Timer operations

A process can suspend itself for a specific period of time with the function sleep or suspend itself indefinitely with the function pause until a signal arrives to reactivate the process. The function alarm schedules a signal to arrive at a specific time, so a pause suspension need not be indefinite.

#include <stdio.h>
#include <signal.h>

struct sigaction new_act, old_act;
int alarm_count = 5;    /* initialize number of alarms */

main () {
   void alarm_action();
/*
 * pass signal and function to sigaction
 */
   new_act.sa_handler = alarm_action;
   sigaction(SIGALRM, &new_act, &old_act);

   alarm(5);          /* set alarm clock for 5 seconds */

   pause(); /* suspend process until receipt of signal */
}

void alarm_action() {
/*
 * print the number of alarms remaining
 */
   printf("\t<%d\007>", alarm_count);
/*
 * pass signal and function to sigaction
 */
   new_act.sa_handler = alarm_action;
   sigaction(SIGALRM, &new_act, &old_act);

   alarm(5);            /* set alarm clock for 5 seconds */
   if (--alarm_count)   /* decrement alarm count */
      pause();          /* suspend process */
}

The preceding example shows how you can use the signal, alarm and pause system calls to alternately suspend and resume a program.