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    1   /*
    2    * Copyright 2012 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  package org.jboss.netty.util.internal;
    17
    18  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
    19  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
    20
    21  final class AtomicFieldUpdaterUtil {
    22
    23      private static final boolean AVAILABLE;
    24
    25      static final class Node {
    26          volatile Node next;
    27          Node() {
    28              super();
    29          }
    30      }
    31
    32      static {
    33          boolean available = false;
    34          try {
    35              AtomicReferenceFieldUpdater<Node, Node> tmp =
    36                  AtomicReferenceFieldUpdater.newUpdater(
    37                          Node.class, Node.class, "next");
    38
    39              // Test if AtomicReferenceFieldUpdater is really working.
    40              Node testNode = new Node();
    41              tmp.set(testNode, testNode);
    42              if (testNode.next != testNode) {
    43                  // Not set as expected - fall back to the safe mode.
    44                  throw new Exception();
    45              }
    46              available = true;
    47          } catch (Throwable t) {
    48              // Running in a restricted environment with a security manager.
    49          }
    50          AVAILABLE = available;
    51      }
    52
    53      static <T, V> AtomicReferenceFieldUpdater<T, V> newRefUpdater(Class<T> tclass, Class<V> vclass, String fieldName) {
    54          if (AVAILABLE) {
    55              return AtomicReferenceFieldUpdater.newUpdater(tclass, vclass, fieldName);
    56          } else {
    57              return null;
    58          }
    59      }
    60
    61      static <T> AtomicIntegerFieldUpdater<T> newIntUpdater(Class<T> tclass, String fieldName) {
    62          if (AVAILABLE) {
    63              return AtomicIntegerFieldUpdater.newUpdater(tclass, fieldName);
    64          } else {
    65              return null;
    66          }
    67      }
    68
    69      static boolean isAvailable() {
    70          return AVAILABLE;
    71      }
    72
    73      private AtomicFieldUpdaterUtil() {
    74          // Unused
    75      }
    76  }