Description

   This routine unblocks all threads waiting on the specified
   condition variable cond. Calling this routine implies that data
   guarded by the associated mutex has changed, so that it might be
   possible for one or more waiting threads to proceed. The threads
   that are unblocked shall contend for the mutex according to their
   respective scheduling policies (if applicable).

   If only one of the threads waiting on a condition variable may be
   able to proceed, but one of those threads can proceed, then use
   pthread_cond_signal() instead.

   Whether the associated mutex is locked or unlocked, you can still
   call this routine. However, if predictable scheduling behavior is
   required, that mutex should then be locked by the thread calling
   the pthread_cond_broadcast() routine.

   If no threads are waiting on the specified condition variable,
   this routine takes no action. The broadcast does not propagate to
   the next condition variable wait.