Re: CAsyncSocket Assertion When Terminating

=?Utf-8?B?Sm9l?= <>
Wed, 25 Apr 2007 12:54:03 -0700

Is this the code that's giving the assert:

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

Mike - Hi. Yes, that is it.

If so, then one helpful way to diagnose winsock errors is to call
WSAGetLastError(). I recognize that the above code is part of MFC and can't
be changed, but you could insert the call to WSAGetLastError() directly
after your call to Close(), and then after the assert fires, you could
continue with single-step execution and then tell us what WSAGetLastError()
returns. (My guess it that WSAGetLastError() will return WSAENOTSOCK.)

I gave it a shot. After I got the assertion I selected Ignore, stepped to
the WSAGetLastError() and 0 was returned (I tried with Retry and got the same

Don't change the socket handle to INVALID_SOCKET. As you and others have
recognized, it's a terrible hack that masks the coding error without fixing

Yeah, it looks like the MainFrm is going to work out for me.

One thought about the source of the error. You mentioned that the call to
Close() is inside the OnDestroy() handler. Depending on where Close() is
called inside the handler, the window might have already been destroyed.
The reason that this might be important, is that CAsyncSocket works by
creating a hidden window. (The WndProc of this hidden window is the thing
that's responsible for calling all your OnReceive and other OnXxx
functions.) Maybe the hidden window has also already been destroyed too,
which somehow leads to the assert you are seeing.

The code is located just before the CFormView::OnDestroy() that's in
CMyappView::OnDestroy(). Yeah, it could be the hidden window is already
destroyed at this point - don't know. :-S


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