When threads are present, this routine causes a thread to wait
    for the specified condition variable cond to be signaled or
    broadcast.

    Calling this routine in a single-threaded environment is a coding
    error. Because no other thread exists to issue a call to tis_
    cond_signal() or tis_cond_broadcast(),  using this routine in a
    single-threaded environment forces the program to exit.

    For further information about actions taken when threads are
    present, refer to the pthread_cond_wait() description.