com.gemstone.gemfire.internal.cache.lru.Sizeable Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of gemfire-core Show documentation

SnappyData store based off Pivotal GemFireXD

The newest version!

/*
 * 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.cache.lru;

/**
 * An interface that allows an object to define its own size.

 *
 *Sample Implementation

 *public int getSizeInBytes(){

    // The sizes of the primitive as well as object instance variables are calculated:

    
    int size = 0;

    
    // Add overhead for this instance.

    size += Sizeable.PER_OBJECT_OVERHEAD;


    // Add object references (implements Sizeable)

    // value reference = 4 bytes 

    
    size += 4;

    
    // Add primitive instance variable size

    // byte bytePr = 1 byte

    // boolean flag = 1 byte

    
    size += 2;

    
    // Add individual object size
 
    size += (value.getSizeInBytes());
 
     
    return size;

  }

 *
 * @author David Whitlock
 *
 * @since 3.2
 */
public interface Sizeable {

  /** The overhead of an object in the VM in bytes */
  public static final int PER_OBJECT_OVERHEAD = 8; // TODO for a 64bit jvm with small oops this is 12; for other 64bit jvms it is 16

  /**
   * Returns the size (in bytes) of this object including the {@link
   * #PER_OBJECT_OVERHEAD}.
   */
  public int getSizeInBytes();

}