UDP 多线程 相互 守候 服务 C 源代码

UDP (User Datagram Protocol) 是一种无连接的传输层协议，它并不保证数据包的顺序、可靠性或及时到达。在多线程环境中，如果要在UDP服务中实现相互守候（即客户端等待服务器响应或服务器等待客户端请求），通常需要结合多路复用（Multiplexing）技术来处理并发连接。

下面是一个简化的C语言示例，展示了使用多线程在一个简单的UDP服务器上接收客户端消息，并对每个客户端发送回应的基本框架：

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <pthread.h>

#define PORT 12345

void* client_thread(void* arg) {
    int client_sock = *(int*)arg;
    char buffer[1024];
    while (1) {
        ssize_t bytes_received = recvfrom(client_sock, buffer, sizeof(buffer), 0, NULL, NULL);
        if (bytes_received > 0) {
            printf("Received from client: %s\n", buffer);
            sendto(client_sock, "Server received your message.", strlen("Server received your message."), 0, (struct sockaddr*)&client_addr, bytes_received); // 发送回应
        } else if (bytes_received == 0) {
            printf("Client disconnected.\n");
            close(client_sock);
            break;
        } else {
            perror("recvfrom failed");
            break;
        }
    }
    pthread_exit(NULL);
}

int main() {
    int server_sock, one = 1;
    struct addrinfo hints, *res, *ptr;
    char address[] = "0.0.0.0";
    const char* service = "12345";

    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC; // Allow IPv4 and IPv6
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_flags = AI_PASSIVE;

    getaddrinfo(address, service, &hints, &res);

    server_sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
    setsockopt(server_sock, SOL_SOCKET, SO_REUSEADDR, (char *)&one, sizeof(one));

    bind(server_sock, res->ai_addr, res->ai_addrlen);
    freeaddrinfo(res);

    printf("Server started on port %d\n", ntohs(server_sock));

    for (ptr = res; ptr != NULL; ptr = ptr->ai_next) {
        pthread_create(&thread_id, NULL, client_thread, (void*)&server_sock);
    }

    // Main thread will receive incoming connections
    while (1) {
        socklen_t len = sizeof(struct sockaddr_in);
        ssize_t bytes_received = recvfrom(server_sock, buffer, sizeof(buffer), 0, (struct sockaddr*)&client_addr, &len);
        if (bytes_received > 0) {
            printf("New connection: %s:%d\n", inet_ntoa(((struct sockaddr_in*)&client_addr)->sin_addr), ntohs(((struct sockaddr_in*)&client_addr)->sin_port));
            pthread_create(&thread_id, NULL, client_thread, (void*)&server_sock);
        } else {
            perror("recvfrom failed");
            break;
        }
    }

    return 0;
}