Coding MPP Programs to Process IMS Transactions

5.4

Coding MPP Programs to Process IMS Transactions:

A COBOL Programmer’s Practicum

NE Canadian IMS Regional User GroupSeptember 16 – 19

Deepak Kohli ([email protected])

© Copyright IBM Corporation 2016

• IMS Architecture• IMS Transaction Queuing & Scheduling• Coding MPPs – Getting the Transaction Message– Sending the reply message to the originating terminal– Sending the reply message to an alternate destination• Alternate PCBs• Program to Program Message switch• Express Alternate PCBs

– SYNC or COMMIT Point– Abnormal Termination / Error Handling– Programming Tips

Agenda

© Copyright IBM Corporation 2016 2

TERMINALSMASTER TERMINAL TERMINALSTERMINALS

TELE-COMMUNI-CATIONS

MESSAGE SCHEDULING

CHECKPOINT

RESTARTCOMMON SERVICE

CONTROLREGION

MESSAGE QUEUES

MESSAGE QUEUES

DBRC

APPLICATION PROGRAM

APPLICATION PROGRAM

MESSAGEPROCESSING REGION(“MPR”, 0 or more)

BATCHMESSAGE

PROCESSINGREGION(“BMP”,0 or more)

IMS DATABASES

DATA LANGUAGE/1

DL/I SUBORDINATEADDRESSSPACE

(“DLISAS”)

IMS architecture

IMS System Log


Transaction Message Queuing

CLASSES TRANSACTIONS (PRIORITY)

004 SKILLUPD (8)SKILLINQ (5)PAYROLL (4)

002 INVENT (10)STOKSTAT (8)

003 ORDER (6)RECEIVE (4)

Transaction Class & Priority


• Transactions are queued by Class and• Within class by priority

• Classes: 1 – 999• Priority: 0 - 14

NORMAL PRIORITYLIMIT PRIORITYLIMIT COUNTQUEUE COUNTPROCESSING LIMIT

NORMAL PRIORITYLIMIT PRIORITYLIMIT COUNTQUEUE COUNTPROCESSING LIMIT

TIME TIME TIME1 2 3

5 10 1030 30 308 31 020 20 20

TIME TIME TIME1 2 3

12 12 124 4 42 1 35 5 5

5 510

8 8 8

CLASS 001SKILLINQ

TRANSACTION

MESSAGE 1

MESSAGE N

CLASS 001

~~

MESSAGE 1

SKILLUPD TRANSACTION

MESSAGE N

~~

Transaction Priorities


Application programs are automatically scheduled into Message Processing Regions (MPRs)

MESSAGE 1

SKILLUPDCLASS=1,PRTY=8

MESSAGE N

SKILLINQCLASS=1,PRTY=5

MESSAGE 1

MESSAGE N

~~

~~

Sch Te ad su kler

IMS/MPR1

Classes2,3,4,1

IMS/MPR2

Classes4,5,6,7

IMS/MPR3

Classes3,4,5,6

CLASS 001

CLASS 001

Transaction Scheduling


Reply (outbound) Message Queuing

LOGICAL TERMINAL

ABC

LOGICAL TERMINAL

XYZ

MESSAGES

PHYSICAL TERMINAL 1

MESSAGES

PHYSICAL DEVICE 2

APPLICATION PROGRAM

PHYSICAL TERMINAL 3

IMS/TM(Control Region)

Transaction Manager

IMS/MPR(Message Processing Region)

Logical terminal concept


X Y

X (LTERMA)X (LTERMX)X (LTERMO)X (LTERMX)

Y (LTERMB)Y (LTERMZ)Y (LTERMA)

LTERM QUEUES

LTERMA LTERMB

REPLY (X)REPLY (Y) REPLY (Y)

Queuing Transaction & Reply messages


1 2 3 … Classes

Transaction Codes

11

Coding MPP Programs

MESSAGE REGIONREGION CONTROLLER (DFSRRC00)

APPLICATION PROGRAM

GET TRAN MESSAGE

PROCESSACCESS DBs

SEND REPLY MESSAGE

RETURN IF NO MORE

LANGUAGE INTERFACE(DFSLI000)

MPP Program flow

12© Copyright IBM Corporation 2016

Getting the Transaction Message

PCBs (in PSBs) for Transaction processing #1 < ---- I/O PCB >

#2 PCB TYPE=TP,MODIFY=YES

#3 PCB TYPE=DB……

PSBGEN PSBNAME=PSB_name,

• TP– IOPCB• Not explicitly coded in PSB– Will be the first of the list of PCBs passed to an IMS program at entry in almost all cases, but will always be the first PCB for application programs that execute with an Online system

• Used to receive or send a message in IMS TM programs– Alternate TP PCB• Used to receive or send a messages to destinations other than where input transaction was received from• Two sub-types: MODIFY-able and un-MODIFY-able

• DB– Used to read or update a database - same as with IMS DB only


LOGICAL TERMINAL

PAYROLL

Application program

DATABASEPCB

MASK

MASK TPPCB

ADDRESS

NAME

Logical structures and logical terminals


I/O PCB

TP PCB1

DB PCB1

I/O PCB

TP PCB

DB PCB

APPLICATION PROGRAM PSB

PROCEDURE DIVISION.

