编写支持多线程的基于windows socket的C语言程序，

以下是一个简单的基于 Windows Socket 的多线程 C 语言程序：

#include <stdio.h>
#include <winsock2.h>
#include <windows.h>

#define PORT 8080
#define MAX_CLIENTS 5

// 线程参数结构体
typedef struct {
    SOCKET client_socket;
    SOCKADDR_IN client_address;
} ThreadArgs;

// 线程函数
DWORD WINAPI handle_client(LPVOID lpParam) {
    ThreadArgs *args = (ThreadArgs *)lpParam;
    SOCKET client_socket = args->client_socket;
    SOCKADDR_IN client_address = args->client_address;
    char buffer[1024] = {0};

    printf("Handling client %s:%d\n", inet_ntoa(client_address.sin_addr), ntohs(client_address.sin_port));

    // 接受客户端消息并回复
    while (1) {
        int read_size = recv(client_socket, buffer, sizeof(buffer), 0);
        if (read_size <= 0) {
            // 客户端关闭连接或发生错误
            break;
        }
        printf("Received message from client %s:%d: %s\n", inet_ntoa(client_address.sin_addr), ntohs(client_address.sin_port), buffer);
        send(client_socket, buffer, read_size, 0);
    }

    // 关闭连接
    printf("Closing connection with client %s:%d\n", inet_ntoa(client_address.sin_addr), ntohs(client_address.sin_port));
    closesocket(client_socket);
    free(args);
    return 0;
}

int main() {
    WSADATA wsa_data;
    SOCKET server_socket, client_socket;
    SOCKADDR_IN server_address, client_address;
    int client_address_size = sizeof(client_address);
    DWORD thread_id;

    // 初始化 Winsock
    if (WSAStartup(MAKEWORD(2, 2), &wsa_data) != 0) {
        printf("WSAStartup failed\n");
        return 1;
    }

    // 创建服务器套接字
    if ((server_socket = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
        printf("Failed to create server socket\n");
        return 1;
    }

    // 绑定服务器地址和端口
    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = INADDR_ANY;
    server_address.sin_port = htons(PORT);
    if (bind(server_socket, (SOCKADDR *)&server_address, sizeof(server_address)) == SOCKET_ERROR) {
        printf("Failed to bind server socket\n");
        return 1;
    }

    // 开始监听连接请求
    if (listen(server_socket, MAX_CLIENTS) == SOCKET_ERROR) {
        printf("Failed to listen for connections\n");
        return 1;
    }
    printf("Listening on port %d...\n", PORT);

    // 接受客户端连接并创建线程处理
    while ((client_socket = accept(server_socket, (SOCKADDR *)&client_address, &client_address_size)) != INVALID_SOCKET) {
        ThreadArgs *args = (ThreadArgs *)malloc(sizeof(ThreadArgs));
        args->client_socket = client_socket;
        args->client_address = client_address;
        CreateThread(NULL, 0, handle_client, (LPVOID)args, 0, &thread_id);
    }

    // 关闭服务器套接字和 Winsock
    closesocket(server_socket);
    WSACleanup();
    return 0;
}

在此示例中，我们使用了 Windows Socket 的 API 来创建服务器套接字、绑定地址和端口、监听连接请求、接受客户端连接，并在每个客户端连接上创建一个新的线程来处理消息收发。我们使用了 `CreateThread` 函数来创建新线程，并将客户端的套接字和地址作为参数传递给线程函数 `handle_client`。线程函数中，我们使用 `recv` 函数接受客户端的消息，并使用 `send` 函数回复相同的消息。如果客户端关闭连接或发生错误，我们将关闭连接并退出线程。注意，在此示例中我们并未处理多个客户端同时请求连接的情况，这可能会导致一些问题，例如有些客户端会因为连接超时而无法成功连接。为了处理此类情况，我们可以使用多线程或异步 I/O 来处理客户端连接。