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Q258235: BUG: Memory Leak with ATL Containment

Article: Q258235
Product(s): Microsoft C Compiler
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): kbActiveX kbATL kbCOMt kbContainer kbCtrl kbATL300bug kbGrpDSMFCATL
Last Modified: 26-JUN-2001

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The information in this article applies to:

- The Microsoft Active Template Library (ATL) 3.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

A memory leak occurs when hosting an ActiveX control in an Active Template
Library (ATL) control container. This memory leak also occurs at design time.

CAUSE
=====

When the control is activated, the container provides its in-place accelerator
table. The container creates the accelerator table by making a call to the
CreateAcceleratorTable function. The memory thus allocated is never released by
ATL.

RESOLUTION
==========

To work around this problem, perform the following steps:

1. Make a copy of the Atlhost.h file, and name it Fixatlhost.h.

2. In the Fixatlhost.h file, add a data member of type HACCEL to the
  CAxHostWindow class.

3. Modify the IOleInPlaceSite::GetWindowContext method by storing the HACCEL
  that is returned by the call to CreateAcceleratorTable in the new data
  member.

4. To release the memory, call DestroyAcceleratorTable on the cached HACCEL in
  the IOleInPlaceSite::OnInPlaceDeactivate method.

5. Save these changes to Fixatlhost.h.

6. In the Stdafx.h file, comment out Atlhost.h and include FixAtlHost.h instead:

      // #include <atlhost.h>
      #include "FixAtlHost.h" 

This technique works only in Debug or ReleaseMinDependency builds. It does not
work in ReleaseMinSize builds, because in that case Atl.dll would be used, not
the code in Fixatlhost.h.

STATUS
======

Microsoft has confirmed that this is a bug in the Microsoft products that are
listed at the beginning of this article.

MORE INFORMATION
================

When an ATL control is in-place activated in an ATL container, the control's
server calls the container's IOleInPlaceSite::GetWindowContext method, which
fills in an OLEINPLACEFRAMEINFO structure. In this method, the container creates
an accelerator table by using the CreateAcceleratorTable API. OLE uses the
information in this structure to determine whether a message maps to one of the
container's accelerators. Because this memory has been allocated by the
container, it is the container's responsibility to call DestroyAcceleratorTable
to effectively release the memory.

Additional query words:

======================================================================
Keywords          : kbActiveX kbATL kbCOMt kbContainer kbCtrl kbATL300bug kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbATLsearch kbATL300
Version           : WINDOWS:3.0
Issue type        : kbbug
Solution Type     : kbnofix

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