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Java > Open Source Codes > org > apache > activemq > memory > buffer > SizeBasedMessageBuffer


1 /**
2  *
3  * Licensed to the Apache Software Foundation (ASF) under one or more
4  * contributor license agreements. See the NOTICE file distributed with
5  * this work for additional information regarding copyright ownership.
6  * The ASF licenses this file to You under the Apache License, Version 2.0
7  * (the "License"); you may not use this file except in compliance with
8  * the License. You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18 package org.apache.activemq.memory.buffer;
19
20 import java.util.ArrayList JavaDoc;
21 import java.util.Iterator JavaDoc;
22 import java.util.List JavaDoc;
23
24 /**
25  * A {@link MessageBuffer} which evicts from the largest buffers first.
26  *
27  * @version $Revision: 1.1 $
28  */
29 public class SizeBasedMessageBuffer implements MessageBuffer {
30
31     private int limit = 100 * 64 * 1024;
32     private List JavaDoc bubbleList = new ArrayList JavaDoc();
33     private int size;
34     private Object JavaDoc lock = new Object JavaDoc();
35
36     public SizeBasedMessageBuffer() {
37     }
38
39     public SizeBasedMessageBuffer(int limit) {
40         this.limit = limit;
41     }
42
43     public int getSize() {
44         synchronized (lock) {
45             return size;
46         }
47     }
48
49     /**
50      * Creates a new message queue instance
51      */
52     public MessageQueue createMessageQueue() {
53         MessageQueue queue = new MessageQueue(this);
54         synchronized (lock) {
55             queue.setPosition(bubbleList.size());
56             bubbleList.add(queue);
57         }
58         return queue;
59     }
60
61     /**
62      * After a message queue has changed we may need to perform some evictions
63      *
64      * @param delta
65      * @param queueSize
66      */
67     public void onSizeChanged(MessageQueue queue, int delta, int queueSize) {
68         synchronized (lock) {
69             bubbleUp(queue, queueSize);
70
71             size += delta;
72             while (size > limit) {
73                 MessageQueue biggest = (MessageQueue) bubbleList.get(0);
74                 size -= biggest.evictMessage();
75
76                 bubbleDown(biggest, 0);
77             }
78         }
79     }
80
81     public void clear() {
82         synchronized (lock) {
83             for (Iterator JavaDoc iter = bubbleList.iterator(); iter.hasNext();) {
84                 MessageQueue queue = (MessageQueue) iter.next();
85                 queue.clear();
86             }
87             size = 0;
88         }
89     }
90
91     protected void bubbleUp(MessageQueue queue, int queueSize) {
92         // lets bubble up to head of queueif we need to
93 int position = queue.getPosition();
94         while (--position >= 0) {
95             MessageQueue pivot = (MessageQueue) bubbleList.get(position);
96             if (pivot.getSize() < queueSize) {
97                 swap(position, pivot, position + 1, queue);
98             }
99             else {
100                 break;
101             }
102         }
103     }
104
105     protected void bubbleDown(MessageQueue biggest, int position) {
106         int queueSize = biggest.getSize();
107         for (int second = position + 1, end = bubbleList.size(); second < end; second++) {
108             MessageQueue pivot = (MessageQueue) bubbleList.get(second);
109             if (pivot.getSize() > queueSize) {
110                 swap(position, biggest, second, pivot);
111             }
112             else {
113                 break;
114             }
115             position = second;
116         }
117     }
118
119     protected void swap(int firstPosition, MessageQueue first, int secondPosition, MessageQueue second) {
120         bubbleList.set(firstPosition, second);
121         bubbleList.set(secondPosition, first);
122         first.setPosition(secondPosition);
123         second.setPosition(firstPosition);
124     }
125 }
126
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