ruby session concurrency problem

sessionconcurrency

class FoosController < ApplicationController
  def zero
    session[:zero] = "zero"
    sleep 1
    render :text => "zero: #{session[:zero]}<br/>one: #{session[:one]}<br/>two: #{session[:two]}
    <br/>three: #{session[:three]}"
  end
  
  def one
    session[:one] = "one"
    sleep 1
    render :text => "zero: #{session[:zero]}<br/>one: #{session[:one]}<br/>two: #{session[:two]}
    <br/>three: #{session[:three]}"
  end
  
  def two
    session[:two] = "two"
    sleep 1
    render :text => "zero: #{session[:zero]}<br/>one: #{session[:one]}<br/>two: #{session[:two]}
    <br/>three: #{session[:three]}"
  end
  
  def three
    session[:three] = "three"
    sleep 1
    render :text => "zero: #{session[:zero]}<br/>one: #{session[:one]}<br/>two: #{session[:two]}
    <br/>three: #{session[:three]}"
  end
end