CICS

CICS (Customer Information Control System, current: CICS Transaction Server for z/OS 6.x) runs online transactions: thousands of short programs executing concurrently for terminal users, web services, and APIs.

37.1 Concepts

4-character ID (e.g., CINQ) mapped to a starting program One running instance of a transaction

Exec Interface Block: EIBCALEN (COMMAREA length), EIBAID (key pressed), EIBTRNID, EIBRESP

Up to 32 KB of data passed between programs or saved between pseudo-conversational steps Channels & containers

Modern replacement for COMMAREA: named containers of any size grouped in a channel

Basic Mapping Support: defines 3270 screens (maps) with assembler macros; generates a physical map and a COBOL symbolic-map copybook Translator / coprocessor

Converts EXEC CICS into calls (CICS compiler option for the integrated translator)

37.2 Pseudo-conversational design

A conversational program waits for the user while holding resources — it doesn't scale. A pseudo-conversational program sends a screen, then ends with RETURN TRANSID(...) COMMAREA(...); when the user presses a key, CICS starts a new task of the same transaction, passing the saved COMMAREA. The program checks EIBCALEN to know whether it is the first invocation.

User types CINQ ──► task 1: EIBCALEN = 0 → send empty map → RETURN TRANSID('CINQ') COMMAREA
User enters ID  ──► task 2: EIBCALEN > 0 → RECEIVE MAP → READ FILE → SEND MAP → RETURN TRANSID
User presses F3 ──► task 3: send goodbye text → RETURN (no TRANSID) → conversation ends

37.3 BMS map

The generated symbolic map (COPY CUSTSET) contains CUSTMAPI (input) and CUSTMAPO (output) structures with, for each named field, suffixes L (length), F (flag), A (attribute), I (input), and O (output) — e.g., CUSTIDI, CUSTIDL, NAMEO, MSGO.

CUSTSET  DFHMSD TYPE=&SYSPARM,MODE=INOUT,LANG=COBOL,TIOAPFX=YES
CUSTMAP  DFHMDI SIZE=(24,80),CTRL=(FREEKB,FRSET)
         DFHMDF POS=(1,30),LENGTH=12,ATTRB=ASKIP,INITIAL='CUST INQUIRY'
         DFHMDF POS=(3,1),LENGTH=12,ATTRB=ASKIP,INITIAL='CUSTOMER ID:'
CUSTID   DFHMDF POS=(3,14),LENGTH=6,ATTRB=(UNPROT,NUM,IC)
         DFHMDF POS=(3,21),LENGTH=1,ATTRB=ASKIP
         DFHMDF POS=(5,1),LENGTH=5,ATTRB=ASKIP,INITIAL='NAME:'
NAME     DFHMDF POS=(5,14),LENGTH=30,ATTRB=(ASKIP,BRT)
         DFHMDF POS=(7,1),LENGTH=8,ATTRB=ASKIP,INITIAL='BALANCE:'
BAL      DFHMDF POS=(7,14),LENGTH=15,ATTRB=(ASKIP,BRT)
MSG      DFHMDF POS=(23,1),LENGTH=79,ATTRB=(ASKIP,BRT)
         DFHMSD TYPE=FINAL
         END

37.4 Inquiry program

Notes: CICS programs must not use STOP RUN, ACCEPT, DISPLAY (to a terminal), or COBOL file I/O — CICS commands do all I/O. RESP options with DFHRESP(...) replace the old HANDLE CONDITION style.

IDENTIFICATION DIVISION.
       PROGRAM-ID. CUSTINQ.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-RESP              PIC S9(8) COMP.
       01  WS-COMMAREA.
           05  WS-LAST-CUST-ID  PIC X(6).
       01  WS-BYE-MSG           PIC X(20) VALUE "SESSION ENDED".
       01  ED-BAL               PIC -ZZZ,ZZZ,ZZ9.99.
           COPY CUSTSET.
           COPY CUSTREC.
           COPY DFHAID.
       LINKAGE SECTION.
       01  DFHCOMMAREA          PIC X(6).
       PROCEDURE DIVISION.
       0000-MAIN.
           IF EIBCALEN = 0
               MOVE LOW-VALUES TO CUSTMAPO
               MOVE "ENTER A CUSTOMER ID, F3 TO EXIT" TO MSGO
               PERFORM 8000-SEND-MAP-ERASE
           ELSE
               MOVE DFHCOMMAREA TO WS-COMMAREA
               EVALUATE EIBAID
                   WHEN DFHPF3
                       EXEC CICS SEND TEXT FROM(WS-BYE-MSG)
                            LENGTH(LENGTH OF WS-BYE-MSG)
                            ERASE FREEKB
                       END-EXEC
                       EXEC CICS RETURN END-EXEC
                   WHEN OTHER
                       PERFORM 2000-PROCESS-INPUT
               END-EVALUATE
           END-IF
           
…

37.5 More CICS commands

LINK PROGRAM(...) COMMAREA(...) / CHANNEL(...) Call a program and return XCTL PROGRAM(...) Transfer control (no return)

READ, WRITE, REWRITE, DELETE, STARTBR/READNEXT/ENDBR FILE(...) VSAM file access WRITEQ TS/READQ TS, WRITEQ TD

Temporary storage (scratchpad) and transient data queues PUT CONTAINER/GET CONTAINER... CHANNEL(...) Channels and containers START TRANSID(...) Start a transaction asynchronously SYNCPOINT / SYNCPOINT ROLLBACK

Commit or back out recoverable resources (VSAM, Db2, MQ) Embedded SQL works in CICS programs too (Db2 attachment). CICS also exposes COBOL programs as web services and JSON/REST endpoints (with z/OS Connect — Chapter 40).