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      1 /*
      2  * Copyright (C) 2015 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 com.android.camera.processing.memory;
     18 
     19 import com.google.common.base.Preconditions;
     20 
     21 import javax.annotation.Nullable;
     22 import javax.annotation.concurrent.GuardedBy;
     23 import javax.annotation.concurrent.ThreadSafe;
     24 
     25 /**
     26  * Simple resource based memory pool that can automatically return
     27  * items back to the memory pool when closed.
     28  */
     29 @ThreadSafe
     30 public abstract class SimpleLruResourcePool<TKey, TValue> implements LruResourcePool<TKey, TValue> {
     31     @GuardedBy("mLock")
     32     private final LruPool<TKey, TValue> mLruPool;
     33 
     34     private final Object mLock;
     35 
     36     public SimpleLruResourcePool(int lruSize) {
     37         Preconditions.checkArgument(lruSize > 0);
     38 
     39         mLock = new Object();
     40         mLruPool = new LruPool<>(lruSize);
     41     }
     42 
     43     @Override
     44     public Resource<TValue> acquire(TKey key) {
     45         TValue value;
     46         synchronized (mLock) {
     47             value = mLruPool.acquire(key);
     48         }
     49 
     50         // We may not reach a point where we have have a value to reuse,
     51         // create a new one.
     52         if(value == null) {
     53             value = create(key);
     54         }
     55 
     56         return new SynchronizedResource<>(this, key, value);
     57     }
     58 
     59     /**
     60      * Create a new value for a given key.
     61      */
     62     protected abstract TValue create(TKey key);
     63 
     64     /**
     65      * Recycle or reset a given value before it is added back to the pool,
     66      * by default, this does nothing.
     67      */
     68     protected TValue recycle(TKey key, TValue value) {
     69         return value;
     70     }
     71 
     72     /**
     73      * Returns an item to the LruPool.
     74      */
     75     private void release(TKey key, TValue value) {
     76         mLruPool.add(key, recycle(key, value));
     77     }
     78 
     79     /**
     80      * This is a closable resource that returns the underlying value to the pool
     81      * when the object is closed.
     82      */
     83     @ThreadSafe
     84     private static final class SynchronizedResource<TKey, TValue> implements Resource<TValue> {
     85         private final Object mLock;
     86         private final SimpleLruResourcePool<TKey, TValue> mPool;
     87 
     88         @GuardedBy("mLock")
     89         private TKey mKey;
     90 
     91         @GuardedBy("mLock")
     92         private TValue mValue;
     93 
     94         public SynchronizedResource(SimpleLruResourcePool<TKey, TValue> pool,
     95               TKey key, TValue value) {
     96             mPool = pool;
     97             mKey = key;
     98             mValue = value;
     99 
    100             mLock = new Object();
    101         }
    102 
    103         @Nullable
    104         @Override
    105         public TValue get() {
    106             synchronized (mLock) {
    107                 if (mValue != null) {
    108                     return mValue;
    109                 }
    110             }
    111             return null;
    112         }
    113 
    114         @Override
    115         public void close() {
    116             synchronized (mLock) {
    117                 if (mValue != null) {
    118                     mPool.release(mKey, mValue);
    119                     mValue = null;
    120                     mKey = null;
    121                 }
    122             }
    123         }
    124     }
    125 }
    126