Program Control

What program control means in CICS

• Program control is how CICS programs invoke other programs and return control.
• The main program control commands are LINK, XCTL and RETURN.
• LOAD and RELEASE manage programs in storage. DELETE PROGRAM removes a program definition.
• Every program invoked by LINK or XCTL must be defined to CICS.
• Program control is cheaper than a COBOL CALL when you need CICS services, because CICS manages the invocation.

Logical levels in program control are shown below:-

Logical levels

• Each LINK creates a new logical level below the current program.
• XCTL keeps control at the same logical level. It replaces the current program.
• A plain RETURN moves control up one logical level.
• RETURN TRANSID ends the task but schedules the next execution of a pseudo-conversational program.
• Deep LINK nesting uses more storage. Prefer XCTL chains when control never needs to come back.

LOAD and RELEASE

• LOAD brings a program into storage so you can access its address.
• RELEASE drops a program that was loaded with LOAD.
• Most programs do not need LOAD. CICS loads programs automatically on LINK and XCTL.
• Example:-
  EXEC CICS LOAD PROGRAM('CUSTPGM') END-EXEC. . . * use the program . EXEC CICS RELEASE PROGRAM('CUSTPGM') END-EXEC.