[SystemZ][ZOS] Fix the usage of pthread_t within libc++

[zibi]

Summary

This is the the minimal change introduced in D88599 to unblock the controversial change and discussion of proper separation between thread from thread id which will continue in D88599.

This patch will address the differences of definition of pthread_t on z/OS vs. Linux and other OS. Main trick to make the code work on z/OS relies on redefining libcpp_thread_id type and _LIBCPP_NULL_THREAD macro. This is necessary to separate initialization of libcxx_thread_id from the one of __libcxx_thread_t;

[ldionne]

Properly separating __libcpp_thread_t from __libcpp_thread_id seems like a conceptual "bugfix" to me, so I like it.

However, POSIX says of pthread_t:

Used to identify a thread.

It's not much, but I would expect pthread_t to look like a thread ID of some sort, like something you can compare. Are you sure the pthread_t on zOS is conforming?

[zibi]

In D91875#2408688, @ldionne wrote:

It's not much, but I would expect pthread_t to look like a thread ID of some sort, like something you can compare. Are you sure the pthread_t on zOS is conforming?

The pthread_t is conforming on z/OS. It can be compared to other pthread_t objects via the pthread_equal function as specified in POSIX.4a.

[zibi]

ping

[ldionne]

libcxx/include/__threading_support

97

Why don't we always define it that way? This is valid also on other platforms, no?

[zibi]

libcxx/include/__threading_support

97

Yeap, let's do that. Thanks for suggestion.

[zibi]

Unify pthread_t initialization across all platforms.

libcxx/include/__config

#  if defined(__FreeBSD__) || \
       defined(__wasi__) || \
       defined(__NetBSD__) || \
       defined(__NuttX__) || \
       defined(__linux__) || \
       defined(__GNU__) || \
       defined(__APPLE__) || \
       defined(__CloudABI__) || \
       defined(__sun__) || \
+      defined(__MVS__) || \
       (defined(__MINGW32__) && __has_include(<pthread.h>))
 #    define _LIBCPP_HAS_THREAD_API_PTHREAD
 #  elif defined(__Fuchsia__)
      // TODO(44575): Switch to C11 thread API when possible.
 #    define _LIBCPP_HAS_THREAD_API_PTHREAD
 #  elif defined(_LIBCPP_WIN32API)
 #    define _LIBCPP_HAS_THREAD_API_WIN32
 #  else

libcxx/include/__threading_support

 
 #if defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
 # include <__external_threading>
 #elif !defined(_LIBCPP_HAS_NO_THREADS)
 
 #if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 # include <pthread.h>
 # include <sched.h>
-# ifdef __APPLE__
+# if defined(__APPLE__) || defined(__MVS__)
 #  define _LIBCPP_NO_NATIVE_SEMAPHORES
 # endif
 # ifndef _LIBCPP_NO_NATIVE_SEMAPHORES
 # include <semaphore.h>
 # endif
 #elif defined(_LIBCPP_HAS_THREAD_API_C11)
 # include <threads.h>
 #endif

 # define _LIBCPP_SEMAPHORE_MAX SEM_VALUE_MAX
 #endif
 
 // Execute once
 typedef pthread_once_t __libcpp_exec_once_flag;
 #define _LIBCPP_EXEC_ONCE_INITIALIZER PTHREAD_ONCE_INIT
 
 // Thread id
+#if defined(__MVS__)
+  typedef unsigned long long __libcpp_thread_id;
+#else
   typedef pthread_t __libcpp_thread_id;
+#endif
 
 // Thread
-#define _LIBCPP_NULL_THREAD 0U
-
+#define _LIBCPP_NULL_THREAD ((__libcpp_thread_t()))
 typedef pthread_t __libcpp_thread_t;
 
 // Thread Local Storage
 typedef pthread_key_t __libcpp_tls_key;
 
 #define _LIBCPP_TLS_DESTRUCTOR_CC
 #elif defined(_LIBCPP_HAS_THREAD_API_C11)
 // Mutex
int __libcpp_execute_once(__libcpp_exec_once_flag *flag,
                           void (*init_routine)()) {
   return pthread_once(flag, init_routine);
 }
 
 // Thread id
 // Returns non-zero if the thread ids are equal, otherwise 0
 bool __libcpp_thread_id_equal(__libcpp_thread_id t1, __libcpp_thread_id t2)
 {
-  return pthread_equal(t1, t2) != 0;
+  return t1 == t2;
 }
 
 // Returns non-zero if t1 < t2, otherwise 0
 bool __libcpp_thread_id_less(__libcpp_thread_id t1, __libcpp_thread_id t2)
 {
   return t1 < t2;
 }
 
 // Thread
 bool __libcpp_thread_isnull(const __libcpp_thread_t *__t) {
   return *__t == __libcpp_thread_t();
 }
 
 int __libcpp_thread_create(__libcpp_thread_t *__t, void *(*__func)(void *),
                            void *__arg)
 {
   return pthread_create(__t, nullptr, __func, __arg);
 }
 
 __libcpp_thread_id __libcpp_thread_get_current_id()
 {
-  return pthread_self();
+  const __libcpp_thread_t thread = pthread_self();
+  return __libcpp_thread_get_id(&thread);
 }
 
 __libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t *__t)
 {
+#if defined(__MVS__)
+  return __t->__;
+#else
   return *__t;
+#endif
 }
 
 int __libcpp_thread_join(__libcpp_thread_t *__t)
 {
   return pthread_join(*__t, nullptr);
 }
 
 int __libcpp_thread_detach(__libcpp_thread_t *__t)

 // Returns non-zero if t1 < t2, otherwise 0
 bool __libcpp_thread_id_less(__libcpp_thread_id t1, __libcpp_thread_id t2)
 {
   return t1 < t2;
 }
 
 // Thread
 bool __libcpp_thread_isnull(const __libcpp_thread_t *__t) {
-  return *__t == 0;
+  return __libcpp_thread_get_id(__t) == 0;
 }
 
 int __libcpp_thread_create(__libcpp_thread_t *__t, void *(*__func)(void *),
                            void *__arg)
 {
   int __ec = thrd_create(__t, reinterpret_cast<thrd_start_t>(__func), __arg);
   return __ec == thrd_nomem ? ENOMEM : __ec;
 }