Description

   This routine destroys the specified read-write lock object by
   uninitializing it, and should be called when the object is no
   longer referenced in your program. After this routine is called,
   the Threads Library may reclaim internal storage used by the
   specified read-write lock object. The effect of subsequent use of
   the lock is undefined until the lock is reinitialized by another
   call to pthread_rwlock_init().

   It is illegal to destroy a locked read-write lock.

   The results of this routine are unpredictable if the specified
   read-write lock object does not currently exist or is not
   initialized. This routine destroys the read-write lock object
   specified by the rwlock argument and releases any resources that
   the object used.

   A destroyed read-write lock object can be reinitialized using the
   pthread_rwlock_init() routine. The results of otherwise
   referencing a destroyed read-write lock object are undefined.