When user labels are to be processed as data set descriptors, one of your label processing routines receives control for each user label of the specified type. Your routine can include, exclude, or modify the user label. Processing of user labels as data set descriptors is indicated on an EXITS statement with keyword parameters that name the label processing routine to be used.

The user exit routine receives control each time the OPEN, EOV, or CLOSE routine encounters a user label of the type specified.

Figure 1 illustrates the action of the system at OPEN, EOV, or CLOSE time. When OPEN, EOV, or CLOSE recognizes a user label and when SUL has been specified on the DD statement for the data set, control is passed to the utility program. Then, if an exit has been specified for this type of label, the utility program passes control to the user routine. Your routine processes the label and returns control, along with a return code, to the utility program. The utility program then returns control to OPEN, EOV, or CLOSE.

This cycle is repeated up to eight times, depending upon the number of user labels in the group and the return codes supplied by your routine.

Figure 1. System Action at OPEN, EOV, or CLOSE Time