（二）Socket I/O模型之异步选择(WSAAsyncSelect)

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使用异步选择模型，应用程序可在一个套接字上，接收以Windows消息为基础的网络事件通知。具体的做法是在建好一个套接字后，调用WSAAsyncSelect函数。 

服务器端代码： 

// write by larry  // 2009-8-20  // This is a server using WSAAsyncSelect model.  #include "stdafx.h"  #include <winsock.h>  #include <tchar.h>  #define PORT  5150  #define MSGSIZE  1024  #define WM_SOCKET  WM_USER+0  #pragma comment(lib, "ws2_32.lib")  LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);  int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)  {      static TCHAR szAppName[] = _T("AsyncSelect Model");      HWND hwnd;      MSG msg;      WNDCLASS wndclass;      wndclass.style         = CS_HREDRAW | CS_VREDRAW;      wndclass.lpfnWndProc   = WndProc;      wndclass.cbClsExtra    = 0;      wndclass.cbWndExtra    = 0;      wndclass.hInstance     = hInstance;      wndclass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);      wndclass.hCursor       = LoadCursor(NULL, IDC_ARROW);      wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);      wndclass.lpszMenuName  = NULL;      wndclass.lpszClassName = szAppName;      if (!RegisterClass(&wndclass))      {          MessageBox(NULL, _T("This program requires Windows NT!"), szAppName, MB_ICONERROR);          return 0;      }      hwnd = CreateWindow(szAppName, // window class name          _T("AsyncSelect Model"),   // window caption          WS_OVERLAPPEDWINDOW,       // window stype          CW_USEDEFAULT,             // initial x postion          CW_USEDEFAULT,             // initial y postion          CW_USEDEFAULT,             // initial x size          CW_USEDEFAULT,             // initial y size          NULL,                      // parent window handle          NULL,                      // window menu handle          hInstance,                 // program instance handle          NULL);                     // creation parameters      ShowWindow(hwnd, nCmdShow);      UpdateWindow(hwnd);      while (GetMessage(&msg, NULL, 0, 0))      {          TranslateMessage(&msg);          DispatchMessage(&msg);      }      return msg.wParam;  }  LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)  {      WSADATA wsaData;      static SOCKET sListen;      SOCKET sClient;      SOCKADDR_IN local, client;      int ret, iAddrSize = sizeof(client);      char szMessage[MSGSIZE];      switch (message)      {      case WM_CREATE:          // 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);          // Associate listening socket with FD_ACCEPT event          WSAAsyncSelect(sListen, hwnd, WM_SOCKET, FD_ACCEPT);          return 0;      case WM_DESTROY:          closesocket(sListen);          WSACleanup();          PostQuitMessage(0);          return 0;      case WM_SOCKET:          if (WSAGETSELECTERROR(lParam))          {              closesocket(wParam);              break;          }          switch (WSAGETSELECTEVENT(lParam))          {          case FD_ACCEPT:              // Accept a connection from client              sClient = accept(wParam, (sockaddr*)&client, &iAddrSize);              // Associate client socket with FD_READ and FD_CLOSE event              WSAAsyncSelect(sClient, hwnd, WM_SOCKET, FD_READ | FD_CLOSE);              break;          case FD_READ:              ret = recv(wParam, szMessage, MSGSIZE, 0);              if (ret == 0 || (ret == SOCKET_ERROR && WSAGetLastError() == WSAECONNRESET))              {                  closesocket(wParam);              }              else              {                  szMessage[ret] = '\0';                  send(wParam, szMessage, strlen(szMessage), 0);              }              break;          case FD_CLOSE:              closesocket(wParam);              break;          }          return 0;      }      return DefWindowProc(hwnd, message, wParam, lParam);  }  

服务器端得主要流程： 
1.在WM_CREATE消息处理函数中，初始化Windows Socket library，创建监听套接字，绑定，监听，并且调用WSAAsyncSelect函数表示我们关心在监听套接字上发生的FD_ACCEPT事件； 
2.自定义一个消息WM_SOCKET，一旦在我们所关心的套接字（监听套接字和客户端套接字）上发生了某个事件，系统就会调用WndProc并且message参数被设置为WM_SOCKET； 
3.在WM_SOCKET的消息处理函数中，分别对FD_ACCEPT、FD_READ和FD_CLOSE事件进行处理； 
4.在窗口销毁消息(WM_DESTROY)的处理函数中，我们关闭监听套接字，清除Windows Socket library 

WSAAsyncSelect函数的网络事件类型可以有以下一种： 
FD_READ 应用程序想要接收有关是否可读的通知，以便读入数据 
FD_WRITE 应用程序想要接收有关是否可写的通知，以便写入数据 
FD_OOB 应用程序想接收是否有带外（OOB）数据抵达的通知 
FD_ACCEPT 应用程序想接收与进入连接有关的通知 
FD_CONNECT 应用程序想接收与一次连接或者多点join操作完成的通知 
FD_CLOSE 应用程序想接收与套接字关闭有关的通知 
FD_QOS 应用程序想接收套接字“服务质量”（QoS）发生更改的通知 
FD_GROUP_QOS  应用程序想接收套接字组“服务质量”发生更改的通知（现在没什么用处，为未来套接字组的使用保留） 
FD_ROUTING_INTERFACE_CHANGE 应用程序想接收在指定的方向上，与路由接口发生变化的通知 
FD_ADDRESS_LIST_CHANGE  应用程序想接收针对套接字的协议家族，本地地址列表发生变化的通知