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Q177135: PRB: Do not Call ODBC Within DLL_PROCESS_DETACH Case

Article: Q177135
Product(s): Microsoft C Compiler
Version(s): 2.5,2.6,5.0,6.0
Operating System(s): 
Keyword(s): kbDatabase kbMFC kbODBC kbVC kbVC500 kbVC600 kbGrpDSVCDB kbGrpDSMDAC kbDSupport kbMDAC2
Last Modified: 24-AUG-2001

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The information in this article applies to:

- 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 Data Access Components versions 2.5, 2.6 
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SYMPTOMS
========

When using the MFC Database classes or calling ODBC functions within the
DLL_PROCESS_DETACH case of the DllMain() function, an access violation can occur
especially if the DLL links to the MFC DLL (which does a LoadLibrary call to
call ODBC). For example, calling CDatabase::Close() from the destructor of a
global static object in the DLL causes an access violation error in ODBC32.DLL.

CAUSE
=====

Because there are no guarantees of the order by which DLLs receive the
DLL_PROCESS_DETACH case, it is possible that the ODBC handle memory can be freed
before your DLL's DllMain() function gets called with DLL_PROCESS_DETACH.
Therefore, any calls to ODBC using those handles can cause a crash.

RESOLUTION
==========

Do not call ODBC functions or use the MFC ODBC classes in destructors of global
objects within DLLs or in the DllMain() DLL_PROCESS_DETACH case.

Instead use a termination function in the DLL which the application can call
before exiting.

STATUS
======

This behavior is by design.

Additional query words: crash hang hung halts GPF AV inproc kbmfc kbVC500 kbVC600

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Keywords          : kbDatabase kbMFC kbODBC kbVC kbVC500 kbVC600 kbGrpDSVCDB kbGrpDSMDAC kbDSupport kbMDAC250 kbMDAC260 
Technology        : kbVCsearch kbAudDeveloper kbMDACSearch kbMDAC250 kbMDAC260 kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : :2.5,2.6,5.0,6.0
Issue type        : kbprb

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