//
   //  ========================================================================
   //  Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.io;
  
  import java.nio.ByteBuffer;
  import java.util.Queue;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.ConcurrentMap;
  
  import org.eclipse.jetty.util.BufferUtil;
  
  public class MappedByteBufferPool implements ByteBufferPool
  {
      private final ConcurrentMap<Integer, Queue<ByteBuffer>> directBuffers = new ConcurrentHashMap<>();
      private final ConcurrentMap<Integer, Queue<ByteBuffer>> heapBuffers = new ConcurrentHashMap<>();
      private final int factor;
  
      public MappedByteBufferPool()
      {
          this(1024);
      }
  
      public MappedByteBufferPool(int factor)
      {
          this.factor = factor;
      }
  
      @Override
      public ByteBuffer acquire(int size, boolean direct)
      {
          int bucket = bucketFor(size);
          ConcurrentMap<Integer, Queue<ByteBuffer>> buffers = buffersFor(direct);
  
          ByteBuffer result = null;
          Queue<ByteBuffer> byteBuffers = buffers.get(bucket);
          if (byteBuffers != null)
              result = byteBuffers.poll();
  
          if (result == null)
          {
              int capacity = bucket * factor;
              result = direct ? BufferUtil.allocateDirect(capacity) : BufferUtil.allocate(capacity);
          }
  
          BufferUtil.clear(result);
          return result;
      }
  
      @Override
      public void release(ByteBuffer buffer)
      {
          if (buffer == null)
              return; // nothing to do
          
          // validate that this buffer is from this pool
          assert((buffer.capacity() % factor) == 0);
          
          int bucket = bucketFor(buffer.capacity());
          ConcurrentMap<Integer, Queue<ByteBuffer>> buffers = buffersFor(buffer.isDirect());
  
          // Avoid to create a new queue every time, just to be discarded immediately
          Queue<ByteBuffer> byteBuffers = buffers.get(bucket);
          if (byteBuffers == null)
          {
              byteBuffers = new ConcurrentLinkedQueue<>();
              Queue<ByteBuffer> existing = buffers.putIfAbsent(bucket, byteBuffers);
              if (existing != null)
                  byteBuffers = existing;
          }
  
          BufferUtil.clear(buffer);
          byteBuffers.offer(buffer);
      }
  
      public void clear()
      {
          directBuffers.clear();
          heapBuffers.clear();
      }
  
      private int bucketFor(int size)
      {
         int bucket = size / factor;
         if (size % factor > 0)
             ++bucket;
         return bucket;
     }
 
     // Package local for testing
     ConcurrentMap<Integer, Queue<ByteBuffer>> buffersFor(boolean direct)
     {
         return direct ? directBuffers : heapBuffers;
     }
 }