Description

   This routine initializes the condition variable cond with
   attributes specified in the attr argument. If attr is NULL, the
   default condition variable attributes are used.

   A condition variable is a synchronization object used in
   conjunction with a mutex. A mutex controls access to data that
   is shared among threads; a condition variable allows threads to
   wait for that data to enter a defined state.

   Condition variables are not owned by a particular thread. Any
   associated storage is not automatically deallocated when the
   creating thread terminates.

   Use the macro PTHREAD_COND_INITIALIZER to initialize statically
   allocated condition variables to the default condition variable
   attributes. To invoke this macro, enter:

      pthread_cond_t condition = PTHREAD_COND_INITIALIZER

   When statically initialized, a condition variable should not also
   be initialized using pthread_cond_init(). Also, a statically
   initialized condition variable need not be destroyed using
   pthread_cond_destroy().

   Under certain circumstances it might be impossible to wait upon
   a statically initialized condition variable when the process
   virtual address space (or some other memory limit) is nearly
   exhausted. In such a case pthread_cond_wait() or pthread_cond_
   timedwait() can return [ENOMEM]. To avoid this possibility,
   initialize critical condition variables using pthread_cond_
   init().