ENTRY 'DLITCBL' USING I-O-PCB, TP-PCB1, DB-PCB1.

ENTRY statement


LOGICAL TERMINAL NAME 8RESERVED 2STATUS CODE 2DATE 4TIME 4INPUT SEQUENCE NUMBER 4MESSAGE FORMAT NAME 8USERID 8GROUP 8TIMESTAMP 12

I/O PCB



LINKAGE SECTION.

01 IO-PCB. 03 IO-LTERM PIC X(8). 03 FILLER PIC XX. 03 IO-STATUS-CODE PIC XX. 03 IO-DATE-YYDDD PIC S9(7) COMP-3. 03 IO-TIME-HHMMSS-T PIC S9(6)V9 COMP-3. 03 IO-MSG-NO PIC S9(9) COMP. 03 IO-MOD-NAME PIC X(8). 03 IO-USERID PIC X(8).

I/O PCB defined in the Linkage Section

Getting Tran Message – Single Segment • GET UNIQUE

CALL ‘CBLTDLI’ USING GUIO-PCBMESSAGE-INPUT

• MESSAGE-INPUT defined in WORKING-STORAGE SECTION

• Successful call results in ‘bb’ status code• ‘QC’ status code – no more transactions


Getting Tran Message - Multi-Segment message • GET UNIQUE – for first segment

CALL ‘CBLTDLI’ USING GUIO-PCBMESSAGE-INPUT

• GET NEXT – for subsequent segments

CALL ‘CBLTDLI’ USING GNIO-PCBMESSAGE-NEXT-SEGMENT

– ‘QD’ status code – no more segments for this transaction message.


GET UNIQUE

GET NEXT

PROCESS MESSAGE

INSERT

GO GET NEXT MESSAGE

GO BACK/RETURN IF NO MORE

Call sequence


SINGLE SEGMENT

LL ZZ PARTSTAT 123456789

MULTI SEGMENTLL ZZ ORDER HEADER

LL ZZ ITEM 1•••LL ZZ ITEM N

Message LayoutsLL ZZ TRANCODE SEGMENT

LL ZZ SEGMENT 2•••LL ZZ SEGMENT N

SINGLESEGMENTMESSAGE

MULTISEGMENTMESSAGE


Sending the Reply MessageBack to the originating LTERM

Sending Output message

1. Build and format reply in I/O area

2. Calculate length (LL) and store in I/O area prefix– LL includes LLZZ (that is, Message + 4)

3. CALL ‘CBLTDLI’ USING ISRTIO-PCBOUTPUT-MESSAGE.


OUTPUT MESSAGE 2

INPUT MESSAGE 3

(no more) INPUT MESSAGE

'QD' STATUS CODE

'QC' STATUS CODE

Message processing flowGET UNIQUEGET NEXTGET NEXT

INSERTINSERTINSERT

GET UNIQUEGET NEXT

INSERTINSERT

GET UNIQUEGET NEXTGET NEXT

INSERT

GET UNIQUE

RETURN

INPUT MESSAGE 1

OUTPUT MESSAGE 1

INPUT MESSAGE 2'QD' STATUS CODE

'QD' STATUS CODE

OUTPUT MESSAGE 3

* All status codes 'bb' except where noted25© Copyright IBM Corporation 2016

Sending the Reply MessageTo an alternate destination

LL ZZ RECEIPT 1000 WIDGETS

LL ZZ TRANSACION SUCCESSSFULY PROCESSED

LL ZZ PAYMT XYZ COMPLETE

LL ZZ ORDER XYZ GOODS RECEIVED

ACCOUNTS PAYABLE LTERM (PCB #2)

RECEIVING LTERM (I/O PCB)

RECEIVING LTERM (I/O PCB)

PAYMT TRAN QUEUE (PCB #3)

RECEIPT PROGRAM

Alternate output destinations

optional


RECEIVE

PAYABLE

PAYMT

RECEIVING TERMINAL

ACCOUNTS PAYABLE TERMINAL

PAYMENTS PROGRAM

I/O PCB

ALTERNATE PCB

ALTERNATE PCB

Alternate PCBs


Alternate PCBs for Transaction processing PCB TYPE=TP, LTERM=WXYZ

PCB TYPE=TP, NAME=PAYMT

PCB TYPE=TP,MODIFY=YES

PCB TYPE=DB

PSBGEN PSBNAME=PSB_name


Alternate PCB Types • Fixed (or Un-modifiable) Alternate TP PCB– Destination is hard coded in the PSB

• Modifiable Alternate TP PCBs– Destination will be specified by the program via a CHANGE DL/I call.

• Express PCBs


PROCEDURE DIVISION.

ENTRY 'DLITCBL' USING I-O-PCB, ALT1, ALT2, DB-PCB.

ENTRY Statement with Alternate PCBs


LOGICAL TERMINAL NAME/TRAN CODE 8

RESERVED2

STATUS CODE2

Alternate PCB format



LINKAGE SECTION.

