alarm(2)                          SDK R4.11                         alarm(2)


NAME
       alarm - set a process alarm clock

SYNOPSIS
       #include <unistd.h>

       unsigned int alarm (sec)
       unsigned int sec;

   where:
       sec            The number of real-time seconds to wait before sending
                      SIGALRM to the caller

DESCRIPTION
       Alarm sets the caller's per-process real-time alarm clock to send the
       signal SIGALRM to the calling process after the number of real-time
       seconds specified by sec have elapsed.  Alarm requests are not
       stacked; successive calls reset the calling process's alarm clock.
       If sec is 0, any previous alarm request is canceled.  Alarm(2) uses
       the same ITIMER_REAL interval timer that setitimer(2) uses.  Fork(2)
       resets the alarm clock in the child to 0.  A process created by
       exec(2) inherits the time left on the old process's alarm clock.

       As with any signal, a process must enter the kernel in order to take
       delivery of the SIGALRM.  Thus, if a process sets an alarm and then
       continues to run in user space, the delivery of the alarm signal will
       be delayed until the process is forced to reenter the kernel.  A
       process will enter the kernel if (1) its timeslice runs out (2) it is
       preempted by a higher priority process (3) it takes an exception, or
       (4) the processor on which it is running receives a hardware
       interrupt.

RETURN VALUE
       Alarm returns the amount of time remaining on the process's alarm
       clock from a previous call.  If zero, no previous alarm was set.

DIAGNOSTICS
       None.

SEE ALSO
       getitimer(2), pause(2), setitimer(2), signal(2), sigpause(2),
       sigset(2).


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