| 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 | } |