linux C epoll机制示例代码

以下是一个简单的Linux C epoll机制示例代码，用于监听文件描述符的可读事件：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/epoll.h>

#define MAX_EVENTS 10

int main() {
    int fd, sockfd, n, epollfd;
    char buffer[256];
    struct sockaddr_in serveraddr, clientaddr;
    socklen_t clientlen = sizeof(clientaddr);
    struct epoll_event ev, events[MAX_EVENTS];

    // 创建socket
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        perror("ERROR opening socket");
        exit(1);
    }

    // 绑定地址
    bzero((char *) &serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_addr.s_addr = INADDR_ANY;
    serveraddr.sin_port = htons(5000);
    if (bind(sockfd, (struct sockaddr *) &serveraddr, sizeof(serveraddr)) < 0) {
        perror("ERROR on binding");
        exit(1);
    }

    // 监听
    listen(sockfd, 5);

    // 创建epoll实例
    epollfd = epoll_create1(0);
    if (epollfd == -1) {
        perror("epoll_create1");
        exit(EXIT_FAILURE);
    }

    // 添加sockfd到epoll实例中
    ev.events = EPOLLIN;
    ev.data.fd = sockfd;
    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1) {
        perror("epoll_ctl: sockfd");
        exit(EXIT_FAILURE);
    }

    // 等待事件发生
    while (1) {
        n = epoll_wait(epollfd, events, MAX_EVENTS, -1);
        for (int i = 0; i < n; i++) {
            // 如果是sockfd可读事件，则接收客户端连接
            if (events[i].data.fd == sockfd) {
                fd = accept(sockfd, (struct sockaddr *) &clientaddr, &clientlen);
                if (fd < 0) {
                    perror("ERROR on accept");
                    exit(1);
                }
                printf("Client connected\n");

                // 将新的连接fd添加到epoll实例中
                ev.events = EPOLLIN;
                ev.data.fd = fd;
                if (epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
                    perror("epoll_ctl: fd");
                    exit(EXIT_FAILURE);
                }
            } 
            // 如果是其他fd可读事件，则接收数据
            else {
                bzero(buffer, 256);
                if (read(events[i].data.fd, buffer, 255) < 0) {
                    perror("ERROR reading from socket");
                    exit(1);
                }
                printf("Message received: %s\n", buffer);
            }
        }
    }

    // 关闭socket和epoll实例
    close(sockfd);
    close(epollfd);
    return 0;
}

以上代码监听端口5000，接收客户端连接并接收数据。通过epoll机制，可以同时监控多个文件描述符的可读事件，从而提高程序的效率。