1/*
2 * Copyright (C) 2009 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.gallery3d.common;
18
19import java.lang.ref.ReferenceQueue;
20import java.lang.ref.WeakReference;
21import java.util.HashMap;
22import java.util.LinkedHashMap;
23import java.util.Map;
24
25/**
26 * An LRU cache which stores recently inserted entries and all entries ever
27 * inserted which still has a strong reference elsewhere.
28 */
29public class LruCache<K, V> {
30
31    private final HashMap<K, V> mLruMap;
32    private final HashMap<K, Entry<K, V>> mWeakMap =
33            new HashMap<K, Entry<K, V>>();
34    private ReferenceQueue<V> mQueue = new ReferenceQueue<V>();
35
36    @SuppressWarnings("serial")
37    public LruCache(final int capacity) {
38        mLruMap = new LinkedHashMap<K, V>(16, 0.75f, true) {
39            @Override
40            protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
41                return size() > capacity;
42            }
43        };
44    }
45
46    private static class Entry<K, V> extends WeakReference<V> {
47        K mKey;
48
49        public Entry(K key, V value, ReferenceQueue<V> queue) {
50            super(value, queue);
51            mKey = key;
52        }
53    }
54
55    @SuppressWarnings("unchecked")
56    private void cleanUpWeakMap() {
57        Entry<K, V> entry = (Entry<K, V>) mQueue.poll();
58        while (entry != null) {
59            mWeakMap.remove(entry.mKey);
60            entry = (Entry<K, V>) mQueue.poll();
61        }
62    }
63
64    public synchronized boolean containsKey(K key) {
65        cleanUpWeakMap();
66        return mWeakMap.containsKey(key);
67    }
68
69    public synchronized V put(K key, V value) {
70        cleanUpWeakMap();
71        mLruMap.put(key, value);
72        Entry<K, V> entry = mWeakMap.put(
73                key, new Entry<K, V>(key, value, mQueue));
74        return entry == null ? null : entry.get();
75    }
76
77    public synchronized V get(K key) {
78        cleanUpWeakMap();
79        V value = mLruMap.get(key);
80        if (value != null) return value;
81        Entry<K, V> entry = mWeakMap.get(key);
82        return entry == null ? null : entry.get();
83    }
84
85    public synchronized void clear() {
86        mLruMap.clear();
87        mWeakMap.clear();
88        mQueue = new ReferenceQueue<V>();
89    }
90}
91