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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
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  package org.apache.cassandra.utils.memory;
  
  import java.lang.management.BufferPoolMXBean;
  import java.lang.management.ManagementFactory;
  import java.nio.ByteBuffer;
  import java.util.List;
  
  import org.junit.Assert;
  import org.junit.Test;
  
  import org.assertj.core.api.Assertions;
  
  public class MemoryUtilTest
  {
  
      @Test
      public void testClean()
      {
          // We assert direct pool state changes as no ByteBuffer state changes are observable as a result of cleaner
          // executing.
          BufferPoolMXBean directPool = getDirectBufferPool();
  
          int bufferSize = 1024 * 1024; // some non-insignificant size
          ByteBuffer original = ByteBuffer.allocateDirect(bufferSize);
  
          long memoryUsedBefore = directPool.getMemoryUsed();
          MemoryUtil.clean(original);
          long memoryUsedAfter = directPool.getMemoryUsed();
  
          Assert.assertEquals("Direct memory used should decrease by buffer capacity",
                              // Allow 5% tolerance for other activities
                              memoryUsedBefore - bufferSize, memoryUsedAfter, bufferSize * 0.05);
      }
  
      @Test
      public void testCleanViewDoesNotThrow()
      {
          // Use a large buffer to likely get mmap'd memory from the OS. This ensures that if cleaning a view incorrectly
          // unmaps the original buffer's memory, subsequent access to 'original' would more reliably fail.
          // For context: glibc's mmap threshold is 32MB on 64-bit systems
          ByteBuffer original = ByteBuffer.allocateDirect(64 * 1024 * 1024);
  
          ByteBuffer slice = original.slice();
          MemoryUtil.clean(slice);
          try
          {
              original.putInt(10);
          }
          catch (Exception exc)
          {
              Assertions.fail("Unable to write to original buffer after cleaning (slice). " + exc.getMessage(), exc);
          }
  
          ByteBuffer duplicate = original.duplicate();
          MemoryUtil.clean(duplicate);
  
          try
          {
              original.putInt(10);
          }
          catch (Exception exc)
          {
              Assertions.fail("Unable to write to original buffer after cleaning (duplicate). " + exc.getMessage(), exc);
          }
      }
  
      @Test
      public void testCleanNonDirectDoesNotThrow()
      {
          ByteBuffer original = ByteBuffer.allocate(16);
          MemoryUtil.clean(original);
      }
  
      private static BufferPoolMXBean getDirectBufferPool()
      {
          List<BufferPoolMXBean> pools = ManagementFactory.getPlatformMXBeans(BufferPoolMXBean.class);
          for (BufferPoolMXBean pool : pools)
          {
              if (pool.getName().equals("direct"))
              {
                  return pool;
              }
          }
          throw new IllegalArgumentException("Direct buffer pool not found");
      }
  }