ticker_demo.c

understanding unix/linux programming source code(bruce molay)

/* ticker_demo.c
 *    demonstrates use of interval timer to generate reqular
 *    signals, which are in turn caught and used to count down
 */

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

int main()
{
	void	countdown(int);

	signal(SIGALRM, countdown);
	if ( set_ticker(500) == -1 )
		perror("set_ticker");
	else
		while( 1 )
			pause();
	return 0;
}

void countdown(int signum)
{
	static int num = 10;
	printf("%d ..", num--);
	fflush(stdout);
	if ( num < 0 ){
		printf("DONE!\n");
		exit(0);
	}
}

/* [from set_ticker.c]
 * set_ticker( number_of_milliseconds )    
 *      arranges for interval timer to issue SIGALRM's at regular intervals
 *      returns -1 on error, 0 for ok
 *      arg in milliseconds, converted into whole seconds and microseconds
 *      note: set_ticker(0) turns off ticker
 */

int set_ticker( int n_msecs )
{
        struct itimerval new_timeset;
        long    n_sec, n_usecs;

        n_sec = n_msecs / 1000 ;		/* int part	*/
        n_usecs = ( n_msecs % 1000 ) * 1000L ;	/* remainder	*/

        new_timeset.it_interval.tv_sec  = n_sec;        /* set reload       */
        new_timeset.it_interval.tv_usec = n_usecs;      /* new ticker value */
        new_timeset.it_value.tv_sec     = n_sec  ;      /* store this       */
        new_timeset.it_value.tv_usec    = n_usecs ;     /* and this         */

	return setitimer(ITIMER_REAL, &new_timeset, NULL);
}