Knowledge Base

PRB: Do not Call ODBC Within DLL_PROCESS_DETACH Case

Article ID: 177135

Article Last Modified on 12/8/2003

Microsoft Visual C++ 5.0 Enterprise Edition
Microsoft Visual C++ 6.0 Enterprise Edition
Microsoft Visual C++ 5.0 Professional Edition
Microsoft Visual C++ 6.0 Professional Edition
Microsoft Visual C++ 6.0 Standard Edition
Microsoft Data Access Components 2.5
Microsoft Data Access Components 2.6

This article was previously published under Q177135

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

Keywords: kbdatabase kbprb KB177135