About this chapter

This chapter discusses the use of exit routines for LU 6.2 application programs. The complete description of the attention (ATTN) exit routine is found here, as are LU 6.2 considerations for exits that are not specific to LU 6.2.

The complete description of the exits not specific to LU 6.2, and the use of RPL exits, is found in z/OS Communications Server: SNA Programming. A description of how exit routines work under authorized path and a description of the differences between an exit routine running under a task control block (TCB) and a service request block (SRB) can also be found in z/OS Communications Server: SNA Programming.

LU 6.2 application programs use exit routines the same way that other application programs use them. The application program can supply VTAM® with a list of special-purpose exit routines (EXLST exit routines) that are scheduled by the VTAM program to handle external events, such as the receipt of a session-initiation request. In addition, application programs can supply the address of an exit routine in the RPL, which VTAM schedules when the requested RPL operation completes. In all of these cases, VTAM interrupts the mainline program to allow the exit routine to execute.

As part of its LU 6.2 support, VTAM handles many external events that EXLST routines handle for other LU types or for application-implemented LU 6.2s. Consequently, not all EXLST exit routines are meaningful for VTAM LU 6.2 support. In addition, the scope of other EXLST exit routines is much more narrow. As far as LU 6.2 support is concerned, for example, VTAM schedules the SCIP exit routine on receipt only of a BIND request. All other session control requests for supported LU 6.2 sessions are handled by VTAM. The EXLST exit routines that VTAM schedules for its LU 6.2 application programs are:

ATTN
LERAD
LOGON
LOSTERM
RELREQ
SCIP
SYNAD
TPEND

The use of all these routines is optional. However, use of the ATTN, LERAD, SYNAD, and TPEND exit routines is strongly recommended. The other exit routines need to be used for LU 6.2 application programs only if the application program requires the function provided by the exit routines. Only the ATTN exit routine is unique to LU 6.2 application programs. Only the effect of exit routines on LU 6.2 application programs is discussed here. Requirements for the ATTN exit are the same as for any other EXLST exit in regards to authorized path and processing under a TCB or SRB.