Overlapped I/O模型--事件通知【摘录自《Windows网络编程》】

原文：http://www.cnblogs.com/NeuqUstcIim/archive/2008/08/16/1269479.html

 

重叠I / O的事件通知方法要求将Wi n 3 2事件对象与W S A O V E R L A P P E D结构关联在一起。若使用一个W S A O V E R L A P P E D结构，发出像W S A S e n d和W S A R e c v这样的I / O调用，它们会立即返回。

    一个重叠I / O请求最终完成后，我们的应用程序要负责取回重叠I / O操作的结果。一个重叠请求操作最终完成之后，在事件通知方法中， Wi n s o c k会更改与一个W S A O V E R L A P P E D结构对应的一个事件对象的事件传信状态，将其从“未传信”变成“已传信”。 由于一个事件对象

已分配给W S A O V E R L A P P E D结构，所以只需简单地调用W S AWa i t F o r M u l t i p l e E v e n t s函数，从而判断出一个重叠I / O调用在什么时候完成。

   注意： W S AWa i t F o r M u l t i p l e E v e n t s返回只是说明重叠IO操作完成，但是是成功的完成还是失败的完成还要调用W S A G e t O v e r l a p p e dR e s u l t（取得重叠结构）函数

    如W S A G e t O v e r l a p p e d R e s u l t函数调用成功，返回值就是T R U E。这意味着我们的重叠I / O操作已成功完成，而且由l p c b Tr a n s f e r参数指向的值已进行了更新。

 

   我们向大家阐述了如何编制一个简单的服务器应用，令其在一个套接字上对重叠I / O操作进行管理，程序完全利用了前述的事件通知机制。对该程序采用的编程步骤总结如下：
1) 创建一个套接字，开始在指定的端口上监听连接请求。
2) 接受一个进入的连接请求。
3) 为接受的套接字新建一个W S A O V E R L A P P E D结构，并为该结构分配一个事件对象句柄。也将事件对象句柄分配给一个事件数组，以便稍后由W S AWa i t F o r M u l t i p l e E v e n t s函数使用。
4) 在套接字上投递一个异步W S A R e c v请求，指定参数为W S A O V E R L A P P E D结构。
注意函数通常会以失败告终，返回S O C K E T _ E R R O R错误状态W S A _ I O _ P E N D I N G
（I/O操作尚未完成）。
5) 使用步骤3 )的事件数组，调用W S AWa i t F o r M u l t i p l e E v e n t s函数，并等待与重叠调用关联在一起的事件进入“已传信”状态（换言之，等待那个事件的“触发”）。
6) WSAWa i t F o r M u l t i p l e E v e n t s函数完成后，针对事件数组，调用W S A R e s e t E v e n t（重设事件）函数，从而重设事件对象，并对完成的重叠请求进行处理。
7) 使用W S A G e t O v e r l a p p e d R e s u l t函数，判断重叠调用的返回状态是什么。
8) 在套接字上投递另一个重叠W S A R e c v请求。

9) 重复步骤5 ) ~ 8 )。

#include "stdafx.h"
 #include <winsock2.h>

 #define DATA_BUFSIZE 4096

 #pragma comment(lib, "ws2_32.lib")

 int _tmain(int argc, _TCHAR* argv[])
 {
     DWORD EventTotal = 0,RecvBytes = 0, Flags = 0;
     char buffer[DATA_BUFSIZE];

     WSABUF DataBuf;
     WSAEVENT EventArray[WSA_MAXIMUM_WAIT_EVENTS];
     WSAOVERLAPPED AcceptOverlapped;
     SOCKET Listen,Accept;

     //step1:
     //start Winsock and set up a listening socket
     WSADATA wsaData;
     WSAStartup(MAKEWORD(2,2), &wsaData);

     ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
     u_short port = 27015;
     char* ip;
     sockaddr_in service;
     service.sin_family = AF_INET;
     service.sin_port = htons(port);
     hostent* thisHost;
     thisHost = gethostbyname("");
     ip = inet_ntoa (*(struct in_addr *)*thisHost->h_addr_list);

     service.sin_addr.s_addr = inet_addr(ip);

     //-----------------------------------------
     // Bind the listening socket to the local IP address
     // and port number
     bind(ListenSocket, (SOCKADDR *) &service, sizeof(SOCKADDR));

