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/*
 * Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
 *
 * 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. See accompanying
 * LICENSE file.
 */
package com.gemstone.gemfire.internal.size;

import java.io.IOException;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.Map;
import java.util.Properties;

import com.gemstone.gemfire.cache.Declarable;
import com.gemstone.gemfire.cache.util.ObjectSizer;
import com.gemstone.gemfire.internal.util.concurrent.CopyOnWriteWeakHashMap;

/**
 * An implementation of {@link ObjectSizer} that calculates an accurate, in
 * memory size of for the first instance of each class that it sees. After the
 * first size calculation, it will return the same size for every instance of
 * that class.
 * 
 * This sizer is a compromise between generating accurate sizes for every object
 * and performance. It should work well for objects that are fairly constant
 * in size. For completely accurate sizing, use {@link ReflectionObjectSizer}
 * 
 * @author dsmith
 * 
 */
public class SizeClassOnceObjectSizer implements ObjectSizer, Serializable, Declarable {
  
  private static final SizeClassOnceObjectSizer INSTANCE = new SizeClassOnceObjectSizer();
  
  private transient final Map savedSizes = new CopyOnWriteWeakHashMap();
  
  private transient final ReflectionObjectSizer sizer = ReflectionObjectSizer.getInstance();
  
  public int sizeof(Object o) {
    if(o == null) {
      return 0;
    }
    int wellKnownObjectSize = WellKnownClassSizer.sizeof(o);
    if(wellKnownObjectSize != 0) {
      return wellKnownObjectSize;
    }
    
    //Now do the sizing
    Class clazz = o.getClass();
    Integer size = savedSizes.get(clazz);
    if(size == null) {
      size = Integer.valueOf(sizer.sizeof(o));
      savedSizes.put(clazz, size);
    }
    return size.intValue();
  }
  
  public static SizeClassOnceObjectSizer getInstance() {
    return INSTANCE;
  }
  
  //This object is serializable because EvictionAttributes is serializable
  //We want to resolve to the same singleton when deserializing
  private void writeObject(java.io.ObjectOutputStream out)
  throws IOException {
    
  }
  
  private void readObject(java.io.ObjectInputStream in)
    throws IOException, ClassNotFoundException {
  }
  
  private Object readResolve() throws ObjectStreamException {
    return INSTANCE;
  }

  private SizeClassOnceObjectSizer() {
    
  }

  public void init(Properties props) {
    // TODO Auto-generated method stub
    
  }
}