To begin monitoring your event queue, invoke the IXLLIST macro with REQUEST=MONITOR_EVENTQ and ACTION=START. You also specify the index of the list notification vector entry (VECTORINDEX) to be associated with the event queue.

If you want to have your list transition exit receive control when the event queue changes from empty to non-empty, specify DRIVEEXIT=YES, If you omit the DRIVEEXIT parameter or code DRIVEEXIT=NO, you indicate your intention to monitor the event queue's transitions by a different means.

When you start transition monitoring of an event queue, the system initializes the associated vector entry to indicate the current state of the event queue: empty or non-empty.