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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.util.concurrent.atomic.AtomicReferenceFieldUpdater;
20  
21  abstract class MpscLinkedQueueTailRef<E> extends MpscLinkedQueuePad1<E> {
22  
23      private static final long serialVersionUID = 8717072462993327429L;
24  
25      @SuppressWarnings("rawtypes")
26      private static final AtomicReferenceFieldUpdater<MpscLinkedQueueTailRef, MpscLinkedQueueNode> UPDATER;
27  
28      static {
29          @SuppressWarnings("rawtypes")
30          AtomicReferenceFieldUpdater<MpscLinkedQueueTailRef, MpscLinkedQueueNode> updater;
31          updater = PlatformDependent.newAtomicReferenceFieldUpdater(MpscLinkedQueueTailRef.class, "tailRef");
32          if (updater == null) {
33              updater = AtomicReferenceFieldUpdater.newUpdater(
34                      MpscLinkedQueueTailRef.class, MpscLinkedQueueNode.class, "tailRef");
35          }
36          UPDATER = updater;
37      }
38  
39      private transient volatile MpscLinkedQueueNode<E> tailRef;
40  
41      protected final MpscLinkedQueueNode<E> tailRef() {
42          return tailRef;
43      }
44  
45      protected final void setTailRef(MpscLinkedQueueNode<E> tailRef) {
46          this.tailRef = tailRef;
47      }
48  
49      @SuppressWarnings("unchecked")
50      protected final MpscLinkedQueueNode<E> getAndSetTailRef(MpscLinkedQueueNode<E> tailRef) {
51          // LOCK XCHG in JDK8, a CAS loop in JDK 7/6
52          return (MpscLinkedQueueNode<E>) UPDATER.getAndSet(this, tailRef);
53      }
54  }