Websockets server multithreaded

import tornado.websocket
import tornado.httpserver
import tornado.ioloop
import tornado.web
import tornado.gen
import time

from tornado import gen
from threading import Thread

connections = set()

class WebSocketHandler(tornado.websocket.WebSocketHandler):
    def initialize(self):
      print 'Websocket opened'

    def open(self):
        print 'New connection'
        connections.add(self)
        self.write_message('test')
      
    def on_message(self, message):
        print message
      
    def on_close(self):
        connections.remove(self)
        print 'Connection closed'

    def write_message(self, message):
        print ("Sending: ", message)

    def test(self):
        self.write_message("scheduled!")

def make_app():
    return tornado.web.Application([
    (r'/ws', WebSocketHandler),
    ])

def read_function():
    while True:
        time.sleep(5) # a while loop to simulate the reading
        print 'read serial'
        str = 'string to send'
        [client.write_message(str) for client in connections]

if __name__ == '__main__':
    thread = Thread(target = read_function)

    application = make_app()
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(8888)
    thread.start()
    tornado.ioloop.IOLoop.instance().start()
    thread.join()
    print 'test'