[SystemZ][z/OS] Add OPEN_THREAD version of pthread function call

[abhina.sreeskantharajan]

Summary

Enable OPEN_THREAD version of pthread functions on z/OS.

[abhina.sreeskantharajan]

fix patch

[zibi]

LGTM, with format suggestion.

libcxx/include/__threading_support

426

[abhina.sreeskantharajan]

formatting

[zibi]

LGTM

[abhina.sreeskantharajan]

ping :)

[philnik]

libcxx/include/__threading_support

423

When are __MVS__, __SUSV3_THR and _OPEN_THREADS set? Are they z/OS-specific flags? If not, are they changing the behaviour for other platforms libc++ supports?

[ldionne]

Let's try not add obscure platform-specific #ifdefs like that. pthread_getspecific_d8_np doesn't even return something on Google, so this is pretty obscure as far as this open source project is concerned.

This whole code block is under _LIBCPP_HAS_THREAD_API_PTHREAD, and z/OS doesn't seem to support pthread since it's missing these functions. Instead, z/OS should either provide that API, or you can introduce another "threading back-end" other than the pthread or C11 one.

libcxx/include/__threading_support

 int __libcpp_thread_join(__libcpp_thread_t *__t)
 {
   return pthread_join(*__t, nullptr);
 }
 
 _LIBCPP_HIDE_FROM_ABI inline
 int __libcpp_thread_detach(__libcpp_thread_t *__t)
 {
+#if !defined(__MVS__) || defined( __SUSV3_THR)
   return pthread_detach(*__t);
+#elif defined(_OPEN_THREADS)
+  return pthread_detach(__t);
+#else
+  #error pthread_detach function is not available
+#endif
 }
 
 _LIBCPP_HIDE_FROM_ABI inline
 void __libcpp_thread_yield()
 {
   sched_yield();
 }
 

 int __libcpp_tls_create(__libcpp_tls_key *__key, void (*__at_exit)(void *))
 {
   return pthread_key_create(__key, __at_exit);
 }
 
 _LIBCPP_HIDE_FROM_ABI inline
 void *__libcpp_tls_get(__libcpp_tls_key __key)
 {
+#if !defined(__MVS__) || defined( __SUSV3_THR)
   return pthread_getspecific(__key);
+#elif defined(_OPEN_THREADS)
+  return pthread_getspecific_d8_np(__key);
+#else
+  #error pthread_getspecific function is not available
+#endif
 }
 
 _LIBCPP_HIDE_FROM_ABI inline
 int __libcpp_tls_set(__libcpp_tls_key __key, void *__p)
 {
     return pthread_setspecific(__key, __p);
 }