form.inc

 *   The batch array.
 * @param $set_id
 *   The id of the set to process.
 */
function _batch_populate_queue(&$batch, $set_id) {
  $batch_set = &$batch['sets'][$set_id];

  if (isset($batch_set['operations'])) {
    $batch_set += [
      'queue' => [
        'name' => 'drupal_batch:' . $batch['id'] . ':' . $set_id,
        'class' => $batch['progressive'] ? 'Drupal\Core\Queue\Batch' : 'Drupal\Core\Queue\BatchMemory',
      ],
    ];

    $queue = _batch_queue($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 $batch_set
 *   The batch set.
 *
 * @return \Drupal\Core\Queue\QueueInterface|null
 *   The queue object.
 */
function _batch_queue($batch_set) {
  static $queues;

  if (!isset($queues)) {
    $queues = [];
  }

  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, \Drupal::database());
    }
    return $queues[$class][$name];
  }
}

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