install_run_task

install_run_task($task, &$install_state)

function install_run_task($task, &$install_state) {
  $function = $task['function'];

  if ($task['type'] == 'form') {
    return install_get_form($function, $install_state);
  }
  elseif ($task['type'] == 'batch') {
    // Start a new batch based on the task function, if one is not running
    // already.
    $current_batch = \Drupal::state()->get('install_current_batch');
    if (!$install_state['interactive'] || !$current_batch) {
      $batches = $function($install_state);
      if (empty($batches)) {
        // If the task did some processing and decided no batch was necessary,
        // there is nothing more to do here.
        return;
      }
      // Create a one item list of batches if only one batch was provided.
      if (isset($batches['operations'])) {
        $batches = array($batches);
      }
      foreach ($batches as $batch) {
        batch_set($batch);
        // For interactive batches, we need to store the fact that this batch
        // task is currently running. Otherwise, we need to make sure the batch
        // will complete in one page request.
        if ($install_state['interactive']) {
          \Drupal::state()->set('install_current_batch', $function);
        }
        else {
          $batch = &batch_get();
          $batch['progressive'] = FALSE;
        }
      }
      // Process the batch. For progressive batches, this will redirect.
      // Otherwise, the batch will complete.
      // Disable the default script for the URL and clone the object, as
      // batch_process() will add additional options to the batch URL.
      $url = Url::fromUri('base:install.php', ['query' => $install_state['parameters'], 'script' => '']);
      $response = batch_process($url, clone $url);
      if ($response instanceof Response) {
        if ($session = \Drupal::request()->getSession()) {
          $session->save();
        }
        // Send the response.
        $response->send();
        exit;
      }
    }
    // If we are in the middle of processing this batch, keep sending back
    // any output from the batch process, until the task is complete.
    elseif ($current_batch == $function) {
      $output = _batch_page(\Drupal::request());
      // Because Batch API now returns a JSON response for intermediary steps,
      // but the installer doesn't handle Response objects yet, just send the
      // output here and emulate the old model.
      // @todo Replace this when we refactor the installer to use a request-
      //   response workflow.
      if ($output instanceof Response) {
        $output->send();
        $output = NULL;
      }
      // The task is complete when we try to access the batch page and receive
      // FALSE in return, since this means we are at a URL where we are no
      // longer requesting a batch ID.
      if ($output === FALSE) {
        // Return nothing so the next task will run in the same request.
        \Drupal::state()->delete('install_current_batch');
        return;
      }
      else {
        // We need to force the page request to end if the task is not
        // complete, since the batch API sometimes prints JSON output
        // rather than returning a themed page.
        $install_state['task_not_complete'] = $install_state['stop_page_request'] = TRUE;
        return $output;
      }
    }
  }

  else {
    // For normal tasks, just return the function result, whatever it is.
    return $function($install_state);
  }
}