org.apache.openejb.util.Memoizer Maven / Gradle / Ivy
/*
* 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 implements Computable {
private final ConcurrentMap> cache = new ConcurrentHashMap>();
private final Computable c;
/**
* Constructs a new Memoizer with the specified cache source.
*
* @param c is the cache value source algorithm
* @throws NullPointerException
* if c is null
*/
public Memoizer(Computable 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 future = cache.get(key);
if (future == null) {
Callable eval = new Callable() {
public V call() throws Exception {
return c.compute(key);
}
};
FutureTask futureTask = new FutureTask(eval);
future = cache.putIfAbsent(key, futureTask);
if (future == null) {
future = futureTask;
futureTask.run();
}
}
try {
return future.get();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}
}