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1   /*
2    * Copyright 2014 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  
17  package io.netty.util.internal;
18  
19  import java.io.Serializable;
20  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
21  
22  
23  abstract class MpscLinkedQueueHeadRef<E> extends MpscLinkedQueuePad0<E> implements Serializable {
24  
25      private static final long serialVersionUID = 8467054865577874285L;
26  
27      @SuppressWarnings("rawtypes")
28      private static final AtomicReferenceFieldUpdater<MpscLinkedQueueHeadRef, MpscLinkedQueueNode> UPDATER;
29  
30      static {
31          @SuppressWarnings("rawtypes")
32          AtomicReferenceFieldUpdater<MpscLinkedQueueHeadRef, MpscLinkedQueueNode> updater;
33          updater = PlatformDependent.newAtomicReferenceFieldUpdater(MpscLinkedQueueHeadRef.class, "headRef");
34          if (updater == null) {
35              updater = AtomicReferenceFieldUpdater.newUpdater(
36                      MpscLinkedQueueHeadRef.class, MpscLinkedQueueNode.class, "headRef");
37          }
38          UPDATER = updater;
39      }
40  
41      private transient  volatile MpscLinkedQueueNode<E> headRef;
42  
43      protected final MpscLinkedQueueNode<E> headRef() {
44          return headRef;
45      }
46  
47      protected final void setHeadRef(MpscLinkedQueueNode<E> headRef) {
48          this.headRef = headRef;
49      }
50  
51      protected final void lazySetHeadRef(MpscLinkedQueueNode<E> headRef) {
52          UPDATER.lazySet(this, headRef);
53      }
54  }