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.activemq.memory.buffer;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  
  /**
   * A {@link MessageBuffer} which evicts from the largest buffers first.
   * 
   * 
   */
  public class SizeBasedMessageBuffer implements MessageBuffer {
  
      private int limit = 100 * 64 * 1024;
      private List<MessageQueue> bubbleList = new ArrayList<MessageQueue>();
      private int size;
      private Object lock = new Object();
  
      public SizeBasedMessageBuffer() {
      }
  
      public SizeBasedMessageBuffer(int limit) {
          this.limit = limit;
      }
  
      public int getSize() {
          synchronized (lock) {
              return size;
          }
      }
  
      /**
       * Creates a new message queue instance
       */
      public MessageQueue createMessageQueue() {
          MessageQueue queue = new MessageQueue(this);
          synchronized (lock) {
              queue.setPosition(bubbleList.size());
              bubbleList.add(queue);
          }
          return queue;
      }
  
      /**
       * After a message queue has changed we may need to perform some evictions
       * 
       * @param delta
       * @param queueSize
       */
      public void onSizeChanged(MessageQueue queue, int delta, int queueSize) {
          synchronized (lock) {
              bubbleUp(queue, queueSize);
  
              size += delta;
              while (size > limit) {
                  MessageQueue biggest = bubbleList.get(0);
                  size -= biggest.evictMessage();
  
                  bubbleDown(biggest, 0);
              }
          }
      }
  
      public void clear() {
          synchronized (lock) {
              for (Iterator<MessageQueue> iter = bubbleList.iterator(); iter.hasNext();) {
                  MessageQueue queue = iter.next();
                  queue.clear();
              }
              size = 0;
          }
      }
  
      protected void bubbleUp(MessageQueue queue, int queueSize) {
          // lets bubble up to head of queueif we need to
          int position = queue.getPosition();
          while (--position >= 0) {
              MessageQueue pivot = bubbleList.get(position);
              if (pivot.getSize() < queueSize) {
                  swap(position, pivot, position + 1, queue);
              } else {
                  break;
              }
          }
      }
  
      protected void bubbleDown(MessageQueue biggest, int position) {
          int queueSize = biggest.getSize();
          int end = bubbleList.size();
          for (int second = position + 1; second < end; second++) {
              MessageQueue pivot = bubbleList.get(second);
              if (pivot.getSize() > queueSize) {
                  swap(position, biggest, second, pivot);
              } else {
                  break;
              }
              position = second;
          }
      }
  
      protected void swap(int firstPosition, MessageQueue first, int secondPosition, MessageQueue second) {
          bubbleList.set(firstPosition, second);
          bubbleList.set(secondPosition, first);
          first.setPosition(secondPosition);
          second.setPosition(firstPosition);
      }
  }
  