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IV54745: TEN SECOND DELAY SOMETIMES SEEN DURING AN MQOPEN WHEN MULTIPLE APPLICATIONS CONNECT IN BINDINGS MODE TO WMQ V7.0 ON AIX

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APAR status

  • Closed as program error.

Error description

  • When using WMQ 7.0 on AIX and multiple applications connect
    concurrently in bindings mode and a specific queue, a
    10 second delay can occasionally occur during an MQOPEN.
    

Local fix

Problem summary

  • ****************************************************************
    USERS AFFECTED:
    Any user running MQ v7.x on AIX
    
    
    Platforms affected:
    AIX
    
    ****************************************************************
    PROBLEM SUMMARY:
    An MQ thread which was trying to obtain a lock was incorrectly
    going into a wait state when the lock was in fact available to
    be
    taken.
    
    IBM were able to capture the problem while AIX trace was
    running. The sequence of trace leading to the failure shows
    that one or more updates to fields used by WebSphere MQ in its
    locking code were not visible to other threads when they should
    have been, which led to an inappropriate code path being taken.
    
    After a low-level code review it was discovered that an
    incorrect
    assumption about the visibility of a variable changed by the AIX
    _clear_lock() function meant that it was possible for another
    thread to miss that the update had occurred. This caused the
    other thread to enter a wait state instead of taking ownership
    of the lock.
    

Problem conclusion

  • The MQ locking code was modified so that it used an explicit
    __sync() call
    which has the effect of making changes made by _clear_lock()
    visible to
    all threads and also prevents speculative execution of
    instructions following
    the __sync()
    
    ---------------------------------------------------------------
    The fix is targeted for delivery in the following PTFs:
    
    Version    Maintenance Level
    v7.0       7.0.1.13
    v7.1       7.1.0.6
    v7.5       7.5.0.5
    v8.0       8.0.0.1
    
    
    The latest available maintenance can be obtained from
    'WebSphere MQ Recommended Fixes'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
    
    If the maintenance level is not yet available information on
    its planned availability can be found in 'WebSphere MQ
    Planned Maintenance Release Dates'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
    ---------------------------------------------------------------
    

Temporary fix

Comments

APAR Information

  • APAR number

    IV54745

  • Reported component name

    WMQ AIX V7

  • Reported component ID

    5724H7221

  • Reported release

    700

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2014-01-30

  • Closed date

    2014-04-28

  • Last modified date

    2016-03-16

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    WMQ AIX V7

  • Fixed component ID

    5724H7221

Applicable component levels

  • R700 PSY

       UP

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Document Information

Modified date:
16 March 2016