Flask + SSE: why is time.sleep () required?

I am creating a flash application that will run background processes (c multiprocessing.Process

) polling a web service for new data, a data queue so that the Server-Sent-Events endpoint can pass it to the client.

Sample code:

#!/usr/bin/env python
from __future__ import print_function
import itertools
import time
from flask import Flask, Response, redirect, request, url_for

from multiprocessing import Process, Queue

def f(q):
    for i, c in enumerate(itertools.cycle('ABCDEFG')):
        time.sleep(1) 
        q.put( c )


app = Flask(__name__)

q = Queue()

@app.route('/')
def index():
    if request.headers.get('accept') == 'text/event-stream':
        def events():
            for i, c in enumerate(itertools.cycle('ABCDEFG')):
                #yield "data: %s \n\n" % (q.get())
                yield "data: %s \n\n" % (c)
                time.sleep(0.01)
        return Response(events(), content_type='text/event-stream')
    return redirect(url_for('static', filename='index.html'))


if __name__ == "__main__":
    p = Process(target=f, args=(q,))
    p.start()

    app.run(host='localhost', debug=True, port=23423)

    p.join()

      

        
        
        
      

    

The problem is, in Chrome, if I delete time.delay(0.01)

after yield

, SSE seems to hang (client side).