Re: IBM z/OS compatibility issues - pthread

[Bruno Haible]

Hello Daniel,

> PTHREAD ENVIRONMENT
> 
> z/OS has effectively two major pthread interfaces: _OPEN_THREADS, and
> _UNIX95_THREADS. The latter is the one you want to use, because its API
> is compatible with other systems. (_OPEN_THREADS uses e.g. a different
> signature for pthread_getspecific() that comes from a draft POSIX
> specification; refer to
> 
>     
> https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.4.0/com.ibm.zos.v2r4.bpxbd00/ptgetsp.htm
> 
> for the gory details. pthread_detach() is different, too, and
> pthread_cond_timedwait() can return EAGAIN.)
> 
> Additional information on z/OS feature test macros, if desired:
> 
>     
> https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.4.0/com.ibm.zos.v2r4.bpxbd00/ftms.htm
> 
> More specifically, to get a suitable pthreads interface, you need to
> #define _UNIX95_THREADS and _XOPEN_SOURCE=600.

I'd suggest to add this to the recommended values of CC and CXX in
https://gitlab.com/ghwiki/gnow-how/wikis/Platforms/Configuration

> (This could perhaps be
> added to AC_USE_SYSTEM_EXTENSIONS for this system.)

I'm not sure adding these flags in AC_USE_SYSTEM_EXTENSIONS or
gl_USE_SYSTEM_EXTENSIONS would work for all packages. For the majority,
probably yes, but for all of them? Not sure.

> However, one annoyance of _UNIX95_THREADS is that it does not define
> PTHREAD_RWLOCK_INITIALIZER, supposedly because the SUSv3 standard (which
> is what that feature test macro requests) does not specify it. However,
> IBM does provide the "implementation-defined"
> PTHREAD_RWLOCK_INITIALIZER_NP, which can be used in its place. See the
> note here:
> 
>     
> https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.4.0/com.ibm.zos.v2r4.bpxbd00/rp0r0i.htm
> 
> I would thus suggest adding something like the following to
> lib/pthread.in.h:
> 
>     #if defined(__MVS__) && !defined(PTHREAD_RWLOCK_INITIALIZER)
>     # define PTHREAD_RWLOCK_INITIALIZER PTHREAD_RWLOCK_INITIALIZER_NP
>     #endif

Tell the package maintainers to import the gnulib module 'pthread-rwlock'.
It will deal with the missing PTHREAD_RWLOCK_INITIALIZER; this issue occurs
also on some older Solaris versions.

Bruno