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      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          */
     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          */
     65         public boolean release(T instance);
     66     }
     67 
     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          */
     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")
     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
    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 
    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          */
    147         public SynchronizedPool(int maxPoolSize) {
    148             super(maxPoolSize);
    149         }
    150 
    151         @Override
    152         public T acquire() {
    153             synchronized (mLock) {
    154                 return super.acquire();
    155             }
    156         }
    157 
    158         @Override
    159         public boolean release(T element) {
    160             synchronized (mLock) {
    161                 return super.release(element);
    162             }
    163         }
    164     }
    165 }