|
1
11 package org.eclipse.core.internal.utils;
12
13 import org.eclipse.core.runtime.Assert;
14
15
20 public class Cache {
21 public class Entry implements KeyedHashSet.KeyedElement {
22 Object  cached;
23 Object key;
24 Entry next;
25 Entry previous;
26 long timestamp;
27
28 public Entry(Object key, Object cached, long timestamp) {
29 this.key = key;
30 this.cached = cached;
31 this.timestamp = timestamp;
32 }
33
34 public boolean compare(KeyedHashSet.KeyedElement other) {
35 if (!(other instanceof Entry))
36 return false;
37 Entry otherEntry = (Entry) other;
38 return key.equals(otherEntry.key);
39 }
40
41
42 public void discard() {
43 unchain();
44 cached = null;
45 entries.remove(this);
46 }
47
48 public Object getCached() {
49 return cached;
50 }
51
52 public Object getKey() {
53 return key;
54 }
55
56 public int getKeyHashCode() {
57 return key.hashCode();
58 }
59
60 public Entry getNext() {
61 return next;
62 }
63
64 public Entry getPrevious() {
65 return previous;
66 }
67
68 public long getTimestamp() {
69 return timestamp;
70 }
71
72 public boolean isHead() {
73 return previous == null;
74 }
75
76 public boolean isTail() {
77 return next == null;
78 }
79
80
81 void makeHead() {
82 Entry oldHead = head;
83 head = this;
84 next = oldHead;
85 previous = null;
86 if (oldHead == null)
87 tail = this;
88 else
89 oldHead.previous = this;
90 }
91
92 public void setCached(Object cached) {
93 this.cached = cached;
94 }
95
96 public void setTimestamp(long timestamp) {
97 this.timestamp = timestamp;
98 }
99
100 public String toString() {
101 return key + " -> " + cached + " [" + timestamp + ']'; }
103
104
105 void unchain() {
106 if (tail == this)
108 tail = previous;
109 else
110 next.previous = previous;
111 if (head == this)
113 head = next;
114 else
115 previous.next = next;
116 }
117 }
118
119 KeyedHashSet entries;
120 Entry head;
121 private int maximumCapacity;
122 Entry tail;
123 private double threshold;
124
125 public Cache(int maximumCapacity) {
126 this(Math.min(KeyedHashSet.MINIMUM_SIZE, maximumCapacity), maximumCapacity, 0.25);
127 }
128
129 public Cache(int initialCapacity, int maximumCapacity, double threshold) {
130 Assert.isTrue(maximumCapacity >= initialCapacity, "maximum capacity < initial capacity"); Assert.isTrue(threshold >= 0 && threshold <= 1, "threshold should be between 0 and 1"); Assert.isTrue(initialCapacity > 0, "initial capacity must be greater than zero"); entries = new KeyedHashSet(initialCapacity);
134 this.maximumCapacity = maximumCapacity;
135 this.threshold = threshold;
136 }
137
138 public void addEntry(Object key, Object toCache) {
139 addEntry(key, toCache, 0);
140 }
141
142 public Entry addEntry(Object key, Object toCache, long timestamp) {
143 Entry newHead = (Entry) entries.getByKey(key);
144 if (newHead == null)
145 entries.add(newHead = new Entry(key, toCache, timestamp));
146 newHead.cached = toCache;
147 newHead.timestamp = timestamp;
148 newHead.makeHead();
149 int extraEntries = entries.size() - maximumCapacity;
150 if (extraEntries > maximumCapacity * threshold)
151 packEntries(extraEntries);
154 return newHead;
155 }
156
157 public Entry getEntry(Object key) {
158 return getEntry(key, true);
159 }
160
161 public Entry getEntry(Object key, boolean update) {
162 Entry existing = (Entry) entries.getByKey(key);
163 if (existing == null)
164 return null;
165 if (!update)
166 return existing;
167 existing.unchain();
168 existing.makeHead();
169 return existing;
170 }
171
172 public Entry getHead() {
173 return head;
174 }
175
176 public Entry getTail() {
177 return tail;
178 }
179
180 private void packEntries(int extraEntries) {
181 Entry current = tail;
183 for (; current != null && extraEntries > 0; extraEntries--) {
184 current.discard();
185 current = current.previous;
186 }
187 }
188
189 public long size() {
190 return entries.size();
191 }
192
193 public void discardAll() {
194 entries.clear();
195 }
196
197 public void dispose() {
198 discardAll();
199 entries = null;
200 }
201 }
202 |
Popular Tags |
Java API By Example, From Geeks To Geeks.