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      1 /*
      2  * Copyright (C) 2010 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 com.android.gallery3d.util;
     18 
     19 import java.lang.ref.ReferenceQueue;
     20 import java.lang.ref.WeakReference;
     21 import java.util.ArrayList;
     22 import java.util.HashMap;
     23 import java.util.Set;
     24 
     25 public class IdentityCache<K, V> {
     26 
     27     private final HashMap<K, Entry<K, V>> mWeakMap =
     28             new HashMap<K, Entry<K, V>>();
     29     private ReferenceQueue<V> mQueue = new ReferenceQueue<V>();
     30 
     31     public IdentityCache() {
     32     }
     33 
     34     private static class Entry<K, V> extends WeakReference<V> {
     35         K mKey;
     36 
     37         public Entry(K key, V value, ReferenceQueue<V> queue) {
     38             super(value, queue);
     39             mKey = key;
     40         }
     41     }
     42 
     43     private void cleanUpWeakMap() {
     44         Entry<K, V> entry = (Entry<K, V>) mQueue.poll();
     45         while (entry != null) {
     46             mWeakMap.remove(entry.mKey);
     47             entry = (Entry<K, V>) mQueue.poll();
     48         }
     49     }
     50 
     51     public synchronized V put(K key, V value) {
     52         cleanUpWeakMap();
     53         Entry<K, V> entry = mWeakMap.put(
     54                 key, new Entry<K, V>(key, value, mQueue));
     55         return entry == null ? null : entry.get();
     56     }
     57 
     58     public synchronized V get(K key) {
     59         cleanUpWeakMap();
     60         Entry<K, V> entry = mWeakMap.get(key);
     61         return entry == null ? null : entry.get();
     62     }
     63 
     64     // This is currently unused.
     65     /*
     66     public synchronized void clear() {
     67         mWeakMap.clear();
     68         mQueue = new ReferenceQueue<V>();
     69     }
     70     */
     71 
     72     // This is for debugging only
     73     public synchronized ArrayList<K> keys() {
     74         Set<K> set = mWeakMap.keySet();
     75         ArrayList<K> result = new ArrayList<K>(set);
     76         return result;
     77     }
     78 }
     79