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package com.hybhub.util.concurrent;

import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Queue backed by a set so duplicate elements are not allowed.
 * @param  the type of elements held in this queue
 */
public abstract class ConcurrentSetQueue extends ConcurrentSetCollection implements Queue {

	ConcurrentSetQueue(final int capacity) {
		super(capacity);
	}

	@Override
	public boolean offer(final E e) {
		return super.offer(e);
	}

	@Override
	public E poll() {
		final AtomicInteger count = this.count;
		if (count.get() == 0) {
			return null;
		}
		E x = null;
		int c = -1;
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lock();
		try {
			if (count.get() > 0) {
				x = set.iterator().next();
				set.spliterator();
				set.remove(x);
				c = count.getAndDecrement();
				if (c > 1) {
					notEmpty.signal();
				}
			}
		} finally {
			takeLock.unlock();
		}
		if (c == capacity) {
			signalNotFull();
		}
		return x;	}

	@Override
	public E element() {
		E x = peek();
		if (x != null) {
			return x;
		}
		else {
			throw new NoSuchElementException();
		}
	}

	@Override
	public E peek() {
		if (count.get() == 0) {
			return null;
		}
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lock();
		try {
			return set.iterator().next();
		} finally {
			takeLock.unlock();
		}
	}

	@Override
	public E remove() {
		E x = poll();
		if (x != null) {
			return x;
		}
		else {
			throw new NoSuchElementException();
		}

	}
}