io.netty.util.internal.MpscLinkedQueueNode Maven / Gradle / Ivy

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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * 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.
 */

package io.netty.util.internal;

import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

public abstract class MpscLinkedQueueNode {

    @SuppressWarnings("rawtypes")
    private static final AtomicReferenceFieldUpdater nextUpdater;

    static {
        @SuppressWarnings("rawtypes")
        AtomicReferenceFieldUpdater 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 next;

    final MpscLinkedQueueNode next() {
        return next;
    }

    final void setNext(final MpscLinkedQueueNode 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);
    }
}