# File lib/amq/client/async/adapters/event_machine.rb, line 126
        def register_connection_callback(&block)
          unless block.nil?
            # delay calling block we were given till after we receive
            # connection.open-ok. Connection will notify us when
            # that happens.
            self.on_open do
              block.call(self)
            end
          end
        end