org.apache.activemq.util.Promise 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.activemq.util;
import java.util.ArrayList;
import java.util.concurrent.*;
/**
*
* Used to implement callback based result passing of a promised computation.
* Can be converted to a future using the future() method.
*
*
* @author Hiram Chirino
*/
public class Promise extends PromiseCallback {
ArrayList> callbacks = new ArrayList>(1);
T value;
Throwable error;
Future future=null;
private class PromiseFuture extends PromiseCallback implements Future {
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 future() {
if( future == null ) {
PromiseFuture future = new PromiseFuture();
watch(future);
this.future = future;
}
return future;
}
public void watch(PromiseCallback 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> 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);
}
}
}
}