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Explain re-entrancy as applies to CICS.
CICS Interview Questions
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Explain re-entrancy as applies to CICS.
Reentrant program is a program which does not modify itself so that it can reenter to itself and continue processing after an interruption by the operating system which, during the interruption, executes other OS task including OS tasks of the same program. It is also called a "reenterable" program or "serially reusable" program
A quasi-reentrant program is a reentrant program under the CICS enviroment. That is, the quasi-reentrant program is a CICS program which does not modify itself. That way it can reenter to itself and continue processing after an interruption by CICS which, during the interruption executes other tasks inluding CICS tasks of the same program. In order to maintain the quasi- reentrancy, a CICS application program must follow the follow convention:
Constants in Working Storage: The quasi-reentrant program defines only constants in its ordinary data area (e.g. working Storage Section). These constants will never be modified and shared by the tasks
Variable in Dynamic Working Storage: The quasi reentrant program acquires a unique storage area ( called Dynamic Working Storage - DWS) dynamically for each task by issuing the CICS macro equivalent GETMAIN. All variables will be placed in this DWS for each task. All counter would have to be initialized after the DWS has been acquired.
Restriction on Program Alteration: The program must not alter the program itself. If it alters a CICS macro or command. it must restore the alteration before the subsequent CICS macro or command.
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