YA SizedQueue, uses pattern [key, Range, Array].

rinda_sizedqueue.rb

  class ChannelSpace
    class ChannelHandle
      def initialize(ts, size)
        @ts = ts
        @size = size
        @name = Object.new
        @ts.write([@name, 0, []])
      end

      def write(value)
        _, _, ary = @ts.take([@name, 0...@size, nil])
        ary.push(value)
        value
      ensure
        @ts.write([@name, ary.size, ary])
      end

      def read
        _, _, ary = @ts.take([@name, 1..@size, nil])
        ary.shift
      ensure
        @ts.write([@name, ary.size, ary])
      end
    end

    def initialize
      @ts = Rinda::TupleSpace.new
    end
    
    def open(size)
      ChannelHandle.new(@ts, size)
    end
  end