Question

Working on an app in android I have used Asynctask class, Works fine when i tested on my Android device running on 2.3.5, but the problem i am facing is, same is not working for my tablet 4.0.4

While testing, got to know that prexecute() is being called but doInbackground() not being called, however doInbackground() is being called on device(2.3.5).

One of the reason i believe for the problem is that the processor of Tablet is much faster than that of device, so may be some threading issues, dats why, to tackle this, i have used some flags, and used Thread.sleep() in a do while loop so that when condition is true, it works, but no luck, i am stuck in the loop itself. Here is my code:

MyAsyncTask object = new MyAsyncTask (MainActivity.this);
runOnUiThread(new Runnable() {
    public void run() {         

        try {
            if (object.isReady() || !object.isStarting()) {
                return;
            }

            object.execute();

            do {
                Thread.sleep(1000);             
            } while (!object.isReady() && object.isStarting());

            if(!object.isReady()) { 
                return;
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }           
});

AsynctaskClass:

public class MyAsyncTask extends AsyncTask<Void, Void, Boolean>{

    private ProgressDialog dialog;
    private Context context;
    private boolean isStarting = false;
    private boolean isReady = false;


    public AsyncUpdatesofJquery(Context context) {
        this.context = context;
        isStarting = true;
        isReady = false;
    }

    public boolean isStarting() {
        return isStarting;
    }

    public boolean isReady() {
        return isReady;
    }

    @Override
    protected void onPreExecute() {

        isStarting = true;
        isReady = false;
        dialog = new ProgressDialog(context); 
        dialog.setMessage("Downloading Files, Please wait...");
        dialog.show();
    }

    @Override
    protected Boolean doInBackground(Void... params) {

        isReady = true;
        isStarting = false;
        downloadFiles(context); // my background task

        return true;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        super.onPostExecute(result);
        context.startActivity(new Intent(context, NewActivity.class));
        dialog.dismiss();
        isReady = false;
        isStarting = false;

    }
}

Answer 1

The multi-threading model changed between 2.3.5 and 4.0.4. AsyncTask now defaults to having all subclasses in an application using the same thread (i.e. only one AsyncTask can run at a time!). It’s explained here:

When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. Starting with HONEYCOMB, tasks are executed on a single thread to avoid common application errors caused by parallel execution.

If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.

With that in mind, it could be that another AsyncTask is running in your app, thereby preventing this one from ever starting. That would explain why it works fine on your 2.3.5 device, but not your 4.0.4 tablet.