C timer example

setinterval.c

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/timerfd.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>

void setnonblock(int sockfd)
{
    int opts;
    opts = fcntl(sockfd, F_GETFL);
    if (opts < 0) {
        perror("GETFL");
    }
    opts = (opts | O_NONBLOCK);
    if (fcntl(sockfd, F_SETFL, opts) < 0) {
        perror("SETFL");
    }
}

int main()
{
    int efd =epoll_create(256);
    setnonblock(efd);
    struct epoll_event ev, events[256];
    int i;

    int tfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK);
    if (tfd < 0) {
        perror("timer create");
        return 1;
    }

    struct itimerspec newValue;
    struct itimerspec oldValue;
    memset(&newValue, 0, sizeof newValue);
    memset(&oldValue, 0, sizeof oldValue);
    struct timespec ts;
    ts.tv_sec = 5;
    ts.tv_nsec = 0;

    newValue.it_value = ts;
    newValue.it_interval = ts;
    if (timerfd_settime(tfd, 0, &newValue, &oldValue) < 0) {
        perror("settime");
        return 1;
    }

    ev.data.fd = tfd;
    ev.events = EPOLLIN | EPOLLET;

    if (epoll_ctl(efd, EPOLL_CTL_ADD, tfd, &ev) < 0) {
        perror("epoll add");
        return 1;
    }

    int num = 0;
    while (1) {
       if ((num=epoll_wait(efd, events, 256, 1000)) > 0) {
            for (i = 0; i < num; i++) {
                if (events[i].data.fd == tfd) {
                    printf("timeout\n");
                    if (timerfd_settime(tfd, 0, &newValue, &oldValue) < 0) {
                        perror("settime");
                        return 1;
                    }
                    if (epoll_ctl(efd, EPOLL_CTL_MOD, tfd, &ev) < 0) {
                        perror("epoll add");
                        return 1;
                    }
                }
            }
        }
    }
    return 0;
  }