code: public function shutdown(): void
      {
          if ($this->childPID) {
              $message = '{type}: QUIT received; shutting down after child completes work';
          } else {
              $message = '{type}: QUIT received; shutting down';
          }
  
          $this->logger->notice($message, ['type' => $this->name]);
          $this->doShutdown();
      }
docs: {@inheritdoc}
  
  @return void