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CICS - What is quasi-reentrant program?

asked mar August 4, 2014 11:12 AM  

What is quasi-reentrant program?


1 Answers

answered By Mswami   0  
A quasi-reentrant program is a program that is in a consistent state when control is passed to it, both on entry, and before and after each EXEC CICS command. Such quasi-reentrancy guarantees that each invocation of an application program is unaffected by previous runs, or by concurrent multithreading through the program by multiple CICS tasks.

CICS runs user programs under a CICS-managed task control block (TCB). If your programs are defined as quasi-reentrant (on the CONCURRENCY attribute of the program resource definition), CICS always invokes them under the CICS quasi-reentrant (QR TCB). The requirements for a quasi-reentrant program in a multithreading context are less stringent than if the program were to run concurrently on multiple TCBs.

CICS requires that an application program is reentrant so that it guarantees consistent conditions. In practice, an application program might not be truly reentrant; CICS expects "quasi-reentrancy".

For example, application programs could modify their executable code, or the variables defined within the program storage, but these changes must be undone, or the code and variables reinitialized, before there is any possibility of the task losing control and another task running the same program.

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