PI36541: EXTRA CHANGE_MODE WHEN GOING FROM QR TCB BACK TO OPEN TCB.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• You are running a threadsafe program and have
  CONCURRENCY=REQUIRED specified.  You are running on an OPEN
  TCB, your program does a LINK PROG to a non-threadsafe program
  and CICS switches to the QR TCB to run.
  .
   Once the non-threadsafe program is done CICS returns back to
  the OPEN TCB.  In doing so you find CICS actually does three
  TCB CHANGE_MODE's to get back to the OPEN TCB.  Instead of just
  doing one CHANGE_MODE from the QR TCB to the OPEN TCB.
  .
   So an extra CHANGE_MODE to get back to the OPEN TCB occurs in
  order to do a  DISSOCIATE_THREAD again and then back to the QR
  and then finally to the OPEN TCB.
  
  Additional Symptom(s) Search Keyword(s): KIXREVDAM
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: An additional TCB change mode takes     *
  *                      place when linking to a                 *
  *                      concurrency(required) program.          *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  CICS TS 5.1 has improved the performance of CICS Java
  applications using JDBC/SQLJ by allowing DB2 access from the T8
  TCB rather than forcing a switch to an L8 TCB as in previous
  releases. The previous mechanism was required since DB2 is
  called under the L8 TCB at end of task syncpoint, when the
  T8 TCB has gone away, and so needed the L8 to be the CICS
  TCB associated with the DB2 thread. With the new mechanism,
  the T8 TCB can call DB2 and be associated with the thread;
  however, the CICS RMI has a switch_application_environment
  mechanism that allows DB2 to dissociate the TCB from the
  DB2 thread during certain operations, such as a subsequent
  EXEC CICS LINK command. Further calls to DB2 (for API or
  syncpoints) can reassociate the thread with the TCB in
  use at the time.
    The TRUE interest profile bit UEFMSWAE is used to indicate
  that a task has an interest in switch application
  environments - DFHD2EX1 sets it on when a call to DB2 is made.
  However, the bit is not turned off when a dissociate call to
  DB2 occurs. This means that subsequent switch_application_
  environment calls will invoke the CICS RMI and call DFHD2EX1
  and DFHD2D2, before the CICS DB2 attach logic determines that
  no dissociation is required. Since the TRUE is OPENAPI, it
  requires a switch to the L8 TCB in order to determine this.
    In the customer's case, a concurrency(required) program
  called DB2 (associating its open TCB with the DB2 thread).
  It then linked to a concurrency(quasirent) program, which
  drives the switch_application_environment logic and called
  DB2 to dissociate the thread from the TCB. When the new
  program issued its own link to a concurrency(required) program,
  CICS switched from QR to L8 in order to call the CICS DB2
  TRUE, only to find no dissociatation was required. CICS
  returned to QR, before switching back to the L8 to drive the
  concurrency(required) program. This was an unnecessary TCB
  switch since the DB2 thread was already dissociated at this
  point in time.
  KEYWORDS: CHANGE_MODE DFHDSAT DFHDSATM DFHAPEXM
            apex_switch_application_environment
  

Problem conclusion

• DFHD2EX1 has been changed to switch UEFMSWAE off when a
  dissociate call to DB2 has taken place.
  

Temporary fix

• FIX AVAILABLE BY PTF ONLY
  

Comments

• ×**** PE15/12/23 FIX IN ERROR. SEE APAR PI54515  FOR DESCRIPTION
  

APAR Information

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

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

  UI26932 UI26933

Modules/Macros

• DFHD2EX1
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R800 PSY UI26932

     UP15/05/02 P F505

• R900 PSY UI26933

     UP15/05/02 P F505

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.