[libcxx] Two more threading dependencies

[rmaprath]

Summary

Bumped into these while working on the externally threaded variant. I think it makes most sense to group these two under the main threading API. This greatly simplifies the presentation of the externally threaded library variant as well.

[bcraig]

include/__threading_support

187

Why does this need to go in threading_support? Seems like this is mostly orthogonal to threading. libcxxabi seems like the better place to hold changes to terminate anyway.

[rmaprath]

include/__threading_support

187

I can clearly see the argument against it, was bit unsure of it myself.

Now, the reason I want this the most is because of the externally threaded API, where I need to do some cleanup of the storage allocated in __libcpp_thread_create(). See the change I had to do in D20328 (thread.cpp) where I introduced a __libcpp_thread_finalize() function just for the cleanup. Thought it would be much cleaner to bundle up the two together so that I can avoid an explicit #ifdef in the sources.

Is that enough of a justification? Or should I stick to the explicit #ifdef in the externally-threaded variant? I don't have a strong opinion here, either way is fine, this version is slightly more preferred.

[bcraig]

include/__threading_support

187

I guess this is fine. I just need to tell myself (and maybe it should be commented in the code?) that this isn't trying to replace std::terminate, it's trying to replace a chunk of the std::thread dtor. Having a custom hook for the std::thread dtor is reasonable, and this is a reasonable default implementation.

Note that you only get a chance to do things here when a user does naughty things and lets a joinable thread reach the std::thread dtor.

[rmaprath]

Added a comment about ~std::thread() hook.

@EricWF: Gentle ping.

[rmaprath]

Most of this is no longer needed. I'll submit patches for the parts that are actually needed (e.g. nanosleep) later on. Thanks.

include/__threading_support

 #pragma GCC system_header
 #endif
 
 #ifndef _LIBCPP_HAS_NO_THREADS
 
 #if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 #include <pthread.h>
 #include <sched.h>
+#include <time.h>
+#include <exception>
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 
 // Mutex
 #define _LIBCPP_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER

 
 inline _LIBCPP_ALWAYS_INLINE
 __libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t* __t)
 {
     return *__t;
 }
 
 inline _LIBCPP_ALWAYS_INLINE
+int __libcpp_thread_nanosleep(const timespec *req, timespec *rem)
+{
+    return nanosleep(req, rem);
+}
+
+inline _LIBCPP_ALWAYS_INLINE
 int __libcpp_thread_join(__libcpp_thread_t* __t)
 {
     return pthread_join(*__t, 0);
 }
 
 inline _LIBCPP_ALWAYS_INLINE
 int __libcpp_thread_detach(__libcpp_thread_t* __t)
 {
     return pthread_detach(*__t);
 }
 
 inline _LIBCPP_ALWAYS_INLINE
 void __libcpp_thread_yield()
 {
     sched_yield();
 }
 
+inline _LIBCPP_ALWAYS_INLINE
+void __libcpp_thread_terminate()
+{
+    std::terminate();
+}
+
 // Thread local storage
 typedef pthread_key_t __libcpp_tl_key;
 
 inline _LIBCPP_ALWAYS_INLINE
 int __libcpp_tl_create(__libcpp_tl_key* __key, void (*__at_exit)(void*))
 {
     return pthread_key_create(__key, __at_exit);
 }

src/thread.cpp

 #if defined(_WIN32)
 #include <windows.h>
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 thread::~thread()
 {
+    // custom hook allowing thread implementations to control
+    // the ~std::tread() behavior.
     if (__t_ != 0)
-        terminate();
+        __libcpp_thread_terminate();
 }
 
 void
 thread::join()
 {
     int ec = EINVAL;
     if (__t_ != 0)
     {

             ts.tv_nsec = static_cast<decltype(ts.tv_nsec)>((ns-s).count());
         }
         else
         {
             ts.tv_sec = ts_sec_max;
             ts.tv_nsec = giga::num - 1;
         }
 
-        while (nanosleep(&ts, &ts) == -1 && errno == EINTR)
+        while (__libcpp_thread_nanosleep(&ts, &ts) == -1 && errno == EINTR)
             ;
     }
 }
 
 }  // this_thread
 
 __thread_specific_ptr<__thread_struct>&
 __thread_local_data()