(三)Socket I/O模型之事件选择(WSAEventSelect)

时间:2022-05-30 00:00:47

转自:点击打开链接


WSAEventSelect和WSAAsyncSelect模型类似,它也允许应用程序在一个或多个套接字上,接收以事件为基础的网络事件通知。对于WSAAsyncSelect模型采用的网络事件来说,它们均可原封不动地移植到事件选择模型上。在用事件选择模型开发的应用程序中,也能接收和处理所有那些事件。该模型最主要的差别在于网络事件会投递至一个事件对象句柄,而非投递至一个窗口例程。 

服务器端代码: 

// write by larry  
// 2009-8-20  
// This is a server using WSAEventSelect model.  
#include "stdafx.h"  
#include <WINSOCK2.H>  
#include <stdio.h>  
#pragma comment(lib, "ws2_32.lib")  
#define PORT  5150  
#define MSGSIZE  1024  
int g_iTotalConn = 0;  
SOCKET g_CliSocketArr[MAXIMUM_WAIT_OBJECTS];  
WSAEVENT g_CliEventArr[MAXIMUM_WAIT_OBJECTS];  
DWORD WINAPI WorkerThread(LPVOID lpParam);  
void Cleanup(int index);  
int main(int argc, char* argv[])  
{  
    WSADATA wsaData;  
    SOCKET sListen, sClient;  
    SOCKADDR_IN local, client;  
    DWORD dwThreadId;  
    int iAddrSize = sizeof(SOCKADDR_IN);  
    // 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));  
        // Associate socket with network event  
        g_CliSocketArr[g_iTotalConn] = sClient;  
        g_CliEventArr[g_iTotalConn] = WSACreateEvent();  
        WSAEventSelect(g_CliSocketArr[g_iTotalConn], g_CliEventArr[g_iTotalConn], FD_READ|FD_CLOSE);  
        g_iTotalConn++;  
    }  
    return 0;  
}  
DWORD WINAPI WorkerThread(LPVOID lpParam)  
{  
    int ret, index;  
    WSANETWORKEVENTS NetworkEvents;  
    char szMessage[MSGSIZE];  
    while (TRUE)  
    {  
        ret = WSAWaitForMultipleEvents(g_iTotalConn, g_CliEventArr, FALSE, 1000, FALSE);  
        if (ret == WSA_WAIT_FAILED || ret == WSA_WAIT_TIMEOUT)  
        {  
            continue;  
        }  
        index = ret - WSA_WAIT_EVENT_0;  
        WSAEnumNetworkEvents(g_CliSocketArr[index], g_CliEventArr[index], &NetworkEvents);  
        if (NetworkEvents.lNetworkEvents & FD_READ)  
        {  
            // Receive message from client  
            ret = recv(g_CliSocketArr[index], szMessage, MSGSIZE, 0);  
            if (ret == 0 || (ret == SOCKET_ERROR && WSAGetLastError() == WSAECONNRESET))  
            {  
                Cleanup(index);  
            }  
            else  
            {  
                szMessage[ret] = '\0';  
                send(g_CliSocketArr[index], szMessage, strlen(szMessage), 0);  
            }  
        }  
        if (NetworkEvents.lNetworkEvents & FD_CLOSE)  
        {  
            Cleanup(index);  
        }  
    }  
    return 0;  
}  
void Cleanup(int index)  
{  
    closesocket(g_CliSocketArr[index]);  
    WSACloseEvent(g_CliEventArr[index]);  
    if (index < g_iTotalConn-1)  
    {  
        g_CliSocketArr[index] = g_CliSocketArr[g_iTotalConn-1];  
        g_CliEventArr[index] = g_CliEventArr[g_iTotalConn-1];  
    }  
    g_iTotalConn--;  
}


事件选择模型也比较简单,实现起来也不是太复杂,它的基本思想是将每个套接字都和一个WSAEVENT对象对应起来,并且在关联的时候指定需要关注的哪些网络事件。一旦在某个套接字上发生了我们关注的事件(FD_READ和FD_CLOSE),与之相关联的WSAEVENT对象被Signaled。程序定义了两个全局数组,一个套接字数组,一个WSAEVENT对象数组,其大小都是MAXIMUM_WAIT_OBJECTS(64),两个数组中的元素一一对应。 

同样的,这里的程序没有考虑两个问题,一是不能无条件的调用accept,因为我们支持的并发连接数有限。解决方法是将套接字按 MAXIMUM_WAIT_OBJECTS分组,每MAXIMUM_WAIT_OBJECTS个套接字一组,每一组分配一个工作者线程;或者采用 WSAAccept代替accept,并回调自己定义的Condition Function。第二个问题是没有对连接数为0的情形做特殊处理,程序在连接数为0的时候CPU占用率为100%。