org.codehaus.groovy.runtime.memoize.LRUProtectionStorage Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.codehaus.groovy.runtime.memoize;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* Protects stored resources from eviction from memory following the LRU (Last Recently Used) strategy.
* If the maximum size has been reached all newly added elements will cause the oldest element to be removed from the storage
* in order not to exceed the maximum capacity.
* The touch method can be used to renew an element and move it to the from the LRU queue.
*
* @author Vaclav Pech
*/
final class LRUProtectionStorage extends LinkedHashMap implements ProtectionStorage {
private static final long serialVersionUID = 1L;
private final int maxSize;
public LRUProtectionStorage(final int maxSize) {
this.maxSize = maxSize;
}
/**
* The eldest entry should be removed when we reached the maximum cache size
*/
@Override
protected boolean removeEldestEntry(final Map.Entry eldest) {
return size() > maxSize;
}
/**
* The touch method can be used to renew an element and move it to the from of the LRU queue.
*
* @param key The key of the element to renew
* @param value A value to newly associate with the key
*/
public synchronized void touch(final Object key, final Object value) {
remove(key);
put(key, value);
}
/**
* Makes sure the retrieved object is moved to the head of the LRU list
*/
@Override
public synchronized Object get(final Object key) {
final Object value = remove(key);
if (value != null) put(key, value);
return value;
}
/**
* Performs a shallow clone
*
* @return The cloned instance
*/
@Override
public Object clone() {
return super.clone();
}
}