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   * 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.utils;
  
  import java.nio.ByteBuffer;
  
  import org.junit.Test;
  
  import org.github.jamm.MemoryMeter;
  import org.github.jamm.MemoryMeter.Guess;
  
  import static org.github.jamm.MemoryMeter.ByteBufferMode.SLAB_ALLOCATION_NO_SLICE;
  import static org.junit.Assert.assertEquals;
  
  public class ObjectSizesTest
  {
      // We use INSTRUMENTATION as principal strategy as it is our reference strategy
      private static final MemoryMeter meter = MemoryMeter.builder()
                                                          .withGuessing(Guess.INSTRUMENTATION, Guess.UNSAFE)
                                                          .build();
  
      @Test
      public void testSizeOnHeapExcludingData()
      {
          // single empty heap buffer
          checkBufferSizeExcludingData(ByteBuffer.allocate(0), 0);
  
          // single non-empty heap buffer
          checkBufferSizeExcludingData(ByteBuffer.allocate(10), 10);
  
          // single empty direct buffer
          checkBufferSizeExcludingData(ByteBuffer.allocateDirect(0), 0);
  
          // single non-empty direct buffer
          checkBufferSizeExcludingData(ByteBuffer.allocateDirect(10), 0);
  
          // heap buffer being a prefix slab
          ByteBuffer buffer = (ByteBuffer) ByteBuffer.allocate(10).duplicate().limit(8);
          checkBufferSizeExcludingData(buffer, 8);
  
          // heap buffer being a suffix slab
          buffer = (ByteBuffer) ByteBuffer.allocate(10).duplicate().position(1);
          checkBufferSizeExcludingData(buffer, 9);
  
          // heap buffer being an infix slab
          buffer = (ByteBuffer) ByteBuffer.allocate(10).duplicate().position(1).limit(8);
          checkBufferSizeExcludingData(buffer, 7);
      }
  
      private void checkBufferSizeExcludingData(ByteBuffer buffer, int dataSize)
      {
          assertEquals(meter.measureDeep(buffer, SLAB_ALLOCATION_NO_SLICE) - dataSize, ObjectSizes.sizeOnHeapExcludingDataOf(buffer));
      }
  
      @Test
      public void testSizeOnHeapExcludingDataArray()
      {
          checkBufferSizeExcludingDataArray(0, new ByteBuffer[0]);
  
          // single heap buffer
          checkBufferSizeExcludingDataArray(0, ByteBuffer.allocate(0));
  
          // multiple buffers
          checkBufferSizeExcludingDataArray(10, ByteBuffer.allocate(0), ByteBuffer.allocate(10), ByteBuffer.allocateDirect(10));
  
          // heap buffer being a prefix slab
          ByteBuffer prefix = (ByteBuffer) ByteBuffer.allocate(10).duplicate().limit(8);
  
          // heap buffer being a suffix slab
          ByteBuffer suffix = (ByteBuffer) ByteBuffer.allocate(10).duplicate().position(1);
          checkBufferSizeExcludingDataArray(8 + 9, prefix, suffix);
      }
  
      private void checkBufferSizeExcludingDataArray(int dataSize, ByteBuffer... buffers)
      {
          assertEquals(meter.measureDeep(buffers, SLAB_ALLOCATION_NO_SLICE) - dataSize, ObjectSizes.sizeOnHeapExcludingDataOf(buffers));
      }
  
      @Test
      public void testSizeOnHeapOf()
      {
          // single empty heap buffer
          checkBufferSize(ByteBuffer.allocate(0));
  
          // single non-empty heap buffer
          checkBufferSize(ByteBuffer.allocate(10));
  
          // single empty direct buffer
          checkBufferSize(ByteBuffer.allocateDirect(0));
  
          // single non-empty direct buffer
          checkBufferSize(ByteBuffer.allocateDirect(10));
  
          // heap buffer being a prefix slab
          ByteBuffer buffer = (ByteBuffer) ByteBuffer.allocate(10).duplicate().limit(8);
          checkBufferSize(buffer);
  
          // heap buffer being a suffix slab
          buffer = (ByteBuffer) ByteBuffer.allocate(10).duplicate().position(1);
          checkBufferSize(buffer);
  
          // heap buffer being an infix slab
          buffer = (ByteBuffer) ByteBuffer.allocate(10).duplicate().position(1).limit(8);
          checkBufferSize(buffer);
      }
  
      private void checkBufferSize(ByteBuffer buffer)
      {
          assertEquals(meter.measureDeep(buffer, SLAB_ALLOCATION_NO_SLICE), ObjectSizes.sizeOnHeapOf(buffer));
      }
  
      @Test
      public void testSizeOnHeapOfArray()
      {
          checkBufferArraySize(new ByteBuffer[0]);
  
          // single heap buffer
          checkBufferArraySize(ByteBuffer.allocate(0));
  
          // multiple buffers
          checkBufferArraySize(ByteBuffer.allocate(0), ByteBuffer.allocate(10), ByteBuffer.allocateDirect(10));
      }
  
      private void checkBufferArraySize(ByteBuffer... buffers)
      {
          assertEquals(meter.measureDeep(buffers, SLAB_ALLOCATION_NO_SLICE), ObjectSizes.sizeOnHeapOf(buffers));
      }
  }