Drupal → Как передать переменную из конструктора Batch в его finished callback

/**
 * Form submit.
 */
function mymodule_myform_submit($form, &$form_state) {
  ...
  $batch = array(
    'operations' => $operations,
    'finished' => 'mymodule_batch_finished',
    'foo' => 'bar',
  );
 
  batch_set($batch);
}
 
/**
 * Batch finished callback.
 */
function mymodule_batch_finished($success, $results, $operations) {
  $batch_set = _batch_current_set();
  debug($batch_set['foo']);
}