001/*
002 * BridJ - Dynamic and blazing-fast native interop for Java.
003 * http://bridj.googlecode.com/
004 *
005 * Copyright (c) 2010-2013, Olivier Chafik (http://ochafik.com/)
006 * All rights reserved.
007 *
008 * Redistribution and use in source and binary forms, with or without
009 * modification, are permitted provided that the following conditions are met:
010 * 
011 *     * Redistributions of source code must retain the above copyright
012 *       notice, this list of conditions and the following disclaimer.
013 *     * Redistributions in binary form must reproduce the above copyright
014 *       notice, this list of conditions and the following disclaimer in the
015 *       documentation and/or other materials provided with the distribution.
016 *     * Neither the name of Olivier Chafik nor the
017 *       names of its contributors may be used to endorse or promote products
018 *       derived from this software without specific prior written permission.
019 * 
020 * THIS SOFTWARE IS PROVIDED BY OLIVIER CHAFIK AND CONTRIBUTORS ``AS IS'' AND ANY
021 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
022 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
023 * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
024 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
025 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
026 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
027 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
028 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
029 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
030 */
031package org.bridj.util;
032
033import java.lang.reflect.Constructor;
034import java.util.HashMap;
035import java.util.Map;
036import java.util.Map.Entry;
037import java.util.concurrent.ConcurrentHashMap;
038
039/**
040 * Cache that creates its missing values automatically, using the value class'
041 * default constructor (override {@link ConcurrentCache#newInstance(Object)} to
042 * call another constructor)
043 */
044public class ConcurrentCache<K, V> {
045
046    protected final ConcurrentHashMap<K, V> map = new ConcurrentHashMap<K, V>();
047    protected final Class<V> valueClass;
048
049    public ConcurrentCache(Class<V> valueClass) {
050        this.valueClass = valueClass;
051    }
052    private volatile Constructor<V> valueConstructor;
053
054    private Constructor<V> getValueConstructor() {
055        if (valueConstructor == null) {
056            try {
057                valueConstructor = valueClass.getConstructor();
058                if (valueConstructor != null && valueConstructor.isAccessible()) {
059                    valueConstructor.setAccessible(true);
060                }
061            } catch (Exception ex) {
062                throw new RuntimeException("No accessible default constructor in class " + (valueClass == null ? "null" : valueClass.getName()), ex);
063            }
064        }
065        return valueConstructor;
066    }
067
068    protected V newInstance(K key) {
069        try {
070            return getValueConstructor().newInstance();
071        } catch (Exception ex) {
072            throw new RuntimeException("Failed to call constructor " + valueConstructor, ex);
073        }
074    }
075
076    public V get(K key) {
077        V v = map.get(key);
078        if (v == null) {
079            V newV = newInstance(key);
080            V oldV = map.putIfAbsent(key, newV);
081            if (oldV != null) {
082                v = oldV;
083            } else {
084                v = newV;
085            }
086        }
087        return v;
088    }
089
090    public void clear() {
091        map.clear();
092    }
093
094    public Iterable<Entry<K, V>> entrySet() {
095        return map.entrySet();
096    }
097}