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