Microsoft KB Archive/830475

= Message Queuing Application May Fail in Mqoa.dll with an Access Violation =

Article ID: 830475

Article Last Modified on 2/20/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows 2000 Advanced Server

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SYMPTOMS
A Microsoft Message Queuing (also known as MSMQ) component that uses the EnableNotification method call and is written in Microsoft Visual Basic may result in an access violation.



CAUSE
This access violation occurs because of a race condition between threads in the Mqoa.dll file. When this problem occurs, the running program thread calls the MSMQQueue.EnableNotification method. The message is peeked immediately and is dispatched to the MSMQEvent event handler. Because the MSMQEvent event handler is in a multithreaded apartment (MTA), the call is dispatched to a worker thread. This worker thread will execute the event handler code and may take some time to complete.

The race condition starts when the program thread exits and runs its destructor. Because the MSMQEvent event handler is an apartment thread, the release event is dispatched to the MSMQEvent event handler, and the MSMQEvent object is released from memory. In the meantime, the event handler worker thread still tries to finish processing the event message. When the worker thread tries to reference the MSMQEvent object, an access violation occurs because the MSMQEvent object has been released from memory. For additional information about race conditions, click the following article number to view the article in the Microsoft Knowledge Base:

317723 INFO: What Are Race Conditions and Deadlocks?

For additional information about multithreaded apartments (MTA), click the following article number to view the article in the Microsoft Knowledge Base:

150777 INFO: Descriptions and Workings of OLE Threading Models



Hotfix Information
A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

Prerequisites
No prerequisites are required.

Restart Requirement
You must restart your computer after you apply this hotfix.

Hotfix Replacement Information
This hotfix does not replace any other hotfixes.

File Information
The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.   Date         Time   Version            Size    File name --  21-Oct-2003  14:03  5.0.0.778         281,360  Mq1repl.dll 20-Sep-2003 17:23  5.0.0.778          14,096  Mq1sync.exe 02-Oct-2003 19:21  5.0.0.785          76,016  Mqac.sys 21-Oct-2003 14:03  5.0.0.783         217,360  Mqads.dll 20-Sep-2003 17:23  5.0.0.761          25,360  Mqbkup.exe 21-Oct-2003 14:03  5.0.0.785          76,560  Mqdscli.dll 21-Oct-2003 14:03  5.0.0.773          42,256  Mqdssrv.dll 20-Sep-2003 17:23  5.0.0.759          98,064  Mqmig.exe 21-Oct-2003 14:03  5.0.0.759         265,488  Mqmigrat.dll 21-Oct-2003 14:03  5.0.0.787         222,480  Mqoa.dll 21-Oct-2003 14:03  5.0.0.784          10,000  Mqperf.dll 21-Oct-2003 14:03  5.0.0.786         433,936  Mqqm.dll 21-Oct-2003 14:03  5.0.0.778         102,672  Mqrt.dll 21-Oct-2003 14:03  5.0.0.776          70,928  Mqsec.dll 21-Oct-2003 14:03  5.0.0.783         400,656  Mqsnap.dll 21-Oct-2003 14:03  5.0.0.762          23,824  Mqupgrd.dll 21-Oct-2003 14:03  5.0.0.782         110,864  Mqutil.dll 21-Oct-2003 14:03  5.0.0.748          64,784  Msmq.cpl 09-Oct-2003 00:18  5.4.1.0             6,656  Spmsg.dll 09-Oct-2003 00:19  5.4.1.0           140,800  Spuninst.exe 09-Oct-2003 00:19  5.4.1.0            22,016  Spcustom.dll



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section of this article.

Additional query words: msmq mqoa AV failure fail

Keywords: kbhotfixserver kbqfe kbbug kbfix kbqfe kbwin2000presp5fix KB830475

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