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   /*
    * Copyright (c) 2017 Baidu, Inc. All Rights Reserve.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.baidu.fsg.uid.utils;
  
  import java.util.concurrent.atomic.AtomicLong;
  
  /**
   * Represents a padded {@link AtomicLong} to prevent the FalseSharing problem<p>
   * 
   * The CPU cache line commonly be 64 bytes, here is a sample of cache line after padding:<br>
   * 64 bytes = 8 bytes (object reference) + 6 * 8 bytes (padded long) + 8 bytes (a long value)
   * 
   * @author yutianbao
   */
  public class PaddedAtomicLong extends AtomicLong {
      private static final long serialVersionUID = -3415778863941386253L;
  
      /** Padded 6 long (48 bytes) */
      public volatile long p1, p2, p3, p4, p5, p6 = 7L;
  
      /**
       * Constructors from {@link AtomicLong}
       */
      public PaddedAtomicLong() {
          super();
      }
  
      public PaddedAtomicLong(long initialValue) {
          super(initialValue);
      }
  
      /**
       * To prevent GC optimizations for cleaning unused padded references
       */
      public long sumPaddingToPreventOptimization() {
          return p1 + p2 + p3 + p4 + p5 + p6;
      }
  
  }