（一）Socket I/O模型之选择(select)

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在windows平台构建网络应用，必须了解socket I/O模型。windows提供了选择(select)、异步选择(WSAAsyncSelect)、事件选择(WSAEventSelect)、重叠I /O(overlapped I/O)和完成端口(completion port)。 

一、客户端代码 

#include "stdafx.h"  
#include <WINSOCK2.H>  
#include <stdio.h>  
#pragma comment(lib, "ws2_32.lib")  
#define SERVER_ADDRESS  "192.168.10.56"  
#define PORT  5150  
#define MSGSIZE  1024  
int main(int argc, char* argv[])  
{  
    WSADATA wsaData;  
    SOCKET sClient;  
    SOCKADDR_IN server;  
    char szMessage[MSGSIZE];  
    int ret;  
    // Initialize windows socket library  
    WSAStartup(0x0202, &wsaData);  
    // Create client socket  
    sClient = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);  
    // Connect to server  
    memset(&server, 0, sizeof(SOCKADDR_IN));  
    server.sin_family = AF_INET;  
    server.sin_addr.S_un.S_addr = inet_addr(SERVER_ADDRESS);  
    server.sin_port = htons(PORT);  
    connect(sClient, (sockaddr*)&server, sizeof(SOCKADDR_IN));  
    while (TRUE)   
    {  
        printf("Send:");  
        gets(szMessage);  
        // Send message  
        send(sClient, szMessage, strlen(szMessage), 0);  
        // Receive message  
        ret = recv(sClient, szMessage, MSGSIZE, 0);  
        szMessage[ret] = '\0';  
        printf("Received [%d bytes]: '%s'\n", ret, szMessage);  
    }  
    // Clean up  
    closesocket(sClient);  
    WSACleanup();  
    return 0;  
}  

这是一个最简单的客户端代码，负责发送数据，然后接受返回。 

二、使用select模型的服务器 

// write by larry  
// 2009-8-20  
// This is server using select model.  
#include "stdafx.h"  
#include <winsock.h>  
#include <stdio.h>  
#define PORT  5150  
#define MSGSIZE  1024  
#pragma comment(lib, "ws2_32.lib")  
int g_iTotalConn = 0;  
SOCKET g_CliSocketArr[FD_SETSIZE];  
DWORD WINAPI WorkerThread(LPVOID lpParam);  
int main(int argc, char* argv[])  
{  
    WSADATA wsaData;  
    SOCKET sListen, sClient;  
    SOCKADDR_IN local, client;  
    int iAddrSize = sizeof(SOCKADDR_IN);  
    DWORD dwThreadId;  
    // Initialize windows socket library  
    WSAStartup(0x0202, &wsaData);  
    // Create listening socket  
    sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);  
    // Bind  
    local.sin_family = AF_INET;  
    local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);  
    local.sin_port = htons(PORT);  
    bind(sListen, (sockaddr*)&local, sizeof(SOCKADDR_IN));  
    // Listen  
    listen(sListen, 3);  
    // Create worker thread  
    CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId);  
    while (TRUE)   
    {  
        // Accept a connection  
        sClient = accept(sListen, (sockaddr*)&client, &iAddrSize);  
        printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));  
        // Add socket to g_CliSocketArr  
        g_CliSocketArr[g_iTotalConn++] = sClient;  
    }  
    return 0;  
}  
DWORD WINAPI WorkerThread(LPVOID lpParam)  
{  
    int i;  
    fd_set fdread;  
    int ret;  
    struct timeval tv = {1, 0};  
    char szMessage[MSGSIZE];  
    while (TRUE)   
    {  
        FD_ZERO(&fdread);  
        for (i = 0; i < g_iTotalConn; i++)   
        {  
            FD_SET(g_CliSocketArr[i], &fdread);  
        }  
        // We only care read event  
        ret = select(0, &fdread, NULL, NULL, &tv);  
        if (ret == 0)   
        {  
            // Time expired  
            continue;  
        }  
        for (i = 0; i < g_iTotalConn; i++)   
        {  
            if (FD_ISSET(g_CliSocketArr[i], &fdread))   
            {  
                // A read event happened on g_CliSocketArr  
                ret = recv(g_CliSocketArr[i], szMessage, MSGSIZE, 0);  
                if (ret == 0 || (ret == SOCKET_ERROR && WSAGetLastError() == WSAECONNRESET))   
                {  
                    // Client socket closed  
                    printf("Client socket %d closed.\n", g_CliSocketArr[i]);  
                    closesocket(g_CliSocketArr[i]);  
                    if (i < g_iTotalConn-1)   
                    {  
                        g_CliSocketArr[i--] = g_CliSocketArr[--g_iTotalConn];  
                    }  
                }   
                else   
                {  
                    // We reveived a message from client  
                    szMessage[ret] = '\0';  
                    send(g_CliSocketArr[i], szMessage, strlen(szMessage), 0);  
                }  
            }  
        }  
    }  
}  

这是异步模型中最简单的一种，服务器端的几个主要流程如下：  

1.创建监听套接字，绑定，监听； 
2.创建工作者线程； 
3.创建一个套接字数组，用来存放当前所有活动的客户端套接字，每accept一个连接就更新一次数组； 
4.接受客户端的连接。