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Cygwin with clock_gettime and CLOCK_MONOTONIC - gives always 0
- From: Tobias Burnus <burnus at net-b dot de>
- To: cygwin at cygwin dot com, Corinna Vinschen <corinna-cygwin at cygwin dot com>, Christopher Faylor <cgf at gcc dot gnu dot org>
- Date: Thu, 11 Apr 2013 15:37:37 +0200
- Subject: Cygwin with clock_gettime and CLOCK_MONOTONIC - gives always 0
- References: <5166A0B3 dot 70801 at net-b dot de>
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using clock_gettime with CLOCK_MONOTONIC fails on Cygwin; it always
gives 0. That breaks code compiled with GCC's gfortran which uses
system_clock in libgfortran.
libgfortran uses CLOCK_MONOTONIC if defined and otherwise it falls back
to CLOCK_REALTIME (which works); however, Cygwin defines both. Maybe a
better check would be _POSIX_MONOTONIC_CLOCK , however, that is also
defined with Cygwin .
First, is a known problem that clock_gettime gives the wrong result?
Secondly, do you have an idea how to test for it? One could use an exec
test in configure, but that does not nicely work with cross
compilations, which are commonly done for GCC.
See http://gcc.gnu.org/ml/fortran/2013-04/msg00085.html for the thread
at GCC, where the issue showed up.
(The issue is new since GCC 4.6 (2011-01-31) as that's the first GCC
version where libgfortran uses clock_gettime (when available); before
gettimeofday was used. See also GCC bugreport 56919. And CLOCK_MONOTONIC
appeared in Cygwin around the same time [Aug 2010], cf. )
 Cf. Cygwin-1.7.6 announcement at
http://cygwin.com/ml/cygwin-announce/2010-08/msg00019.html and the
"#define _POSIX_MONOTONIC_CLOCK 200112L" patch at
http://sourceware.org/ml/newlib/2010/msg00454.html Note that Linux's
glibc has in /usr/include/bits/posix_opt.h a more careful value: "/* The
monotonic clock might be available. */", "#define
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