net.sf.ehcache.store.Policy Maven / Gradle / Ivy
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/**
* Copyright Terracotta, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.sf.ehcache.store;
import net.sf.ehcache.Element;
/**
* An eviction policy.
*
* The Cache will use a policy at startup. There are three policy implementations provided in ehcache:
* LRU, LFU and FIFO. However many other policies are possible. That the policy
* has access to the whole element enables policies based on the key, value, metadata, statistics, or a combination of
* any of the above.
*
* @author Greg Luck
*/
public interface Policy {
/**
* @return the name of the Policy. Inbuilt examples are LRU, LFU and FIFO.
*/
String getName();
/**
* Finds the best eviction candidate based on the sampled elements. What distinguishes
* this approach from the classic data structures approach is that an Element contains
* metadata (e.g. usage statistics) which can be used for making policy decisions,
* while generic data structures do not. It is expected that implementations will take
* advantage of that metadata.
*
* @param sampledElements this should be a random subset of the population
* @param justAdded we probably never want to select the element just added.
* It is provided so that it can be ignored if selected. May be null.
* @return the selected Element
*/
Element selectedBasedOnPolicy(Element[] sampledElements, Element justAdded);
/**
* Compares the desirableness for eviction of two elements
*
* @param element1 the element to compare against
* @param element2 the element to compare
* @return true if the second element is preferable for eviction to the first element
* under ths policy
*/
boolean compare(Element element1, Element element2);
}