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| Source file | Conditionals | Statements | Methods | TOTAL | |||||||||||||||
| LRUCache.java | 25% | 77.8% | 100% | 76.3% |
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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 org.apache.commons.logging.Log; | |
| 8 | import org.apache.commons.logging.LogFactory; | |
| 9 | ||
| 10 | import java.util.*; | |
| 11 | ||
| 12 | /** | |
| 13 | * <p>LRU (Least Recently Used) algorithm for the cache.</p> | |
| 14 | * | |
| 15 | * <p>Since release 2.3 this class requires Java 1.4 | |
| 16 | * to use the <code>LinkedHashSet</code>. Use prior OSCache release which | |
| 17 | * require the Jakarta commons-collections <code>SequencedHashMap</code> | |
| 18 | * class or the <code>LinkedList</code> class if neither of the above | |
| 19 | * classes are available.</p> | |
| 20 | * | |
| 21 | * <p>No synchronization is required in this class since the | |
| 22 | * <code>AbstractConcurrentReadCache</code> already takes care of any | |
| 23 | * synchronization requirements.</p> | |
| 24 | * | |
| 25 | * @version $Revision: 1.3 $ | |
| 26 | * @author <a href="mailto:salaman@teknos.com">Victor Salaman</a> | |
| 27 | * @author <a href="mailto:fbeauregard@pyxis-tech.com">Francois Beauregard</a> | |
| 28 | * @author <a href="mailto:abergevin@pyxis-tech.com">Alain Bergevin</a> | |
| 29 | * @author <a href="mailto:chris@swebtec.com">Chris Miller</a> | |
| 30 | */ | |
| 31 | public class LRUCache extends AbstractConcurrentReadCache { | |
| 32 | ||
| 33 | private static final Log log = LogFactory.getLog(LRUCache.class); | |
| 34 | ||
| 35 | /** | |
| 36 | * Cache queue containing all cache keys. | |
| 37 | */ | |
| 38 | private Collection list = new LinkedHashSet(); | |
| 39 | ||
| 40 | /** | |
| 41 | * A flag indicating whether there is a removal operation in progress. | |
| 42 | */ | |
| 43 | private volatile boolean removeInProgress = false; | |
| 44 | ||
| 45 | /** | |
| 46 | * Constructs an LRU Cache. | |
| 47 | */ | |
| 48 | 60 | public LRUCache() { |
| 49 | 60 | super(); |
| 50 | } | |
| 51 | ||
| 52 | /** | |
| 53 | * Constructors a LRU Cache of the specified capacity. | |
| 54 | * | |
| 55 | * @param capacity The maximum cache capacity. | |
| 56 | */ | |
| 57 | 36 | public LRUCache(int capacity) { |
| 58 | 36 | this(); |
| 59 | 36 | maxEntries = capacity; |
| 60 | } | |
| 61 | ||
| 62 | /** | |
| 63 | * An item was retrieved from the list. The LRU implementation moves | |
| 64 | * the retrieved item's key to the front of the list. | |
| 65 | * | |
| 66 | * @param key The cache key of the item that was retrieved. | |
| 67 | */ | |
| 68 | 8258 | protected void itemRetrieved(Object key) { |
| 69 | // Prevent list operations during remove | |
| 70 | 8258 | while (removeInProgress) { |
| 71 | 0 | try { |
| 72 | 0 | Thread.sleep(5); |
| 73 | } catch (InterruptedException ie) { | |
| 74 | } | |
| 75 | } | |
| 76 | ||
| 77 | // We need to synchronize here because AbstractConcurrentReadCache | |
| 78 | // doesn't prevent multiple threads from calling this method simultaneously. | |
| 79 | 8258 | synchronized (list) { |
| 80 | 8258 | list.remove(key); |
| 81 | 8258 | list.add(key); |
| 82 | } | |
| 83 | } | |
| 84 | ||
| 85 | /** | |
| 86 | * An object was put in the cache. This implementation adds/moves the | |
| 87 | * key to the end of the list. | |
| 88 | * | |
| 89 | * @param key The cache key of the item that was put. | |
| 90 | */ | |
| 91 | 12303 | protected void itemPut(Object key) { |
| 92 | // Since this entry was just accessed, move it to the back of the list. | |
| 93 | 12303 | synchronized (list) { // A further fix for CACHE-44 |
| 94 | 12303 | list.remove(key); |
| 95 | 12303 | list.add(key); |
| 96 | } | |
| 97 | } | |
| 98 | ||
| 99 | /** | |
| 100 | * An item needs to be removed from the cache. The LRU implementation | |
| 101 | * removes the first element in the list (ie, the item that was least-recently | |
| 102 | * accessed). | |
| 103 | * | |
| 104 | * @return The key of whichever item was removed. | |
| 105 | */ | |
| 106 | 7228 | protected Object removeItem() { |
| 107 | 7228 | removeInProgress = true; |
| 108 | ||
| 109 | 7228 | Object toRemove; |
| 110 | ||
| 111 | 7228 | try { |
| 112 | 7228 | toRemove = removeFirst(); |
| 113 | } catch (Exception e) { | |
| 114 | // List is empty. | |
| 115 | // this is theorically possible if we have more than the size concurrent | |
| 116 | // thread in getItem. Remove completed but add not done yet. | |
| 117 | // We simply wait for add to complete. | |
| 118 | 0 | do { |
| 119 | 0 | try { |
| 120 | 0 | Thread.sleep(5); |
| 121 | } catch (InterruptedException ie) { | |
| 122 | } | |
| 123 | 0 | } while (list.size() == 0); |
| 124 | ||
| 125 | 0 | toRemove = removeFirst(); |
| 126 | } | |
| 127 | ||
| 128 | 7228 | removeInProgress = false; |
| 129 | ||
| 130 | 7228 | return toRemove; |
| 131 | } | |
| 132 | ||
| 133 | /** | |
| 134 | * Remove specified key since that object has been removed from the cache. | |
| 135 | * | |
| 136 | * @param key The cache key of the item that was removed. | |
| 137 | */ | |
| 138 | 90 | protected void itemRemoved(Object key) { |
| 139 | 90 | list.remove(key); |
| 140 | } | |
| 141 | ||
| 142 | /** | |
| 143 | * Removes the first object from the list of keys. | |
| 144 | * | |
| 145 | * @return the object that was removed | |
| 146 | */ | |
| 147 | 7228 | private Object removeFirst() { |
| 148 | 7228 | Iterator it = list.iterator(); |
| 149 | 7228 | Object toRemove = it.next(); |
| 150 | 7228 | it.remove(); |
| 151 | ||
| 152 | 7228 | return toRemove; |
| 153 | } | |
| 154 | } |
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