KB193101 - FIX: An unhandled exception occurs when you use MFC sockets in secondary threads in an MFC Visual C++ 6.0 application

Article ID: 193101

Article Last Modified on 6/1/2005

Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition

This article was previously published under Q193101

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
   }

This function should be called once in each secondary thread before the first socket is created in the new thread.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section.

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, click the following article numberw to view the articlew in the Microsoft Knowledge Base:

194022 Visual Studio 6.0 service packs, what, where, why

194295 How to tell that a Visual Studio service pack is 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 the behavior

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:
175668 MultiSoc: Illustrates using sockets in multiple threads
Run the application and create a socket in a secondary thread.

REFERENCES

For more information, click the following article number to view the article in the Microsoft Knowledge Base:

175668 MultiSoc: Illustrates using sockets in multiple threads

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

Keywords: kbtshoot kbbug kbfix kbnoupdate kbwinsock kbvs600sp3fix KB193101