Question

public void OnBtnSendClick(View v)
{
    byte[] bytes = ...;  // array is assigned here

    SendTask task = new SendTask();
    task.execute(new byte[][] {bytes});   // this line is executed
}

private class SendTask extends AsyncTask<byte[], Void, String>
{
    @Override
    protected String doInBackground(byte[]... parameters) 
    {
            Log.i(LOG_TAG, "SendTask.doInBackground started");   // this line is not executed
            return "OK";
    }

    @Override
    protected void onPostExecute(String result) 
    {
            // ...
    }
}

This code worked with android:targetSdkVersion="9" in the manifest. I changed it to android:targetSdkVersion="15", and now SendTask.doInBackground is not executed. In debugger I see that task.execute line is executed, but doInBackground is never called.

BTW, the program contains another AsyncTask, which is successfully running.

Answer 1

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.

http://developer.android.com/reference/android/os/AsyncTask.html

On API >= 11 by default only one AsyncTask is executed at a time.

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

One way to overcome this issue is to create a BaseTask and make all your tasks extends it

public class BaseTask extends AsyncTask
{
    ...

    public void fireInTheHole()
    {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
            this.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        else
            this.execute();
    }

    ...
}

Then when you need to execute it, simply call myTask.fireInTheHole() instead of myTask.execute()