Question

Win32 Winsock non-blocking socket for connect()

Asked by: DaveHope

Hi,

I've done enough googling on this and am about to go bald so figured i'd give in and ask here.

I'd like to make this non-blocking, to speed up the process, allowing me to specify a timeout. If that's not possible i'd like to thread it as a last resort to allow multiple connection attempts.

My code is as follows:
-------------------------
    /*
     * Make sure we're dealing with a valid socket.
     */
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET)
    {
        WSACleanup();                                                      // Cleanup Winsock.
        perror("Socket");
        exit(-1);
    }

    SOCKADDR_IN addr;                                                      // Socket address information.
    addr.sin_family = AF_INET;                                          // Address family internet.
    addr.sin_addr = *((LPIN_ADDR)*rh->h_addr_list);            // IP to connect to.
    addr.sin_port = htons(port);                                    // Port to connect on.

      /*
       * Try and connect to the port.
      */
      if ((connect(sock,(struct sockaddr *) &addr, sizeof(addr))) == 0)
      {
        return 0;
      }
      else
      {
        return 1;
      }

      /*
       * Close socket.
       */
    close(sock);
-------------------------

If someone could point out what I need to use to make this non-blocking that'd be great. I'd rather not use Winsock2 stuff like WSAEVENT.

Cheers,

Dave

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Asked On
2008-06-05 at 01:57:09ID23459442
Tags

C++

,

Win32

Topics

Winsock

,

C++ Programming Language

Participating Experts
1
Points
500
Comments
7

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Answers

 

by: jkrPosted on 2008-06-05 at 07:23:55ID: 21719776

You'll need the Winsock-specific APIs for non-blocking sockets and WSA_FLAG_OVERLAPPED in particular - see http://support.microsoft.com/kb/181611 ("Socket overlapped I/O versus blocking/nonblocking mode") and http://www.codeproject.com/KB/IP/SimpleIOCPApp.aspx ("A simple application using I/O Completion Ports and WinSock"):

//Overlapped I/O follows the model established
 
//in Windows and can be performed only on 
 
//sockets created through the WSASocket function 
 
ListenSocket = WSASocket(AF_INET, SOCK_STREAM, 0, 
                       NULL, 0, WSA_FLAG_OVERLAPPED);
if (INVALID_SOCKET == ListenSocket) 
{
     printf("\nError occurred while opening socket: %ld.", 
                                       WSAGetLastError());
     goto error;
}
else
{
     printf("\nWSASocket() successful.");
}

                                              
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by: DaveHopePosted on 2008-06-05 at 23:11:26ID: 21726596

Thanks jkr,

How'd that integrate into my code? - Also, WillI still be able to return a success / failure for the connect?

Cheers,

Dave

 

by: jkrPosted on 2008-06-06 at 14:16:22ID: 21732758

Well, replace the 'socket()' calls with thir respective 'WSASocket()' counterparts and follow the instructions in the article ;o)

>>WillI still be able to return a success / failure for the connect?

'connect()' itself can hardly be non-blocking, only the data transfer can.

 

by: DaveHopePosted on 2008-06-11 at 01:37:31ID: 21757885

In which case, perhaps i'm missing something.

When connect() is called, there's a huge delay whilst the application / tcp stack tries to connect to given port. If that port is closed, or the target system is down there's a huge delay whilst it sits there trying to connect.

How can I prevent that delay? - If it doesn't connect instantly, timeout after a short period of time.

 

by: jkrPosted on 2008-06-11 at 14:49:19ID: 21764413

Why don't you 'connect()' in a separate thread?

 

by: DaveHopePosted on 2008-06-12 at 00:50:08ID: 21766976

Hi Jkr,

Perhaps that's the best/only option then. Could you provide an example?

 

by: jkrPosted on 2008-06-12 at 13:31:16ID: 21773431

Well, like

#define WM_MYCONNECT WM_USER + 1
 
struct ConnectData {
  socket* ps;
  HWND hNotify;
};
 
 
DWORD WINAPI ConnectThread(LPVOID pv) {
 
  ConnectData* pcd = (ConnectData*) pv;
 
  connect(*pcd->ps,...);
 
  SendMessage(pcd->hNotify,WM_MYCONNECT, 0, 0);
 
  return 0;
}
 
//...
ConnectData cd;
 
socket s;
 
cd.ps = &s;
cd.hNotify = hWnd; // window to send notification message to
 
DWORD dwTID;
 
CreateThread(NULL,0,ConnectThread,(LPVOID)&s,0,&dwTID);

                                              
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