     //-----------------------------------------
     // Set the socket to listen for incoming
     // connection requests
     listen(ListenSocket, 1);
     printf("Listening\n");

     //step2:
     Accept=accept(Listen,NULL,NULL);

     //step3:
     //set up an overlapped structure
     EventArray[EventTotal]=WSACreateEvent();//先存到事件数组中
     ZeroMemory(&AcceptOverlapped,sizeof(WSAOVERLAPPED));
     AcceptOverlapped.hEvent = EventArray[EventTotal];

     DataBuf.len = DATA_BUFSIZE;
     DataBuf.buf =buffer;

     EventTotal++;

     //step4:
     //投递WSARecv准备在Accept套接字上接收数据
     WSARecv(Accept,&DataBuf,1,&RecvBytes,&Flag,&AcceptOverlapped,NULL);

     while (TRUE){
         //step5:
         //等待overlapped IO调用的完成
         DWORD Index;
         Index = WSAWaitForMultipleEvents(EventTotal, EventArray, FALSE, WSA_INFINITE, FALSE);

         //step6:
         // Reset the signaled event
         WSAResetEvent(EventArray[Index - WSA_WAIT_EVENT_0]);

         //step7:
         // Determine the status of the overlapped event
         WSAGetOverlappedResult(AcceptSocket, &AcceptOverlapped, &BytesTransferred, FALSE, &Flags);


         // If the connection has been closed, close the accepted socket
         if (BytesTransferred == 0) {
             printf("Closing Socket %d\n", AcceptSocket);
             closesocket(AcceptSocket);
             WSACloseEvent(EventArray[Index - WSA_WAIT_EVENT_0]);
             return;
         }

         // If data has been received,do something with received data
         //DataBuf contains the received data

         //step8:
         //post another WSARecv () request on the socket
         Flag=0;
         ZeroMemory(&AcceptOverlapped,sizeof(WSAOVERLAPPED));
         AcceptOverlapped.hEvent=EventArray[Index - WSA_WAIT_EVENT_0];//该事件对象已经被复位

         DataBuf.len = DATA_BUFSIZE;
         DataBuf.buf =buffer;

         WSARecv(Accept,&DataBuf,1,&RecvBytes,&Flag,&AcceptOverlapped,NULL);
     }
     return 0;
 }

改进后的程序（并非实际可以运行的程序，只是为了理清思路）：

#define LISTEN_PORT 5000
 #define DATA_BUFSIZE 8192
 #define POST_RECV 0X01
 #define POST_SEND 0X02

 int main( )
 {
     LPPER_HANDLE_DATA lpPerHandleData;
     SOCKET hListenSocket;
     SOCKET hClientSocket;
     SOCKADDR_IN ClientAddr;
     int nAddrLen;
     HANDLE hThread;

     // Start WinSock and create a listen socket.

     listen(hListenSocket, 5);
     for (; ;)
     {
         nAddrLen = sizeof(SOCKADDR);
         hClientSocket = accept(hListenSocket, (LPSOCKADDR)&ClientAddr, &nAddrLen);

         lpPerHandleData = (LPPER_HANDLE_DATA)malloc(sizeof(PER_HANDLE_DATA));
         lpPerHandleData->hSocket = hClientSocket;
         // 注意这里将连接的客户端的IP地址，保存到了lpPerHandleData字段中了
         strcpy(lpPerHandleData->szClientIP, inet_ntoa(ClientAddr.sin_addr));

         // 为本次客户请求产生子线程
         hThread = CreateThread(
             NULL,
             0,
             OverlappedThread,
             lpPerHandleData, // 将lpPerHandleData传给子线程
             0,
             NULL
             );
         CloseHandle(hThread);
     }
     return 0;
 }

 DWORD WINAPI OverlappedThread(LPVOID lpParam)
 {
     LPPER_HANDLE_DATA lpPerHandleData = (LPPER_HANDLE_DATA)lpParam;
     WSAOVERLAPPED Overlapped;
     WSABUF wsaBuf;
     WSAEVENT EventArray[WSA_MAXIMUM_WAIT_EVENTS];//事件对象数组

     DWORD dwEventTotal = 0, // 程序中事件的总数
     char Buffer[DATA_BUFSIZE];
     BOOL bResult;
     int nResult;

     EventArray[dwEventTotal] = WSACreateEvent();

     ZeroMemory(&Overlapped, sizeof(WSAOVERLAPPED));

