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Article ID: 240955 - Last Review: February 28, 2014 - Revision: 2.3

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Any multithreaded program may wait forever on a WaitForMultipleObjects call when waiting on multiple mutexes. This behavior occurs when the thread making the API call is already holding one on the mutexes.

For example, assume a program with two threads and two mutexes. Thread A owns mutex 1 and thread B owns mutex 2. If thread A calls WaitForMultipleObjects on both mutex 1 and mutex 2 with bWaitAll=TRUE, the call waits for mutex 2 to be released by thread B. However, the call never returns, even after thread B releases mutex 2.


This behavior occurs because the Windows NT kernel is not handling the WaitForMultipleObjects call correctly for multiple mutexes.


A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:;EN-US;CNTACTMS (;en-us;cntactms)
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.

The English-language version of this fix should have the following file attributes or later:
  Date       Time                 Size      File name     Platform
  09/01/99   06:11 PM             931,584   Ntoskrnl.exe  Intel
  09/01/99   06:13 PM             951,680   Ntkrnlmp.exe  Intel

  09/01/99   06:10 PM             1,381,824 Ntoskrnl.exe  Alpha
  09/01/99   06:10 PM             1,410,112 Ntkrnlmp.exe  Alpha


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

  • Microsoft Windows NT 4.0 Service Pack 4
  • Microsoft Windows NT 4.0 Service Pack 5
  • Microsoft Windows NT 4.0 Service Pack 6
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Workstation 4.0
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