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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  }