New MFC 4.2 deadlock problem

michael berganovsky -- michael_berganovsky@ibi.com
Wednesday, August 21, 1996

     Environment: MSVC 4.2, NT 3.51 SP4

     We are building single threaded OLE intensive MFC application using
     MFC 4.2 DLL. We are running  into very serious problem which we
     believe is attributable to MFC 4.2 implementation.

     APPLICATION USING MFC 4.2 and OLE2 HANGS!!!

     To make things simple - whenever our application makes call to a
     functions from OLE32.DLL, OLEAUT32.DLL or OLEPRO32.DLL for the first
     time it ends up in GetProcAddress for the specified function. (see
     oledata.cpp and oleimpl.h in MFC sources). At least in WinNT (and
     according to Matt Pietrek in Win95) GetProcAddress acquires process'
     critical section. In MFC 4.2 Microsoft added new code in DLLMain
     implementation which may conflict with GetProcAddress (or any other
     synchronized on process' critical section calls). In shared build of
     MFC this code is linked into MFC42.DLL and in debug build into
     MFC42D.DLL and MFCO42D.DLL (see dllmodul.cpp and dllole.cpp in MFC
     sources).

     In our case DllMain from MFCO42D.DLL or MFC42.DLL got called with
     DLL_THREAD_DETACH when some service thread (created by KERNEL32) other
     then our main thread exits. It is guarded by process critical section.
     But our main thread is running and calls some function from
     OLEAUT32.DLL for example VariantClear, which ends up in
     GetProcAddress( hInstance, "VariantClear" ), which in turn blocks on
     acquiring process critical section.

     Now main thread is waiting for DllMain to return to release critical
     section. But inside of DllMain AfxOleTermOrFreeLib calls
     CoFreeUnusedLibraries which tries to SendMessage to the window created
     in main thread which is blocked on process critical section. That does
     it. We hang!

     It looks like ANY application using shared MFC 4.2 or ActiveX
     components linked with MFC 4.2 is in danger!

     --Good luck

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Mike Blaszczak -- mikeblas@nwlink.com
Sunday, August 25, 1996

At 12:35 PM 8/21/96 edt, you wrote:

>     Now main thread is waiting for DllMain to return to release critical
>     section. But inside of DllMain AfxOleTermOrFreeLib calls
>     CoFreeUnusedLibraries which tries to SendMessage to the window created
>     in main thread which is blocked on process critical section. That does
>     it. We hang!

>     It looks like ANY application using shared MFC 4.2 or ActiveX
>     components linked with MFC 4.2 is in danger!

This problem has been fixed for the MFC 4.2a patch.

.B ekiM
http://www.nwlink.com/~mikeblas   <--- trip report central
1995 Honda VFR750F (Serial number 00050!)  4 Corners 1996!
1987 Yamaha FZ700 (damaged)                AMA, HRC, VFROC
     These words are my own: I do not speak for Microsoft.

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