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/*
 * Copyright 2008 Kasper Nielsen.
 * 
 * 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://cake.codehaus.org/LICENSE
 * 
 * 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.cake.cache.policy.paging;

import static org.codehaus.cake.cache.CacheEntry.HITS;

import org.codehaus.cake.cache.CacheEntry;
import org.codehaus.cake.cache.policy.spi.AbstractHeapReplacementPolicy;

/**
 * 
 * However, the LFU policy has a number of drawbacks: it requires logarithmic implementation complexity in cache size,
 * pays little attention to recent history, and does not adapt well to changing access patterns since it accumulates
 * stale pages with high frequency counts that may no longer be useful.
 * 
 * @param 
 *            the type of keys maintained by the cache
 * @param 
 *            the type of values maintained by the cache
 */
public class LFUReplacementPolicy extends AbstractHeapReplacementPolicy {
    /** A unique policy name. */
    public static final String NAME = "LFU";

    public LFUReplacementPolicy() {
        // This is used to make sure that the cache will lazy register the HITS attribute
        // if the user has not already done so using CacheAttributeConfiguration#add(Attribute...)}
        dependSoft(HITS);
    }

    @Override
    protected int compareEntry(CacheEntry o1, CacheEntry o2) {
        return HITS.compare(o1, o2);
    }

    @Override
    public void touch(CacheEntry entry) {
        siftDown(entry);// hits has been incremented
    }
}