def consume
      unless consumer_channels
        @consumer_channels ||= consumer_connections.map do |conn|
          open_channel(conn, config.prefetch)
        end

        subscriptions.each { |args| subscribe(*args) }
      end

      self
    end
def consume
      unless consumer_channels
        @consumer_channels ||= consumer_connections.map do |conn|
          open_channel(conn, config.prefetch)
        end

        subscriptions.each { |args| subscribe(*args) }
      end

      self
    end
Opens connections, channels, and sets up and specified subscriptions
 invoking {Messaging::Consumer#on_message} when a payload is received.

 Evaluation: Eager - This is only required to evaluate and declare the
 subscriptions which have been deffered using class .subscribe

 @return [Messaging::Consumer]
 @api public