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.spark.unsafe.memory;
  
  import javax.annotation.concurrent.GuardedBy;
  import java.lang.ref.WeakReference;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.Map;
  
  import org.apache.spark.unsafe.Platform;
  
  /**
   * A simple {@link MemoryAllocator} that can allocate up to 16GB using a JVM long primitive array.
   */
  public class HeapMemoryAllocator implements MemoryAllocator {
  
    @GuardedBy("this")
    private final Map<Long, LinkedList<WeakReference<MemoryBlock>>> bufferPoolsBySize =
      new HashMap<>();
  
    private static final int POOLING_THRESHOLD_BYTES = 1024 * 1024;
  
    /**
     * Returns true if allocations of the given size should go through the pooling mechanism and
     * false otherwise.
     */
    private boolean shouldPool(long size) {
      // Very small allocations are less likely to benefit from pooling.
      return size >= POOLING_THRESHOLD_BYTES;
    }
  
    @Override
    public MemoryBlock allocate(long size) throws OutOfMemoryError {
      if (shouldPool(size)) {
        synchronized (this) {
          final LinkedList<WeakReference<MemoryBlock>> pool = bufferPoolsBySize.get(size);
          if (pool != null) {
            while (!pool.isEmpty()) {
              final WeakReference<MemoryBlock> blockReference = pool.pop();
              final MemoryBlock memory = blockReference.get();
              if (memory != null) {
                assert (memory.size() == size);
                return memory;
              }
            }
            bufferPoolsBySize.remove(size);
          }
        }
      }
      long[] array = new long[(int) ((size + 7) / 8)];
      MemoryBlock memory = new MemoryBlock(array, Platform.LONG_ARRAY_OFFSET, size);
      if (MemoryAllocator.MEMORY_DEBUG_FILL_ENABLED) {
        memory.fill(MemoryAllocator.MEMORY_DEBUG_FILL_CLEAN_VALUE);
      }
      return memory;
    }
  
    @Override
    public void free(MemoryBlock memory) {
      final long size = memory.size();
      if (MemoryAllocator.MEMORY_DEBUG_FILL_ENABLED) {
        memory.fill(MemoryAllocator.MEMORY_DEBUG_FILL_FREED_VALUE);
      }
      if (shouldPool(size)) {
        synchronized (this) {
          LinkedList<WeakReference<MemoryBlock>> pool = bufferPoolsBySize.get(size);
          if (pool == null) {
            pool = new LinkedList<>();
            bufferPoolsBySize.put(size, pool);
          }
          pool.add(new WeakReference<>(memory));
        }
      } else {
        // Do nothing
      }
    }
  }
  