FIX: Assertion Failed, Line 505 of Sockcore.cpp

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, version 1.52
      - Microsoft Visual C++, 32-bit Edition, version 2.1, 2.2
  

SYMPTOMS

An MFC application that uses the socket classes fails with a message similar to the following:

In MFC 3.1 or 3.2, the assertion appears as:

   Assertion Failed: <app name>: File sockcore.cpp, Line 505

   Assertion Failed: <app name>: File sockcore.cpp, Line 484

CAUSE

When all sockets are closed, the socket handle maps are emptied and the socket notification window is destroyed.

MFC maintains an auxiliary queue of socket notification messages. If any messages remain in this queue when the last socket is closed, then this assertion failure will occur when any new sockets are opened and an attempt is made to process these left-over notifications.

RESOLUTION

Purge the auxiliary queue of all messages when the last socket is closed. In this context, last does not mean previous; it means the socket that was closed, leaving no sockets open for that thread.

This problem can be remedied by overriding the CAsyncSocket::Close member function in your CAsyncSocket-derived or CSocket-derived class. The following implementation of this override will take care of the problem:

void CMySocket::Close()

  // If Deriving from CSocket, then use:
  CSocket::Close();
  // Otherwise, use:
  // CAsyncSocket::Close();
  AFX_THREAD_STATE* pThreadState = AfxGetThreadState();
  if (pThreadState->m_mapSocketHandle.IsEmpty())
  {   // **** LAST SOCKET ****
    while (!pThreadState->m_listSocketNotifications.IsEmpty())
      delete pThreadState->m_listSocketNotifications.RemoveHead();
    pThreadState->m_listSocketNotifications.RemoveAll();
  }

To handle the case where a socket object is deleted before Close is called, also override the virtual destructor to make sure the correct version of Close is called:

CMySocket::~CMySocket() {

  if (m_hSocket != INVALID_SOCKET)
    Close();

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in the version of MFC that ships with Microsoft Visual C++, 32-bit Edition, version 4.0.