/**
  * {@inheritdoc}
  */
 protected function flush(AdapterInterface $adapter)
 {
     if (!empty($this->messages)) {
         $adapter->acknowledge($this->messages);
         $this->messages = [];
     }
 }
 /**
  * {@inheritdoc}
  */
 protected function acknowledge(MessageInterface $message, AdapterInterface $adapter, $result = null)
 {
     $adapter->acknowledge([$message]);
 }