ObjectPipeDecoupler.java

/*
 * Copyright 2013, 2014 Deutsche Nationalbibliothek
 *
 * 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 org.culturegraph.mf.flowcontrol;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

import org.culturegraph.mf.framework.FluxCommand;
import org.culturegraph.mf.framework.ObjectPipe;
import org.culturegraph.mf.framework.ObjectReceiver;
import org.culturegraph.mf.framework.annotations.Description;
import org.culturegraph.mf.framework.annotations.In;
import org.culturegraph.mf.framework.annotations.Out;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * creates a new thread in which subsequent flow elements run.
 *
 * @param <T>
 *            Object type
 *
 * @author Markus Micheal Geipel
 */
@In(Object.class)
@Out(Object.class)
@Description("creates a new thread in which subsequent flow elements run.")
@FluxCommand("decouple")
public final class ObjectPipeDecoupler<T> implements ObjectPipe<T, ObjectReceiver<T>> {

	public static final int DEFAULT_CAPACITY = 10000;
	private static final Logger LOG = LoggerFactory.getLogger(ObjectPipeDecoupler.class);

	private final BlockingQueue<Object> queue;
	private Thread thread;
	private ObjectReceiver<T> receiver;
	private boolean debug;

	public ObjectPipeDecoupler() {
		queue = new LinkedBlockingQueue<Object>(DEFAULT_CAPACITY);
	}

	public ObjectPipeDecoupler(final int capacity) {
		queue = new LinkedBlockingQueue<Object>(capacity);
	}

	public ObjectPipeDecoupler(final String capacity) {
		queue = new LinkedBlockingQueue<Object>(Integer.parseInt(capacity));
	}

	public void setDebug(final boolean debug) {
		this.debug = debug;
	}

	@Override
	public void process(final T obj) {

		if (null == thread) {
			start();
		}
		try {
			queue.put(obj);
			if (debug) {
				LOG.info("Current buffer size: " + queue.size());
			}
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt();
		}
	}

	private void start() {
		thread = new Thread(new Feeder<T>(receiver, queue));
		thread.start();
	}

	@Override
	public <R extends ObjectReceiver<T>> R setReceiver(final R receiver) {
		if (null != thread) {
			throw new IllegalStateException("Receiver cannot be changed while processing thread is running.");
		}

		this.receiver = receiver;
		return receiver;
	}

	@Override
	public void resetStream() {
		queue.add(Feeder.BLUE_PILL);
	}

	@Override
	public void closeStream() {
		queue.add(Feeder.RED_PILL);
		try {
			thread.join();
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt();
		}
		thread = null;
	}

	/**
	 * Pushes the content in the {@link BlockingQueue} to the receiver.
	 * @param <T>
	 */
	static final class Feeder<T> implements Runnable {
		public static final Object RED_PILL = new Object();
		public static final Object BLUE_PILL = new Object();

		private final ObjectReceiver<T> receiver;
		private final BlockingQueue<Object> queue;

		public Feeder(final ObjectReceiver<T> receiver, final BlockingQueue<Object> queue) {
			this.receiver = receiver;
			this.queue = queue;
		}

		@SuppressWarnings("unchecked")
		// OK because queue is only filled with T by Decoupler<T>
		@Override
		public void run() {
			try {
				while (true) {
					final Object object = queue.take();
					if (RED_PILL == object) {
						receiver.closeStream();
						break;
					}
					if (BLUE_PILL == object) {
						receiver.resetStream();
						continue;
					}
					receiver.process((T) object);
				}
			} catch (InterruptedException e) {
				Thread.currentThread().interrupt();
			}
		}
	}
}