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Date: Thu, 11 Apr 2013 22:46:05 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Cc: fortran AT gcc DOT gnu DOT org
Subject: Re: Cygwin with clock_gettime and CLOCK_MONOTONIC - gives always 0
Message-ID: <20130411204605.GA11358@calimero.vinschen.de>
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On Apr 11 22:35, Tobias Burnus wrote:
> Corinna Vinschen wrote:
> >On Apr 11 21:13, Tobias Burnus wrote:
> >>Where is actually the source code of the clock_gettime, which Cygwin
> >>uses? I thought that it was newlib. But looking at
> >>http://sourceware.org/cgi-bin/cvsweb.cgi/src/newlib/libc/sys/linux/clock_gettime.c?cvsroot=src
> >>the code should return -1 for "clock_gettime (CLOCK_MONOTONIC" as
> >>CLOCK_MONOTONIC (= 4) is not handled, only CLOCK_REALTIME (= 1,
> >>according to src/newlib/libc/include/time.h).
> >>
> >>However, as both you and Angelo get a zero return value, I must look
> >>at the wrong file.
> >Yes, for Cygwin it's
> >http://cygwin.com/cgi-bin/cvsweb.cgi/src/winsup/cygwin/timer.cc?cvsroot=src
> 
> Well, it's "times.cc" not "timer.cc". I think the problem with
> Cygwin was a red herring. But there are a bunch of problems:
> 
> 
> a) Angelo's code to initialize the random seed assumes that
> Fortran's "system_clock" and the "clock_gettime(CLOCK_MONOTONIC" it
> calls give a result where 0 is the beginning of the epoch (like on
> Linux/glibc) or the system start up (as Windows'
> GetTickCount/GetTickCount64). However, QueryPerformanceCounter
> (probably intrinsically, but at least as used by Cygwin) returns
> some time based on the startup time

http://cygwin.com/ml/cygwin/2013-04/msg00191.html

> - and as the frequency seems to
> be slow such that the result is 0 or (nearly) the same number for
> the startup. Thus, the random_seed initialization doesn't work as
> expected on Cygwin/Windows.
> 
> b) Newlib is broken. For clock_gettime, CLOCK_MONOTONIC is not
> implemented. But both CLOCK_MONOTONIC and even
> _POSIX_MONOTONIC_CLOCK (with value 200112L) are defined.

No, newlib is right.   Look again.  In libc/include/time.h
CLOCK_MONOTONIC is only defined if _POSIX_MONOTONIC_CLOCK is defined.
In libc/include/sys/features.h, _POSIX_MONOTONIC_CLOCK is only
defined for RTEMS and Cygwin.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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