1 /**
2  * Copyright (c) 2012, Google Inc.
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 
18 package com.android.mail.utils;
19 
20 import com.google.common.collect.Lists;
21 
22 import java.util.Deque;
23 
24 /**
25  * This class maintains a cache of soft references to objects.  This allows callers to use a pool
26  * of object instances
27  * @param <T>
28  */
29 public class ObjectCache<T> {
30     public interface Callback<T> {
newInstance()31         T newInstance();
onObjectReleased(T object)32         void onObjectReleased(T object);
33     }
34 
35     private final Deque<T> mDataStore = Lists.newLinkedList();
36 
37     private final Callback<T> mCallback;
38     private final int mMaxSize;
39 
40     /**
41      * Creates a new ObjectCache instance
42      * @param callbacks Callback object that that will return a new instance of the object, and
43      *        perform any cleanup when the object is released back to the cache
44      */
ObjectCache(Callback<T> callbacks, int maxSize)45     public ObjectCache(Callback<T> callbacks, int maxSize) {
46         mCallback = callbacks;
47         mMaxSize = maxSize;
48     }
49 
50     /**
51      * Returns an instance of the specified object type, creating a new instance if needed.
52      */
get()53     public T get() {
54         T result;
55         synchronized (mDataStore) {
56             result = mDataStore.poll();
57         }
58         if (result == null) {
59             result = mCallback.newInstance();
60         }
61         return result;
62     }
63 
64     /**
65      * Releases the specified object back to the cache.  Once an object is released, it can be
66      * returned by subsequent calls to get()
67      */
release(T objectToCache)68     public void release(T objectToCache) {
69         synchronized (mDataStore) {
70             if (mDataStore.size() < mMaxSize) {
71                 mCallback.onObjectReleased(objectToCache);
72                 mDataStore.add(objectToCache);
73             }
74         }
75     }
76 }
77