form.inc

  drupal_theme_initialize();

  if (isset($batch)) {
    // Add process information
    $process_info = array(
      'current_set' => 0,
      'progressive' => TRUE,
      'url' => $url,
      'url_options' => array(),
      'source_url' => $_GET['q'],
      'redirect' => $redirect,
      'theme' => $GLOBALS['theme_key'],
      'redirect_callback' => $redirect_callback,
    );
    $batch += $process_info;

    // The batch is now completely built. Allow other modules to make changes
    // to the batch so that it is easier to reuse batch processes in other
    // environments.
    drupal_alter('batch', $batch);

    // Assign an arbitrary id: don't rely on a serial column in the 'batch'
    // table, since non-progressive batches skip database storage completely.
    $batch['id'] = db_next_id();

    // Move operations to a job queue. Non-progressive batches will use a
    // memory-based queue.
    foreach ($batch['sets'] as $key => $batch_set) {
      _batch_populate_queue($batch, $key);
    }

    // Initiate processing.
    if ($batch['progressive']) {
      // Now that we have a batch id, we can generate the redirection link in
      // the generic error message.
      $t = get_t();
      $batch['error_message'] = $t('Please continue to <a href="@error_url">the error page</a>', array('@error_url' => url($url, array('query' => array('id' => $batch['id'], 'op' => 'finished')))));

      // Clear the way for the drupal_goto() redirection to the batch processing
      // page, by saving and unsetting the 'destination', if there is any.
      if (isset($_GET['destination'])) {
        $batch['destination'] = $_GET['destination'];
        unset($_GET['destination']);
      }

      // Store the batch.
      db_insert('batch')
        ->fields(array(
          'bid' => $batch['id'],
          'timestamp' => REQUEST_TIME,
          'token' => drupal_get_token($batch['id']),
          'batch' => serialize($batch),
        ))
        ->execute();

      // Set the batch number in the session to guarantee that it will stay alive.
      $_SESSION['batches'][$batch['id']] = TRUE;

      // Redirect for processing.
      $function = $batch['redirect_callback'];
      if (function_exists($function)) {
        $function($batch['url'], array('query' => array('op' => 'start', 'id' => $batch['id'])));
      }
    }
    else {
      // Non-progressive execution: bypass the whole progressbar workflow
      // and execute the batch in one pass.
      require_once DRUPAL_ROOT . '/includes/batch.inc';
      _batch_process();
    }
  }
}

/**
 * Retrieves the current batch.
 */
function &batch_get() {
  // Not drupal_static(), because Batch API operates at a lower level than most
  // use-cases for resetting static variables, and we specifically do not want a
  // global drupal_static_reset() resetting the batch information. Functions
  // that are part of the Batch API and need to reset the batch information may
  // call batch_get() and manipulate the result by reference. Functions that are
  // not part of the Batch API can also do this, but shouldn't.
  static $batch = array();
  return $batch;
}

/**
 * Populates a job queue with the operations of a batch set.
 *
 * Depending on whether the batch is progressive or not, the BatchQueue or
 * BatchMemoryQueue handler classes will be used.
 *
 * @param $batch
 *   The batch array.
 * @param $set_id
 *   The id of the set to process.
 * @return
 *   The name and class of the queue are added by reference to the batch set.
 */
function _batch_populate_queue(&$batch, $set_id) {
  $batch_set = &$batch['sets'][$set_id];

  if (isset($batch_set['operations'])) {
    $batch_set += array(
      'queue' => array(
        'name' => 'drupal_batch:' . $batch['id'] . ':' . $set_id,
        'class' => $batch['progressive'] ? 'BatchQueue' : 'BatchMemoryQueue',
      ),
    );

    $queue = _batch_queue($batch_set);
    $queue->createQueue();
    foreach ($batch_set['operations'] as $operation) {
      $queue->createItem($operation);
    }

    unset($batch_set['operations']);
  }
}

/**
 * Returns a queue object for a batch set.
 *
 * @param $batch_set
 *   The batch set.
 * @return
 *   The queue object.
 */
function _batch_queue($batch_set) {
  static $queues;

  // The class autoloader is not available when running update.php, so make
  // sure the files are manually included.
  if (!isset($queues)) {
    $queues = array();
    require_once DRUPAL_ROOT . '/modules/system/system.queue.inc';
    require_once DRUPAL_ROOT . '/includes/batch.queue.inc';
  }

  if (isset($batch_set['queue'])) {
    $name = $batch_set['queue']['name'];
    $class = $batch_set['queue']['class'];

    if (!isset($queues[$class][$name])) {
      $queues[$class][$name] = new $class($name);
    }
    return $queues[$class][$name];
  }
}

/**
 * @} End of "defgroup batch".
 */