wait() method on thread not working Android

Question

I have a few downloads that are submitted as tasks to a ThreadPoolExecutor . Now, I am creating this ThreadPoolExecutor in a global class that extends Application. I am storing all the submitted tasks in a HashMap with ids.

I have a ListView in a Fragment . This ListView item contains pause and resume buttons. When I click on the list item itself, the download FutureTask is submitted to the global pool executor. Now, when I click on the pause button of the ListView item, I want that particular thread to pause/wait.

I have the onClick method of the pause button in my list view's custom adapter. So, when I click the button, in my adapter class, I get all the threads that are currently running, put them in an array and then get the thread with the name I want from the array. I can see in my log that the thread I want to get is running with the name I set. So once I get that thread, I do wait() on it.

In the onclick of my resume button, I notify that particular thread and set the flag to pause as false so that the thread resumes. But, the download inside that thread actually keeps running even after clicking pause. I do not know where I am going wrong.

My GlobalState Class:

public class GlobalState extends Application{

HashMap<String, Future<?>> futureMapMain = new HashMap<String, Future<?>>();

    ThreadPoolExecutor mainExec = new ThreadPoolExecutor(2, 2, 2000, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(), new YourThreadFactory());

public void submitTaskMain(String name, Thread task){
        Future<?> longRunningTaskFuture = mainExec.submit(task);
        futureMapMain.put(name, longRunningTaskFuture);
    }

    public HashMap<String, Future<?>> getFutureMap(){
        return futureMapMain;
    }

    public ThreadPoolExecutor getMainExeutor(){
        return mainExec;
    }

public class YourThreadFactory implements ThreadFactory {
           public Thread newThread(Runnable r) {
             return new Thread(r, gettName());
           }
         }
}

My Download Method that is written inside my fragment class. gets executed on list item click:

public void abDownloadTask(){

Thread dThread = new Thread(new Runnable() {

                final Handler pdfHandler = new Handler();

                @Override
                public void run() {
                    for(something){
/* DOES SOME DOWNLOAD USING url.getcontent() with different urls in a loop and stores files to sd card. */
}
}
}
dThread.setName(threadname);
            Log.d("Tel Frag", "Thread name set as: "+dThread.getName());
            mainGs.settName(threadname);
            mainGs.submitTaskMain(threadname, dThread);
}

onclick of my pause button inside custom list adapter:

    pause.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

                needToPause = true;

                Runnable runnable = new Runnable() {

                    @Override
                    public void run() {
                        // TODO Auto-generated method stub

                        Set<Thread> threadSet = Thread.getAllStackTraces().keySet();
                        Thread[] threadArray = threadSet.toArray(new Thread[threadSet.size()]);
                        Log.d("CLA", "Threads running size: "+threadArray.length); 

                        Thread neededThread = null;

                         for ( Thread thread : threadArray ){
                             Log.d("CustomListAdapter", "Thread name in array: "+thread.getName());
                                if (thread.getName( ).equals(threadname)){
                                    neededThread = thread;
                                }
                         }   

                         if(neededThread!=null){
                            while(needToPause){
                                synchronized  (neededThread) {
                                        try {
                                            neededThread.wait();
                                        } catch (InterruptedException e) {
                                            // TODO Auto-generated catch block
                                            e.printStackTrace();
                                        }
                                }
                            }
                         } 
                    }
                };
                new Thread(runnable).start();

                notifyDataSetChanged();
        }
    });

onclick of my resume button written inside custom list adapter class:

resume.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

            needToPause = false;

            Set<Thread> threadSet = Thread.getAllStackTraces().keySet();
            Thread[] threadArray = threadSet.toArray(new Thread[threadSet.size()]);

             for ( Thread thread : threadArray ){
                    if ( thread.getName( ).equals(threadname) ){
                        thread.notify();
                    }
             }  


            notifyDataSetChanged();
        }
    });

I have been trying to figure it out for 2 days now but no luck. I went through a lot of examples and stackoverflow questions. I am just trying to get a thread by its name and then pause and resume it. Any help would be appreciated. Thank you!

Answer 1

You can't reliably use wait() and notify() on Thread objects. This is clearly stated in the Javadoc. You already have Future objects, you shouldn't be using other mechanisms anyway.