signal.c

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

static void  sig_alrm(int);	/* one handler for both signals */
time_t start,stop;
int main(void)
{
	signal(SIGALRM,sig_alrm);
	start = time(NULL);
	for ( ; ; ){ 
		sleep(4);
		printf("[%ld] add an alarm\n",time(NULL)-start);
		alarm(3);	
	}
}

static void sig_alrm(int signo)		/* argument is signal number */
{
	printf("[%ld] enter alram\n",time(NULL) - start);
	sleep(5);
	printf("[%ld] completed \n",time(NULL) - start);