Description

   This routine unlocks the Threads Library global mutex. Because
   the global mutex is recursive, the unlock occurs when each call
   to pthread_lock_global_np() has been matched by a call to this
   routine. For example, if you called pthread_lock_global_np()
   three times, pthread_unlock_global_np() unlocks the global mutex
   when you call it the third time.

   If no threads are waiting for the global mutex, it becomes
   unlocked with no current owner. If one or more threads are
   waiting to lock the global mutex, this routine causes one thread
   to unblock and to try to acquire the global mutex. The scheduling
   policy is used by this routine to determine which thread is
   awakened. For the policies SCHED_FIFO and SCHED_RR, a blocked
   thread is chosen in priority order, using first-in/first-out
   (FIFO) within priorities.