001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.activemq.memory.buffer;
018
019import java.util.ArrayList;
020import java.util.Iterator;
021import java.util.List;
022
023/**
024 * A {@link MessageBuffer} which evicts from the largest buffers first.
025 * 
026 * 
027 */
028public class SizeBasedMessageBuffer implements MessageBuffer {
029
030    private int limit = 100 * 64 * 1024;
031    private List<MessageQueue> bubbleList = new ArrayList<MessageQueue>();
032    private int size;
033    private Object lock = new Object();
034
035    public SizeBasedMessageBuffer() {
036    }
037
038    public SizeBasedMessageBuffer(int limit) {
039        this.limit = limit;
040    }
041
042    public int getSize() {
043        synchronized (lock) {
044            return size;
045        }
046    }
047
048    /**
049     * Creates a new message queue instance
050     */
051    public MessageQueue createMessageQueue() {
052        MessageQueue queue = new MessageQueue(this);
053        synchronized (lock) {
054            queue.setPosition(bubbleList.size());
055            bubbleList.add(queue);
056        }
057        return queue;
058    }
059
060    /**
061     * After a message queue has changed we may need to perform some evictions
062     * 
063     * @param delta
064     * @param queueSize
065     */
066    public void onSizeChanged(MessageQueue queue, int delta, int queueSize) {
067        synchronized (lock) {
068            bubbleUp(queue, queueSize);
069
070            size += delta;
071            while (size > limit) {
072                MessageQueue biggest = bubbleList.get(0);
073                size -= biggest.evictMessage();
074
075                bubbleDown(biggest, 0);
076            }
077        }
078    }
079
080    public void clear() {
081        synchronized (lock) {
082            for (Iterator<MessageQueue> iter = bubbleList.iterator(); iter.hasNext();) {
083                MessageQueue queue = iter.next();
084                queue.clear();
085            }
086            size = 0;
087        }
088    }
089
090    protected void bubbleUp(MessageQueue queue, int queueSize) {
091        // lets bubble up to head of queueif we need to
092        int position = queue.getPosition();
093        while (--position >= 0) {
094            MessageQueue pivot = bubbleList.get(position);
095            if (pivot.getSize() < queueSize) {
096                swap(position, pivot, position + 1, queue);
097            } else {
098                break;
099            }
100        }
101    }
102
103    protected void bubbleDown(MessageQueue biggest, int position) {
104        int queueSize = biggest.getSize();
105        int end = bubbleList.size();
106        for (int second = position + 1; second < end; second++) {
107            MessageQueue pivot = bubbleList.get(second);
108            if (pivot.getSize() > queueSize) {
109                swap(position, biggest, second, pivot);
110            } else {
111                break;
112            }
113            position = second;
114        }
115    }
116
117    protected void swap(int firstPosition, MessageQueue first, int secondPosition, MessageQueue second) {
118        bubbleList.set(firstPosition, second);
119        bubbleList.set(secondPosition, first);
120        first.setPosition(secondPosition);
121        second.setPosition(firstPosition);
122    }
123}