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.Iterator;
020import java.util.LinkedList;
021
022/**
023 * A {@link MessageBuffer} which evicts messages in arrival order so the oldest
024 * messages are removed first.
025 * 
026 * 
027 */
028public class OrderBasedMessageBuffer implements MessageBuffer {
029
030    private int limit = 100 * 64 * 1024;
031    private LinkedList<MessageQueue> list = new LinkedList<MessageQueue>();
032    private int size;
033    private Object lock = new Object();
034
035    public OrderBasedMessageBuffer() {
036    }
037
038    public OrderBasedMessageBuffer(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        return new MessageQueue(this);
053    }
054
055    /**
056     * After a message queue has changed we may need to perform some evictions
057     * 
058     * @param delta
059     * @param queueSize
060     */
061    public void onSizeChanged(MessageQueue queue, int delta, int queueSize) {
062        synchronized (lock) {
063            list.addLast(queue);
064            size += delta;
065            while (size > limit) {
066                MessageQueue biggest = list.removeFirst();
067                size -= biggest.evictMessage();
068            }
069        }
070    }
071
072    public void clear() {
073        synchronized (lock) {
074            for (Iterator<MessageQueue> iter = list.iterator(); iter.hasNext();) {
075                MessageQueue queue = iter.next();
076                queue.clear();
077            }
078            size = 0;
079        }
080    }
081
082}