def <<(message)
      @mutex.lock
      begin
        if mailbox_full || @dead
          dead_letter(message)
          return
        end
        if message.is_a?(SystemEvent)
          # SystemEvents are high priority messages so they get added to the
          # head of our message queue instead of the end
          @messages.unshift message
        else
          @messages << message
        end

        @condition.signal
        nil
      ensure
        begin
          @mutex.unlock
        rescue
          nil
        end
      end
    end
def <<(message)
      @mutex.lock
      begin
        if mailbox_full || @dead
          dead_letter(message)
          return
        end
        if message.is_a?(SystemEvent)
          # SystemEvents are high priority messages so they get added to the
          # head of our message queue instead of the end
          @messages.unshift message
        else
          @messages << message
        end

        @condition.signal
        nil
      ensure
        begin
          @mutex.unlock
        rescue
          nil
        end
      end
    end
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