Question

I have this simple flask/gevent demo code.

#!/usr/bin/env python
import gevent
from gevent.pywsgi import WSGIServer
from gevent import monkey
monkey.patch_socket()

from flask import Flask, Response

app = Flask(__name__)

@app.route('/')
def stream():
    def gen():
        for i in range(10):
            yield "data: %d\r\n" % i
            gevent.sleep(1)
    return Response(gen())

if __name__ == '__main__':
    http = WSGIServer(('', 5000), app)
    http.serve_forever()

When I run it and open multiple urls in the browser, all but one of them block. What am I doing wrong?

I have tried running it with monkey.patch_all(), and running it with gunicorn streaming:app -k gevent – it still blocks in the browser.

Answer 1

Multiple tabs in browsers will block. That doesn’t mean gevent/gunicorn isn’t running the requests concurrently. I tried it with concurrent curl requests and XmlHttpRequest – it works as expected. Also note that curl buffers output. “\r\n” is required to make it print line by line.

Sidenote: Thanks to mitsuhiko on #pocoo for resolving it. If you haven’t tried flask, you should. Both mitushiko and flask are awesome.