tqueue.rb

class TQueue
  def initialize
    @r = Concurrent::TVar.new []
    @w = Concurrent::TVar.new []
  end

  def write(a)
    t = Concurrent::Transaction.current
    as = t.read(@w)
    as.push(a)
    t.write(@w, as)
  end

  def read
    t = Concurrent::Transaction.current
    r = t.read(@r)

    if !r.empty?
      x, *xs = r
      t.write(@r, xs)
      return x
    else
      ys = t.read(@w)
      if ys.empty?
        Concurrent.abort_transaction
      else
        z, *zs = ys
        t.write(@w, [])
        t.write(@r, zs)

        return z
      end
    end
  end
end