IT31861: A queue manager may stop delivering messages to the client when the client uses MQCB/MQCTL APIs

APAR status

• Closed as program error.

Error description

• An application connecting as a client (eg. over TCP/IP) uses
  "asynchronous consumer" APIs MQCB and MQCTL.
  
  After a while, the queue manager entered a state where it
  stopped delivering messages from the server to the client. There
  were no FDCs or errors written by the MQ code to indicate this
  condition exists.
  

Local fix

• End and restart the application.
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  Users of MQ's asynchronous consumer APIs from a client (eg.
  TCP/IP) program.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  This was a race condition where the two threads in the SVRCONN
  channel that serve the application changed a pointer in a data
  block that they both share.
  
  When this happened, a counter (the number of active consumers)
  being updated by one thread was updated on the wrong data block.
   So, later the counter was smaller than it should have been, and
  the decision logic running at that time, chose not to re-start
  the flow of messages to the client.
  

Problem conclusion

• A resolution has been found to avoid the race condition, so that
  both of these threads can continue their work safely, avoiding
  the problem.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.1 CD    9.1.5
  
  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 is sysrouted FROM one or more of the following:

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

Fix information

• Fixed component name

  MQ APPLIANCE M2

• Fixed component ID

  5737H4700

Applicable component levels