PM51907: HANG IN ASYNC CONSUME PROCESSING WHEN AN MDB IS LISTENING ON A NON-DURABLE SUBSCRIPTION AND IS CONNECTING TO THE QSG NAME

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When the MDB listener starts, an async consumer TCB is created
  to monitor the subscription's queue for messages. When the first
  message is found, the MQ async consume code performs a
  callback on the async consume TCB to drive the JMS code for
  processing the message.
  
  Part of this code creates a new Server Session (still on the
  async consume TCB). This alters the current context for the
  hconn on which the call is made.
  
  The actual execution of the MDB is then handled off to another
  TCB, and the async consume TCB goes back to monitoring for
  messages.
  
  Because the context has been changed, the queue manager detects
  that there are no active callbacks for the current context, and
  fails the call. This causes the async consume thread to go into
  a wait and process no more messages
  .
  Additional Symptoms:
  .
  MQRC_NO_CALLBACKS_ACTIVE
  .
  A poison message processing can alters the context details for
  the
  thread, and these aren't correctly restored before returning to
  the
  async consumer processing. The async consumer attempts to
  request
  messages using the wrong context, and the resulting
  MQRC_NO_CALLBACKS_ACTIVE error causes the async consume
  thread to terminate without any notification being passed back
  to the JMS code.
  .
  Looking on the GTF trace, I can see that an MQ call from an
  async consumer task failed with MQRC 2446 =
  MQRC_NO_CALLBACKS_ACTIVE.
  .
  Example:
  ...........
  USRD9 5EA ASCB 00FC8B80            JOBN XXXXX
  CSQW073I EXIT:  MQ user parameter trace
  INTERNAL_SPIGETM
      Thread... 1538C398  Userid... 00000000  00000000
      pGMO..... 1D0EB200  BufferL.. 0000034B  pBuffer.. 25850000
  MQRC_NO_CALLBACKS_ACTIVE
  ...
  Hobj..... 00000000  pMsgDesc. 1D0EB090
  DataL.... 00000000  SPIGMO... 1D0EB360
  

Local fix

• This error can be bypassed if the customer is able to change
  their MDB listener to connect using a specific qmgr name.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of Websphere MQ for z/OS Version 7 *
  *                 Release 0 Modifications 1.                   *
  ****************************************************************
  * PROBLEM DESCRIPTION: When an MDB in WSAS is listening in     *
  *                      bindings mode using pub/sub on a        *
  *                      non-durable subscription and the        *
  *                      connection name given is a QSG, a       *
  *                      MQRC2446 may be returned and the        *
  *                      listener appear to hang.                *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  An MDB listener is configured in WSAS to connect to the QSG
  group name in bindings mode.  The listener is monitoring for
  messages using a non-durable subscription to a topic.
  
  When the listener is started, the subscription is created, and
  an async consume process is started to monitor the
  subscription's queue for messages.
  
  The first message arrives, and the async consume thread drives
  the message callback function in the JMS code.
  
  The message is delivered to the MDB and is processed
  successfully.
  
  During the processing of the first message the MDB alters the
  context on the bloa being used by the async consumer.
  
  When the async consumer tries to check for another message, it
  fails with MQRC_NO_CALLBACKS_ACTIVE (MQRC2446).
  
  The async consumer hangs, and no further messages are processed
  for the listener.
  
  The problem occurs because the context required to determine the
  registered callback functions is not restored after a callback
  function has reset it.
  

Problem conclusion

• The async consumer code has been changed to ensure the context
  in the bloa is restored following the return from a callback
  function.
  010Y
  CSQBLB1
  CSQBLB1X
  CSQBLB16
  CSQBLB2
  CSQBLB2X
  CSQBLB26
  CSQBLB3
  CSQBLB3X
  CSQBLB36
  CSQBLB4X
  CSQBLB46
  CSQBLB5X
  CSQBLB56
  CSQBMCSM
  CSQBMCST
  CSQBMCS2
  

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:

  PM60244 UK77191

Modules/Macros

• CSQBLB1  CSQBLB1X CSQBLB16 CSQBLB2  CSQBLB2X
  CSQBLB26 CSQBLB3  CSQBLB3X CSQBLB36 CSQBLB4X CSQBLB46 CSQBLB5X
  CSQBLB56 CSQBMCSM CSQBMCST CSQBMCS2
  

Fix information

• Fixed component name

  WMQ Z/OS V7

• Fixed component ID

  5655R3600

Applicable component levels

• R010 PSY UK77191

     UP12/04/11 P F204

Fix is available

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