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1   /*
2    * Copyright 2009 Red Hat, Inc.
3    *
4    * Red Hat licenses this file to you under the Apache License, version 2.0
5    * (the "License"); you may not use this file except in compliance with the
6    * 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  package org.jboss.netty.util.internal;
17  
18  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
19  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
20  
21  /**
22   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
23   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
24   * @version $Rev: 2080 $, $Date: 2010-01-26 18:04:19 +0900 (Tue, 26 Jan 2010) $
25   */
26  class AtomicFieldUpdaterUtil {
27  
28      private static final boolean AVAILABLE;
29  
30      static final class Node {
31          volatile Node next;
32          Node() {
33              super();
34          }
35      }
36  
37      static {
38          boolean available = false;
39          try {
40              AtomicReferenceFieldUpdater<Node, Node> tmp =
41                  AtomicReferenceFieldUpdater.newUpdater(
42                          Node.class, Node.class, "next");
43  
44              // Test if AtomicReferenceFieldUpdater is really working.
45              Node testNode = new Node();
46              tmp.set(testNode, testNode);
47              if (testNode.next != testNode) {
48                  // Not set as expected - fall back to the safe mode.
49                  throw new Exception();
50              }
51              available = true;
52          } catch (Throwable t) {
53              // Running in a restricted environment with a security manager.
54          }
55          AVAILABLE = available;
56      }
57  
58      static <T, V> AtomicReferenceFieldUpdater<T,V> newRefUpdater(Class<T> tclass, Class<V> vclass, String fieldName) {
59          if (AVAILABLE) {
60              return AtomicReferenceFieldUpdater.newUpdater(tclass, vclass, fieldName);
61          } else {
62              return null;
63          }
64      }
65  
66      static <T> AtomicIntegerFieldUpdater<T> newIntUpdater(Class<T> tclass, String fieldName) {
67          if (AVAILABLE) {
68              return AtomicIntegerFieldUpdater.newUpdater(tclass, fieldName);
69          } else {
70              return null;
71          }
72      }
73  
74      static boolean isAvailable() {
75          return AVAILABLE;
76      }
77  
78      private AtomicFieldUpdaterUtil() {
79          // Unused
80      }
81  }