def exit
      @queues.each_key do |name|
        @queues[name] = nil
      end
      Runner.pool.shutdown
      Runner.pool.wait_for_termination
    end
def exit
      @queues.each_key do |name|
        @queues[name] = nil
      end
      Runner.pool.shutdown
      Runner.pool.wait_for_termination
    end
:nodoc: