Review Function Routines/Function Codes, which describes both the general environment on entry to your function routine and other programming considerations that your function routine should take into account.

If you decide to set up your subsystem to handle Early Notification of End-of-Task calls, make sure that your function routine is in place before you enable the subsystem for SSI function code 50. IBM® recommends that you use the IEFSSVT macro to notify MVS™ that your subsystem should be given control whenever Early Notification of End-of-Task calls are made. IEFSSVT macro services are available only to dynamic subsystems. Subsystems that are not dynamic can still use the IEFJSVEC service; see Building the SSVT and Enabling Your Subsystem for New Functions for more information.

The subsystem function routine runs in the address space of the ending task. Because each subsystem function routine is called for every ending task, the subsystem function routine should not be a long running program. That is, the function routine should quickly determine if the subsystem was ever associated with the ending task and, if not, return to the system. Also, do not code a function routine that enters an explicit WAIT or uses a system service that enters a WAIT. Entering a WAIT can cause degraded system performance.

The function routine receives control in the following environment:

Figure 1 shows the environment on entry to the function routine for SSI function code 50.

Figure 1. Environment on Entry to the Function Routine for SSI Function Code 50