docs: public void shutdown() {
          stopListenting();
  
          // Shut down all event loops to terminate all threads.
          if (bossGroup != null) {
              bossGroup.shutdownGracefully(0, 5, TimeUnit.SECONDS);
          }
          if (workerGroup != null) {
              workerGroup.shutdownGracefully(0, 5, TimeUnit.SECONDS);
          }
  
          if (bossGroup != null) {
              bossGroup.terminationFuture().syncUninterruptibly();
          }
          if (workerGroup != null) {
              workerGroup.terminationFuture().syncUninterruptibly();
          }
  
          backend.close();
  
          log.info("completed shutdown of {}", this);
      }