When you are planning to write a JES2 exit routine, you need to consider the environment in which the exit routine runs and other general programming considerations (such as, the programming language to use to code your exit routine, linkage conventions that are required, return codes to set, and reentrant code requirements to follow). IBM-defined exits provides the specific programming considerations you need for writing exit routines for the IBM-defined exits. You should use IBM-defined exits with the information in this topic when writing your exit routine. Should you decide to implement your own installation-defined exit in JES2, you need to investigate all the exit-specific programming considerations yourself. See Establishing installation-defined exits for more information.