| /* |
| * 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.openejb.util; |
| |
| import java.util.concurrent.Callable; |
| import java.util.concurrent.ConcurrentHashMap; |
| import java.util.concurrent.ConcurrentMap; |
| import java.util.concurrent.ExecutionException; |
| import java.util.concurrent.Future; |
| import java.util.concurrent.FutureTask; |
| |
| public class Memoizer<K, V> implements Computable<K, V> { |
| private final ConcurrentMap<K, Future<V>> cache = new ConcurrentHashMap<K, Future<V>>(); |
| |
| private final Computable<K, V> c; |
| |
| /** |
| * Constructs a new <code>Memoizer</code> with the specified cache source. |
| * |
| * @param c is the cache value source algorithm |
| * @throws NullPointerException |
| * if c is null |
| */ |
| public Memoizer(Computable<K, V> c) { |
| if(c == null) throw new NullPointerException("Computable cache value source algorithm may not be null"); |
| this.c = c; |
| } |
| |
| public V compute(final K key) throws InterruptedException { |
| while (true) { |
| Future<V> future = cache.get(key); |
| if (future == null) { |
| |
| Callable<V> eval = new Callable<V>() { |
| public V call() throws Exception { |
| return c.compute(key); |
| } |
| }; |
| FutureTask<V> futureTask = new FutureTask<V>(eval); |
| future = cache.putIfAbsent(key, futureTask); |
| if (future == null) { |
| future = futureTask; |
| futureTask.run(); |
| } |
| } |
| try { |
| return future.get(); |
| } catch (ExecutionException e) { |
| e.printStackTrace(); |
| } |
| } |
| } |
| } |