Thursday, June 15, 2017

Android:java.util.concurrent.ThreadPoolExecutor

By Hường Hana 8:00 AM , Leave a Comment

In my app there is RecyclerView with tons of images in it.Images are loaded as user scrolls RecyclerView with this code:

    if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)         loader.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,url);     else         loader.execute(url);

Unfortunately sometimes when user scrolls fast this error occurs:

Task android.os.AsyncTask$3@73f1d84 rejected from  java.util.concurrent.ThreadPoolExecutor@8f5f96d[Running, pool size = 9,  active threads = 9, queued tasks = 128, completed tasks = 279]

Is there way to detect if poolExecutor is full and skip image loading?

Whole Image class:

public class Image extends ImageView { private AsyncTask<String,Integer,Bitmap> loader;  public Image(Context context) {     super(context);     this.setScaleType(ScaleType.FIT_XY); }  public Image(Context context, AttributeSet attrs) {     super(context, attrs);     this.setScaleType(ScaleType.FIT_XY); }  public void loadURL(String url) {     if(loader!=null)         loader.cancel(true);     loader=new AsyncTask<String, Integer, Bitmap>() {         @Override         protected Bitmap doInBackground(String... params) {             URL url = null;             byte[] bytes = null;             HttpURLConnection connection=null;             try {                 url = new URL(params[0]);                 connection=(HttpURLConnection) url.openConnection();                 connection.setRequestProperty("Connection", "close");                 connection.setRequestMethod("GET");                 connection.setUseCaches(true);                 InputStream is = null;                 is=connection.getInputStream();                 bytes = IOUtils.toByteArray(is);             } catch (MalformedURLException e) {                 e.printStackTrace();             } catch (ProtocolException e) {                 e.printStackTrace();             } catch (IOException e) {                 e.printStackTrace();             }             if (connection!=null)                 connection.disconnect();             Bitmap res=null;             if(!isCancelled() && bytes!=null)                 res=BitmapFactory.decodeByteArray(bytes,0,bytes.length);             return res;         }         @Override         protected void onPostExecute(Bitmap res) {             if(res!=null) {                 setImageBitmap(res);                 _animate();             }         }     };     if (this.getDrawable()!=null) {         Bitmap bmp=((BitmapDrawable) this.getDrawable()).getBitmap();         this.setAnimation(null);         if (bmp!=null) {             bmp.recycle();             //Log.d("image","recycled");         }         this.setImageBitmap(null);     }     /*     ThreadPoolExecutor e =(ThreadPoolExecutor) Executors.newFixedThreadPool(9);     Log.d("pool size",e.getActiveCount()+"/"+e.getMaximumPoolSize());     if (e.getActiveCount() == e.getMaximumPoolSize()) {     }     */     //start loading     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)         loader.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url);     else         loader.execute(url); } private void _animate() {     ValueAnimator bgAnim= ValueAnimator.ofObject(new IntEvaluator(),0,255);     bgAnim.setDuration(500);     bgAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {         @Override         public void onAnimationUpdate(ValueAnimator animation) {             Image.this.getDrawable().setAlpha((int) (animation.getAnimatedValue()));         }     });     bgAnim.start(); }

}

7 Answers

Answers 1

I answer that before (here, here, here and here and probably others) and I answer it again for you: Do not try to re-invent the wheel!

Image loading/caching is a very complex task in Android and a lot of good very developers already did that. Threading is just one of the issues, but I can see from your code you have a memory leak, there's no caching so you'll re-download images again if scroll back to it, HttpURLConnection is a crappy network layer.

So, the way to solve this (IMHO) it's just to re-use work done by other developers. Good examples of libraries you should consider for that are:

Picasso is my favorite, so to use it you need to simply call:

Picasso.with(context).load(url).into(imgView);

and it all be handled for you.

