FIX: ExitInstance() Not Called in _USRDLL DLL

The information in this article applies to:

• The Microsoft Foundation Classes (MFC), included with

      - Microsoft Visual C++ 32-bit Edition, version 1.0
  

SYMPTOMS

CWinApp::ExitInstance() never gets called for the CWinApp object in a _USRDLL built with the Microsoft Foundation Classes (MFC) for Windows NT, version 2.1.

CAUSE

The DLLMain function for a _USRDLL is provided by MFC. This function can be found in the MFC source directory (MSVC\MFC\SRC by default) in the file WINMAIN.CPP. Unlike a Windows 3.1 DLL, which has both an initialization and a termination function, a Windows NT DLL calls one function, DLLMain(), for both purposes. The DLLMain() function supplied by MFC has no call to ExitInstance() when DLL_PROCESS_DETACH is received.

RESOLUTION

Provide your own DLLMain() function in your _USRDLL project by copying the current DLLMain() implementation into a new .CPP module and add the new .CPP file to your project. Modify the new DLLMain() to add the calls to ExitInstance() where necessary. The new module would look like this:

   //
   // FILE - DLLMAIN.CPP
   //

   #include <afxwin.h>

   extern "C" int APIENTRY
   DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
   {
        if (dwReason == DLL_PROCESS_ATTACH)
        {
             // Initialize DLL's instance(/module) not the app's
             if (!AfxWinInit(hInstance, NULL, "", 0))
             {
                  AfxWinTerm();
                  return 0;       // Init Failed
             }

             // initialize the single instance DLL
             if (!AfxGetApp()->InitInstance())
             {
              if(AfxGetApp()!=NULL)
                 AfxGetApp()->ExitInstance();
                AfxWinTerm();
                return 0;       // Init Failed
             }
        }
        else if (dwReason == DLL_PROCESS_DETACH)
        {
           if(AfxGetApp()!=NULL)
              AfxGetApp()->ExitInstance();

             // Terminate the library before destructors are called
             AfxWinTerm();
        }

        return 1;   // ok
   }

   //
   // EOF - DLLMAIN.CPP
   //

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. This problem was corrected in MFC version 3.0, included with Microsoft Visual C++ 32-bit Edition, version 2.0.