VMS Help POSIX Threads, PTHREAD routines, pthread_cond_signal_int_np, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This routine wakes one thread waiting on the specified condition
    variable. It can only be called from a software interrupt handler
    routine (such as from a Tru64 UNIX signal handler or OpenVMS
    AST). Calling this routine implies that it might be possible for
    a single waiting thread to proceed.

    The scheduling policies of the waiting threads determine which
    thread is awakened. For policies SCHED_FIFO and SCHED_RR, a
    blocked thread is chosen in priority order, using first-in/first-
    out (FIFO) within priorities.

    This routine does not cause a thread blocked on a condition
    variable to resume execution immediately. A thread resumes
    execution at some time after the interrupt handler routine
    returns. If no threads are waiting on the condition variable
    at the time of the call to pthread_cond_signal_int_np(), the next
    future waiting thread will be automatically released (that is,
    it will not actually wait). This routine establishes a "pending"
    wake if necessary.

    You can call this routine regardless of whether the associated
    mutex is either locked or unlocked. (Never lock a mutex from an
    interrupt handler routine.)

                                   NOTE

       This routine allows you to signal a condition variable from
       a software interrupt handler. Do not call this routine from
       noninterrupt code. To signal a condition variable from the
       normal noninterrupt level, use pthread_cond_signal().