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   /*
    * Copyright 2013 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.buffer;
  
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  
  import io.netty.util.internal.ReferenceCountUpdater;
  
  /**
   * Abstract base class for {@link ByteBuf} implementations that count references.
   */
  public abstract class AbstractReferenceCountedByteBuf extends AbstractByteBuf {
      private static final long REFCNT_FIELD_OFFSET =
              ReferenceCountUpdater.getUnsafeOffset(AbstractReferenceCountedByteBuf.class, "refCnt");
      private static final AtomicIntegerFieldUpdater<AbstractReferenceCountedByteBuf> AIF_UPDATER =
              AtomicIntegerFieldUpdater.newUpdater(AbstractReferenceCountedByteBuf.class, "refCnt");
  
      private static final ReferenceCountUpdater<AbstractReferenceCountedByteBuf> updater =
              new ReferenceCountUpdater<AbstractReferenceCountedByteBuf>() {
          @Override
          protected AtomicIntegerFieldUpdater<AbstractReferenceCountedByteBuf> updater() {
              return AIF_UPDATER;
          }
          @Override
          protected long unsafeOffset() {
              return REFCNT_FIELD_OFFSET;
          }
      };
  
      // Value might not equal "real" reference count, all access should be via the updater
      @SuppressWarnings({"unused", "FieldMayBeFinal"})
      private volatile int refCnt;
  
      protected AbstractReferenceCountedByteBuf(int maxCapacity) {
          super(maxCapacity);
          updater.setInitialValue(this);
      }
  
      @Override
      boolean isAccessible() {
          // Try to do non-volatile read for performance as the ensureAccessible() is racy anyway and only provide
          // a best-effort guard.
          return updater.isLiveNonVolatile(this);
      }
  
      @Override
      public int refCnt() {
          return updater.refCnt(this);
      }
  
      /**
       * An unsafe operation intended for use by a subclass that sets the reference count of the buffer directly
       */
      protected final void setRefCnt(int refCnt) {
          updater.setRefCnt(this, refCnt);
      }
  
      /**
       * An unsafe operation intended for use by a subclass that resets the reference count of the buffer to 1
       */
      protected final void resetRefCnt() {
          updater.resetRefCnt(this);
      }
  
      @Override
      public ByteBuf retain() {
          return updater.retain(this);
      }
  
      @Override
      public ByteBuf retain(int increment) {
          return updater.retain(this, increment);
      }
  
      @Override
      public ByteBuf touch() {
          return this;
      }
  
      @Override
      public ByteBuf touch(Object hint) {
          return this;
      }
  
      @Override
     public boolean release() {
         return handleRelease(updater.release(this));
     }
 
     @Override
     public boolean release(int decrement) {
         return handleRelease(updater.release(this, decrement));
     }
 
     private boolean handleRelease(boolean result) {
         if (result) {
             deallocate();
         }
         return result;
     }
 
     /**
      * Called once {@link #refCnt()} is equals 0.
      */
     protected abstract void deallocate();
 }