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Q202197: BUG: Freeing Resource DLLs in ExitInstance Causes Error

Article: Q202197
Product(s): Microsoft C Compiler
Version(s): 5.0,6.0
Operating System(s): 
Keyword(s): kbole kbDLL kbMFC kbVC kbVC500bug kbVC600bug kbOSWin95bug kbGrpDSMFCATL
Last Modified: 07-FEB-2002

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
   - Microsoft Visual C++.NET (2002) 
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SYMPTOMS
========

In Windows 95, calling FreeLibrary() on the resource DLLs in the ExitInstance()
function of the COleControl-derived class causes an application error.

CAUSE
=====

This is a bug in Windows 95. When FreeLibrary() is called on resource DLLs,
Windows 95 is running through the chain of DLLs in that process and looking for
other DLLs that have a zero reference count. This causes other DLLs to be
unloaded too soon.

RESOLUTION
==========

Move the FreeLibrary() calls to the destructor function of the
COleControl-derived class.

STATUS
======

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

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Use Control Wizard to generate an ActiveX control project.

2. Create a non-MFC resource-ONLY DLL. Make sure you specify the /NOENTRY switch
  in the Project, Settings dialog box.

3. Call LoadLibrary in InitInstance() of the control's CWinApp-derived class.

4. Call FreeLIbrary in ExitInstance() of the control's CWinApp-derived class.

5. Build the resource-ONLY DLL and the ActiveX control projects. Make sure the
  .dll file is being placed in the same directory as the .ocx file.

6. At the MS-DOS prompt, change to the directory where both the .ocx and .dll
  files are found. Type "REGSVR32 mycontrol.OCX".

RESULTS: You will get an application error dialog box and the "control is
registered successfully" dialog box.

REFERENCES
==========

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Yeong-Kah
Tam, Microsoft Corporation.


Additional query words: ocx ExitInstance FreeLibrary LoadLibraryEx LoadLibrary

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Keywords          : kbole kbDLL kbMFC kbVC kbVC500bug kbVC600bug kbOSWin95bug kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : :5.0,6.0
Issue type        : kbbug

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