写一个epoll例子

好的，这里是一个简单的 epoll 例子：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/epoll.h>

#define MAX_EVENTS 10

int main(int argc, char *argv[]) {
    int listen_sock, conn_sock, epoll_fd, nfds, i, n;
    struct sockaddr_in serv_addr, cli_addr;
    socklen_t cli_len = sizeof(cli_addr);
    struct epoll_event ev, events[MAX_EVENTS];
    char buffer[1024];

    if ((listen_sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(8080);

    if (bind(listen_sock, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    if (listen(listen_sock, SOMAXCONN) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    if ((epoll_fd = epoll_create1(0)) < 0) {
        perror("epoll_create1");
        exit(EXIT_FAILURE);
    }

    ev.events = EPOLLIN;
    ev.data.fd = listen_sock;

    if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, listen_sock, &ev) < 0) {
        perror("epoll_ctl: listen_sock");
        exit(EXIT_FAILURE);
    }

    while (1) {
        nfds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
        if (nfds < 0) {
            perror("epoll_wait");
            exit(EXIT_FAILURE);
        }

        for (i = 0; i < nfds; ++i) {
            if (events[i].data.fd == listen_sock) {
                conn_sock = accept(listen_sock, (struct sockaddr *) &cli_addr, &cli_len);
                if (conn_sock < 0) {
                    perror("accept");
                    exit(EXIT_FAILURE);
                }

                ev.events = EPOLLIN;
                ev.data.fd = conn_sock;

                if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, conn_sock, &ev) < 0) {
                    perror("epoll_ctl: conn_sock");
                    exit(EXIT_FAILURE);
                }
            } else {
                n = read(events[i].data.fd, buffer, sizeof(buffer));
                if (n < 0) {
                    perror("read");
                    exit(EXIT_FAILURE);
                }
                if (n == 0) {
                    if (epoll_ctl(epoll_fd, EPOLL_CTL_DEL, events[i].data.fd, NULL) < 0) {
                        perror("epoll_ctl: conn_sock");
                        exit(EXIT_FAILURE);
                    }
                    close(events[i].data.fd);
                } else {
                    if (write(events[i].data.fd, buffer, n) < 0) {
                        perror("write");
                        exit(EXIT_FAILURE);
                    }
                }
            }
        }
    }

    return 0;
}

这个程序监听端口 8080，并使用 epoll 实现了一个简单的回显服务器。它可以同时处理多个连接，当有新连接到来时，将其加入 epoll 监听队列中，当某个连接的数据可读时，就读取并回显给客户端。