Use CICS Threadsafe Applications

Configuration Best Practices › Tuning for Improved Performance and Lower TCO › Use CICS Threadsafe Applications

Define eligible CICS threadsafe application programs that use the CA IDMS interface as CONCURRENCY (THREADSAFE), API (OPENAPI), or both in the CICS TS System Definition (CSD) file.

Business Value:

Using CICS threadsafe applications can significantly increase throughput of tasks in the CICS region, improve response time and decrease costs. The CICS TS Open Transaction Environment (OTE) enables multiple tasks to execute the same THREADSAFE program simultaneously operating on different TCBs.

Additional Considerations:

CICS programs that are truly threadsafe should be declared with the CONCURRENCY attribute of THREADSAFE.

Note: A program may be threadsafe even though it contains a non-threadsafe EXEC CICS command.

A program that meets the following criteria should also be declared with the API attribute of OPENAPI:

The program is threadsafe.
The program contains no non-threadsafe commands or minimal non-threadsafe EXEC CICS commands (for example, a single EXEC CICS SEND command that is executed as the last command before the program terminates).

Programs defined with the OPENAPI attribute will be dispatched on an OPEN TCB and returned to an OPEN TCB after temporary assignment to the Quasi-reentrant (QR) TCB during the execution of a non-threadsafe command.

Carefully evaluate each program before declaring it with program attributes of THREADSAFE or OPENAPI. If a non-threadsafe program is defined as THREADSAFE, unpredictable results may occur, including task or system abends and data corruption. If a program containing many non-threadsafe EXEC CICS commands is declared as OPENAPI, performance may suffer due to excessive swaps between the OPEN TCB and the QR TCB.

More Information:

For general information on CICS TS threadsafe programming, consult the appropriate IBM documentation.

For more information on implementing CICS threadsafe programming with the CA IDMS interface, see the CA IDMS System Operations Guide.