用C语言举例应用select和epoll

一、select应用举例

下面的代码演示了如何使用select函数进行I/O多路复用，同时处理多个客户端的连接和消息收发：

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

#define MAX_CLIENTS 10
#define BUFFER_SIZE 1024

int main(int argc, char *argv[])
{
    int server_socket, client_socket[MAX_CLIENTS], max_fd, activity, i, valread, sd;
    struct sockaddr_in server_addr, client_addr;
    fd_set readfds;
    char buffer[BUFFER_SIZE];

    // 创建服务器socket
    if ((server_socket = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置服务器socket地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(8888);

    // 绑定服务器socket到地址
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 监听客户端连接
    if (listen(server_socket, MAX_CLIENTS) == -1) {
        perror("listen failed");
        exit(EXIT_FAILURE);
    }

    // 初始化客户端socket数组
    for (i = 0; i < MAX_CLIENTS; i++) {
        client_socket[i] = 0;
    }

    // 输出服务器信息
    printf("Server started on port %d\n", ntohs(server_addr.sin_port));

    while (1) {
        // 清空文件描述符集合
        FD_ZERO(&readfds);

        // 添加服务器socket到集合中
        FD_SET(server_socket, &readfds);
        max_fd = server_socket;

        // 添加客户端socket到集合中
        for (i = 0; i < MAX_CLIENTS; i++) {
            sd = client_socket[i];

            // 如果socket有效，添加到集合中
            if (sd > 0) {
                FD_SET(sd, &readfds);
            }

            // 更新最大文件描述符
            if (sd > max_fd) {
                max_fd = sd;
            }
        }

        // 等待文件描述符上有活动事件
        activity = select(max_fd + 1, &readfds, NULL, NULL, NULL);

        if ((activity < 0) && (errno != EINTR)) {
            perror("select failed");
            exit(EXIT_FAILURE);
        }

        // 如果服务器socket有连接请求，处理连接
        if (FD_ISSET(server_socket, &readfds)) {
            int new_socket, addrlen = sizeof(client_addr);

            if ((new_socket = accept(server_socket, (struct sockaddr *)&client_addr, (socklen_t *)&addrlen)) == -1) {
                perror("accept failed");
                exit(EXIT_FAILURE);
            }

            // 输出新客户端信息
            printf("New connection, socket fd is %d, ip is : %s, port : %d\n", new_socket, inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

            // 添加新客户端socket到数组中
            for (i = 0; i < MAX_CLIENTS; i++) {
                if (client_socket[i] == 0) {
                    client_socket[i] = new_socket;
                    break;
                }
            }
        }

        // 处理客户端socket上的消息
        for (i = 0; i < MAX_CLIENTS; i++) {
            sd = client_socket[i];

            if (FD_ISSET(sd, &readfds)) {
                if ((valread = read(sd, buffer, BUFFER_SIZE)) == 0) {
                    // 客户端关闭连接
                    getpeername(sd, (struct sockaddr *)&client_addr, (socklen_t *)&addrlen);
                    printf("Client disconnected, ip is : %s, port : %d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
                    close(sd);
                    client_socket[i] = 0;
                } else {
                    // 处理客户端消息
                    buffer[valread] = '\0';
                    printf("Received message from client[%d], message is : %s\n", i, buffer);
                }
            }
        }
    }

    return 0;
}

二、epoll应用举例

下面的代码演示了如何使用epoll函数进行I/O多路复用，同时处理多个客户端的连接和消息收发：

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

#define MAX_CLIENTS 10
#define BUFFER_SIZE 1024

int main(int argc, char *argv[])
{
    int server_socket, client_socket, epoll_fd, i, valread, sd;
    struct sockaddr_in server_addr, client_addr;
    struct epoll_event event, events[MAX_CLIENTS];
    char buffer[BUFFER_SIZE];

    // 创建服务器socket
    if ((server_socket = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置服务器socket地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(8888);

    // 绑定服务器socket到地址
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 监听客户端连接
    if (listen(server_socket, MAX_CLIENTS) == -1) {
        perror("listen failed");
        exit(EXIT_FAILURE);
    }

    // 创建epoll文件描述符
    if ((epoll_fd = epoll_create(MAX_CLIENTS)) == -1) {
        perror("epoll_create failed");
        exit(EXIT_FAILURE);
    }

    // 添加服务器socket到epoll事件中
    event.events = EPOLLIN;
    event.data.fd = server_socket;

    if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_socket, &event) == -1) {
        perror("epoll_ctl failed");
        exit(EXIT_FAILURE);
    }

    // 输出服务器信息
    printf("Server started on port %d\n", ntohs(server_addr.sin_port));

    while (1) {
        // 等待epoll事件触发
        int num_events = epoll_wait(epoll_fd, events, MAX_CLIENTS, -1);

        // 处理所有触发的事件
        for (i = 0; i < num_events; i++) {
            // 如果是服务器socket有连接请求，处理连接
            if (events[i].data.fd == server_socket) {
                int addrlen = sizeof(client_addr);

                if ((client_socket = accept(server_socket, (struct sockaddr *)&client_addr, (socklen_t *)&addrlen)) == -1) {
                    perror("accept failed");
                    exit(EXIT_FAILURE);
                }

                // 输出新客户端信息
                printf("New connection, socket fd is %d, ip is : %s, port : %d\n", client_socket, inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

                // 将客户端socket添加到epoll事件中
                event.events = EPOLLIN;
                event.data.fd = client_socket;

                if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_socket, &event) == -1) {
                    perror("epoll_ctl failed");
                    exit(EXIT_FAILURE);
                }
            } else {
                // 处理客户端socket上的消息
                sd = events[i].data.fd;

                if ((valread = read(sd, buffer, BUFFER_SIZE)) == 0) {
                    // 客户端关闭连接
                    getpeername(sd, (struct sockaddr *)&client_addr, (socklen_t *)&addrlen);
                    printf("Client disconnected, ip is : %s, port : %d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
                    close(sd);
                } else {
                    // 处理客户端消息
                    buffer[valread] = '\0';
                    printf("Received message from client, message is : %s\n", buffer);
                }
            }
        }
    }

    return 0;
}