[Mesa-dev] [PATCH v2] c11/threads: Use PTHREAD_MUTEX_RECURSIVE by default

[Felix Janda]

Emil Velikov wrote:
> On 3 February 2015 at 02:53, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> > Hi Felix,
> >

Thanks for the review.

> > On 2 February 2015 at 19:04, Felix Janda <felix.janda at posteo.de> wrote:
> >> Previously PTHREAD_MUTEX_RECURSIVE_NP had been used on linux for
> >> compatibility with old glibc. Since mesa defines __GNU_SOURCE__
> >> on linux PTHREAD_MUTEX_RECURSIVE is also available since at least
> >> 1998. So we can unconditionally use the portable version
> >> PTHREAD_MUTEX_RECURSIVE.
> >> ---
> >> Previous patch didn't work as intended since on glibc these are
> >> part of an enum and not defines.
> >>
> > From a quick look at {e,}glibc sources [1]
> >
> >    PTHREAD_MUTEX_RECURSIVE_NP,
> >    ...
> >    #if defined __USE_UNIX98 || defined __USE_XOPEN2K8
> >    ...
> >    PTHREAD_MUTEX_RECURSIVE = PTHREAD_MUTEX_RECURSIVE_NP,
> >    ...
> >
> > Which does not seem to have relation with _GNU_SOURCE_ as the commit
> > mentions. Note I don't even pretend to know the convoluted web of
> > macros, so I could be a bit off :-)
> >

_GNU_SOURCE basically stands for "enable everything". I've checked that
for glibc 2.1 it defined _XOPEN_SOURCE=500 which in turn defines
__USE_UNIX98.

> Upon closer look things could be fine, as
> 
>   linux/gnu: _GNU_SOURCE sets _POSIX_C_SOURCE 200809L.
> With the latter of which guarding the __USE_XOPEN2K8  definition.
> 
>   cygwin: (hmm does it even set __linux*) we set _XOPEN_SOURCE=700.
> Which is the guard for __USE_XOPEN2K8.

http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_system

seems to indicate that it doesn't. I don't think that anything but
glibc has PTHREAD_MUTEX_RECURSIVE_NP.

> If one wants to be extra careful we can change
>   #if defined(__linux__) || defined(__linux)
> to check for the said old versions of glibc, but I believe we should be safe.

#if defined(__GLIBC__) is fine, too. Unless you care about hurd:
https://bugzilla.gnome.org/show_bug.cgi?id=377066

Something along this line is necessary (and sufficient) to compile
mesa unmodified with musl libc.

Felix