https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98507
Janne Blomqvist <jb at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jb at gcc dot gnu.org
--- Comment #5 from Janne Blomqvist <jb at gcc dot gnu.org> ---
(In reply to anlauf from comment #1)
> Not a confirmation, just an observation: libgfortran/intrinsics/time_1.h
> prefers gettimeofday over clock_gettime, whereas the Linux manpages have:
>
> GETTIMEOFDAY(2) Linux Programmer's Manual
> GETTIMEOFDAY(2)
>
> CONFORMING TO
> SVr4, 4.3BSD. POSIX.1-2001 describes gettimeofday() but not
> settimeofday().
> POSIX.1-2008 marks gettimeofday() as obsolete, recommending the use
> of clock_get-
> time(2) instead.
>
>
> Janne chose this prioritization in 2012, but there is no comment explaining
> his choice. Should this be revisited?
Usage of gettimeofday() was, and still is, ubiquitous. In find it hard to
imagine any C library would remove it just because POSIX has deprecated it,
unless they want a significant fraction of applications to stop working.
That being said, my main motivation for preferring gettimeofday() was that back
then clock_gettime was not found in the glibc libc.so but rather in librt
(which is part of glibc, but not linked by default for single-threaded
programs). See the weakref trickery in intrinsics/system_clock.c for how using
clock_gettime on glibc < 2.17 was done, where there was a real motivation for
using clock_gettime, namely to access the monotonic clock. So preferring
gettimeofday() in time_1.h:gf_gettime() meant that as many targets as possible
used the same code path as glibc targets, reducing the risk of target-specific
bugs that I would have difficulty deciphering considering I was developing on
Linux myself.
However, this is all water under the bridge by now, as clock_gettime is part of
glibc libc.so since glibc 2.17. So I think switching the order now in 2021 is
perfectly fine. As an additional datapoint, per
https://man7.org/linux/man-pages/man7/vdso.7.html all Linux targets that
provide gettimeofday() as a VDSO also provide clock_gettime() as a VDSO, so no
concerns there either.
As a minor nit, now that clock_gettime() is the "main" implementation for
gf_gettime() you might want to change it to return nanoseconds rather than
microseconds, and update the callers.
