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comparison src/com/go/trove/util/Cache.java @ 0:3dc0c5604566

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Initial checkin of blitz 2.0 fcs - no installer yet.
author Dan Creswell <dan.creswell@gmail.com>
date Sat, 21 Mar 2009 11:00:06 +0000
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1 /* ====================================================================
2 * Trove - Copyright (c) 1997-2000 Walt Disney Internet Group
3 * ====================================================================
4 * The Tea Software License, Version 1.1
5 *
6 * Copyright (c) 2000 Walt Disney Internet Group. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 *
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 *
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in
17 * the documentation and/or other materials provided with the
18 * distribution.
19 *
20 * 3. The end-user documentation included with the redistribution,
21 * if any, must include the following acknowledgment:
22 * "This product includes software developed by the
23 * Walt Disney Internet Group (http://opensource.go.com/)."
24 * Alternately, this acknowledgment may appear in the software itself,
25 * if and wherever such third-party acknowledgments normally appear.
26 *
27 * 4. The names "Tea", "TeaServlet", "Kettle", "Trove" and "BeanDoc" must
28 * not be used to endorse or promote products derived from this
29 * software without prior written permission. For written
30 * permission, please contact opensource@dig.com.
31 *
32 * 5. Products derived from this software may not be called "Tea",
33 * "TeaServlet", "Kettle" or "Trove", nor may "Tea", "TeaServlet",
34 * "Kettle", "Trove" or "BeanDoc" appear in their name, without prior
35 * written permission of the Walt Disney Internet Group.
36 *
37 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40 * DISCLAIMED. IN NO EVENT SHALL THE WALT DISNEY INTERNET GROUP OR ITS
41 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
42 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
43 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
44 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
45 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
46 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
47 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
48 * ====================================================================
49 *
50 * For more information about Tea, please see http://opensource.go.com/.
51 */
52
53 package com.go.trove.util;
54
55 import java.util.*;
56
57 /******************************************************************************
58 * Cache is a SoftHashMap that is guaranteed to have the most recently used
59 * entries available. Calling "get" or "put" updates the internal MRU list,
60 * but calling "containsKey" or "containsValue" will not.
61 * <p>
62 * Like its base class, Cache is not thread-safe and must be wrapped with
63 * Collections.synchronizedMap to be made thread-safe.
64 *
65 * @author Brian S O'Neill
66 * @version
67 * <!--$$Revision: 1.1 $-->, <!--$$JustDate:--> 01/05/30 <!-- $-->
68 */
69 public class Cache extends SoftHashMap {
70 private final int mMaxRecent;
71 // Contains hard references to entries.
72 private final UsageMap mUsageMap;
73
74 /**
75 * Construct a Cache with an amount of recently used entries that are
76 * guaranteed to always be in the Cache.
77 *
78 * @param maxRecent maximum amount of recently used entries guaranteed to
79 * be in the Cache.
80 * @throws IllegalArgumentException if maxRecent is less than or equal to
81 * zero.
82 */
83 public Cache(int maxRecent) {
84 if (maxRecent <= 0) {
85 throw new IllegalArgumentException
86 ("Max recent must be greater than zero: " + maxRecent);
87 }
88 mMaxRecent = maxRecent;
89 mUsageMap = new UsageMap();
90 }
91
92 /**
93 * Piggyback this Cache onto another one in order for the map of recently
94 * used entries to be shared. If this Cache is more active than the one
95 * it attaches to, then more of its most recently used entries will be
96 * guaranteed to be in the Cache, possibly bumping out entries from the
97 * other Cache.
98 */
99 public Cache(Cache cache) {
100 mMaxRecent = cache.mMaxRecent;
101 mUsageMap = cache.mUsageMap;
102 }
103
104 public Object get(Object key) {
105 Object value = super.get(key);
106 if (value != null || super.containsKey(key)) {
107 adjustMRU(key, value);
108 }
109 return value;
110 }
111
112 public Object put(Object key, Object value) {
113 if (value == null) {
114 value = new Null();
115 }
116 adjustMRU(key, value);
117 return super.put(key, value);
118 }
119
120 public Object remove(Object key) {
121 synchronized (mUsageMap) {
122 mUsageMap.remove(key);
123 }
124 return super.remove(key);
125 }
126
127 public void clear() {
128 super.clear();
129 synchronized (mUsageMap) {
130 mUsageMap.clear();
131 }
132 }
133
134 private void adjustMRU(Object key, Object value) {
135 synchronized (mUsageMap) {
136 Object existing = mUsageMap.get(key);
137
138 if (existing != null) {
139 if (value == null && existing instanceof Null) {
140 value = existing;
141 }
142 }
143 else {
144 if (!mUsageMap.containsKey(key)) {
145 // A new entry will be put into the UsageMap, so remove
146 // least recently used if MRU is too big.
147 while (mUsageMap.size() >= mMaxRecent) {
148 mUsageMap.remove(mUsageMap.lastKey());
149 }
150 }
151 }
152
153 mUsageMap.put(key, value);
154 }
155 }
156 }