gunicorn doesn't process simultaneous requests concurrently

Question

I am trying to serve long running requests using gunicorn and its async workers but I can't find any examples that I can get to work. I used the example here but tweaked to add a fake delay (sleep for 5s) before returning the response:

def app(environ, start_response):
    data = "Hello, World!\n"
    start_response("200 OK", [
        ("Content-Type", "text/plain"),
        ("Content-Length", str(len(data)))
    ])
    time.sleep(5)
    return iter([data])

Then I run gunicorn so:

gunicorn -w 4 myapp:app -k gevent

When I open up two browser tabs and type in http://127.0.0.1:8000/ in both of them and send the requests almost at the same time, the requests appear to get processed sequentially - one returns after 5 seconds and the other returns after a further 5 seconds.

Q. I am guessing the sleep isn't gevent friendly? But there are 4 workers and so even if the type of worker was 'sync' two workers should handle two requests simultaneously?

Answer 1

I just ran into the same thing, opened a question here: Requests not being distributed across gunicorn workers . The result is, it appears that the browser serializes access to the same page. I'm guessing perhaps this has something to do w/ cacheability, i.e. the browser thinks it's likely the page is cacheable, wait until it loads finds out it isn't so it makes another request and so on.

Answer 2

Give gevent.sleep a shot instead of time.sleep.

It's weird that this is happening with -w 4, but -k gevent is an async worker type, so it's possible gunicorn is feeding both requests to the same client. Assuming that's what's happening, time.sleep will lock your process unless you use gevent.monkey.patch_all().