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      1 /*
      2  * Copyright (C) 2012 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.mms.util;
     18 
     19 import com.android.mms.LogTag;
     20 
     21 import java.util.ArrayList;
     22 import java.util.HashMap;
     23 import java.util.HashSet;
     24 import java.util.Set;
     25 import java.util.concurrent.Executor;
     26 import java.util.concurrent.LinkedBlockingQueue;
     27 import java.util.concurrent.ThreadFactory;
     28 import java.util.concurrent.ThreadPoolExecutor;
     29 import java.util.concurrent.TimeUnit;
     30 import java.util.concurrent.atomic.AtomicInteger;
     31 
     32 import android.content.Context;
     33 import android.net.Uri;
     34 import android.os.Handler;
     35 import android.util.Log;
     36 
     37 /**
     38  * Base class {@link BackgroundLoaderManager} used by {@link MessagingApplication} for loading
     39  * items (images, thumbnails, pdus, etc.) in the background off of the UI thread.
     40  * <p>
     41  * Public methods should only be used from a single thread (typically the UI
     42  * thread). Callbacks will be invoked on the thread where the ThumbnailManager
     43  * was instantiated.
     44  * <p>
     45  * Uses a thread-pool ExecutorService instead of AsyncTasks since clients may
     46  * request lots of images around the same time, and AsyncTask may reject tasks
     47  * in that case and has no way of bounding the number of threads used by those
     48  * tasks.
     49  *
     50  * Based on BooksImageManager by Virgil King.
     51  */
     52 abstract class BackgroundLoaderManager {
     53     private static final String TAG = LogTag.TAG;
     54 
     55     private static final int MAX_THREADS = 2;
     56 
     57     /**
     58      * URIs for which tasks are currently enqueued. Don't enqueue new tasks for
     59      * these, just add new callbacks.
     60      */
     61     protected final Set<Uri> mPendingTaskUris;
     62 
     63     protected final HashMap<Uri, Set<ItemLoadedCallback>> mCallbacks;
     64 
     65     protected final Executor mExecutor;
     66 
     67     protected final Handler mCallbackHandler;
     68 
     69     BackgroundLoaderManager(Context context) {
     70         mPendingTaskUris = new HashSet<Uri>();
     71         mCallbacks = new HashMap<Uri, Set<ItemLoadedCallback>>();
     72         final LinkedBlockingQueue<Runnable> queue = new LinkedBlockingQueue<Runnable>();
     73         final int poolSize = MAX_THREADS;
     74         mExecutor = new ThreadPoolExecutor(
     75                 poolSize, poolSize, 5, TimeUnit.SECONDS, queue,
     76                 new BackgroundLoaderThreadFactory(getTag()));
     77         mCallbackHandler = new Handler();
     78     }
     79 
     80     /**
     81      * Release memory if possible.
     82      */
     83     public void onLowMemory() {
     84         clear();
     85     }
     86 
     87     public void clear() {
     88     }
     89 
     90     /**
     91      * Return a tag that will be used to name threads so they'll be visible in the debugger.
     92      */
     93     public abstract String getTag();
     94 
     95     /**
     96      * Attempts to add a callback for a resource.
     97      *
     98      * @param uri the {@link Uri} of the resource for which a callback is
     99      *            desired.
    100      * @param callback the callback to register.
    101      * @return {@code true} if the callback is guaranteed to be invoked with
    102      *         a non-null result (as long as there is no error and the
    103      *         callback is not canceled), or {@code false} if the callback
    104      *         cannot be registered with this task because the result for
    105      *         the desired {@link Uri} has already been discarded due to
    106      *         low-memory.
    107      * @throws NullPointerException if either argument is {@code null}
    108      */
    109     public boolean addCallback(Uri uri, ItemLoadedCallback callback) {
    110         if (Log.isLoggable(TAG, Log.DEBUG)) {
    111             Log.d(TAG, "Adding image callback " + callback);
    112         }
    113         if (uri == null) {
    114             throw new NullPointerException("uri is null");
    115         }
    116         if (callback == null) {
    117             throw new NullPointerException("callback is null");
    118         }
    119         Set<ItemLoadedCallback> callbacks = mCallbacks.get(uri);
    120         if (callbacks == null) {
    121             callbacks = new HashSet<ItemLoadedCallback>(4);
    122             mCallbacks.put(uri, callbacks);
    123         }
    124         callbacks.add(callback);
    125         return true;
    126     }
    127 
    128     public void cancelCallback(ItemLoadedCallback callback) {
    129         if (Log.isLoggable(TAG, Log.DEBUG)) {
    130             Log.d(TAG, "Cancelling image callback " + callback);
    131         }
    132         for (final Uri uri : mCallbacks.keySet()) {
    133             final Set<ItemLoadedCallback> callbacks = mCallbacks.get(uri);
    134             callbacks.remove(callback);
    135         }
    136     }
    137 
    138     /**
    139      * Copies the elements of a {@link Set} into an {@link ArrayList}.
    140      */
    141     @SuppressWarnings("unchecked")
    142     protected static <T> ArrayList<T> asList(Set<T> source) {
    143         return new ArrayList<T>(source);
    144     }
    145 
    146     /**
    147      * {@link ThreadFactory} which sets a meaningful name for the thread.
    148      */
    149     private static class BackgroundLoaderThreadFactory implements ThreadFactory {
    150         private final AtomicInteger mCount = new AtomicInteger(1);
    151         private final String mTag;
    152 
    153         public BackgroundLoaderThreadFactory(String tag) {
    154             mTag = tag;
    155         }
    156 
    157         public Thread newThread(final Runnable r) {
    158             Thread t =  new Thread(r, mTag + "-" + mCount.getAndIncrement());
    159 
    160             if (t.getPriority() != Thread.MIN_PRIORITY)
    161                 t.setPriority(Thread.MIN_PRIORITY);
    162 
    163             return t;
    164         }
    165     }
    166 }
    167