on_msg.rb

    # The context will call this method for each msg sucessfully processed
    # by the worker.
    #
    def on_msg(msg)

      puts(fancy_print(msg, @noisy)) if @noisy

      return if msg['action'] == 'noop'

      @on_msg_mutex.synchronize do

        @seen << msg
        @log << msg

        while @log.size > @log_max; @log.shift; end
        while @seen.size > @log_max; @seen.shift; end
      end
    end