code: public ServerBuilder workerGroup(EventLoopGroup workerGroup, boolean shutdownOnStop) {
          this.workerGroup = requireNonNull(workerGroup, "workerGroup");
          shutdownWorkerGroupOnStop = shutdownOnStop;
          return this;
      }
docs: Sets the worker {@link EventLoopGroup} which is responsible for performing socket I/O and running
  {@link Service#serve(ServiceRequestContext, Request)}.
  If not set, {@linkplain CommonPools#workerGroup() the common worker group} is used.
  
  @param shutdownOnStop whether to shut down the worker {@link EventLoopGroup}
  when the {@link Server} stops