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;
  
  /**
   * This is a simple implementation of the MemoryRequestServer that creates space on the Java heap
   * for the requesting application. This capability is only available for direct, off-heap
   * allocated memory.
   *
   * <p>Using this default implementation could be something like the following:
   *
   * <blockquote><pre>
   * class OffHeap {
   *   WritableMemory mem;
   *   MemoryRequestServer memReqSvr = null;
   *
   *   void add(Object something) {
   *
   *     if (outOfSpace) { // determine if out-of-space
   *       long spaceNeeded = ...
   *
   *       //Acquire the MemoryRequestServer from the direct Memory the first time.
   *       //Once acquired, this can be reused if more memory is needed later.
   *       //This is required for the default implementation because it returns memory on heap
   *       // and on-heap memory does not carry a reference to the MemoryRequestServer.
   *       memReqSvr = (memReqSvr == null) ? mem.getMemoryRequestServer() : memReqSvr;
   *
   *       //Request bigger memory
   *       WritableMemory newMem = memReqSvr.request(mem, spaceNeeded);
   *
   *       //Copy your data from the current memory to the new one and resize
   *       moveAndResize(mem, newMem);
   *
   *       //You are done with the old memory, so request close.
   *       //Note that it is up to the owner of the WritableHandle whether or not to
   *       // actually close the resource.
   *       memReqSvr.requestClose(mem, newMem);
   *
   *       mem = newMem; //update your reference to memory
   *     }
   *
   *     //continue with the add process
   *   }
   * }
   * </pre></blockquote>
   *
   *
   * @author Lee Rhodes
   */
  public final class DefaultMemoryRequestServer implements MemoryRequestServer {
  
    /**
     * {@inheritDoc}
     *
     * <p>By default this allocates new memory requests on the Java heap.
     */
    @Override
    public WritableMemory request(final WritableMemory currentWritableMemory, final long capacityBytes) {
      final WritableMemory wmem = WritableMemory.allocate((int)capacityBytes, currentWritableMemory.getByteOrder());
      return wmem;
    }
  
    /**
     * {@inheritDoc}
     *
     * <p>This method does nothing in this default implementation because it is application specific.
     * This method must be overridden to explicitly close if desired.
     * Otherwise, the AutoCloseable will eventually close the resource.
     */
    @Override
    public void requestClose(final WritableMemory memToRelease, final WritableMemory newMemory) {
      //do nothing
    }
  
  }
  