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A super fast inter-thread transfer queue.
There is a newer version: 1.3.1
/*
 * MentaQueue => http://mentaqueue.soliveirajr.com
 * Copyright (C) 2012  Sergio Oliveira Jr. ([email protected])
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.mentaqueue;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

import org.mentaqueue.util.Builder;

public class BlockingLinkedQueue implements Queue {

	private final static int DEFAULT_CAPACITY = 1026 * 16;

	private final java.util.concurrent.ConcurrentLinkedQueue pool;
	private final List polledElements;
	private final LinkedList queue;
	private final Object lock = new Object();
	private final int capacity;

	public BlockingLinkedQueue(int capacity, Builder builder) {
		pool = new java.util.concurrent.ConcurrentLinkedQueue();
		polledElements = new LinkedList();
		queue = new LinkedList();
		this.capacity = capacity;
		for (int i = 0; i < capacity; i++) {
			pool.offer(builder.newInstance());
		}
	}

	public BlockingLinkedQueue(Builder builder) {
		this(DEFAULT_CAPACITY, builder);
	}
	
	private final static  Builder createBuilder(final Class klass) {
		return new Builder() {
			@Override
            public E newInstance() {
	            try {
	            	return klass.newInstance();
	            } catch(Exception e) {
	            	throw new RuntimeException(e);
	            }
            }
		};
	}
	
	public BlockingLinkedQueue(Class klass) {
		this(createBuilder(klass));
	}
	
	public BlockingLinkedQueue(int capacity, Class klass) {
		this(capacity, createBuilder(klass));
	}


	@Override
	public E nextToOffer() {
		return pool.poll();
	}

	@Override
	public void offer(E e) {
		synchronized(lock) {
			int size = queue.size();
			if (size == capacity) {
				try {
					lock.wait();
				} catch(Exception exc) {
					return;
				}
			}
			queue.add(e);
			if (size == 0) {
				lock.notify();
			}
		}
	}

	@Override
	public long available() {
		synchronized(lock) {
			if (queue.size() == 0) {
				try {
					lock.wait();
				} catch(Exception e) {
					return 0;
				}
			}
			return queue.size();
		}
	}

	@Override
	public E poll() {
		E elem;
		synchronized(lock) {
			elem = queue.removeFirst();
			if (queue.size() == capacity - 1) {
				lock.notify();
			}
		}
		polledElements.add(elem);
		return elem;
	}

	@Override
	public void done() {
		Iterator iter = polledElements.iterator();
		while(iter.hasNext()) {
			pool.offer(iter.next());
			iter.remove();
		}
	}
}