POSIX Timers POSIX Timer with SIGEV_THREAD notification


Example

This example demonstrates POSIX Timer usage with CLOCK_REALTIME clock and SIGEV_THREAD notification method.

#include <stdio.h>  /* for puts() */
#include <string.h> /* for memset() */
#include <unistd.h> /* for sleep() */
#include <stdlib.h> /* for EXIT_SUCCESS */

#include <signal.h> /* for `struct sigevent` and SIGEV_THREAD */
#include <time.h>   /* for timer_create(), `struct itimerspec`,
                     * timer_t and CLOCK_REALTIME 
                     */

void thread_handler(union sigval sv) {
        char *s = sv.sival_ptr;

        /* Will print "5 seconds elapsed." */
        puts(s);
}

int main(void) {
        char info[] = "5 seconds elapsed.";
        timer_t timerid;
        struct sigevent sev;
        struct itimerspec trigger;

        /* Set all `sev` and `trigger` memory to 0 */
        memset(&sev, 0, sizeof(struct sigevent));
        memset(&trigger, 0, sizeof(struct itimerspec));

        /* 
         * Set the notification method as SIGEV_THREAD:
         *
         * Upon timer expiration, `sigev_notify_function` (thread_handler()),
         * will be invoked as if it were the start function of a new thread.
         *
         */
        sev.sigev_notify = SIGEV_THREAD;
        sev.sigev_notify_function = &thread_handler;
        sev.sigev_value.sival_ptr = &info;

        /* Create the timer. In this example, CLOCK_REALTIME is used as the
         * clock, meaning that we're using a system-wide real-time clock for
         * this timer.
         */
        timer_create(CLOCK_REALTIME, &sev, &timerid);

        /* Timer expiration will occur withing 5 seconds after being armed
         * by timer_settime().
         */
        trigger.it_value.tv_sec = 5;

        /* Arm the timer. No flags are set and no old_value will be retrieved.
         */
        timer_settime(timerid, 0, &trigger, NULL);

        /* Wait 10 seconds under the main thread. In 5 seconds (when the
         * timer expires), a message will be printed to the standard output
         * by the newly created notification thread.
         */
        sleep(10);

        /* Delete (destroy) the timer */
        timer_delete(timerid);

        return EXIT_SUCCESS;
}