AtomicQueue.java

/*
 * Copyright (c) 2008-2010, Matthias Mann
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
 * following conditions are met:
 * 
 * * Redistributions of source code must retain the above copyright notice, this list of conditions and the following
 * disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and
 * the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the
 * name of Matthias Mann nor the names of its contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.badlogic.gdx.utils;

import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReferenceArray;

/**
 * A queue that allows one thread to call {@link #put(Object)} and another thread to call {@link #poll()}. Multiple
 * threads must not call these methods.
 * 
 * @author Matthias Mann
 */
public class AtomicQueue<T> {
	private final AtomicInteger writeIndex = new AtomicInteger();
	private final AtomicInteger readIndex = new AtomicInteger();
	private final AtomicReferenceArray<T> queue;

	public AtomicQueue(int capacity) {
		queue = new AtomicReferenceArray(capacity);
	}

	private int next(int idx) {
		return idx + 1 & queue.length() - 1;
	}

	public boolean put(T value) {
		int write = writeIndex.get();
		int read = readIndex.get();
		int next = next(write);
		if (next == read)
			return false;
		queue.set(write, value);
		writeIndex.set(next);
		return true;
	}

	public T poll() {
		int read = readIndex.get();
		int write = writeIndex.get();
		if (read == write)
			return null;
		T value = queue.get(read);
		readIndex.set(next(read));
		return value;
	}
}