Re: proper way to close a socket?

Hector Santos <>
Thu, 18 Mar 2010 10:12:55 -0400
Bill wrote:


I tried to study and understand your code. Am I right that you are basically
polling the socket until it either connects or the connection attempt times

It is basically waiting on signals. You don't have to do this. You
can simply override the Close() method and replace it with this:

void CMyClientSocket::Close()
    if (m_hSocket != INVALID_SOCKET)
    VERIFY(SOCKET_ERROR != closesocket(m_hSocket));
    //CAsyncSocket::KillSocket(m_hSocket, this);
    m_hSocket = INVALID_SOCKET;

Notice the commenting out the CAsyncSocket::KillSocket(). That allows
you to invalidate the handle and continue to get a callback.

Now you can CLICK abort and call:


Is there an advantage to this over waiting for the OnConnect call to come
with either no error meaning conencted or an error meaning timeout?

It allows you to monitor it. You can have a progress bar, you can have
a countdown, etc, you can shorten the timeout to 5, 10 seconds, etc!

But when using a Close() override, you can set a timer instead.

Will the OnConnect call always always always come in?

Based on what I see, yes, IFF the handlers are still active for the
m_hSocket and CWnd thread

It seems a shame that there is no way to abort a connection attempt until it
gives up and gives the timeout.

You can do the above.

 > I'm wondering where does the timeout call come from?

Its default for the socket stack. I don't see off hand how to change
it other than emulate the behavior (countdown) and/or use ::select()
to detect it yourself.

There is nothing kludgy about this, this is par for the course if you
want this type of monitoring behavior.

If I'm trying to connect to an IP address that doesn't exist,
then I'm guessing that it's the socket code in Windows of my own PC that is
giving me the timeout. If that's the case, I'm surprised that it can't
coordinate that with a deleted object or one where Close was already called.

Not with delete, but with Close() override.


I suppose I could do one more thing. If the user presses the button to close
the connection before it's connected, I can leave that socket undeleted to
wait for the OnConnect and then delete itself inside the OnConnect call. If
the user presses the button again to make a new connection, I can create a
new socket to handle that request, even if the abandoned one is still not
shut down.

Personally, you should *never* delete *any* object until everything is
settled. You can also override the destructor and clean things up
yourself first.




"Hector Santos" <> wrote in message

When I added the yield, I threw out the nCountDown timeout calculation.
Change it to this:

BOOL CMyClientSocket::WaitConnect(int nTimeout)
   int nSleep = 100;
   DWORD tFinal = GetTickCount()+nTimeout*1000;
   for (;;) {
      if (GetTickCount() > tFinal) {
         return FALSE;


Hector Santos wrote:

Ok, Bill,

What you need to do is do wait on the Connect() like so:

    if(!m_pClientSocket->Connect(m_toURL, m_toPort)) {
      int err = GetLastError();
      if (err == WSAEWOULDBLOCK) {
         if (!m_pClientSocket->WaitConnect(5)) {
            // WaitConnect Error, Show Error
            err = GetLastError();
      } else {
         // Connect Error, Show Error
         err = GetLastError();

The WaitConnect() and AsyncYield() functions are a member of your socket

BOOL CMyClientSocket::WaitConnect(int nTimeout)
   int nSleep = 100;
   int nCountDown = nTimeout*1000 / nSleep;
   DWORD t1 = GetTickCount();
   for (;;) {
      if (nCountDown <= 0) {
         return FALSE;
      fd_set efds; fd_set wfds;
      FD_ZERO(&efds); FD_ZERO(&wfds);
      FD_SET(m_hSocket, &efds);
      FD_SET(m_hSocket, &wfds);
      struct timeval tv;
      tv.tv_sec = 0;
      tv.tv_usec = nSleep*1000;
      int rc = select(0, NULL, &wfds, &efds, &tv);
      switch (rc) {
      case 0:
         // WE TIMED OUT!!
            /* show timeout in some CListBox
            CString s;
            s.Format("- wait %d | %d",nCountDown, GetTickCount()-t1);
            if (AsyncYield(100)) {
               return FALSE;
      case SOCKET_ERROR:
         if (GetLastError() != WSAEWOULDBLOCK) return FALSE;
         if (FD_ISSET(m_hSocket,&wfds)) {
            // WE CONNECTED!!
            return TRUE;
         if (FD_ISSET(m_hSocket,&efds)) {
            // WE FAILED
            return FALSE;
   return FALSE;

BOOL CMyClientSocket::AsyncYield(DWORD nDelay)
    DWORD nDone = (GetTickCount() + nDelay);
    while (nDone > GetTickCount()){
        MSG msg;
        while (::PeekMessage(&msg,NULL,0,0,PM_REMOVE)){
      if (m_cancel) {
         m_cancel = FALSE;
         return TRUE;
    return FALSE;

My previous message had more details about using the select() socket
function. The wait block will use select() which allows you to detect
read, write and error events. In this case, you need two events:

   write event - signals the connection is ready
   error event - something went wrong

That will do the trick for you.


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