IT33668: MQCTL does not function as expected when issued using MQOP_SUSPEND option

APAR status

• Closed as program error.

Error description

• The MQOP_SUSPEND option on the MQCTL API call pauses the
  consumption  of messages.
  
  The existing behavior is that the application connection
  consumes an extra message after being suspended, regardless of
  whether read-ahead is enabled.
  
  If read-ahead is not enabled for the connection, no messages
  should be consumed after the call is issued.
  

Local fix

• It is possible to work around the problem on the client by
  individually suspending each callback using MQCB(SUSPEND) from
  inside the callback rather than doing a less granular
  MQCTL(SUSPEND) for the connection.
  
  Another possible client-side alternative would be to follow the
  advice for MQCTL(SUSPEND) and have the application close the
  queue if it is not expecting to receive further messages for a
  while:
  
  "MQOP_SUSPEND
  Pause the consuming of messages. This operation releases the
  connection handle.
  This does not have any effect on the reading ahead of messages
  for the application. If you intend to stop consuming messages
  for a long time, consider closing the queue and reopening it
  when consumption continues"
  
  A further workaround is to call MQCTL(STOP) rather than
  MQCTL(SUSPEND).
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  Users of the IBM MQ asynchronous consume functionality that use
  MQCTL(SUSPEND) may be affected by this problem.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  If a client application thread issues MQCTL(SUSPEND) then
  messages may continue to be delivered to the application.  If
  the application does not call MQCTL(RESUME) then these messages
  may be lost, even if they are persistent messages.
  

Problem conclusion

• The IBM MQ code has been modified so that MQCTL(SUSPEND) will
  prevent further messages from being delivered to applications
  until MQCTL(RESUME) is called.
  
  This change in behaviour only applies if none of the queue
  handles being used by consumers under MQCTL control are using
  read-ahead.  If some of your consumers use read-ahead then you
  are advised to use one of the workarounds documented in this
  APAR.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.1 LTS   9.1.0.8
  v9.2 LTS   9.2.0.2
  v9.x CD    9.2.2
  
  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

  IBM MQ BASE MP

• Fixed component ID

  5724H7271

Applicable component levels