All About Exit Routines

The following section contain introductory information about installation exit routines. To start, it is helpful to review the following terminology.

  • Installation Exit Point. An installation exit point is a specific point in component processing at which control passes to an installation exit routine. The macro that calls the user routine uses parameter values from keywords supplied at the initialization of the component. In most cases, the initialization statement defaults are set to cause the exit point to be ignored. However, you can modify macro processing by specifying parameters supplied with operator commands.
  • Replaceable Module. A replaceable module is a load module that the user installation can update, alter, or completely replace. Some replaceable modules are IBM-supplied code that performs a specific function, while others simply branch directly back to the calling program without any additional processing. When you write your exit routine, you replace the IBM-supplied routine with your own. Both the name of the routine and its library location are predefined.
  • Installation Exit Name List. An installation exit name list is similar to an installation exit point. However, rather than directly calling the installation exit routine, the macro addresses a CSECT that contains a list of installation exit routine names. The installation exit routines are then invoked sequentially as they appear in the name list. This processing ends in one of two ways:
    • One of the installation exit routines issues a terminating return code.
    • The end of the name list is reached.

    Your installation provides the routine names by updating, reassembling, and again linkediting the name list CSECT. (It is possible to update the CSECT temporarily using SPZAP. See z/OS MVS Diagnosis: Tools and Service Aids for more information on SPZAP.)

    If you provide no exit routines, the name list contains blank entries.

    In both the installation exit point and installation exit name list methods, the installation defines the installation exit routine names.

  • Dynamic Exit. A user-written or system exit that has been defined to the dynamic exits facility. See Dynamic Exits Facility for more information.