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| 1 // Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file |
| 2 // for details. All rights reserved. Use of this source code is governed by a |
| 3 // BSD-style license that can be found in the LICENSE file. |
| 4 |
| 5 library engine.utilities.lru_cache; |
| 6 |
| 7 import 'dart:collection'; |
| 8 |
| 9 /** |
| 10 * This handler is notified when an item is evicted from the cache. |
| 11 */ |
| 12 typedef EvictionHandler<K, V>(K key, V value); |
| 13 |
| 14 /** |
| 15 * A hash-table based cache implementation. |
| 16 * |
| 17 * When it reaches the specified number of items, the item that has not been |
| 18 * accessed (both get and put) recently is evicted. |
| 19 */ |
| 20 class LRUMap<K, V> { |
| 21 final LinkedHashMap<K, V> _map = new LinkedHashMap<K, V>(); |
| 22 final int _maxSize; |
| 23 final EvictionHandler _handler; |
| 24 |
| 25 LRUMap(this._maxSize, [this._handler]); |
| 26 |
| 27 /** |
| 28 * Returns the value for the given [key] or null if [key] is not |
| 29 * in the cache. |
| 30 */ |
| 31 V get(K key) { |
| 32 V value = _map.remove(key); |
| 33 if (value != null) { |
| 34 _map[key] = value; |
| 35 } |
| 36 return value; |
| 37 } |
| 38 |
| 39 /** |
| 40 * Associates the [key] with the given [value]. |
| 41 * |
| 42 * If the cache is full, an item that has not been accessed recently is |
| 43 * evicted. |
| 44 */ |
| 45 void put(K key, V value) { |
| 46 _map.remove(key); |
| 47 _map[key] = value; |
| 48 if (_map.length > _maxSize) { |
| 49 K evictedKey = _map.keys.first; |
| 50 V evictedValue = _map.remove(evictedKey); |
| 51 if (_handler != null) { |
| 52 _handler(evictedKey, evictedValue); |
| 53 } |
| 54 } |
| 55 } |
| 56 |
| 57 /** |
| 58 * Removes the association for the given [key]. |
| 59 */ |
| 60 void remove(K key) { |
| 61 _map.remove(key); |
| 62 } |
| 63 } |
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