Epoll test with arbitrary event data fd

epoll_test.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>
#include <pthread.h>
#include <sys/epoll.h>

// gcc -Wall epoll_test.c -o epoll_test -lpthread
// ./epoll_test

#define PIPE_READ  (0)
#define PIPE_WRITE (1)
#define MAP_TO_FD  (123)

sem_t gx_main_sem;
int gai_pipe[2];


static void* pvThreadBody(void* pv_arg_data)
{
  int i_epoll_fd = -1;
  int i_wait_ret = -1;
  struct epoll_event x_epoll_temp_event;

  i_epoll_fd = epoll_create1(0);
  memset(&x_epoll_temp_event, 0, sizeof(struct epoll_event));
  x_epoll_temp_event.events = EPOLLIN;
  x_epoll_temp_event.data.fd = MAP_TO_FD;
  printf("Doing epoll_ctl with arg fd=%d and event data fd=%d\n",
         gai_pipe[PIPE_READ], x_epoll_temp_event.data.fd);
  epoll_ctl(i_epoll_fd, EPOLL_CTL_ADD, gai_pipe[PIPE_READ], &x_epoll_temp_event);
  
  memset(&x_epoll_temp_event, 0, sizeof(struct epoll_event));
  sem_post(&gx_main_sem);
  i_wait_ret = epoll_wait(i_epoll_fd, &x_epoll_temp_event, 1, -1);

  printf("Epoll wait result %d, event data fd=%d\n",
         i_wait_ret, x_epoll_temp_event.data.fd);

  return NULL;
}


int main()
{
  pthread_t x_evl_thread;
  sem_init(&gx_main_sem, 0, 0);
  pipe(gai_pipe);
  pthread_create(&x_evl_thread, NULL, pvThreadBody, NULL);
  sem_wait(&gx_main_sem);
  printf("Writing to pipe, write fd=%d, read fd=%d\n",
         gai_pipe[PIPE_WRITE], gai_pipe[PIPE_READ]);
  write(gai_pipe[PIPE_WRITE], "Hello\n", strlen("Hello\n"));
  
  pthread_join(x_evl_thread, NULL);
  
  return 0;
}