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Source file | Conditionals | Statements | Methods | TOTAL | |||||||||||||||
LRUCache.java | 50% | 83,3% | 100% | 81,4% |
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1 | /* | |
2 | * Copyright (c) 2002-2003 by OpenSymphony | |
3 | * All rights reserved. | |
4 | */ | |
5 | package com.opensymphony.oscache.base.algorithm; | |
6 | ||
7 | import java.util.*; | |
8 | ||
9 | /** | |
10 | * <p>LRU (Least Recently Used) algorithm for the cache.</p> | |
11 | * | |
12 | * <p>Since release 2.3 this class requires Java 1.4 | |
13 | * to use the <code>LinkedHashSet</code>. Use prior OSCache release which | |
14 | * require the Jakarta commons-collections <code>SequencedHashMap</code> | |
15 | * class or the <code>LinkedList</code> class if neither of the above | |
16 | * classes are available.</p> | |
17 | * | |
18 | * <p>No synchronization is required in this class since the | |
19 | * <code>AbstractConcurrentReadCache</code> already takes care of any | |
20 | * synchronization requirements.</p> | |
21 | * | |
22 | * @version $Revision: 427 $ | |
23 | * @author <a href="mailto:salaman@teknos.com">Victor Salaman</a> | |
24 | * @author <a href="mailto:fbeauregard@pyxis-tech.com">Francois Beauregard</a> | |
25 | * @author <a href="mailto:abergevin@pyxis-tech.com">Alain Bergevin</a> | |
26 | * @author <a href="mailto:chris@swebtec.com">Chris Miller</a> | |
27 | */ | |
28 | public class LRUCache extends AbstractConcurrentReadCache { | |
29 | ||
30 | private static final long serialVersionUID = -7379608101794788534L; | |
31 | ||
32 | /** | |
33 | * Cache queue containing all cache keys. | |
34 | */ | |
35 | private Collection list = new LinkedHashSet(); | |
36 | ||
37 | /** | |
38 | * A flag indicating whether there is a removal operation in progress. | |
39 | */ | |
40 | private volatile boolean removeInProgress = false; | |
41 | ||
42 | /** | |
43 | * Constructs an LRU Cache. | |
44 | */ | |
45 | 98 | public LRUCache() { |
46 | 98 | super(); |
47 | } | |
48 | ||
49 | /** | |
50 | * Constructors a LRU Cache of the specified capacity. | |
51 | * | |
52 | * @param capacity The maximum cache capacity. | |
53 | */ | |
54 | 68 | public LRUCache(int capacity) { |
55 | 68 | this(); |
56 | 68 | maxEntries = capacity; |
57 | } | |
58 | ||
59 | /** | |
60 | * An item was retrieved from the list. The LRU implementation moves | |
61 | * the retrieved item's key to the front of the list. | |
62 | * | |
63 | * @param key The cache key of the item that was retrieved. | |
64 | */ | |
65 | 10318 | protected void itemRetrieved(Object key) { |
66 | // Prevent list operations during remove | |
67 | 10318 | while (removeInProgress) { |
68 | 0 | try { |
69 | 0 | Thread.sleep(5); |
70 | } catch (InterruptedException ie) { | |
71 | } | |
72 | } | |
73 | ||
74 | // We need to synchronize here because AbstractConcurrentReadCache | |
75 | // doesn't prevent multiple threads from calling this method simultaneously. | |
76 | 10318 | synchronized (list) { |
77 | 10318 | list.remove(key); |
78 | 10318 | list.add(key); |
79 | } | |
80 | } | |
81 | ||
82 | /** | |
83 | * An object was put in the cache. This implementation adds/moves the | |
84 | * key to the end of the list. | |
85 | * | |
86 | * @param key The cache key of the item that was put. | |
87 | */ | |
88 | 65465 | protected void itemPut(Object key) { |
89 | // Since this entry was just accessed, move it to the back of the list. | |
90 | 65465 | synchronized (list) { // A further fix for CACHE-44 |
91 | 65465 | list.remove(key); |
92 | 65465 | list.add(key); |
93 | } | |
94 | } | |
95 | ||
96 | /** | |
97 | * An item needs to be removed from the cache. The LRU implementation | |
98 | * removes the first element in the list (ie, the item that was least-recently | |
99 | * accessed). | |
100 | * | |
101 | * @return The key of whichever item was removed. | |
102 | */ | |
103 | 9065 | protected Object removeItem() { |
104 | 9065 | Object toRemove = null; |
105 | ||
106 | 9065 | removeInProgress = true; |
107 | 9065 | try { |
108 | 9065 | while (toRemove == null) { |
109 | 9065 | try { |
110 | 9065 | toRemove = removeFirst(); |
111 | } catch (Exception e) { | |
112 | // List is empty. | |
113 | // this is theorically possible if we have more than the size concurrent | |
114 | // thread in getItem. Remove completed but add not done yet. | |
115 | // We simply wait for add to complete. | |
116 | 0 | do { |
117 | 0 | try { |
118 | 0 | Thread.sleep(5); |
119 | } catch (InterruptedException ie) { | |
120 | } | |
121 | 0 | } while (list.isEmpty()); |
122 | } | |
123 | } | |
124 | } finally { | |
125 | 9065 | removeInProgress = false; |
126 | } | |
127 | ||
128 | 9065 | return toRemove; |
129 | } | |
130 | ||
131 | /** | |
132 | * Remove specified key since that object has been removed from the cache. | |
133 | * | |
134 | * @param key The cache key of the item that was removed. | |
135 | */ | |
136 | 171 | protected void itemRemoved(Object key) { |
137 | 171 | list.remove(key); |
138 | } | |
139 | ||
140 | /** | |
141 | * Removes the first object from the list of keys. | |
142 | * | |
143 | * @return the object that was removed | |
144 | */ | |
145 | 9065 | private Object removeFirst() { |
146 | 9065 | Object toRemove = null; |
147 | ||
148 | 9065 | synchronized (list) { // A further fix for CACHE-44 and CACHE-246 |
149 | 9065 | Iterator it = list.iterator(); |
150 | 9065 | toRemove = it.next(); |
151 | 9065 | it.remove(); |
152 | } | |
153 | ||
154 | 9065 | return toRemove; |
155 | } | |
156 | } |
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