Description

   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).