Creating an Exit List

To access exit routines during data set processing, you must specify the addresses of your exit routines using the EXLST macro. Any number of ACB macros in a program can indicate the same exit list for the same exit routines to do all the special processing for them, or they can indicate different exit lists. Use exit routines for the following tasks:

Analyzing physical errors. When VSAM finds an error in an I/O operation that the operating system's error routine cannot correct, the error routine formats a message for your physical error analysis routine (the SYNAD user exit) to act on.
Analyzing logical errors. Errors not directly associated with an I/O operation, such as an nonvalid request, cause VSAM to exit to your logical error analysis routine (the LERAD user exit).
End-of-data-set processing. When your program requests a record beyond the last record in the data set, your end-of-data-set routine (the EODAD user exit) is given control. The end of the data set is beyond either the highest addressed or the highest keyed record, if your program is using addressed or keyed access.
Journalizing transactions. To journalize the transactions against a data set, you might specify a journal routine (the JRNAD user exit). To process a key-sequenced data set using addressed access, you need to know if any RBAs changed during keyed processing. When you are processing by key, VSAM exits to your routine for noting RBA changes before writing a control interval in which there is an RBA change. When journalizing transactions for compressed data sets, the RBAs and data lengths represent compressed data. VSAM does not exit to the JRNAD routine for RBA change if the data set is extended addressable.
User processing. User processing exits (UPAD) are available to assist subsystems that need to dispatch new units of work. The UPAD wait exit is given control before VSAM issues any WAIT SVCs. Use the UPAD post exit to make it easier to use cross-memory processing. See Table 1.

The EXLST macro is coordinated with the EXLST parameter of an ACB or GENCB macro used to generate an ACB. To use the exit list, you must code the EXLST parameter in the ACB.

You can use the EXLST macro to build an exit list when the program is assembled, or the GENCB macro to build an exit list when the program is run. For information about the advantages and disadvantages of using GENCB see Manipulating the Contents of Control Blocks.