rails global variable inaccessible in thread - ruby-on-rails

Question

I'm using Faye websockets and Redis to attempt a master/client websocket setup for a slideshow presentation.
The clients' should all follow along with the master (i.e. the master moves forward a slide, a message is sent out to all of the clients, and they all move forward a slide).
The issue I'm having is that my list of client websockets is empty when I access inside the thread created in the initialize function. The separate thread is necessary as Redis' 'subscribe' is a blocking function.
This file is a middleware and runs on app boot up.
I know that the point of global variables in rails is that they're shared across threads, but in my case something seems to be preventing it.
Is there a way to store a list of websockets in a globally accessible place? Globally, as in, for all running instances of the app on the same server.
(can't use Redis for that cause it can't store objects).
require 'faye/websocket'
require 'redis'
class WsCommunication
KEEPALIVE_TIME = 15 #seconds
CHANNEL = 'vip'
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 'client list on thread'
puts $clients
#### prints nothing
$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
end
ws.on :message do |event|
puts 'client list'
puts $clients
### prints the full list of clients
$redis.publish(CHANNEL, event.data)
end
ws.on :close do |event|
$clients.delete(ws)
ws = nil
end
# Return async Rack response
ws.rack_response
else
#app.call(env)
end
end
end