117 lines
2.3 KiB
Java
117 lines
2.3 KiB
Java
/*
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This file is part of Subsonic.
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Subsonic is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Subsonic is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Subsonic. If not, see <http://www.gnu.org/licenses/>.
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Copyright 2009 (C) Sindre Mehus
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*/
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package org.moire.ultrasonic.util;
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import java.lang.ref.SoftReference;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* @author Sindre Mehus
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*/
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public class LRUCache<K, V>
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{
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private final int capacity;
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private final Map<K, TimestampedValue> map;
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public LRUCache(int capacity)
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{
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map = new HashMap<K, TimestampedValue>(capacity);
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this.capacity = capacity;
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}
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public synchronized V get(K key)
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{
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TimestampedValue value = map.get(key);
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V result = null;
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if (value != null)
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{
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value.updateTimestamp();
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result = value.getValue();
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}
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return result;
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}
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public synchronized void put(K key, V value)
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{
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if (map.size() >= capacity)
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{
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removeOldest();
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}
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map.put(key, new TimestampedValue(value));
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}
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public void clear()
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{
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map.clear();
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}
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private void removeOldest()
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{
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K oldestKey = null;
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long oldestTimestamp = Long.MAX_VALUE;
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for (Map.Entry<K, TimestampedValue> entry : map.entrySet())
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{
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K key = entry.getKey();
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TimestampedValue value = entry.getValue();
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if (value.getTimestamp() < oldestTimestamp)
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{
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oldestTimestamp = value.getTimestamp();
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oldestKey = key;
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}
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}
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if (oldestKey != null)
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{
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map.remove(oldestKey);
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}
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}
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private final class TimestampedValue
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{
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private final SoftReference<V> value;
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private long timestamp;
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public TimestampedValue(V value)
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{
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this.value = new SoftReference<V>(value);
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updateTimestamp();
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}
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public V getValue()
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{
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return value.get();
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}
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public long getTimestamp()
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{
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return timestamp;
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}
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public void updateTimestamp()
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{
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timestamp = System.currentTimeMillis();
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}
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}
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} |