FIX: Unhandled Exception Using MFC Sockets in Visual C++ 6.0

• The Microsoft Foundation Classes (MFC), used with:
  • Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

When using MFC sockets in secondary threads in a statically linked MFC Visual C++ 6.0 application, an unhandled exception occurs.

CAUSE

The reason for the unhandled exception is that an object of type CMapPtrToPtr pointer, pointed to by m_pmapSocketHandle, is never created.

RESOLUTION

The handle maps used by the sockets need to be created for each thread. The following code shows a function to do this:

   void SocketThreadInit()
   {
   #ifndef _AFXDLL
   #define _AFX_SOCK_THREAD_STATE AFX_MODULE_THREAD_STATE
   #define _afxSockThreadState AfxGetModuleThreadState()

      _AFX_SOCK_THREAD_STATE* pState = _afxSockThreadState;
      if (pState->m_pmapSocketHandle == NULL)
         pState->m_pmapSocketHandle = new CMapPtrToPtr;
      if (pState->m_pmapDeadSockets == NULL)
         pState->m_pmapDeadSockets = new CMapPtrToPtr;
      if (pState->m_plistSocketNotifications == NULL)
         pState->m_plistSocketNotifications = new CPtrList;

   #endif
   } 

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This bug was corrected in Visual Studio 6.0 Service Pack 3. You will need to call AfxSocketInit() in each thread that uses sockets.

For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:

Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

MORE INFORMATION

In MFC socket applications, AfxSocketInit is called once, by default, in the primary thread. This function creates the handle maps for the primary thread when statically linked to MFC. However, when a secondary thread is created, these per-thread handle maps are not created. AfxSocketInit must be called in each thread to initialize the socket libraries.

Steps to Reproduce Behavior

1. Create an application that creates a socket in a secondary thread and uses MFC in a static link library. You can use the MultiSoc sample described in the following Knowledge Base article by changing the project settings to use MFC in a static library:

   Q175668 FILE: MultiSoc: Illustrates Using Sockets in Multiple Threads




2. Run the application and create a socket in a secondary thread.

REFERENCES

For additional information, please see the following article in the Microsoft Knowledge Base:

Q175668 FILE: MultiSoc: Illustrates Using Sockets in Multiple Threads

© Microsoft Corporation 1998, All Rights Reserved.
Contributions by Isaac L. Varon, Microsoft Corporation

Additional query words: LookupHandle CAsyncSocket AttachHandle GetValueAt assert wincore.cpp 980 Application Error 0xc0000005 m_pHashTable CSocket access violation debug assertion failed

Keywords : kbservicepack kbMFC kbVC600bug kbWinsock kbVS600sp2 kbVS600SP1 kbVS600sp3fix
Version : winnt:6.0
Platform : winnt
Issue type : kbbug