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.

SERIAL_EXECUTOR -> An Executor that executes tasks one at a time in serial order.

THREAD_POOL_EXECUTOR -> An Executor that can be used to execute tasks in > parallel.

sample :

Task task = new Task();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
    task.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR, data);
else
    task.execute(data);