Question

I’m running a WebSocketHandler with Tornado, and I have a while loop inside the Handler. This loop blocks everything – which is very bad. How can I make the tailstream() function asynchronous (a.k.a. non-blocking)? (As it is now, tailstream blocks everything, and makes even new websocket connections impossible. I need it to run for each websocket connection.)

(...)
class WSHandler(tornado.websocket.WebSocketHandler):
    connections = []
    filters = {}


    def allow_draft76(self):
        # for iOS 5.0 Safari
        return True


    def open(self):
        self.write_message('open')
        self.count = db.my_collection.count() - 1
        self.cursor = coll.find(tailable=True, await_data=True, skip=self.count)
        self.tailstream()




    def on_message(self, message):
        print message



    def on_close(self):
        self.connections.remove(self)
        self.cb.stop()
        print 'connection closed'


    @tornado.web.asynchronous
    def tailstream(self):
        while self.cursor.alive:
            try:
                doc = self.cursor.next()
                self.print2web(doc)

            except StopIteration:
                time.sleep(1)



    (...)       

Answer 1

I think while not blocking it. But time.sleep do!

Replace it with yield gen.Task(IOLoop.instance().add_timeout, time.time() + 5) from this answer.

If it will not help – we can think about whole structure of solution.