KeyStoreLruCache.java revision 81e0c8491f22c64300182c652ac2add96888dd2e
1/*
2 * Copyright (C) 2014 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
17package com.android.systemui.recents.model;
18
19import android.util.LruCache;
20
21import java.util.HashMap;
22
23/**
24 * An LRU cache that support querying the keys as well as values. By using the Task's key, we can
25 * prevent holding onto a reference to the Task resource data, while keeping the cache data in
26 * memory where necessary.
27 */
28public class KeyStoreLruCache<V> {
29    // We keep a set of keys that are associated with the LRU cache, so that we can find out
30    // information about the Task that was previously in the cache.
31    HashMap<Integer, Task.TaskKey> mTaskKeys = new HashMap<Integer, Task.TaskKey>();
32    // The cache implementation
33    LruCache<Integer, V> mCache;
34
35    public KeyStoreLruCache(int cacheSize) {
36        mCache = new LruCache<Integer, V>(cacheSize) {
37
38            @Override
39            protected void entryRemoved(boolean evicted, Integer taskId, V oldV, V newV) {
40                mTaskKeys.remove(taskId);
41            }
42        };
43    }
44
45    /** Gets a specific entry in the cache. */
46    final V get(Task.TaskKey key) {
47        return mCache.get(key.id);
48    }
49
50    /**
51     * Returns the value only if the Task has not updated since the last time it was in the cache.
52     */
53    final V getAndInvalidateIfModified(Task.TaskKey key) {
54        Task.TaskKey lastKey = mTaskKeys.get(key.id);
55        if (lastKey != null && (lastKey.lastActiveTime < key.lastActiveTime)) {
56            // The task has updated (been made active since the last time it was put into the
57            // LRU cache) so invalidate that item in the cache
58            remove(key);
59            return null;
60        }
61        // Either the task does not exist in the cache, or the last active time is the same as
62        // the key specified, so return what is in the cache
63        return mCache.get(key.id);
64    }
65
66    /** Puts an entry in the cache for a specific key. */
67    final void put(Task.TaskKey key, V value) {
68        mCache.put(key.id, value);
69        mTaskKeys.put(key.id, key);
70    }
71
72    /** Removes a cache entry for a specific key. */
73    final void remove(Task.TaskKey key) {
74        mCache.remove(key.id);
75        mTaskKeys.remove(key.id);
76    }
77
78    /** Removes all the entries in the cache. */
79    final void evictAll() {
80        mCache.evictAll();
81        mTaskKeys.clear();
82    }
83
84    /** Returns the size of the cache. */
85    final int size() {
86        return mCache.size();
87    }
88
89    /** Trims the cache to a specific size */
90    final void trimToSize(int cacheSize) {
91        mCache.resize(cacheSize);
92    }
93}
94