The performance monitor exit routine (ISTEXCPM) is available as part of the performance monitor interface for the purposes of retrieving statistical data from VTAM®. Only a performance monitor application program (or monitor) using the performance monitor interface should implement this exit routine. For a description of the performance monitor interface, see z/OS Communications Server: SNA Programming.

The primary function of the exit routine is to pass collection data from VTAM to the monitor. The exit routine can be invoked for one of the following conditions:

• A monitor requests the data from VTAM.
• An event occurs within VTAM that warrants sending unrequested data to each monitor.
• SMF collections are in progress and the SMF interval expires.
• An error occurs within VTAM trying to initiate data collection processing for an SMF interval that expired. In this case, no data is actually passed; the invocation is for notification purposes only.

You can use the DISPLAY EXIT command to display information regarding the performance monitor exit routine. Only performance monitors can use a MODIFY EXIT command to activate, deactivate, or replace performance monitor exits without interrupting VTAM processing. See Operator commands for VTAM exit routines for more information about using the MODIFY EXIT command to modify VTAM exit routines. See z/OS Communications Server: SNA Operation for more information about coding the MODIFY EXIT and the DISPLAY EXIT commands.

When the performance monitor exit routine needs to be called, VTAM builds the performance monitor exit parameter list and drives the exit routine. The parameter list is discussed in Performance monitor exit routine parameter list.

The topics that follow contain information needed to write a performance monitor exit.