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Linux file descriptor timers example
* 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
* 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 <>.
#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) {
while (read(fd, &missed, sizeof(missed)) < 0) {
printf("No timer expiry\n");
printf("Number of expiries missed: %lld\n", missed);
return 0;

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rizsi commented Dec 5, 2018

The accuracy of this solution is defined by the POLL_PERIOD. Using blocking read, epoll or select on the timer file descriptor the best accuracy available on the platform could be achieved.

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