EDIT

package eu.etaxonomy.cdm.persistence.validation;

import java.util.Collection;

import java.util.Iterator;

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.TimeUnit;

/**

 * A job queue catering to the needs of the entity validation process. If an entity validation

 * task is submitted to the queue, and the queue already contains tasks validating the exact

 * same entity, those tasks should be removed first, because they are validating a state of the

 * entity that is no longer actual. Note that it is not fatal to validate the entity in those

 * intermediary states, because in the end the final state of the entity does get validated as

 * well. It's just useless and may lead to unnecessary contention of the queue.

 * 

 * @author ayco holleman

 * 

 */

@SuppressWarnings("serial")

class EntityValidationTaskQueue extends ArrayBlockingQueue<Runnable> {

	public EntityValidationTaskQueue(int capacity)

	{

		super(capacity);

	}

	@Override

	public boolean add(Runnable r)

	{

		checkQueue(r);

		return super.add(r);

	}

	@Override

	public boolean offer(Runnable r, long timeout, TimeUnit unit) throws InterruptedException

	{

		checkQueue(r);

		return super.offer(r, timeout, unit);

	}

	@Override

	public boolean offer(Runnable r)

	{

		checkQueue(r);

		return super.offer(r);

	}

	@Override

	public void put(Runnable r) throws InterruptedException

	{

		checkQueue(r);

		super.put(r);

	}

	@Override

	public boolean addAll(Collection<? extends Runnable> c)

	{

		throw new RuntimeException("Submitting multiple validation tasks at once not supported");

	}

	private void checkQueue(Runnable runnable)

	{

		EntityValidationTask newTask = (EntityValidationTask) runnable;

		Iterator<Runnable> iterator = this.iterator();

		while (iterator.hasNext()) {

			EntityValidationTask oldTask = (EntityValidationTask) iterator.next();

			if (oldTask.getEntity().equals(newTask.getEntity())) {

				iterator.remove();

			}

		}

	}

}