# File lib/amq/client/async/channel.rb, line 179
        def qos(prefetch_size = 0, prefetch_count = 32, global = false, &block)
          @connection.send_frame(Protocol::Basic::Qos.encode(@id, prefetch_size, prefetch_count, global))

          self.redefine_callback :qos, &block
          self
        end