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 17 package android.util; 18 19 /** 20 * Helper class for crating pools of objects. An example use looks like this: 21 * <pre> 22 * public class MyPooledClass { 23 * 24 * private static final SynchronizedPool<MyPooledClass> sPool = 25 * new SynchronizedPool<MyPooledClass>(10); 26 * 27 * public static MyPooledClass obtain() { 28 * MyPooledClass instance = sPool.acquire(); 29 * return (instance != null) ? instance : new MyPooledClass(); 30 * } 31 * 32 * public void recycle() { 33 * // Clear state if needed. 34 * sPool.release(this); 35 * } 36 * 37 * . . . 38 * } 39 * </pre> 40 * 41 * @hide 42 */ 43 public final class Pools { 44 45 /** 46 * Interface for managing a pool of objects. 47 * 48 * @param <T> The pooled type. 49 */ 50 public static interface Pool<T> { 51 52 /** 53 * @return An instance from the pool if such, null otherwise. 54 */ acquire()55 public T acquire(); 56 57 /** 58 * Release an instance to the pool. 59 * 60 * @param instance The instance to release. 61 * @return Whether the instance was put in the pool. 62 * 63 * @throws IllegalStateException If the instance is already in the pool. 64 */ release(T instance)65 public boolean release(T instance); 66 } 67 Pools()68 private Pools() { 69 /* do nothing - hiding constructor */ 70 } 71 72 /** 73 * Simple (non-synchronized) pool of objects. 74 * 75 * @param <T> The pooled type. 76 */ 77 public static class SimplePool<T> implements Pool<T> { 78 private final Object[] mPool; 79 80 private int mPoolSize; 81 82 /** 83 * Creates a new instance. 84 * 85 * @param maxPoolSize The max pool size. 86 * 87 * @throws IllegalArgumentException If the max pool size is less than zero. 88 */ SimplePool(int maxPoolSize)89 public SimplePool(int maxPoolSize) { 90 if (maxPoolSize <= 0) { 91 throw new IllegalArgumentException("The max pool size must be > 0"); 92 } 93 mPool = new Object[maxPoolSize]; 94 } 95 96 @Override 97 @SuppressWarnings("unchecked") acquire()98 public T acquire() { 99 if (mPoolSize > 0) { 100 final int lastPooledIndex = mPoolSize - 1; 101 T instance = (T) mPool[lastPooledIndex]; 102 mPool[lastPooledIndex] = null; 103 mPoolSize--; 104 return instance; 105 } 106 return null; 107 } 108 109 @Override release(T instance)110 public boolean release(T instance) { 111 if (isInPool(instance)) { 112 throw new IllegalStateException("Already in the pool!"); 113 } 114 if (mPoolSize < mPool.length) { 115 mPool[mPoolSize] = instance; 116 mPoolSize++; 117 return true; 118 } 119 return false; 120 } 121 isInPool(T instance)122 private boolean isInPool(T instance) { 123 for (int i = 0; i < mPoolSize; i++) { 124 if (mPool[i] == instance) { 125 return true; 126 } 127 } 128 return false; 129 } 130 } 131 132 /** 133 * Synchronized) pool of objects. 134 * 135 * @param <T> The pooled type. 136 */ 137 public static class SynchronizedPool<T> extends SimplePool<T> { 138 private final Object mLock = new Object(); 139 140 /** 141 * Creates a new instance. 142 * 143 * @param maxPoolSize The max pool size. 144 * 145 * @throws IllegalArgumentException If the max pool size is less than zero. 146 */ SynchronizedPool(int maxPoolSize)147 public SynchronizedPool(int maxPoolSize) { 148 super(maxPoolSize); 149 } 150 151 @Override acquire()152 public T acquire() { 153 synchronized (mLock) { 154 return super.acquire(); 155 } 156 } 157 158 @Override release(T element)159 public boolean release(T element) { 160 synchronized (mLock) { 161 return super.release(element); 162 } 163 } 164 } 165 } 166