PRB: Do not Call ODBC Within DLL_PROCESS_DETACH Case

 Last reviewed: December 9, 1997
Article ID: Q177135
The information in this article applies to:
  • Microsoft Visual C++, 32-bit Editions, version 5.0

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
Keywords : MfcDatabase
Technology : odbc
Version : WINDOWS NT:5.0
Platform : NT WINDOWS
Issue type : kbprb

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Last reviewed: December 9, 1997
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