The sublist monitoring function, which is available only with a keyed list structure allocated in a coupling facility of CFLEVEL=3 or higher, allows you to determine whether a sublist in the structure is empty (contains no list entries) or non-empty (contains one or more list entries) without incurring the overhead of accessing the coupling facility. Instead, with the sublist monitoring function, the system queues or withdraws event monitor controls objects on your event queue when a monitored sublist transitions from empty to non-empty or vice versa.