Accessing a variable within a rails thread

I'm building an application for a web-based slide show, where one 'master' user can move between slides and everyone's browsers follow along. To do this, I'm using websockets and Redis for a global channel to send messages through. Each client who connects has there info stored in an array, @clients.Then I have a separate thread for subscribing to the Redis channel, in which there is an 'on.message' block defined which should send a message to everyone in the @clients array, but that array is empty inside this block (not empty anywhere else in the module).

Pretty much following this example:https://devcenter.heroku.com/articles/ruby-websockets

The relevant code, which is in a custom middleware class:

require 'faye/websocket'require 'redis'class WsCommunication  KEEPALIVE_TIME = 15 #seconds  CHANNEL = 'vip-deck'  def initialize(app)    @app = app    @clients = []    uri = URI.parse(ENV['REDISCLOUD_URL'])    Thread.new do      redis_sub = Redis.new(host: uri.host, port: uri.port, password: uri.password)      redis_sub.subscribe(CHANNEL) do |on|        on.message do |channel, msg|          puts @clients.count          ### prints '0,' no clients receive msg          @clients.each { |ws| ws.send(msg) }        end      end    end  end  def call(env)    if Faye::WebSocket.websocket?(env)    ws = Faye::WebSocket.new(env, nil, {ping: KEEPALIVE_TIME})    ws.on :open do |event|      @clients << ws      puts @clients.count      ### prints actual number of clients    end    ws.on :message do |event|      $redis.publish(CHANNEL, event.data)    end    ws.on :close do |event|      @clients.delete(ws)      ws = nil    end    ws.rack_response  else    @app.call(env)  endendend

Is the @clients array empty when accessed inside the new thread because instance variables aren't shared across threads? and if so, how do I share a variable across threads?

I have also tried using $clients (global variable, should be accessible across threads), to no avail.