/*
 * Copyright (c) 2011-2015 Pivotal Software Inc., Inc. All Rights Reserved.
 *
 * 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 reactor.core.queue.internal;

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you 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.
 */

import reactor.core.internal.PlatformDependent;

import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

public abstract class MpscLinkedQueueNode<T> {

	@SuppressWarnings("rawtypes")
	private static final AtomicReferenceFieldUpdater<MpscLinkedQueueNode, MpscLinkedQueueNode> nextUpdater;

	static {
		@SuppressWarnings("rawtypes")
		AtomicReferenceFieldUpdater<MpscLinkedQueueNode, MpscLinkedQueueNode> u;

		u = PlatformDependent.newAtomicReferenceFieldUpdater(MpscLinkedQueueNode.class, "next");
		if (u == null) {
			u = AtomicReferenceFieldUpdater.newUpdater(MpscLinkedQueueNode.class, MpscLinkedQueueNode.class, "next");
		}
		nextUpdater = u;
	}

	@SuppressWarnings("unused")
	private volatile MpscLinkedQueueNode<T> next;

	final MpscLinkedQueueNode<T> next() {
		return next;
	}

	final void setNext(final MpscLinkedQueueNode<T> newNext) {
		// Similar to 'next = newNext', but slightly faster (storestore vs loadstore)
		// See: http://robsjava.blogspot.com/2013/06/a-faster-volatile.html
		nextUpdater.lazySet(this, newNext);
	}

	public abstract T value();

	/**
	 * Sets the element this node contains to {@code null} so that the node can be used as a tombstone.
	 */
	protected T clearMaybe() {
		return value();
	}

	/**
	 * Unlink to allow GC'ed
	 */
	void unlink() {
		setNext(null);
	}
}