Control blocks

The control blocks used in task-related user exit control are the exit program control block (DFHEPB), the task interface element (DFHTIEDS).

Figure 78 shows the main control blocks associated with task-related user exits.

Figure 78. Control blocks associated with task-related user exits
 This figure shows the control blocks used in task-related user exit control, as described in the text.

Field CSAUETBA in the CSA points to the user exit table (UET); UETHEPBC in the UET points to the first exit program block (EPB); and EPBCHAIN in each EPB points to the next EPB in the chain.

Each EPB holds:

One EPB is associated with each enabled task-related user exit program or entry name.

EPBs used for global user exits and for task-related user exits are held on the same EPB chain.

The task-related user exit’s global storage is optional. It is associated with an individual enabled task-related user exit program or entry name. Several task-related user exit programs or entry names can share the same global storage.

For full details of the EPB, see the CICS® Data Areas manual.

The task interface element (TIE) is associated with each associated pair of CICS task and task-related user exit. The first time a CICS task passes control to a particular task-related user exit, a TIE is created. The TIE lasts until task termination.

Note that all TIEs relating to a single task are chained together (more than one TIE is set up when a single CICS task makes use of more than one task-related user exit). The TIEs corresponding to a single EPB (that is, to a single task-related user exit program or entry name) are not chained together.

A global user exit may only use global storage; a task-related user exit may use both global storage and task-local work area.

Field TCATIEBA in the TCA points to the first TIE, and TIECHNA in each TIE points to the next TIE in the chain.

The TIE holds information relevant to all invocations of the task-related user exit for the task concerned. For example, TIEFLAGS holds information concerning the events for which the task-related user exit should be invoked, for example, API calls, syncpoint, and task start.

Figure 79 gives a closer look at the TIE control block chain that is used during the lifetime of a task-related user exit.

Figure 79. Control blocks used during the lifetime of a task-related user exit
 This is a technical drawing showing the control blocks used during the lifetime of a task-related user exit, and their relationships to each other.

For full details of the TIE control blocks, see the CICS Data Areas manual.

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