问为什么我的计时器不是周期性的，而是只超时一次？

EN

#include <stdio.h>
#include <iostream>
#include <errno.h>
#include <dlfcn.h>
#include <assert.h>
#include <sys/mman.h>
#include <new>

#include <limits.h>
#include <sys/epoll.h>
#include <sys/timerfd.h>

using namespace std;

struct epoll_event event;
int timer_fd, efd, no_of_fd;
void myFunc( int i );

int main()
{
  struct itimerspec its;

  its.it_value.tv_sec = 5;
  its.it_value.tv_nsec = 0;

  its.it_interval.tv_sec = 3; // Every 3 seconds interval
  its.it_interval.tv_nsec = 0;


  efd = epoll_create(2);
  timer_fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK);

  if ( timer_fd == -1 )
  {
    fprintf(stderr, "timerfd_create error in start timer");
    return 1;
  }

  event.data.fd = timer_fd;
  event.events = EPOLLIN|EPOLLPRI;

  if ( epoll_ctl(efd, EPOLL_CTL_ADD, timer_fd, &event) == -1 )
  {
     fprintf(stderr, "epoll_ctl error in start timer"); 
     return 1;
  }

  if ( timerfd_settime(timer_fd, 0, &its, NULL) == -1 )
  {
    fprintf(stderr, "timerfd_settime error in start timer");
    return 1;
  }
  myFunc( 10 );
  myFunc( 20 );
  myFunc( 30 );
}

void myFunc( int i )
{
  printf("Inside myFunc %d\n", i);
  no_of_fd = 0;
  struct epoll_event revent;
  errno = 0;
  do {
     no_of_fd = epoll_wait(efd, &revent, 1, -1);
  } while ( no_of_fd < 0 && errno == EINTR );

  if ( no_of_fd < 0 )
  {
    fprintf(stderr, "epoll_wait error in start timer");

  }

  if ( revent.data.fd == timer_fd ) {
     printf("Timer expired \n");    
  }

}