linux_timerfd_example.c

/*
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/timerfd.h>
#include <unistd.h>
#include <fcntl.h>

#define TIMEOUT 3
#define POLL_PERIOD 1

int main(int argc, char *argv[])
{
    int ret;
    int fd = -1;
    struct itimerspec timeout;
    unsigned long long missed;

    /* create new timer */
    fd = timerfd_create(CLOCK_MONOTONIC, 0);
    if (fd <= 0) {
        printf("Failed to create timer\n");
        return 1;
    }

    /* set to non-blocking */
    ret = fcntl(fd, F_SETFL, O_NONBLOCK);
    if (ret) {
        printf("Failed to set to non blocking mode\n");
        return 1;
    }

    /* set timeout */
    timeout.it_value.tv_sec = TIMEOUT;
    timeout.it_value.tv_nsec = 0;
    timeout.it_interval.tv_sec = TIMEOUT; /* recurring */
    timeout.it_interval.tv_nsec = 0;
    ret = timerfd_settime(fd, 0, &timeout, NULL);
    if (ret) {
        printf("Failed to set timer duration\n");
        return 1;
    }

    while (1) {
        printf("Polling\n");
        while (read(fd, &missed, sizeof(missed)) < 0) {
            printf("No timer expiry\n");
            sleep(POLL_PERIOD);
        }
        printf("Number of expiries missed: %lld\n", missed);
    }

    return 0;
}