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      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> {
     31         T newInstance();
     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      */
     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      */
     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      */
     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