org.apache.mahout.common.cache.LFUCache.java Source code

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Here is the source code for org.apache.mahout.common.cache.LFUCache.java

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/**
 * 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.apache.mahout.common.cache;

import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

import org.apache.commons.lang.mutable.MutableLong;
import org.apache.mahout.common.Pair;

public class LFUCache<K, V> implements Cache<K, V> {

    private final SortedMap<Long, Set<K>> evictionMap;

    private final Map<K, Pair<V, MutableLong>> dataMap;

    private final int capacity;

    private int evictionCount;

    public LFUCache(int capacity) {
        this.capacity = capacity;

        evictionMap = new TreeMap<Long, Set<K>>();
        dataMap = new HashMap<K, Pair<V, MutableLong>>(capacity);
    }

    @Override
    public long capacity() {
        return capacity;
    }

    public int getEvictionCount() {
        return this.evictionCount;
    }

    @Override
    public V get(K key) {
        Pair<V, MutableLong> data = dataMap.get(key);
        if (data == null) {
            return null;
        } else {
            V value = data.getFirst();
            MutableLong count = data.getSecond();
            long oldCount = count.longValue();
            count.increment();
            incrementHit(key, oldCount);
            return value;
        }

    }

    public V quickGet(K key) {
        Pair<V, MutableLong> data = dataMap.get(key);
        if (data == null) {
            return null;
        } else {
            return data.getFirst();
        }
    }

    private void incrementHit(K key, long count) {
        Set<K> keys = evictionMap.get(count);
        if (keys == null) {
            throw new ConcurrentModificationException();
        }
        if (keys.remove(key) == false) {
            throw new ConcurrentModificationException();
        }
        if (keys.isEmpty()) {
            evictionMap.remove(count);
        }
        count++;
        Set<K> keysNew = evictionMap.get(count);
        if (keysNew == null) {
            keysNew = new LinkedHashSet<K>();
            evictionMap.put(count, keysNew);
        }
        keysNew.add(key);
    }

    @Override
    public void set(K key, V value) {
        if (dataMap.containsKey(key)) {
            return;
        }
        if (capacity == dataMap.size()) // Cache Full
        {
            removeLeastFrequent();
        }
        MutableLong count = new MutableLong(1L);
        Pair<V, MutableLong> data = new Pair<V, MutableLong>(value, count);
        dataMap.put(key, data);

        Long countKey = 1L;
        Set<K> keys = evictionMap.get(countKey);
        if (keys == null) {
            keys = new LinkedHashSet<K>();
            evictionMap.put(countKey, keys);
        }
        keys.add(key);

    }

    private void removeLeastFrequent() {
        Long key = evictionMap.firstKey();
        Set<K> values = evictionMap.get(key);
        Iterator<K> it = values.iterator();
        K keyToBeRemoved = it.next();
        values.remove(keyToBeRemoved);
        if (values.isEmpty()) {
            evictionMap.remove(key);
        }
        dataMap.remove(keyToBeRemoved);
        evictionCount++;

    }

    @Override
    public long size() {
        return dataMap.size();
    }

    @Override
    public boolean contains(K key) {
        return dataMap.containsKey(key);
    }

}