VTAM® can schedule a LOSTERM exit routine when a session with an application program is terminated or potentially disrupted, or when a conditional terminate request for a session is received. Alternatively, for some of these conditions, an SCIP exit routine is scheduled with UNBIND, or an NSEXIT exit routine is scheduled with CLEANUP. See Session outage notification for details. The application program might issue CLSDST to end the session. (If the application program fails to issue CLSDST, the LU with which the application program is, or was, in session might be unavailable for a session with any other application program. This occurs if the LU is at its session limit as a result of this session.)

If a session outage occurs, VTAM posts any outstanding requests associated with the affected session with an appropriate return code. If there are no outstanding requests, whenever the program makes the next request, it is posted with an appropriate return code.

A LOSTERM exit routine is especially recommended for an application program that does not issue specific-mode communication requests for its sessions, but is driven instead by input arriving as the result of RECEIVE macroinstructions issued in any-mode. Use of the exit routine is also recommended for an application program when there is the possibility that the LU can fill VTAM's buffers (obtained from application program storage) faster than the application program is emptying them with RECEIVE macroinstructions.

An example of a coded LOSTERM exit routine is shown in Sample code of a simple application program.