FIX: ATL EXE Server Based on CComAutoThreadModule May Hang on Registration (202128)

The information in this article applies to:

The Microsoft Active Template Library (ATL) 3.0, when used with:
- Microsoft Visual C++, 32-bit Enterprise Edition 6.0
- Microsoft Visual C++, 32-bit Professional Edition 6.0
- Microsoft Visual C++, 32-bit Learning Edition 6.0

This article was previously published under Q202128

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);

with this code:

   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.

This problem was corrected in Microsoft Visual C++ .NET.

MORE INFORMATION

Use Appwizard to create an ATL EXE.
Insert any type of ATL object in the project.
In Stdafx.h, replace CComModule with CComAutoThreadModule<CComSimpleThreadAllocator>.
Build the project.

NOTE: There is a chance that the server may hang at this point since the custom build step registers the server.
In the Project Settings menu under the Debug tab type "/RegServer" in the Program Arguments dialog box.
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.

Modification Type:	Major	Last Reviewed:	12/11/2003
Keywords:	kbBug kbfix kbLocalSvr kbThread KB202128