PI95725: THREADING MODEL FOR LIBERTY CICS IS NEEDING THE XMATTLCK EXCLUSIVE CAUSING NEW TASKS TO NOT ATTACH.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• You have several tasks in LMQUEUE suspends waiting on the
  XMATTLCK lock.   Normal attaches hold the XMATTLCK shared and
  new threading model for Liberty is designed to request the
  XMATTLCK exclusive.  This is causing a deadlock with the task
  needing the exclusive not getting it until all the shared tasks
  finish.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Deadlock for XMATTLCK leads to          *
  *                      no transactions being attached          *
  *                      for two minutes.                        *
  ****************************************************************
  A CICS system is configured to accept work over MRO, and
  also through a Liberty JVM server running in the region.
  A routed transaction arrives and starts processing the
  attach for a new task. This task becomes a holder of the
  shared XMATTLCK.
  The transaction was routed over MRO, so begins to run the
  DFHMRXM primary client initialisation (INIT_XM_CLIENT) routine.
  Meanwhile, a web request arrives in a Liberty JVM server.
  A new task must be built for this request
  (using BUILD_TRANSACTION) and this new task requests the
  XMATTLCK as an exclusive lock.
  The original MRO task, still holding the XMATTLCK as a shared
  lock, then needs to attach a CITS task. This new CITS also
  needs to become an owner of the shared XMATTLCK, but cannot
  now do so due to the outstanding exclusive request for this
  same lock.
  This system is now deadlocked, and no transaction can be
  attached until a timeout occurs on the MRO task. This takes
  approximately two minutes.
  The original routing transaction will abend AZI6.
  .
  Additional Keywords: abendAZI6 abendAZTB abendAZVA AZTB AZVA
                       msgDFHAC2236 DFHAC2236
  

Problem conclusion

• The CICS transaction attach mechanism has been updated
  to avoid the potential for this deadlock while initialising
  the primary client.
  

Temporary fix

Comments

APAR Information

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

  PI94982

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

  UI55546

Modules/Macros

• DFHXMTA
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R100 PSY UI55546

     UP18/04/28 P F804

Fix is available

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