01 ALT-PCB. 03 ALT_DESTINATION PIC X(8). 03 FILLER PIC XX. 03 ALT-STATUS-CODE PIC XX.

ALT PCB defined in the Linkage Section

Sending Output message to Alternate Destination

1. Build and format reply in I/O area

2. Calculate length (LL) and store in I/O area prefix– LL includes LLZZ (that is, Message + 4)

3. CALL ‘CBLTDLI’ USING ISRTALT-PCBOUTPUT-MESSAGE.


Using a Modifiable PCB for

Alternate destination

'CBLTDLI'

CHNG

MODIFIABLE ALT PCB

LTERM/TRANCODE

bbbbbbbb

PCB BEFORE

LTERMAbb

PCB AFTER

'CHANGE' REMAINS UNTIL:GU TO I/O PCBOR

PGM TERMINATIONOR

ANOTHER CHNG

- RESET TO BLANKS

- PURG REQUIRED BEFORE NEW CHNG

}

CALL

Change call


• Call ‘CBLTDLI’ USING CHNG ALT-PCB DEST

What’s a Program to Program Message Switch

• When one application program kicks of another transaction

1. Application program build the transaction message

2. If using a fixed Alternate PCB, the application issues a ISRT call to the ALT PCB or

3. If using modifiable Alternate PCB, the application issues a CHNG call to the ALT PCB, followed by a ISRT of the message to the ALT PCB.


ISRT

ALTERNATE PCBPAYMT

LL ZZ PAYMT XYZ COMPLETE

I/O PCBRECEIVE

GUI/O PCB (AFTER)RECEIVE

LL ZZ PAYMT XYZ COMPLETE (AFTER)

RECEIPT PROGRAM

CALL

PAYMT PROGRAM

'CBLTDLI'

CALL 'CBLTDLI'

Program to Program Message Switching


PURG DL/I Call

• A Purge Call (Function Code “PURG”) must be issued after sending the last message segment to a Modifiable PCB before another CHNG call can be issued to specify a different destination for subsequent messages.

– i.e. Used to indicate a message is “complete” for a destination.


PURG

I/O PCB OR ALT PCB

LL ZZ SEGMENT - OPTIONAL (INSERTS)

GET UNIQUEINSERTINSERTPURGE (TERMINATES FIRST MESSAGE)

PURGE (With SEGMENT 1 in I/O Area)

'CBLTDLI'

MESSAGE 1SEGMENT 1SEGMENT 2

MESSAGE 2

SEGMENT 1

CALL

Purge call

Inserts then PURGE

PURGE ONLY


EXPRESS PCBs

• There is an option associated with Alternate TP PCBs (modifiable or not).– EXPRESS=YES

• Permits IMS to send messages before the program has reached a Commit Point (but after the PURG call has been issued).


Use of Purge & “EXPRESS=YES” PCBs• PCB TYPE=TP, MODIFY=YES,EXPRESS=YES

• CALL ‘CBLTDLI’ USING CHNGALT-PCBLTERM_NAME.

• CALL ‘CBLTDLI’ USING ISRTALT-PCBMESSAGE-O-AREA.

• CALL ‘CBLTDLI’ USING PURGALT-PCB.


SYNC Point or Commit Point• MPP Programs are called MODE=SNGL programs– After ever transaction is processed, you have reached a SYNC point or Commit point

– i.e. at every GU IOPCB, a SYNC or Commit point is reached

• At SYNC or Commt Point:– Database updates are committed– Log records are written– Output messages are placed on their output queues– Locks are released


Abnormal Termination• When program abnormally terminates:

– Database updates are thrown away– Messages (those not sent express), are deleted– Input message thrown away– Abend is recorded on the IMS log– Abend message is sent by IMS to the terminal– Transaction & program are stopped so that no other messages for that program will be scheduled.

• It’s as if the transaction never happened.


Error Handling• MPPs should attempt to handle exceptions without abending as often as possible.

• When error is encountered, the application program can ask IMS to reverse any database updates since the last sync point

• ROLL DL/I call:– CALL ‘CBLTDLI’ USING ROLL– A U778 abend is issued to the terminal & the input message is deleted.


ROLB DL/I call• ROLB causes IMS to reverse all updates, but the transaction does not abend.

• To reverse updates & delete the incoming message:– CALL ‘CBLTDLI’ USING ROLB IO-PCB.

• To reverse updates & reschedule the message:– CALL ‘CBLTDLI’ USING ROLB IOPCB INPUT-MESSAGE-AREA.– The INPUT-MESSAGE-AREA will return the current input message.


Programming tips• All programs should be written to go back and get another message (GU I/O PCB) ('QC' status returned if no more exist)

• Database requests should be handled with the fewest number of calls

• Message processing programs should not do lengthy database scans or updates

• Never issue file open/close operations - beware of COBOL DISPLAYs.

• Issue all message segment gets/inserts as consecutive calls if possible

• Large, single segment replies take fewer calls and less overhead than smaller, multi segment ones– check system standard for maximum segment size


Thank You!

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Coding MPP Programs to Process IMS Transactions

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