Queue handling incompatible with drupal core.

There is an incompatibility between the Drupal core handling of queues in a cron task and the way Ultimate cron handles them.

I use the following queue definition:

/**
 * Implements hook_cron_queue_info().
 */
function km_dashboard_cron_queue_info() {
  $queues = array();

  $queues[KM_DASHBOARD_MAILQ] = array(
    'worker callback' => array(
      '\KennisMeester\Dashboard\Queue\MailWorker',
      'run',
    ),
    'time' => 60,
  );

  return $queues;
}

Using X Autoload we assure that the callback can be include whenever needed. This works because drupal core uses the following snippet to run the queues (common.php - line: 5384)

  foreach ($queues as $queue_name => $info) {
    if (!empty($info['skip on cron'])) {
      // Do not run if queue wants to skip.
      continue;
    }
    $callback = $info['worker callback'];
    $end = time() + (isset($info['time']) ? $info['time'] : 15);
    $queue = DrupalQueue::get($queue_name);
    while (time() < $end && ($item = $queue->claimItem())) {
      try {
        call_user_func($callback, $item->data);
        $queue->deleteItem($item);
      }
      catch (Exception $e) {
        // In case of exception log it and leave the item in the queue
        // to be processed again later.
        watchdog_exception('cron', $e);
      }
    }
  }

The worker callback is passed through call_user_func, which correctly will make the static call. Ultimate cron however uses

      try {
        $function($item->data);
        $queue->deleteItem($item);
        $items++;
        // Sleep after processing retrieving.
        if ($settings['queue']['item_delay']) {
          usleep($settings['queue']['item_delay'] * 1000000);
        }
      }

Which enforces the callback to be a string which is directly executed, and therefore breaking a callback that is accepted by the core.