     Overlapped.hEvent = EventArray[dwEventTotal]; // 关联事件

     ZeroMemory(Buffer, DATA_BUFSIZE);
     wsaBuf.buf = Buffer;
     wsaBuf.len = sizeof(Buffer);

     lpPerHandleData->nOperateType = POST_RECV; // 记录本次操作是Recv(..)

     dwEventTotal ++; // 总数加一
     dwFlags = 0;

     nResult = WSARecv(
         lpPerHandleData->hSocket, // Receive socket
         &wsaBuf, // 指向WSABUF结构的指针
         1, // WSABUF数组的个数
         &dwNumOfBytesRecved, // 存放当WSARecv完成后所接收到的字节数,实际接收到的字节数
         &dwFlags, // A pointer to flags
         &Overlapped, // A pointer to a WSAOVERLAPPED structure
         NULL // A pointer to the completion routine,this is NULL
         );

     if ( nResult == SOCKET_ERROR && GetLastError() != WSA_IO_PENDING)
     {
         printf("WSARecv(..) failed.\n");
         free(lpPerHandleData);

         closesocket(lpPerHandleData->hSocket;
          WSACloseEvent(EventArray[dwEventTotal]);
         return -1;
     }

     while (TRUE)
     {
         DWORD dwIndex;

         dwIndex = WSAWaitForMultipleEvents(dwEventTotal, EventArray ,
             FALSE ,WSA_INFINITE,FALSE);

        WSAResetEvent(EventArray[dwIndex– WSA_WAIT_EVENT_0]);


         bResult = WSAGetOverlappedResult(
             lpPerHandleData->hSocket,
             &Overlapped,
             &dwBytesTransferred, // 当一个同步I/O完成后,接收到的字节数
             TRUE, // 等待I/O操作的完成
             &dwFlags
             );
         if (bResult == FALSE && WSAGetLastError() != WSA_IO_INCOMPLETE)
         {
             printf("WSAGetOverlappdResult(..) failed.\n");
             free(lpPerHandleData);
             return 0; // 错误退出
         }

         if (dwBytesTransferred == 0)
         {
             printf("客户端已退出,将断开与之的连接!\n");
             closesocket(lpPerHandleData->hSocket);
             free(lpPerHandleData);
             break;
         }

         // 在这里将接收到的数据进行处理
         printf("Received from IP: %s.\ndata: %s\n", lpPerHandleData->szClientIP, wsaBuf.buf);

         // 发送另外一个请求操作
         ZeroMemory(&Overlapped, sizeof(WSAOVERLAPPED));
         lpPerHandleData->nOperateType = POST_RECV;

         dwFlags = 0;
         nResult = WSARecv();
         if (){}

     }

     return 1;
 }

最后的一个改进版本，看上去是个不错的版本，相对来说算是比较实用的。但是使用了过多的全局变量，代码是C风格的，不可取。

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

 #define PORT 5150
 #define MSGSIZE 1024

 #pragma comment(lib, "ws2_32.lib")

 typedef struct
 {
 WSAOVERLAPPED overlap;
 WSABUF Buffer;
 char szMessage[MSGSIZE];
 DWORD NumberOfBytesRecvd;
 DWORD Flags;
 }PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA;

 int g_iTotalConn = 0;
 SOCKET g_CliSocketArr[MAXIMUM_WAIT_OBJECTS];
 WSAEVENT g_CliEventArr[MAXIMUM_WAIT_OBJECTS];
 LPPER_IO_OPERATION_DATA g_pPerIODataArr[MAXIMUM_WAIT_OBJECTS];

 DWORD WINAPI WorkerThread(LPVOID);

 void Cleanup(int);

 int main()
 {
 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_addr.S_un.S_addr = htonl(INADDR_ANY);
 local.sin_family = AF_INET;
 local.sin_port = htons(PORT);
 bind(sListen, (struct sockaddr *)&local, sizeof(SOCKADDR_IN));
 // Listen
 listen(sListen, 3);


//网上的代码如此，好奇怪，为什么是在连接还没开始的时候就创建一个线程，而不是像上面的程序一样，accept一个
//connection创建一个线程，并将从connection 的socket中获取的信息当作形参传递给workThread?
//这里是只创建一个线程为重叠socket I/O操作服务
 // Create worker thread
 CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId);
 while (TRUE)
 {
     // Accept a connection
     sClient = accept(sListen, (struct sockaddr *)&client, &iaddrSize);

