BUG: ATL EXE Server Based on CComAutoThreadModule May Hang on Registration

• The Microsoft Active Template Library (ATL) 3.0, included with:
  • Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

An ATL EXE server based on CComAutoThreadModule<> can hang when being registered or unregistered.

CAUSE

CComAutoThreadModule<>::Init() called in WinMain() creates a thread pool (by default 4 threads). The destructor of global CComAutoThreadModule makes certain these threads terminate before the process terminates. This happens by posting a WM_QUIT message to each of the threads in the thread pool and calling WaitForSingleObject() on the thread handle. The threads are scheduled such that the threads in the pool may not have called GetMessage() and so the message queue is not created. This causes the PostThreadMessage() to fail. Hence, the threads in the pool do not terminate and WaitForSingleObject() waits infinitely for the threads to terminate.

RESOLUTION

In the Altcom.h file, inside the vc98\atl\include directory of destructor in the CComAutoThreadModule function replace the following code:

   ::PostThreadMessage(m_pApartments[i].m_dwThreadID, WM_QUIT, 0, 0); 

   while (::PostThreadMessage(m_pApartments[i].m_dwThreadID, WM_QUIT,
      0, 0) == 0) ::Sleep(100); 

STATUS

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

MORE INFORMATION

1. Use Appwizard to create an ATL EXE.



2. Insert any type of ATL object in the project.



3. In Stdafx.h, replace CComModule with CComAutoThreadModule<CComSimpleThreadAllocator>.



4. Build the project.
   
   NOTE: There is a chance that the server may hang at this point since the custom build step registers the server.



5. In the Project Settings menu under the Debug tab type "/RegServer" in the Program Arguments dialog box.



6. Run the server in the debugger.
   
   NOTE: If it does not hang the first time, repeat this step. Since this is timing related, the problem may not reproduce on certain machines.

Additional query words: kbDSupport

Keywords          : kbATL kbCOMt kbThread kbVC600 kbVC600bug kbATL300 kbATL300bug 
Version           : WINDOWS:3.0
Platform          : WINDOWS 
Issue type        : kbbug 

Last Reviewed: April 22, 1999