/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* Licensed 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 eu.stratosphere.pact.runtime.iterative.concurrent;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* A concurrent data structure that allows the hand-over of an object between a pair of threads
*/
public class Broker<V> {
private final ConcurrentMap<String, BlockingQueue<V>> mediations = new ConcurrentHashMap<String, BlockingQueue<V>>();
/**
* hand in the object to share
*/
public void handIn(String key, V obj) {
if (!retrieveSharedQueue(key).offer(obj)) {
throw new RuntimeException("Could not register the given element, broker slot is already occupied.");
}
}
/** blocking retrieval and removal of the object to share */
public V getAndRemove(String key) {
try {
V objToShare = retrieveSharedQueue(key).take();
mediations.remove(key);
return objToShare;
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
/** blocking retrieval and removal of the object to share */
public void remove(String key) {
mediations.remove(key);
}
/** blocking retrieval and removal of the object to share */
public V get(String key) {
try {
BlockingQueue<V> queue = retrieveSharedQueue(key);
V objToShare = queue.take();
if (!queue.offer(objToShare)) {
throw new RuntimeException("Error: Concurrent modification of the broker slot for key '" + key + "'.");
}
return objToShare;
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
/**
* thread-safe call to get a shared {@link BlockingQueue}
*/
private BlockingQueue<V> retrieveSharedQueue(String key) {
BlockingQueue<V> queue = mediations.get(key);
if (queue == null) {
queue = new ArrayBlockingQueue<V>(1);
BlockingQueue<V> commonQueue = mediations.putIfAbsent(key, queue);
return commonQueue != null ? commonQueue : queue;
} else {
return queue;
}
}
}