使用epoll写一个Linux网络编程的例子

好的，这是一个使用epoll实现的简单的Linux网络编程例子：

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/epoll.h>

#define MAX_EVENTS 1024
#define PORT 12345

int setnonblocking(int sockfd) {
    int flags = fcntl(sockfd, F_GETFL, 0);
    if (flags == -1) {
        return -1;
    }
    flags |= O_NONBLOCK;
    if (fcntl(sockfd, F_SETFL, flags) == -1) {
        return -1;
    }
    return 0;
}

int main(int argc, char *argv[]) {
    int listenfd, connfd, nfds, epollfd;
    ssize_t n;
    char buf[1024];
    struct sockaddr_in servaddr, cliaddr;
    struct epoll_event ev, events[MAX_EVENTS];

    // 创建监听socket，绑定地址和端口
    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(PORT);
    bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
    listen(listenfd, 5);

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

    // 设置监听socket为非阻塞
    if (setnonblocking(listenfd) < 0) {
        perror("setnonblocking");
        exit(EXIT_FAILURE);
    }

    // 添加监听socket事件到epoll
    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = listenfd;
    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
        perror("epoll_ctl: listenfd");
        exit(EXIT_FAILURE);
    }

    // 循环处理epoll事件
    for (;;) {
        nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
        if (nfds == -1) {
            perror("epoll_wait");
            exit(EXIT_FAILURE);
        }

        for (int i = 0; i < nfds; i++) {
            if (events[i].data.fd == listenfd) { // 新连接
                socklen_t clilen = sizeof(cliaddr);
                connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
                if (connfd == -1) {
                    perror("accept");
                    exit(EXIT_FAILURE);
                }

                // 设置连接socket为非阻塞
                if (setnonblocking(connfd) < 0) {
                    perror("setnonblocking");
                    exit(EXIT_FAILURE);
                }

                // 添加连接socket事件到epoll
                ev.events = EPOLLIN | EPOLLOUT | EPOLLET;
                ev.data.fd = connfd;
                if (epoll_ctl(epollfd, EPOLL_CTL_ADD, connfd, &ev) == -1) {
                    perror("epoll_ctl: connfd");
                    exit(EXIT_FAILURE);
                }

                // 打印新连接的客户端地址
                printf("Accepted connection from %s:%d\n",
                       inet_ntoa(cliaddr.sin_addr), ntohs(cliaddr.sin_port));
            } else { // 已连接
                if (events[i].events & EPOLLIN) { // 可读
                    while ((n = read(events[i].data.fd, buf, sizeof(buf))) > 0) {
                        // 处理读取到的数据
                        // ...
                    }
                    if (n == 0) { // 对方关闭连接
                        close(events[i].data.fd);
                        printf("Closed connection on descriptor %d\n",
                               events[i].data.fd);
                    } else if (errno != EAGAIN && errno != EINTR) { // 发生错误
                        perror("read error");
                        close(events[i].data.fd);
                    }
                } else if (events[i].events & EPOLLOUT) { // 可写
                    // 发送数据到连接socket
                    // ...
                } else { // 其他事件
                    printf("Unknown event: %d\n", events[i].events);
                }
            }
        }
    }

    // 关闭监听socket和epoll
    close(listenfd);
    close(epollfd);

    return 0;
}

这个例子使用epoll监听TCP连接事件，支持EPOLLET边缘触发模式和非阻塞IO。当有新连接到来时，将连接socket添加到epoll中，并打印客户端地址；当连接socket可读或可写时，分别处理读取和发送数据。