用C语言实现一个非阻塞的服务器监听程序

在C语言中，要实现一个非阻塞的服务器监听程序，通常会利用`select()`、`epoll()`、或`poll()`等高级IO多路复用函数，这些系统调用可以在多个套接字上同时等待事件发生，而不会被阻塞。这里以`epoll`为例，因为它在Linux平台上性能较好。

以下是一个简单的使用`epoll`的非阻塞服务器监听示例：

#include <stdio.h>
#include <sys/epoll.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define MAX_EVENTS 10
#define PORT 8080

struct event {
    int epoll_fd;
    int socket_fd;
    struct sockaddr_in client_addr;
};

int main() {
    int server_sock, max_events = MAX_EVENTS;
    struct epoll_event events[MAX_EVENTS];
    struct sockaddr_in server_addr, client_addr;
    socklen_t client_len = sizeof(client_addr);
    int epoll_fd;

    // 创建监听套接字
    server_sock = socket(AF_INET, SOCK_STREAM, 0);
    if (server_sock == -1) {
        perror("socket failed");
        return -1;
    }

    // 绑定地址和设置为非阻塞模式
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    if (bind(server_sock, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind failed");
        close(server_sock);
        return -1;
    }
    setsockopt(server_sock, SOL_SOCKET, SO_REUSEADDR, &1, sizeof(int));
    fcntl(server_sock, F_SETFL, O_NONBLOCK);

    // 初始化epoll
    epoll_fd = epoll_create1(0);
    if (epoll_fd == -1) {
        perror("epoll_create1 failed");
        close(server_sock);
        return -1;
    }

    // 将监听套接字加入epoll
    events.events = EPOLLIN | EPOLLET;
    events.data.fd = server_sock;
    if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_sock, &events) == -1) {
        perror("epoll_ctl add failed");
        close(epoll_fd);
        close(server_sock);
        return -1;
    }

    printf("Server listening on port %d...\n", PORT);

    while (true) {
        // epoll_wait等待事件发生
        int num_events = epoll_wait(epoll_fd, events, max_events, -1);
        if (num_events <= 0) {
            perror("epoll_wait error");
            continue;
        }

        for (int i = 0; i < num_events; i++) {
            if (events[i].data.fd == server_sock) { // 新连接到来
                accept(server_sock, (struct sockaddr*)&client_addr, &client_len);
                // 创建新的事件描述符并添加到epoll
                struct event *new_event = realloc(events, sizeof(struct event) * (num_events + 1));
                if (!new_event) {
                    perror("realloc failed");
                    continue;
                }
                new_event[num_events].events = EPOLLIN | EPOLLET;
                new_event[num_events].data.fd = accept(server_sock, NULL, NULL);
                new_event[num_events].data.ptr = NULL;
                if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, new_event[num_events].data.fd, &new_event[num_events]) == -1) {
                    perror("epoll_ctl add failed");
                    close(new_event[num_events].data.fd);
                } else {
                    events = new_event;
                    num_events++;
                }
            } else { // 处理已连接客户端的请求
                char buffer[1024] = {0};
                read(events[i].data.fd, buffer, sizeof(buffer));
                // 这里处理客户端数据逻辑
                printf("Received message from client: %s\n", buffer);
                write(events[i].data.fd, "Hello, Client!", strlen("Hello, Client!"));
                close(events[i].data.fd); // 关闭连接
            }
        }
    }

    free(events);
    close(epoll_fd);
    close(server_sock);
    return 0;
}