Socket I/O模型之选择(select)

http://tangfeng.iteye.com/blog/518135

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。