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      1 /*
      2  * Copyright (C) 2010 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.quicksearchbox.util;
     18 
     19 import android.util.Log;
     20 
     21 import java.util.ArrayList;
     22 import java.util.List;
     23 
     24 /**
     25  * Abstract base class for a one-place cache that holds a value that is produced
     26  * asynchronously.
     27  *
     28  * @param <A> The type of the data held in the cache.
     29  */
     30 public abstract class CachedLater<A> implements NowOrLater<A> {
     31 
     32     private static final String TAG = "QSB.AsyncCache";
     33     private static final boolean DBG = false;
     34 
     35     private final Object mLock = new Object();
     36 
     37     private A mValue;
     38 
     39     private boolean mCreating;
     40     private boolean mValid;
     41 
     42     private List<Consumer<? super A>> mWaitingConsumers;
     43 
     44     /**
     45      * Creates the object to store in the cache. This method must call
     46      * {@link #store} when it's done.
     47      * This method must not block.
     48      */
     49     protected abstract void create();
     50 
     51     /**
     52      * Saves a new value to the cache.
     53      */
     54     protected void store(A value) {
     55         if (DBG) Log.d(TAG, "store()");
     56         List<Consumer<? super A>> waitingConsumers;
     57         synchronized (mLock) {
     58             mValue = value;
     59             mValid = true;
     60             mCreating = false;
     61             waitingConsumers = mWaitingConsumers;
     62             mWaitingConsumers = null;
     63         }
     64         if (waitingConsumers != null) {
     65             for (Consumer<? super A> consumer : waitingConsumers) {
     66                 if (DBG) Log.d(TAG, "Calling consumer: " + consumer);
     67                 consumer.consume(value);
     68             }
     69         }
     70     }
     71 
     72     /**
     73      * Gets the value.
     74      *
     75      * @param consumer A consumer that will be given the cached value.
     76      *        The consumer may be called synchronously, or asynchronously on
     77      *        an unspecified thread.
     78      */
     79     public void getLater(Consumer<? super A> consumer) {
     80         if (DBG) Log.d(TAG, "getLater()");
     81         boolean valid;
     82         A value;
     83         synchronized (mLock) {
     84             valid = mValid;
     85             value = mValue;
     86             if (!valid) {
     87                 if (mWaitingConsumers == null) {
     88                     mWaitingConsumers = new ArrayList<Consumer<? super A>>();
     89                 }
     90                 mWaitingConsumers.add(consumer);
     91             }
     92         }
     93         if (valid) {
     94             if (DBG) Log.d(TAG, "valid, calling consumer synchronously");
     95             consumer.consume(value);
     96         } else {
     97             boolean create = false;
     98             synchronized (mLock) {
     99                 if (!mCreating) {
    100                     mCreating = true;
    101                     create = true;
    102                 }
    103             }
    104             if (create) {
    105                 if (DBG) Log.d(TAG, "not valid, calling create()");
    106                 create();
    107             } else {
    108                 if (DBG) Log.d(TAG, "not valid, already creating");
    109             }
    110         }
    111     }
    112 
    113     /**
    114      * Clears the cache.
    115      */
    116     public void clear() {
    117         if (DBG) Log.d(TAG, "clear()");
    118         synchronized (mLock) {
    119             mValue = null;
    120             mValid = false;
    121         }
    122     }
    123 
    124     public boolean haveNow() {
    125         synchronized (mLock) {
    126             return mValid;
    127         }
    128     }
    129 
    130     public synchronized A getNow() {
    131         synchronized (mLock) {
    132             if (!haveNow()) {
    133                 throw new IllegalStateException("getNow() called when haveNow() is false");
    134             }
    135             return mValue;
    136         }
    137     }
    138 
    139 }
    140