811a5a4a |
1 | /* |
2 | * Copyright (C) 2011 The Android Open Source Project |
3 | * |
4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
5 | * you may not use this file except in compliance with the License. |
6 | * You may obtain a copy of the License at |
7 | * |
8 | * http://www.apache.org/licenses/LICENSE-2.0 |
9 | * |
10 | * Unless required by applicable law or agreed to in writing, software |
11 | * distributed under the License is distributed on an "AS IS" BASIS, |
12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
13 | * See the License for the specific language governing permissions and |
14 | * limitations under the License. |
15 | */ |
16 | |
17 | package android.support.v2.util; |
18 | |
19 | import java.util.LinkedHashMap; |
20 | import java.util.Map; |
21 | |
22 | /** |
23 | * Static library version of {@code android.util.LruCache}. Used to write apps |
24 | * that run on API levels prior to 12. When running on API level 12 or above, |
25 | * this implementation is still used; it does not try to switch to the |
26 | * framework's implementation. See the framework SDK documentation for a class |
27 | * overview. |
28 | */ |
29 | public class LruCache<K, V> { |
30 | private final LinkedHashMap<K, V> map; |
31 | |
32 | /** Size of this cache in units. Not necessarily the number of elements. */ |
33 | private int size; |
34 | private int maxSize; |
35 | |
36 | private int putCount; |
37 | private int createCount; |
38 | private int evictionCount; |
39 | private int hitCount; |
40 | private int missCount; |
41 | |
42 | /** |
43 | * @param maxSize for caches that do not override {@link #sizeOf}, this is |
44 | * the maximum number of entries in the cache. For all other caches, |
45 | * this is the maximum sum of the sizes of the entries in this cache. |
46 | */ |
47 | public LruCache(int maxSize) { |
48 | if (maxSize <= 0) { |
49 | throw new IllegalArgumentException("maxSize <= 0"); |
50 | } |
51 | this.maxSize = maxSize; |
52 | this.map = new LinkedHashMap<K, V>(0, 0.75f, true); |
53 | } |
54 | |
55 | /** |
56 | * Returns the value for {@code key} if it exists in the cache or can be |
57 | * created by {@code #create}. If a value was returned, it is moved to the |
58 | * head of the queue. This returns null if a value is not cached and cannot |
59 | * be created. |
60 | */ |
61 | public final V get(K key) { |
62 | if (key == null) { |
63 | throw new NullPointerException("key == null"); |
64 | } |
65 | |
66 | V mapValue; |
67 | synchronized (this) { |
68 | mapValue = map.get(key); |
69 | if (mapValue != null) { |
70 | hitCount++; |
71 | return mapValue; |
72 | } |
73 | missCount++; |
74 | } |
75 | |
76 | /* |
77 | * Attempt to create a value. This may take a long time, and the map |
78 | * may be different when create() returns. If a conflicting value was |
79 | * added to the map while create() was working, we leave that value in |
80 | * the map and release the created value. |
81 | */ |
82 | |
83 | V createdValue = create(key); |
84 | if (createdValue == null) { |
85 | return null; |
86 | } |
87 | |
88 | synchronized (this) { |
89 | createCount++; |
90 | mapValue = map.put(key, createdValue); |
91 | |
92 | if (mapValue != null) { |
93 | // There was a conflict so undo that last put |
94 | map.put(key, mapValue); |
95 | } else { |
96 | size += safeSizeOf(key, createdValue); |
97 | } |
98 | } |
99 | |
100 | if (mapValue != null) { |
101 | entryRemoved(false, key, createdValue, mapValue); |
102 | return mapValue; |
103 | } else { |
104 | trimToSize(maxSize); |
105 | return createdValue; |
106 | } |
107 | } |
108 | |
109 | /** |
110 | * Caches {@code value} for {@code key}. The value is moved to the head of |
111 | * the queue. |
112 | * |
113 | * @return the previous value mapped by {@code key}. |
114 | */ |
115 | public final V put(K key, V value) { |
116 | if (key == null || value == null) { |
117 | throw new NullPointerException("key == null || value == null"); |
118 | } |
119 | |
120 | V previous; |
121 | synchronized (this) { |
122 | putCount++; |
123 | size += safeSizeOf(key, value); |
124 | previous = map.put(key, value); |
125 | if (previous != null) { |
126 | size -= safeSizeOf(key, previous); |
127 | } |
128 | } |
129 | |
130 | if (previous != null) { |
131 | entryRemoved(false, key, previous, value); |
132 | } |
133 | |
134 | trimToSize(maxSize); |
135 | return previous; |
136 | } |
137 | |
138 | /** |
139 | * @param maxSize the maximum size of the cache before returning. May be -1 |
140 | * to evict even 0-sized elements. |
141 | */ |
142 | private void trimToSize(int maxSize) { |
143 | while (true) { |
144 | K key; |
145 | V value; |
146 | synchronized (this) { |
147 | if (size < 0 || (map.isEmpty() && size != 0)) { |
148 | throw new IllegalStateException(getClass().getName() |
149 | + ".sizeOf() is reporting inconsistent results!"); |
150 | } |
151 | |
152 | if (size <= maxSize || map.isEmpty()) { |
153 | break; |
154 | } |
155 | |
156 | Map.Entry<K, V> toEvict = map.entrySet().iterator().next(); |
157 | key = toEvict.getKey(); |
158 | value = toEvict.getValue(); |
159 | map.remove(key); |
160 | size -= safeSizeOf(key, value); |
161 | evictionCount++; |
162 | } |
163 | |
164 | entryRemoved(true, key, value, null); |
165 | } |
166 | } |
167 | |
168 | /** |
169 | * Removes the entry for {@code key} if it exists. |
170 | * |
171 | * @return the previous value mapped by {@code key}. |
172 | */ |
