一個非同步Socket通訊的例子(Windows)

在Windows下面，使一個socket改成非同步有兩種方法。

 

(1)調用WSAAsyncSelect方法

(2)調用WSAEventSelect方法

 

 

對Socket進行輪尋可以使用Select函數，或者自己通過WSAWaitForMultipleEvents進行輪訓，但WSAWaitForMultipleEvents有一個限制令人很苦惱，即WSAWaitForMultipleEventsWSAWaitForMultipleEvents在每個線程中最多隻能監聽64個Socket，如果需要監聽更多的Socket，則需要啟動多個線程；Select函數雖然也有Socket個數限制，但卻是能最多監聽1024個Socket，比WSAWaitForMultipleEvents多多了。WSAAsyncSelect方法需要有接受響應訊息的視窗控制代碼；下面這個例子採用了WSAEventSelect和WSAWaitForMultipleEvents的方法下載網頁的Socket編程，它採用非同步Socket的方式從百度和Google下載首頁。

 

 

#example.cpp

 

#include "stdafx.h"
#include <errno.h>
#include <string.h>
#include <assert.h>
#include <winsock2.h>
#include <windows.h>
#include <winbase.h>
#include <io.h>

 

int _tmain(int argc, _TCHAR* argv[]){

 

      WSADATA     wsaData;        
      WSAStartup(0x0202, &wsaData);
     
      int  sock[2] ;

      int pos;
      unsigned int port=80;
      int res =0;
      char *str_robots= "GET /index.html HTTP/1.0/r/nHost: www.baidu.com /r/nUser-Agent: Test (Test@263.com)/r/n/r/n ";

     

      struct sockaddr_in server[2]; 
      char buf[10240]; 

      sock[0] = socket(AF_INET, SOCK_STREAM, 0); 
      sock[1] = socket(AF_INET, SOCK_STREAM, 0);

      server[0].sin_family = AF_INET; 
      server[0].sin_port = htons(port);
      server[0].sin_addr.S_un.S_addr = inet_addr( "119.75.213.61" ); //www.baidu.com

      server[1].sin_family = AF_INET; 
      server[1].sin_port = htons(port);
      server[1].sin_addr.S_un.S_addr = inet_addr( "64.233.189.104" ); //www.google.com

 

      WSAEVENT hEvent[2];
      hEvent[0]  = WSACreateEvent();
      hEvent[1]  = WSACreateEvent();
      WSANETWORKEVENTS events;
      WSAEventSelect(sock[0], hEvent[0], FD_READ|FD_WRITE|FD_CONNECT);
      WSAEventSelect(sock[1], hEvent[1], FD_READ|FD_WRITE|FD_CONNECT);

 

      connect(sock[0], (struct sockaddr*)&server[0], sizeof(server));

      connect(sock[1], (struct sockaddr*)&server[1], sizeof(server));

 

      int total = 2;

      

       while(total)
      {  

           res = WSAWaitForMultipleEvents(2, hEvent, FALSE, 10,FALSE); //WSA_INFINITE
           for(int i=0;i<2;i++){
               int result = WSAEnumNetworkEvents(sock[i],hEvent[i],&events);
               if( result == SOCKET_ERROR){
                    printf("Error /n");
                   break;
               }else if(result == WSA_WAIT_TIMEOUT){
                   continue;
              }else{
                  if(events.lNetworkEvents & FD_READ){
                       pos = 0;
                       count =0;
                       do{
                            count = recv(sock[i], buf+pos, 512, 0);
                            pos += count;
                       }while(count>0);
                       buf[pos] = '/0';
                       printf("buf = %s/n",buf);
                       total--;
                  }else if(events.lNetworkEvents & FD_WRITE){
                    send(sock[i],str_robots,strlen(str_robots),0);    
                  }//end if

              }//end if

          }//end for
     }//end while
 

 

return(0);

}

 

對於非同步Socket，如果在Windows下面使用MFC的話，事情就變得容易多了，可以使用CAsyncSocket類，這個類封裝了非同步Socket請求的各種方法。

 

在Linux/Unix系統下編程，可以使用fnctl函數將一個Socket變成非同步，並且通過Select和Poll, epoll進行輪尋。