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epoll(二)：epoll使用

epoll API的核心概念：

  • epoll instance， 使用 epoll_create API创建。
  • 通过epoll_ctl API向epoll instance添加或者移除相关的file descriptor。
  • epoll_wait 等待 I/O 事件，epoll高效的原因就是这个api可以在O(1)的时间复杂度内返回所有的I/O事件。

一个简单的例子: epoll_example.c

#define MAX_EVENTS 5
#define READ_SIZE 10
#include <stdio.h>     // for fprintf()
#include <unistd.h>    // for close(), read()
#include <sys/epoll.h> // for epoll_create1(), epoll_ctl(), struct epoll_event
#include <string.h>    // for strncmp
 
int main()
{
  int running = 1, event_count, i;
  size_t bytes_read;
  char read_buffer[READ_SIZE + 1];
  struct epoll_event event, events[MAX_EVENTS];
  int epoll_fd = epoll_create1(0);
 
  if(epoll_fd == -1)
  {
    fprintf(stderr, "Failed to create epoll file descriptor\n");
    return 1;
  }
 
  event.events = EPOLLIN;
  event.data.fd = 0;
 
  if(epoll_ctl(epoll_fd, EPOLL_CTL_ADD, 0, &event))
  {
    fprintf(stderr, "Failed to add file descriptor to epoll\n");
    close(epoll_fd);
    return 1;
  }
 
  while(running)
  {
    printf("\nPolling for input...\n");
    event_count = epoll_wait(epoll_fd, events, MAX_EVENTS, 30000);
    printf("%d ready events\n", event_count);
    for(i = 0; i < event_count; i++)
    {
      printf("Reading file descriptor '%d' -- ", events[i].data.fd);
      bytes_read = read(events[i].data.fd, read_buffer, READ_SIZE);
      printf("%zd bytes read.\n", bytes_read);
      read_buffer[bytes_read] = '\0';
      printf("Read '%s'\n", read_buffer);
 
      if(!strncmp(read_buffer, "stop\n", 5))
        running = 0;
    }
  }
 
  if(close(epoll_fd))
  {
    fprintf(stderr, "Failed to close epoll file descriptor\n");
    return 1;
  }
  return 0;
}

编译方法：

gcc -Wall -Werror epoll_example.c

参考

目录

2019/11/16