io_future.rb

class IoFuture
  def initialize(io, &block)
    @io, @block = io, block
  end
  
  def to_io
    @io
  end
  
  def value
    @value ||= block.call
  end
end

future1 = IoFuture.new(socket1) { socket1.gets }
future2 = IoFuture.new(socket2) { socket2.gets }

IO.select([future1, future2])