Mercurial > hg > blitz_condensed
comparison src/com/go/trove/util/Cache.java @ 0:3dc0c5604566
Initial checkin of blitz 2.0 fcs - no installer yet.
author | Dan Creswell <dan.creswell@gmail.com> |
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date | Sat, 21 Mar 2009 11:00:06 +0000 |
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-1:000000000000 | 0:3dc0c5604566 |
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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 } |