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Re: Cygwin with clock_gettime and CLOCK_MONOTONIC - gives always 0

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
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

Well, it's "" not "". 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 - 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. However, POSIX states: "If the Monotonic Clock option is supported, all implementations shall support a clock_id of CLOCK_MONOTONIC defined in <time.h>."


* Newlib should be fixed to not define CLOCK_MONOTONIC and _POSIX_MONOTONIC_CLOCK - or it should implement it, otherwise it doesn't follow POSIX.

* Angelo shouldn't use system_clock to set the random seed.

* libgfortran should fall back to gf_gettime (= gettimeofday or clock_gettime CLOCK_REALTIME or time) if clock_gettime returns nonzero to work around the broken netlib (and possibly other implementations of clock_gettime)

* gfortran's example for random_see should be change to not use system_clock for the random seed.

Sorry for misinterpreting the results of Cygwin. And thanks for the reply and testing.


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