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.arrow.memory.rounding;
  
  import org.apache.arrow.memory.util.CommonUtil;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * The default rounding policy. That is, if the requested size is within the chunk size, the rounded
   * size will be the next power of two. Otherwise, the rounded size will be identical to the
   * requested size.
   */
  public class DefaultRoundingPolicy implements RoundingPolicy {
    private static final Logger logger = LoggerFactory.getLogger(DefaultRoundingPolicy.class);
    public final long chunkSize;
  
    /**
     * The variables here and the static block calculates the DEFAULT_CHUNK_SIZE.
     *
     * <p>It was copied from {@link io.netty.buffer.PooledByteBufAllocator}.
     */
    private static final long MIN_PAGE_SIZE = 4096;
  
    private static final long MAX_CHUNK_SIZE = ((long) Integer.MAX_VALUE + 1) / 2;
    private static final long DEFAULT_CHUNK_SIZE;
  
    static {
      long defaultPageSize = Long.getLong("org.apache.memory.allocator.pageSize", 8192);
      try {
        validateAndCalculatePageShifts(defaultPageSize);
      } catch (Throwable t) {
        defaultPageSize = 8192;
      }
  
      int defaultMaxOrder = Integer.getInteger("org.apache.memory.allocator.maxOrder", 11);
      try {
        validateAndCalculateChunkSize(defaultPageSize, defaultMaxOrder);
      } catch (Throwable t) {
        defaultMaxOrder = 11;
      }
      DEFAULT_CHUNK_SIZE = validateAndCalculateChunkSize(defaultPageSize, defaultMaxOrder);
      if (logger.isDebugEnabled()) {
        logger.debug("-Dorg.apache.memory.allocator.pageSize: {}", defaultPageSize);
        logger.debug("-Dorg.apache.memory.allocator.maxOrder: {}", defaultMaxOrder);
      }
    }
  
    private static long validateAndCalculatePageShifts(long pageSize) {
      if (pageSize < MIN_PAGE_SIZE) {
        throw new IllegalArgumentException(
            "pageSize: " + pageSize + " (expected: " + MIN_PAGE_SIZE + ")");
      }
  
      if ((pageSize & pageSize - 1) != 0) {
        throw new IllegalArgumentException("pageSize: " + pageSize + " (expected: power of 2)");
      }
  
      // Logarithm base 2. At this point we know that pageSize is a power of two.
      return Long.SIZE - 1L - Long.numberOfLeadingZeros(pageSize);
    }
  
    private static long validateAndCalculateChunkSize(long pageSize, int maxOrder) {
      if (maxOrder > 14) {
        throw new IllegalArgumentException("maxOrder: " + maxOrder + " (expected: 0-14)");
      }
  
      // Ensure the resulting chunkSize does not overflow.
      long chunkSize = pageSize;
      for (long i = maxOrder; i > 0; i--) {
        if (chunkSize > MAX_CHUNK_SIZE / 2) {
          throw new IllegalArgumentException(
              String.format(
                  "pageSize (%d) << maxOrder (%d) must not exceed %d",
                  pageSize, maxOrder, MAX_CHUNK_SIZE));
        }
        chunkSize <<= 1;
      }
      return chunkSize;
    }
  
    /** The singleton instance. */
    public static final DefaultRoundingPolicy DEFAULT_ROUNDING_POLICY =
        new DefaultRoundingPolicy(DEFAULT_CHUNK_SIZE);
  
    private DefaultRoundingPolicy(long chunkSize) {
      this.chunkSize = chunkSize;
    }
  
    @Override
    public long getRoundedSize(long requestSize) {
      return requestSize < chunkSize ? CommonUtil.nextPowerOfTwo(requestSize) : requestSize;
    }
  }
  