code: /*
   * 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.datasketches.memory.internal;
  
  import static org.apache.datasketches.memory.internal.UnsafeUtil.unsafe;
  
  import java.util.logging.Logger;
  
  /**
   * Provides access to direct (native) memory.
   *
   * @author Roman Leventov
   * @author Lee Rhodes
   */
  @SuppressWarnings("restriction")
  final class AllocateDirect {
    static final Logger LOG = Logger.getLogger(AllocateDirect.class.getCanonicalName());
  
    private final Deallocator deallocator;
    private final long nativeBaseOffset;
    private final MemoryCleaner cleaner;
  
    /**
     * Base Constructor for allocate native memory.
     *
     * <p>Allocates and provides access to capacityBytes directly in native (off-heap) memory
     * leveraging the MemoryImpl interface.
     * The allocated memory will be 8-byte aligned, but may not be page aligned.
     * @param capacityBytes the the requested capacity of off-heap memory. Cannot be zero.
     */
    AllocateDirect(final long capacityBytes) {
      final boolean pageAligned = VirtualMachineMemory.getIsPageAligned();
      final long pageSize = getPageSize();
      final long allocationSize = capacityBytes + (pageAligned ? pageSize : 0);
      final long nativeAddress;
      try {
        nativeAddress = unsafe.allocateMemory(allocationSize);
      } catch (final OutOfMemoryError err) {
        throw new RuntimeException(err);
      }
      if (pageAligned && ((nativeAddress % pageSize) != 0)) {
        //Round up to page boundary
        nativeBaseOffset = (nativeAddress & ~(pageSize - 1L)) + pageSize;
      } else {
        nativeBaseOffset = nativeAddress;
      }
      deallocator = new Deallocator(nativeAddress);
      cleaner = new MemoryCleaner(this, deallocator);
    }
  
    public void close() {
      try {
        if (deallocator.deallocate(false)) {
          // This Cleaner.clean() call effectively just removes the Cleaner from the internal linked
          // list of all cleaners. It will delegate to Deallocator.deallocate() which will be a no-op
          // because the valid state is already changed.
          cleaner.clean();
        }
      } finally {
        ResourceImpl.reachabilityFence(this);
      }
    }
  
    long getNativeBaseOffset() {
      return nativeBaseOffset;
    }
  
    public static int getPageSize() {
      return unsafe.pageSize();
    }
  
    public StepBoolean getValid() {
      return deallocator.getValid();
    }
  
    private static final class Deallocator implements Runnable {
      //This is the only place the actual native address is kept for use by unsafe.freeMemory();
      private final long nativeAddress;
      private final StepBoolean valid = new StepBoolean(true); //only place for this
  
      Deallocator(final long nativeAddress) {
        this.nativeAddress = nativeAddress;
      }
  
      StepBoolean getValid() {
        return valid;
      }
  
      @Override
      public void run() throws IllegalStateException {
        deallocate(true);
      }
  
      boolean deallocate(final boolean calledFromCleaner) throws IllegalStateException {
        if (valid.change()) {
          if (calledFromCleaner) {
            // Warn about non-deterministic resource cleanup.
            LOG.warning("A direct resource was not closed explicitly");
          }
          unsafe.freeMemory(nativeAddress);
          return true;
        }
        return false;
      }
    }
  
  }
  