| /** |
| * 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.activemq.util; |
| |
| |
| import java.util.ArrayList; |
| import java.util.concurrent.*; |
| |
| /** |
| * <p> |
| * Used to implement callback based result passing of a promised computation. |
| * Can be converted to a future using the future() method. |
| * </p> |
| * |
| * @author <a href="http://hiramchirino.com">Hiram Chirino</a> |
| */ |
| public class Promise<T> extends PromiseCallback<T> { |
| |
| ArrayList<PromiseCallback<T>> callbacks = new ArrayList<PromiseCallback<T>>(1); |
| T value; |
| Throwable error; |
| Future<T> future=null; |
| |
| private class PromiseFuture extends PromiseCallback<T> implements Future<T> { |
| CountDownLatch latch = new CountDownLatch(1); |
| |
| public boolean cancel(boolean mayInterruptIfRunning) { |
| return false; |
| } |
| |
| public boolean isCancelled() { |
| return false; |
| } |
| |
| public boolean isDone() { |
| return latch.getCount() == 0; |
| } |
| |
| public T get() throws InterruptedException, ExecutionException { |
| latch.await(); |
| return value(); |
| } |
| |
| public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { |
| if (latch.await(timeout, unit)) { |
| return value(); |
| } else { |
| throw new TimeoutException(); |
| } |
| } |
| |
| public void onComplete(T value, Throwable error) { |
| latch.countDown(); |
| } |
| |
| private T value() throws ExecutionException { |
| if( error!=null ) { |
| throw new ExecutionException(error); |
| } |
| return value; |
| } |
| } |
| |
| public Future<T> future() { |
| if( future == null ) { |
| PromiseFuture future = new PromiseFuture(); |
| watch(future); |
| this.future = future; |
| } |
| return future; |
| } |
| |
| public void watch(PromiseCallback<T> callback) { |
| if (callback == null) |
| throw new IllegalArgumentException("callback cannot be null"); |
| boolean queued = false; |
| synchronized (this) { |
| if (callbacks != null) { |
| callbacks.add(callback); |
| queued = true; |
| } |
| } |
| if (!queued) { |
| callback.onComplete(value, error); |
| } |
| } |
| |
| @Override |
| public void onComplete(T value, Throwable error) { |
| if( value!=null && error !=null ) { |
| throw new IllegalArgumentException("You can not have both a vaule and error"); |
| } |
| ArrayList<PromiseCallback<T>> callbacks; |
| synchronized (this) { |
| callbacks = this.callbacks; |
| if (callbacks != null) { |
| this.value = value; |
| this.error = error; |
| this.callbacks = null; |
| } |
| } |
| if (callbacks != null) { |
| for (PromiseCallback callback : callbacks) { |
| callback.onComplete(this.value, this.error); |
| } |
| } |
| } |
| |
| } |