[libcxx] Fix join.pass.cpp segfault after r271475

[rmaprath]

Summary

After r271475 [1], I'm seeing a segfault in join.pass.cpp on my system.

The test calls std::thread::join() twice and expects it to throw a system_error. It looks like my pthread implementation does not like being called pthread_join with the pthread_t argument set to zero, and decides to segfault. There are few easy ways to fix this, I've gone with the approach taken in std::thread::deatch() so there's more consistency.

[1] http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/std/thread/thread.threads/thread.thread.class/thread.thread.member/join.pass.cpp?r1=271475&r2=271474&pathrev=271475

[rmaprath]

Will commit tomorrow if there are no objections.

Feel free to commit if it looks all right.

/ Asiri

[EricWF]

Thanks for the patch.

[rmaprath]

Thanks. Fixed in r271634.

src/thread.cpp

 {
     if (__t_ != 0)
         terminate();
 }
 
 void
 thread::join()
 {
-    int ec = __libcpp_thread_join(&__t_);
+    int ec = EINVAL;
+    if (__t_ != 0)
+    {
+        ec = __libcpp_thread_join(&__t_);
+        if (ec == 0)
+            __t_ = 0;
+    }
 #ifndef _LIBCPP_NO_EXCEPTIONS
     if (ec)
         throw system_error(error_code(ec, system_category()), "thread::join failed");
-#else
-    (void)ec;
 #endif  // _LIBCPP_NO_EXCEPTIONS
-    __t_ = 0;
 }
 
 void
 thread::detach()
 {
     int ec = EINVAL;
     if (__t_ != 0)
     {