编辑“︁C 语言非阻塞io”︁（章节）

=== 示例：非阻塞网络服务器 ===
以下是一个简单的非阻塞网络服务器示例，使用`select`多路复用：

<syntaxhighlight lang="c">
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

#define PORT 8080
#define MAX_CLIENTS 10

int main() {
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd == -1) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置非阻塞模式
    int flags = fcntl(server_fd, F_GETFL, 0);
    fcntl(server_fd, F_SETFL, flags | O_NONBLOCK);

    struct sockaddr_in address;
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    if (listen(server_fd, MAX_CLIENTS) < 0) {
        perror("listen failed");
        exit(EXIT_FAILURE);
    }

    fd_set readfds;
    int client_sockets[MAX_CLIENTS] = {0};

    while (1) {
        FD_ZERO(&readfds);
        FD_SET(server_fd, &readfds);
        int max_fd = server_fd;

        for (int i = 0; i < MAX_CLIENTS; i++) {
            if (client_sockets[i] > 0) {
                FD_SET(client_sockets[i], &readfds);
                if (client_sockets[i] > max_fd) {
                    max_fd = client_sockets[i];
                }
            }
        }

        int activity = select(max_fd + 1, &readfds, NULL, NULL, NULL);
        if (activity < 0 && errno != EINTR) {
            perror("select error");
        }

        if (FD_ISSET(server_fd, &readfds)) {
            int new_socket = accept(server_fd, NULL, NULL);
            if (new_socket < 0) {
                perror("accept error");
                continue;
            }

            // 设置非阻塞模式
            flags = fcntl(new_socket, F_GETFL, 0);
            fcntl(new_socket, F_SETFL, flags | O_NONBLOCK);

            for (int i = 0; i < MAX_CLIENTS; i++) {
                if (client_sockets[i] == 0) {
                    client_sockets[i] = new_socket;
                    printf("New connection, socket fd: %d\n", new_socket);
                    break;
                }
            }
        }

        for (int i = 0; i < MAX_CLIENTS; i++) {
            if (client_sockets[i] > 0 && FD_ISSET(client_sockets[i], &readfds)) {
                char buffer[1024] = {0};
                ssize_t bytes_read = read(client_sockets[i], buffer, sizeof(buffer));
                if (bytes_read <= 0) {
                    if (bytes_read == 0 || errno == EAGAIN || errno == EWOULDBLOCK) {
                        // 连接关闭或暂时无数据
                        close(client_sockets[i]);
                        client_sockets[i] = 0;
                    } else {
                        perror("read error");
                    }
                } else {
                    printf("Received: %s\n", buffer);
                    write(client_sockets[i], buffer, bytes_read);
                }
            }
        }
    }

    return 0;
}
</syntaxhighlight>