Sometimes for some weird reason you need to use cookie, session or even request objects from controller in models. In my case I needed unique token for each http request inside logic.

First thing got to my mind was to take request object from controller (ActiveDispatch::Request) and grab it’s object_id. But then I realized that I need it in deep layers of application logic, and carrying it from controller would be quite painful.

I tried using a singleton class. It was good idea at first:

# lib/token.rb
require 'singleton'

class Token
  include Singleton

  attr_accessor :token_object

  def self.set(val)
    instance.token_object = val
  end

  def self.get
    instance.token_object.object_id.to_s
  end

end

# app/application_controller.rb
class ApplicationController < ActionController::Base
  before_filter :setup_token

  def setup_token
    Token.set(self.request)
  end
end

I was intended to use Token.get in app.

This way has a potential issue – race condition. If application would not be preforked, but executed in threads, the object could be modified from another thread. I wrote a little test case spawning few threads, setting some value and sleeping for a random time. Value was indeed changed by other threads.

Dmytro Shteflyuk helped me a lot pointing to solution based on thread variables. I found basic idea in Geoff Lane’s blog and came with a simple solution:

class Token
  def self.set(obj)
    Thread.current[:token] = obj
  end

  def self.get
    Thread.current[:token].nil? ? nil : Thread.current[:token].object_id
  end

end