Answers 2

You can check if active threads count is equal to thread pool maximum size then your thread pool is full by using this

ThreadPoolExecutor e =(ThreadPoolExecutor)Executors.newFixedThreadPool(totalnofthreads); if (e.getActiveCount() == e.getMaximumPoolSize()) {  }

Answers 3

To detect if user scrolls fast you can use onFlingListener()

recyclerView.setOnFlingListener(new RecyclerView.OnFlingListener() {      @Override     public boolean onFling(int velocityX, int velocityY) {         isFlinging = checkFlinging(velocityY);          if (isFlinging) {             //Stop image loading here         }          return false;     } });  private boolean checkFlinging(int velocityY) {     return (velocityY < 0 && velocityY < -RECYCLER_VIEW_FLING_VELOCITY)              || (velocityY > 0 && velocityY > RECYCLER_VIEW_FLING_VELOCITY); }

Let me explain a bit, velocityY because I use recyclerView with vertical scrolling (for horizontal scrolling just change this parameter to velocityX), RECYCLER_VIEW_FLING_VELOCITY - your fling velocity, for me RECYCLER_VIEW_FLING_VELOCITY = 7000.

Answers 4

I just relized I can wrap loading code with try/catch:

try {      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)             loader.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url);         else             loader.execute(url);     } catch (RejectedExecutionException e){         e.printStackTrace(); }

Looks like this would be optional solution.

Answers 5

Instead of using AsyncTask.THREAD_POOL_EXECUTOR you can use your own Executor instance with a RejectedExecutionHandler, for example:

private final Executor mExecutor = new ThreadPoolExecutor(0, 8,            1, TimeUnit.SECONDS,            new LinkedBlockingQueue<Runnable>(16),            new ThreadPoolExecutor.DiscardPolicy());

This will create an Executor that runs at most 8 threads, keeps 16 tasks in the queue and drops any tasks above those limits (DiscardPolicy is a predefined RejectedExecutionHandler that does exactly that). You can then pass it to executeOnExecutor().

Alternatively, you might want the images to eventually load. In that case you can use an Executor with an unbounded (i.e. limitless) queue. It will never throw a RejectedExecutionException. Executors utility class has some nice factory method for creating those:

private final Executor mExecutor = Executors.newFixedThreadPool(8);

Answers 6

when ImageView detached from window , cancel the corresponding task of loading url :

public class Image extends ImageView {    @Override protected void onDetachedFromWindow() {     super.onDetachedFromWindow();     if(loader!=null)       loader.cancel(true);   }  }

Answers 7

First of all, why are you still using AsyncTask? the ThreadPool exception is coming because while your scrolling fast the adapter is trying to set an image to a position which is no longer available usually to stop this issue you would disable recycling but that would only make your list slow when handling a large set of data. So i advise you use volley for image loading its easy to implement and handles caching easiily.

      <com.android.volley.toolbox.NetworkImageView             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:id="@+id/mainImage"             android:scaleType="centerCrop"             android:adjustViewBounds="true"             android:maxHeight="270dp"             />

Use above in place of your imageview and create the volleySingleton class to handle all network requests

    public class VolleySingleton { private static VolleySingleton sInstance = null; private RequestQueue mRequestQueue; private ImageLoader imageLoader;  private VolleySingleton(){     mRequestQueue = Volley.newRequestQueue(Application.getAppContext());     imageLoader = new ImageLoader(mRequestQueue, new ImageLoader.ImageCache() {         private final LruCache<String, Bitmap> cache = new LruCache<String, Bitmap>(200);           @Override         public Bitmap getBitmap(String url) {             return cache.get(url);         }           @Override         public void putBitmap(String url, Bitmap bitmap) {             cache.put(url, bitmap);         }      });  } public static VolleySingleton getsInstance(){     if(sInstance == null){         sInstance = new VolleySingleton();     }     return sInstance; } public RequestQueue getmRequestQueue(){     return mRequestQueue; } public ImageLoader getImageLoader() {     return imageLoader; } }

Get an instance of your singleton class then add it to the imageView and your good to go

     imageLoader = VolleySingleton.getsInstance().getImageLoader();     networkImageVeiw.setImageUrl(imageUrl, imageLoader);

Create a class extending android.app.Application so you can get the context in the volleySingleton class

    public class Application extends android.app.Application { private static Application sInstance;  public static Application getsInstance() {     return sInstance; }  public static Context getAppContext() {     return sInstance.getApplicationContext(); }  public static AppEventsLogger logger(){     return logger; }  @Override public void onCreate() {     super.onCreate();     sInstance = this;  } }

Don't forget to go to your manifest.xml and add the name attribute to the application tag to be the name of your application class you just extended

    <application     android:name="com.example.ApplicationClass"
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