CICS® provides three facilities that help to prevent storage violations.
- CICS subsystem storage protection
- prevents user application programs from directly overwriting CICS code
and control blocks.
- Transaction isolation
- prevents a user transaction from directly overwriting user application
storage of other transactions.
- Command protection
- prevents CICS, when processing an EXEC CICS command, from overwriting
storage that the issuing transaction could not itself directly overwrite.
Even if your system uses all the CICS storage
protection facilities, CICS storage violations can occur in certain circumstances
in systems using storage protection. For example:
- An application program could contain the necessary instructions to switch
to CICS key and modify CICS storage.
- An application program could contain the necessary instructions to switch
to the basespace and modify other transactions’ storage.
- An application program could be defined with EXECKEY(CICS) and could thus
modify CICS storage and other transactions’ storage.
- An application could overwrite one or more storage check zones in its
own task-lifetime storage.
To gain the full benefit of CICS storage protection, you need to examine
the storage needs of individual application programs and control the storage
key definitions that are used.
When CICS detects and prevents an attempted storage violation, the name
of the abending program and the address of the area it tried to overwrite
are passed to the program error program (DFHPEP). For programming information
about DFHPEP, see the CICS Customization Guide.
If a storage violation occurs in your system, please read the rest of this
section.
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