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#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#define STARTSEC 10
#define ENDUSEC 500000
#define SPEED 0.8
struct itimerval timer;
void timer_handler(int signum) {
/* Handy structure reference */
struct timeval *tv = &timer.it_value;
printf("Hey we hit the alarm\n\a");
/* Calculate new alarm */
tv->tv_sec *= SPEED;
if (tv->tv_sec == 0) {
/* If tv_usec is 0 set i to 1 sec otherwise half it */
if (tv->tv_usec == 0) {
tv->tv_usec = 999999;
} else if (tv->tv_usec > ENDUSEC) {
tv->tv_usec *= SPEED;
if (tv->tv_usec < ENDUSEC) {
tv->tv_usec = ENDUSEC;
}
} else {
/* Return letting the timer be set to ENDUSEC */
return;
}
}
printf("Set to %d and %d\n", timer.it_value.tv_sec, timer.it_value.tv_usec);
/* Set alarm */
int err = setitimer(ITIMER_REAL, &timer, NULL);
if (err) {
printf("Hey we got an error guys\n");
exit(1);
}
}
int main() {
/* Setup handler for timer */
struct sigaction sa;
memset(&sa, 0, sizeof(sa)); /* Remeber to set all fields to zero */
sa.sa_handler = &timer_handler;
sigaction(SIGALRM, &sa, NULL);
/* Setup timer values */
timer.it_value.tv_sec = STARTSEC;
timer.it_value.tv_usec = 0;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = ENDUSEC;
/* Start the timer */
setitimer(ITIMER_REAL, &timer, NULL);
/* Select signals */
sigset_t sigset;
sigemptyset(&sigset);
sigaddset(&sigset, SIGTERM);
/* Wait for termination */
sigwait(&sigset, NULL);
return 0;
}
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