code: protected function shutdown()
      {
          // Indicate to our main loop that we should stop processing additonal messages
          $this->shutdown = true;
          
          // Get a list of all the messages that have not yet been handled
          $this->args['messages'] = array_filter($this->messages, function($message) {
              if (!isset($message['sent']) || $message['sent'] === false) {
                  return $message;
              }
          });
  
          $redis = new Redis;
          $client = new Client($redis);
  
          // Push the unfinished jobs back onto the priority queue with a priority of 100 
          // So they get processed as soon as possible.
          $client->push(static::class, $this->args, 1, 100);
  
          // Indicate that we've handled SIGTERM, and are ready to shut down
          return true;
      }
docs: Register a shutdown handler
  @return bool