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