IT22503: MQ Java: A java.util.ConcurrentModificationException FFDC can begenerated when a connection is broken

APAR status

• Closed as program error.

Error description

• When a connection in the MQ Java client is disconnected (for
  example by a broken network connection), an FFDC reporting a
  java.util.ConcurrentModificationException can be generated.  The
  FFDC shows information similar to the following:
  
  Source Class     :- com.ibm.mq.jmqi.remote.impl.RemoteRcvThread
  Source Method    :- run()
  ProbeID          :- 05
  Thread           :- name=RcvThread:
  com.ibm.mq.jmqi.remote.impl.RemoteTCPConnection@292459877[
  qmid=QM1,fap=13,channel=MY.SVRCONN,ccsid=819,sharecnv=10,hbint=3
  00,peer=localhost(1414),localport=65734,ssl=no] priority=5
  group=main]
  
  Data
  ----
  
  Description              :-  Unexpected Exception
  Exception cause message  :-  <null>
  Exception summary        :-
  java.util.ConcurrentModificationException[null]
  exception               :-  ExceptionDepth is 2
  Cause:1       :-  java.util.ConcurrentModificationException
  
  StackTrace:1  :-  java.util.ConcurrentModificationException
   at java.util.TreeMap$PrivateEntryIterator.nextEntry
   at java.util.TreeMap$ValueIterator.next
   at com.ibm.mq.jmqi.remote.impl.RemoteConnection.disconnect
   at
  com.ibm.mq.jmqi.remote.impl.RemoteConnection.asyncFailureNotify
   at com.ibm.mq.jmqi.remote.impl.RemoteRcvThread.run
   at java.lang.Thread.run
  

Local fix

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects users of the IBM MQ Java MQI implementation,
  which includes the:
  
    - MQ classes for JMS
    - MQ classes for Java
    - MQ JCA Resource Adapter
    - Managed File Transfer component
  
  when CLIENT transport mode connections to a queue manager are
  used.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  The Java MQI (JMQI) maintains a collection of conversations
  (otherwise known as hConns) that are associated with a
  particular TCP/IP connection to a queue manager.  When a
  conversation is created, it is added to the collection.  When a
  conversation is closed, it is removed from the collection.
  
  If the TCP/IP connection between the client application and the
  queue manager was terminated, then the JMQI code attempted to
  mark all the conversations associated with the connection as
  being disconnected.  To do this it looped over the collection of
  conversations that were maintained.  If another thread was in
  the process of attempting to allocate a new conversation on the
  connection that had just been disconnected, it was possible for
  the conversation to be added to the collection of conversations
  without correct synchronization.  As such, because the
  collection of conversations was structurally changed, the thread
  iterating over it threw a
  java.util.ConcurrentModificationException that resulted in an
  FFDC being generated.
  

Problem conclusion

• The synchronization around accessing the collection of
  conversations allocated to a TCP/IP client connection was
  revised in APAR IT15408:
  
    http://www.ibm.com/support/docview.wss?uid=swg1IT15408
  
  and further extended under APAR IT22127:
  
    http://www.ibm.com/support/docview.wss?uid=swg1IT22127
  
  which resolved the java.util.ConcurrentModificationException in
  the cases described above.
  
  This APAR addresses one further case where a
  java.util.ConcurrentModificationException could be thrown while
  tracing is enabled or an FFDC is being generated for a different
  underlying reason.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v8.0       8.0.0.9
  v9.0 CD    9.0.5
  v9.0 LTS   9.0.0.3
  
  The latest available MQ 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 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 MFT V8.0

• Fixed component ID

  5724H7252

Applicable component levels

• R800 PSY

     UP