running parallel AsyncTask

Another option is using AsyncTaskCompat from support v.4 library.

AsyncTaskCompat.executeParallel(new AsyncTask<Void, Void, Object>() {
    @Override
    protected Object doInBackground(Void... params) {
        // do your parallel task here
        return null;
    }

    @Override
    protected void onPostExecute(Object result) {
        // and fetch result
    }
});

You will need to use a thread pool Executor to execute AsyncTask. Default implementation uses a serial executor running on a single thread

So create a ThreadPoolExecutor and then use

AsyncTask's executeOnExecutor instead of just execute method

There has been a change in AsyncTask from Honeycomb release. Older versions had a Thread pool of 10 threads, so you could run 10 tasks in parallel. But for Honeycomb and up, default is a serial executor, which executes tasks one by one. But you can pass a ThreadPoolExecutor for execution:

   if (Build.VERSION.SDK_INT >= 11) {
     //--post GB use serial executor by default --
     task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
   } else {
     //--GB uses ThreadPoolExecutor by default--
     task.execute();
   }