As of now, we have covered non-conversion and conversion programs. Conversion programs have a major drawback as their think time is considerably high. To overcome this problem, pseudo-conversion programming came into the picture. We will now discuss more about pseudo-conversion programs.
Pseudo-Conversion Program
Following is the sequence of events which take place in a pseudo-conversion program −
- Step 1 − The system sends a message to the screen and terminates the transaction, specifying the transaction to be started when the user input is received.
- Step 2 − The system allocates the resources used by this transaction to other transactions running in the system. So we can utilize the resources in a pseudo-conversion program till the user gives the input.
- Step 3 − The system polls the terminal input at regular intervals of time. When the input is received, it is processed and the output is displayed.
- Step 4 − The application program is loaded into the main storage when needed and released when not in use.
Pseudo Conversion Techniques
The important point to note in pseudo-conversation is passing of data between every task. We will discuss about the techniques for passing data.
COMMAREA
COMMAREA is known as communication area. COMMAREA is used to pass data between tasks. The following example shows how to pass COMMAREA where WSCOMMAREA and WS-COMMAREA-LENGTH are declared in Working Storage Section −
EXEC CICS RETURN
TRANSID ('transaction-id')
COMMAREA (WS-COMMAREA)
LENGTH (WS-COMMAREA-LENGTH)
END-EXEC.
DFHCOMMAREA
DFHCOMMAREA is a special memory area which is provided by CICS to every task.
- It is used to pass data from one program to another program. The programs can exist in the same transaction or in different transaction also.
- It is declared in the Linkage Section of the program at 01 level.
- It should have the same picture clause as WS-COMMAREA.
- Data can be moved back from DFHCOMMAREA to WS-COMMAREA using a MOVE statement.
MOVE DFHCOMMAREA TO WS-COMMAREA.
Example
After sending the map, the task ends and waits for the user response. At this stage, the data needs to be saved, because though the task has ended, the transaction has not. When this transaction is to be resumed, it would require the prior status of the task. User enters the input. This now has to be received by the RECEIVE MAP command and then validated. The following example shows how to declare COMMAREA and DFHCOMMAREA −
WORKING-STORAGE SECTION. 01 WS-COMMAREA. 05 WS-DATA PIC X(10). LINKAGE SECTION. 01 DFHCOMMAREA. 05 LK-DATA PIC X(10).
Pseudo Code
Given below is the logic of pseudo code which we use in pseudo programming −
MOVE DFHCOMMAREA TO WS-COMMAREA
IF EIBCALEN = 0
STEP1: SEND MAP
STEP2: MOVE <internal-transaction-id1> to WS-COMMAREA
STEP3: ISSUE CONDITIONAL RETURN
ELSE
IF WS-COMMAREA = <internal-transaction-id1>
STEP4: RECEIVE MAP
STEP5: PROCESS DATA
STEP6: SEND OUTPUT MAP
STEP7: MOVE <internal-transaction-ID2> to WS-COMMAREA
STEP8: ISSUE CONDITIONAL RETURN
END-IF
END-IF
STEP9: REPEAT STEP3 TO STEP7 UNTIL EXIT
Example
The following example shows a pseudo-conversion program −
******************************************************************
* PROGRAM TO DEMONSTRATE PSEUDO-CONVERSATION *
******************************************************************
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-MESSAGE PIC X(30).
01 WS-COMMAREA PIC X(10) VALUE SPACES.
LINKAGE SECTION.
01 DFHCOMMAREA PIC X(10).
PROCEDURE DIVISION.
MOVE DFHCOMMAREA TO WS-COMMAREA
IF WS-COMMAREA = SPACES
******************************************************************
* TRANSACTION GETTING EXECUTED FOR THE FIRST TIME *
******************************************************************
MOVE 'HELLO' TO WS-MESSAGE
EXEC CICS SEND TEXT
FROM (WS-MESSAGE)
END-EXEC
MOVE 'FIRST' TO WS-COMMAREA
******************************************************************
* TASK ENDS AS A RESULT OF RETURN. IF AID KEY PRESSED, NEXT *
* TRANSACTION SHOULD BE TP002. DATA PASSED FROM WS-COMMAREA TO *
* DFHCOMMAREA *
******************************************************************
EXEC CICS RETURN
TRANSID('TP002')
COMMAREA(WS-COMMAREA)
END-EXEC
******************************************************************
* IF COMMAREA IS NOT EMPTY , THEN TP002 HAS BEEN EXECUTED ONCE *
* ALREADY, USER INTERACTION IS FACILITATED BY RECEIVE *
******************************************************************
ELSE
EXEC CICS RECEIVE
INTO(WS-MESSAGE)
END-EXEC
EXEC CICS SEND TEXT
FROM (WS-MESSAGE)
END-EXEC
******************************************************************
* TASK ENDS AS A RESULT OF RETURN, NO NEXT TRANSACTION SPECIFIED *
* TO BE EXECUTED *
******************************************************************
EXEC CICS RETURN
END-EXEC
END-IF.
Advantages of Pseudo Conversion
Following are the advantages of pseudo conversion −
- The resources are best utilized. Resources are released as soon as the program is suspended temporarily.
- It looks as if it is in conversational mode.
- It has better response time.
Return Statements
Following are the two types of return statements which are used in CICS −
Return-1
When the following unconditional return statement is issued, the task and the transaction (program) is terminated.
EXEC CICS RETURN END-EXEC.
Return-2
When the following conditional return, i.e., return with TRANSID statement is issued, the control returns to the CICS with the next transid to be executed. The next transaction starts when the user presses an AID key.
EXEC CICS RETURN
TRANSID ('trans-id')
[COMMAREA(WS-COMMAREA)]
END-EXEC.
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