DOC: CCriticalSection::Lock Doesn't Do a Timed Wait (151893)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Editions 4.0
- Microsoft Visual C++, 32-bit Editions 4.1
This article was previously published under Q151893 SUMMARY
The CCriticalSection class contains a member function, Lock, that can be
used by a thread to gain ownership of a Critical Section object. There are
two versions of the Lock function, one taking no arguments and the other
taking a DWORD argument. The documentation for the latter version of Lock
states that the DWORD argument specifies the amount of time, in
milliseconds, to wait for the critical section to become available.
This information is not correct. The CCriticalSection class wraps the SDK
CRITICAL_SECTION object. This object does not have the capability for timed
waits. As a consequence, entering or leaving the Critical Section always
results in blocked waits. Hence, when CCriticalSection::Lock is called, the
argument passed is ignored and an infinite wait is executed.
The Mutex object has the capability for timed waits. The functionality of
this object is wrapped by the MFC class CMutex. An MFC application should
use the CMutex class when timed waits are desired.
MORE INFORMATION
CCriticalSection::Lock makes a call to ::EnterCriticalSection. This is a
blocking call that does an infinite wait. For example, if another thread
currently owns the Critical Section object, ::EnterCriticalSection blocks
the execution of the calling thread indefinitely until the other thread
releases its ownership. The classes, such as CEvent, CMutex, and
CSemaphore, that wrap other synchronization objects, make a call to
::WaitForSingleObject from their Lock functions. ::WaitForSingleObject
accepts an argument that identifies the time-out interval and executes a
true timed wait. A Critical Section object cannot be used with
::WaitForSingleObject. Therefore, it is not possible to do a timed wait
with Critical Section objects.
This documentation error was corrected in Visual C++ 4.2 and later versions.
| Modification Type: | Major | Last Reviewed: | 10/17/2003 |
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| Keywords: | kbBug kbdocerr kbdocfix kbfix kbThread kbVC420fix KB151893 |
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