com.ibm.websphere.objectgrid.plugins
Interface EvictorData

All Known Implementing Classes:

EvictorData.SpecialEvictorData

public interface EvictorData

This interface is optionally used by an implementator of the Evictor interface. Application changes applied to a BackingMap are asynchronous from the Evictor activity. The Evictor is not notified of changes to the BackingMap until after application transactions are committed. Consequently, if an Evictor decides to evict a map entry, it is possible that the BackingMap could evict an entry that was different from the original entry it was tracking. For example, consider that an application could execute a transaction that removes a map entry. Before the Evictor is notified of the remove, another transaction inserts a new entry into the BackingMap for the same key as the old entry. Consequently, the Evictor could evict the newly created entry when it meant to evict the old entry. To help close this small timing window, the Evictor can use this interface to associate evictor specific data with a map entry. The Evictor can then do the following:

• store the EvictorData object for a map entry by using the EvictionEventCallback.setEvictorData(Object, EvictorData) method.
• retrieve the EvictorData object for a map entry by using the EvictionEventCallback.getEvictorData(Object) method.
• Conditionally evict a map entry if and only if the cache entry for a specified key has the exact same EvictorData object (the java == operator returns true) associated with it by using the EvictionEventCallback.evictMapEntries(List) method.

Since:

WAS XD 6.0.1, XC10

See Also:

Evictor, EvictionEventCallback

Nested Class Summary

static class

EvictorData.SpecialEvictorData Special value class used for representing the key not being found in the BackingMap.

Field Summary

static EvictorData

KEY_NOT_FOUND A special value indicating that the key was not found.

Method Summary

Object

getKey() Retrieves the key object for this EvictorData instance.

Field Detail

KEY_NOT_FOUND

static final EvictorData KEY_NOT_FOUND

A special value indicating that the key was not found.

Method Detail

getKey

Object getKey()

Retrieves the key object for this EvictorData instance.

Returns:

the same key object that was passed to the EvictionEventCallback.setEvictorData(Object, EvictorData) method when this EvictorData was associated with the map entry with the given key.

See Also:

EvictionEventCallback.setEvictorData(Object, EvictorData)