         //这很好，在accept函数中的后两个形参中获取client的相关信息，并直接在server端的控制台中显示出来
     printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
     g_CliSocketArr[g_iTotalConn] = sClient;//添加到socket数组中

     // Allocate a PER_IO_OPERATION_DATA structure
     g_pPerIODataArr[g_iTotalConn] = ER(LPPER_IO_OPATION_DATA)HeapAlloc(
              GetProcessHeap(),HEAP_ZERO_MEMORY,sizeof(PER_IO_OPERATION_DATA));
     g_pPerIODataArr[g_iTotalConn]->Buffer.len = MSGSIZE;
     g_pPerIODataArr[g_iTotalConn]->Buffer.buf = g_pPerIODataArr[g_iTotalConn]->eszMssage;
     g_CliEventArr[g_iTotalConn] = g_pPerIODataArr[g_iTotalConn]->overlap.hEvent = WSACreateEvent();
     // Launch an asynchronous operation
     WSARecv(
       g_CliSocketArr[g_iTotalConn],
       &g_pPerIODataArr[g_iTotalConn]->Buffer,
       1,
       &g_pPerIODataArr[g_iTotalConn]->NumberOfBytesRecvd,
       &g_pPerIODataArr[g_iTotalConn]->Flags,
       &g_pPerIODataArr[g_iTotalConn]->overlap,
       NULL);

     g_iTotalConn++;
 }

 closesocket(sListen);
 WSACleanup();
 return 0;
 }
 DWORD WINAPI WorkerThread(LPVOID lpParam)
 {
 int ret, index;
 DWORD cbTransferred;
 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;
     WSAResetEvent(g_CliEventArr[index]);
     WSAGetOverlappedResult(
       g_CliSocketArr[index],
       &g_pPerIODataArr[index]->overlap,
       &cbTransferred,
       TRUE,
       &g_pPerIODataArr[g_iTotalConn]->Flags);
     if (cbTransferred == 0)
     {
       // The connection was closed by client
       Cleanup(index);
     }
     else
     {
       // g_pPerIODataArr[index]->szMessage contains the received data
       g_pPerIODataArr[index]->szMessage[cbTransferred] = '\0';
       send(g_CliSocketArr[index], g_pPerIODataArr[index]->szMessage,\
         cbTransferred, 0);
       // Launch another asynchronous operation
       WSARecv(
         g_CliSocketArr[index],
         &g_pPerIODataArr[index]->Buffer,
         1,
         &g_pPerIODataArr[index]->NumberOfBytesRecvd,
         &g_pPerIODataArr[index]->Flags,
         &g_pPerIODataArr[index]->overlap,
         NULL);
     }
 }
 return 0;
 }
 void Cleanup(int index)
 {
 closesocket(g_CliSocketArr[index]);
 WSACloseEvent(g_CliEventArr[index]);
 HeapFree(GetProcessHeap(), 0, g_pPerIODataArr[index]);
 if (index < g_iTotalConn - 1)
 {
     g_CliSocketArr[index] = g_CliSocketArr[g_iTotalConn - 1];
     g_CliEventArr[index] = g_CliEventArr[g_iTotalConn - 1];
     g_pPerIODataArr[index] = g_pPerIODataArr[g_iTotalConn - 1];
 }
 g_pPerIODataArr[--g_iTotalConn] = NULL;
 }

    这个模型与上述其他模型不同的是它使用Winsock2提供的异步I/O函数WSARecv。在调用WSARecv时，指定一个WSAOVERLAPPED结构，这个调用不是阻塞的，也就是说，它会立刻返回。一旦有数据到达的时候，被指定的WSAOVERLAPPED结构中的hEvent被Signaled。由于下面这个语句g_CliEventArr[g_iTotalConn] = g_pPerIODataArr[g_iTotalConn]->overlap.hEvent；

    使得与该套接字相关联的WSAEVENT对象也被Signaled，所以WSAWaitForMultipleEvents的调用操作成功返回。我们现在应该做的就是与调用WSARecv相同的WSAOVERLAPPED结构为参数调用WSAGetOverlappedResult，从而得到本次I/O传送的字节数等相关信息。在取得接收的数据后，把数据原封不动的发送到客户端，然后重新激活一个WSARecv异步操作。