Calling the alarm function with a 0 argument cancels any pending
    alarms.

    Unless it is intercepted or ignored, the signal generated by
    alarm terminates the process. Successive alarm calls reinitialize
    the alarm clock. Alarms are not stacked.

    Because the clock has a 1-second resolution, the signal may
    occur up to 1 second early. If the SIGALRM signal is intercepted,
    resumption of execution may be held up due to scheduling delays.

    When the SIGALRM signal is generated, a call to SYS$WAKE is
    generated whether or not the process is hibernating. The pending
    wake causes the current pause() to return immediately (after
    completing any function that catches the SIGALRM).