content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF 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
   *
   *     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 org.apache.cassandra.cache;
  
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  
  import org.apache.cassandra.io.util.Memory;
  
  public class RefCountedMemory extends Memory implements AutoCloseable
  {
      private volatile int references = 1;
      private static final AtomicIntegerFieldUpdater<RefCountedMemory> UPDATER = AtomicIntegerFieldUpdater.newUpdater(RefCountedMemory.class, "references");
  
      public RefCountedMemory(long size)
      {
          super(size);
      }
  
      /**
       * @return true if we succeed in referencing before the reference count reaches zero.
       * (A FreeableMemory object is created with a reference count of one.)
       */
      public boolean reference()
      {
          while (true)
          {
              int n = UPDATER.get(this);
              if (n <= 0)
                  return false;
              if (UPDATER.compareAndSet(this, n, n + 1))
                  return true;
          }
      }
  
      /** decrement reference count.  if count reaches zero, the object is freed. */
      public void unreference()
      {
          if (UPDATER.decrementAndGet(this) == 0)
              super.free();
      }
  
      public RefCountedMemory copy(long newSize)
      {
          RefCountedMemory copy = new RefCountedMemory(newSize);
          copy.put(0, this, 0, Math.min(size(), newSize));
          return copy;
      }
  
      public void free()
      {
          throw new AssertionError();
      }
  
      public void close()
      {
          unreference();
      }
  }
  