Wednesday, April 18, 2007

Review Topic: CICS: multithreading concepts

Various texts discuss the concepts reentrant, quasi-reentrant, reusable, serially reusable. IBM-Boulder has a comprehensive reference here.

According to IBM, CICS requires that all application programs be quasi-reentrant. Another way to say this is that they must be serially reusable between entry and exit points. IBM also discusses a concept called "threadsafe": "Programs that use appropriate serialization techniques when accessing shared resources are described as threadsafe."

Programs can be defined as running under the quasi-reentrant TCB (Task Control Blaoc) on the CONCURRENCY attribute of resource definition. Quasi reentrant means “reentrant in practice.” CICS normally provides a separate copy of WORKING STORAGE for each user running a particular program (with the same Procedure Division code). This capability is called multithreading.

In compiling command level CICS, normally the RENT RES and NODYNAM options are used.

Here is another good CICS quiz by CORNID on AOL.

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