginPeriod(tc.wPeriodMin) != TIMERR_NOERROR)
>         printf("timeBeginPeriod error %d\n", GetLastError());
> }
> 


Impressive.


I never knew about timeGetDevCaps nor timeBeginPeriod but this
improved the sleep time by making it accurate up to
1000 microseconds, which *is* the behavior I've been
looking for for weeks now.

Here's the new output on my box:

$ ./a.exe
Print elapsed time at every call to usleep()
Elapsed time (sec:microsec) 0:100000
Elapsed time (sec:microsec) 0:101000
Elapsed time (sec:microsec) 0:100000
Elapsed time (sec:microsec) 0:101000
Elapsed time (sec:microsec) 0:101000
Elapsed time (sec:microsec) 0:100000
Elapsed time (sec:microsec) 0:101000
Elapsed time (sec:microsec) 0:100000
Elapsed time (sec:microsec) 0:101000
Elapsed time (sec:microsec) 0:100000

Print elapsed after the loop()
Elapsed time (sec:microsec) 1:26000




Thank you very much.

Best Regards,

Carlo



-- 
Carlo Florendo
Softare Engineer/Network Co-Administrator
Astra Philippines Inc.
UP-Ayala Technopark, Diliman 1101, Quezon City
Philippines
http://www.astra.ph

Member of the Astra Group of Companies
5-3-11 Sekido, Tama City
Tokyo 206-0011, Japan
http://www.astra.co.jp

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