Increasing AsyncTask Duration in a Serie

Question

I have a list of buttons and i want that each fire a loading posting the unique preload of the elements.The problem is that the first complete the running in 200ms, the second in 3sec, and the 3rd never stop loading,... the async don't end completely. I don't know if is a problem of parallelism of the treads. Anyway using rest console everything works perfectly.

public class URLDataReader extends AsyncTask<URL, String, String> {

    Context mContext;
    OnAsyncTaskComplete listener;

    public URLDataReader(Context context, OnAsyncTaskComplete lisener) {
        mContext = context;
        listener = lisener;
    }

    @Override
    protected String doInBackground(URL... data) {


        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(data[0].toString());
        HttpResponse response = null;

        try {

            List<NameValuePair> nameValuePairs = Globals.postUrl();
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            //SETTA I POST IN GLOBALS

            //nameValuePairs.add(new BasicNameValuePair("username", "s.alberti"));
            //nameValuePairs.add(new BasicNameValuePair("password", "65.VALE.61"));
            //execute http post
            response = httpclient.execute(httppost);


        } catch (Exception e) {
            Toast.makeText(mContext, e.getMessage(), Toast.LENGTH_LONG).show();
        }

        try {
            return convertHttpResponseToString(response);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);
        listener.OnAsyncTaskComplete(s);
    }


    private String convertHttpResponseToString(HttpResponse response) throws IOException {
        InputStream responseStream = response.getEntity().getContent();
        Scanner scanner = new Scanner(responseStream, "UTF-8");
        String responseString = scanner.useDelimiter("\\Z").next();
        scanner.close();
        return responseString;
    }
}

    enter code here

GLOBAL

   public static List<NameValuePair> postUrl(){
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
        nameValuePairs.add(new BasicNameValuePair("username", "s.alberti"));
        nameValuePairs.add(new BasicNameValuePair("password", "Vale6165"));
        return nameValuePairs;
    }

FRAGMENT CALLING THE ASYNCTASK

try {
               String ex = extractUni(getContext());

               URL address = new URL("https://api.myuni.it/"+ex+"/login/");
               Toast.makeText(getContext(), address+"",+Toast.LENGTH_SHORT).show();
               URLDataReader pp = new URLDataReader(getContext(), this);
               pp.execute(address);

           } catch (MalformedURLException e) {
               e.printStackTrace();
           }

       }