FIX: CSingleLock: Bogus Assert in CSingleLock::CSingleLock (140669)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Editions 4.0
This article was previously published under Q140669 SYMPTOMS
Passing the address of a CCriticalSection object to the constructor of a
CSingleLock object causes an assertion in the mtex.cpp file at line 97.
This line is in the constructor for CSingleLock.
CAUSE
A Critical Section object cannot be passed to ::WaitForSingleObject. This
is because Critical Section objects do not have a corresponding kernel
object. Because CSingleLock::Lock calls CSyncObject::Lock, which calls
::WaitForSingleObject, the ASSERT tries to catch the case when a Critical
Section object is incorrectly passed to ::WaitForSingleObject.
However, CSyncObject::Lock is virtual and CCriticalSection::Lock is
overridden to make the right call, ::EnterCriticalSection. As a
consequence, ::WaitForSingleObject is never called with a Critical
Section object. Hence the ASSERT statement is bogus.
RESOLUTION
The assert can be safely ignored. ASSERT statements are only evaluated in
debug builds, so this is not a problem with release builds. To get rid of
the assert, remove the assert from the MFC source and rebuild the debug
version of the MFC library. For details on rebuilding the MFC libraries,
please see the Readme.txt file located in the <msdev>\Mfc\Src directory.
The CCriticalSection class does not necessarily have to work with
CSingleLock, so you can avoid this assertion by avoiding the CSingleLock
class entirely. This would involve making a call to CCriticalSection::Lock
directly. See the Help file for CCriticalSection for more information on
this approach.
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products
listed at the beginning of this article. This bug was corrected in
Visual C++ 4.1.
MORE INFORMATION
Because the call to CMultiLock::Lock always calls ::WaitForMultipleObjects
or ::MsgWaitForMultipleObjects, you must make sure that none of the
synchronization objects passed to CMultiLock constructor are of type
CCriticalSection. This means that a similar assertion in the constructor
for CMultiLock in the mtex.cpp file at line 163 is valid.
REFERENCES
CCriticalSection in the Help file.
| Modification Type: | Major | Last Reviewed: | 10/17/2003 |
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| Keywords: | kbBug kbfix kbThread kbVC410fix KB140669 |
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