Exit points and routines

You can modify how IMS processes a unit of work by providing IMS with subroutines (called exit routines) that perform special processing. IMS calls exit routines at various points in its logic flow (called exit points) and allows you to control how IMS performs its work.

One example of modifying how IMS processes a unit of work might be to interrogate an in-flight message (in an MSC environment) to determine if it originated from a test or production system. If it came from a test system, you might want to route that message to an application that collects data about the test system. If the message originated from a production system, you probably would not want to change its destination.

To perform the interrogation of the message, you would code a TM and MSC Message Routing and Control User Exit routine. If you name this routine DFSMSCE0, place it in the IMS.SDFSRESL library, and bind it to that library (or a concatenated library), IMS calls your exit routine when IMS receives the message. When your exit routine is done with its processing, the exit routine returns control to IMS and then IMS resumes processing the message to either the original destination or the test application.

Certain exit routines are required and others are optional. Some IBM-supplied exit routines can be used as is and some require modification before using.

Related reading: For complete information about exit points and exit routines, see IMS Version 15.4 Exit Routines.