173 | public final V remove(K key) { |
174 | if (key == null) { |
175 | throw new NullPointerException("key == null"); |
176 | } |
177 | |
178 | V previous; |
179 | synchronized (this) { |
180 | previous = map.remove(key); |
181 | if (previous != null) { |
182 | size -= safeSizeOf(key, previous); |
183 | } |
184 | } |
185 | |
186 | if (previous != null) { |
187 | entryRemoved(false, key, previous, null); |
188 | } |
189 | |
190 | return previous; |
191 | } |
192 | |
193 | /** |
194 | * Called for entries that have been evicted or removed. This method is |
195 | * invoked when a value is evicted to make space, removed by a call to |
196 | * {@link #remove}, or replaced by a call to {@link #put}. The default |
197 | * implementation does nothing. |
198 | * |
199 | * <p>The method is called without synchronization: other threads may |
200 | * access the cache while this method is executing. |
201 | * |
202 | * @param evicted true if the entry is being removed to make space, false |
203 | * if the removal was caused by a {@link #put} or {@link #remove}. |
204 | * @param newValue the new value for {@code key}, if it exists. If non-null, |
205 | * this removal was caused by a {@link #put}. Otherwise it was caused by |
206 | * an eviction or a {@link #remove}. |
207 | */ |
208 | protected void entryRemoved(boolean evicted, K key, V oldValue, V newValue) {} |
209 | |
210 | /** |
211 | * Called after a cache miss to compute a value for the corresponding key. |
212 | * Returns the computed value or null if no value can be computed. The |
213 | * default implementation returns null. |
214 | * |
215 | * <p>The method is called without synchronization: other threads may |
216 | * access the cache while this method is executing. |
217 | * |
218 | * <p>If a value for {@code key} exists in the cache when this method |
219 | * returns, the created value will be released with {@link #entryRemoved} |
220 | * and discarded. This can occur when multiple threads request the same key |
221 | * at the same time (causing multiple values to be created), or when one |
222 | * thread calls {@link #put} while another is creating a value for the same |
223 | * key. |
224 | */ |
225 | protected V create(K key) { |
226 | return null; |
227 | } |
228 | |
229 | private int safeSizeOf(K key, V value) { |
230 | int result = sizeOf(key, value); |
231 | if (result < 0) { |
232 | throw new IllegalStateException("Negative size: " + key + "=" + value); |
233 | } |
234 | return result; |
235 | } |
236 | |
237 | /** |
238 | * Returns the size of the entry for {@code key} and {@code value} in |
239 | * user-defined units. The default implementation returns 1 so that size |
240 | * is the number of entries and max size is the maximum number of entries. |
241 | * |
242 | * <p>An entry's size must not change while it is in the cache. |
243 | */ |
244 | protected int sizeOf(K key, V value) { |
245 | return 1; |
246 | } |
247 | |
248 | /** |
249 | * Clear the cache, calling {@link #entryRemoved} on each removed entry. |
250 | */ |
251 | public final void evictAll() { |
252 | trimToSize(-1); // -1 will evict 0-sized elements |
253 | } |
254 | |
255 | /** |
256 | * For caches that do not override {@link #sizeOf}, this returns the number |
257 | * of entries in the cache. For all other caches, this returns the sum of |
258 | * the sizes of the entries in this cache. |
259 | */ |
260 | public synchronized final int size() { |
261 | return size; |
262 | } |
263 | |
264 | /** |
265 | * For caches that do not override {@link #sizeOf}, this returns the maximum |
266 | * number of entries in the cache. For all other caches, this returns the |
267 | * maximum sum of the sizes of the entries in this cache. |
268 | */ |
269 | public synchronized final int maxSize() { |
270 | return maxSize; |
271 | } |
272 | |
273 | /** |
274 | * Returns the number of times {@link #get} returned a value. |
275 | */ |
276 | public synchronized final int hitCount() { |
277 | return hitCount; |
278 | } |
279 | |
280 | /** |
281 | * Returns the number of times {@link #get} returned null or required a new |
282 | * value to be created. |
283 | */ |
284 | public synchronized final int missCount() { |
285 | return missCount; |
286 | } |
287 | |
288 | /** |
289 | * Returns the number of times {@link #create(Object)} returned a value. |
290 | */ |
291 | public synchronized final int createCount() { |
292 | return createCount; |
293 | } |
294 | |
295 | /** |
296 | * Returns the number of times {@link #put} was called. |
297 | */ |
298 | public synchronized final int putCount() { |
299 | return putCount; |
300 | } |
301 | |
302 | /** |
303 | * Returns the number of values that have been evicted. |
304 | */ |
305 | public synchronized final int evictionCount() { |
306 | return evictionCount; |
307 | } |
308 | |
309 | /** |
310 | * Returns a copy of the current contents of the cache, ordered from least |
311 | * recently accessed to most recently accessed. |
312 | */ |
313 | public synchronized final Map<K, V> snapshot() { |
314 | return new LinkedHashMap<K, V>(map); |
315 | } |
316 | |
317 | @Override public synchronized final String toString() { |
318 | int accesses = hitCount + missCount; |
319 | int hitPercent = accesses != 0 ? (100 * hitCount / accesses) : 0; |
320 | return String.format("LruCache[maxSize=%d,hits=%d,misses=%d,hitRate=%d%%]", |
321 | maxSize, hitCount, missCount, hitPercent); |
322 | } |
323 | } |