Batch proof of concept

gistfile1.txt

<?php

use Symfony\Component\HttpFoundation\JsonResponse;

function btest_menu() {
  $items['btest'] = array(
    'type' => MENU_CALLBACK,
    'access callback' => TRUE,
    'page callback' => 'btest_page',
  );
  $items['btest'] = array(
    'type' => MENU_CALLBACK,
    'access callback' => TRUE,
    'page callback' => 'btest_js_page',
  );
  return $items;
}

function btest_page() {
  if ($_GET['op'] == 'finished') {
    return array('#markup' => 'done');
  }
  variable_set('btest', 20);
  $js_setting = array(
    'batch' => array(
      'errorMessage' => 'None',
      'initMessage' => 'start',
      'uri' => url('btest/js', array('query' => array('id' => 1))),
    ),
  );
  drupal_add_js($js_setting, 'setting');
  drupal_add_library('system', 'drupal.batch');

  $output = theme('progress_bar', array('percent' => 0, 'message' => 'testing'));
  drupal_set_page_content($output);
  $page = element_info('page');
  $page['#show_messages'] = FALSE;
  return $page;
}

function btest_js_page() {
  $btest = variable_get('btest');
  $percentage = 5 * (20 - $btest);
  $message = "btest value: $btest";
  variable_set('btest', $btest - 1);

  return new JsonResponse(array('status' => TRUE, 'percentage' => (string) $percentage, 'message' => $message));
}