Drupal: batch_process() example

gistfile1.txt

  $batch = array(
    'title' => t('Moving files...'),
    'operations' => array(),
    'init_message' => t('Finding files to move'),
    'progress_message' => t('Processed @current out of @total files.'),
    'error_message' => t('An error occurred during processing.'),
    'finished' => 'xxx_file_finished',
    'progressive' => FALSE,
  );

  foreach ($file_ids as $fid) {
    $batch['operations'][] = array(xxx_move_file', array($fid));
  }

  batch_set($batch);
  batch_process('');

  return '';
}


function xxx_move_file($fid, &$context) {
  
  $file = file_load($fid);

  $moved = file_move($file, 'public://restricted', FILE_EXISTS_ERROR);

}

function xxx_move_file_finished($success, $results, $operations, $time) {
  if ($success) {
    $message = 'it worked',
    drupal_set_message($message);
  }
  else {
    // Handle error case.
  }
}