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Async options for flask app

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From: rimuatkinson+usenet@gmail.com (Rimu Atkinson)
Newsgroups: comp.lang.python
Subject: Async options for flask app
Date: Mon, 18 Sep 2023 10:59:15 +1200
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by: Rimu Atkinson - Sun, 17 Sep 2023 22:59 UTC

Hi all,

I'm writing a fediverse server app, similar to kbin https://kbin.pub/en
and lemmy https://join-lemmy.org/. It's like reddit except anyone can
run a server in the same way email works. This architecture involves a
lot of inter-server communication, potentially involving thousands of
different servers.

So, lots of network I/O. Lots of tasks running in parallel to do I/O
with different servers simultaneously. A fair bit of DB access too.

The current fashion is to do this with cooperative multitasking
(async/await/gevent/etc) to avoid the overhead associated with
continually context switching threads and processes. Correct me if I'm
wrong.

How can I do this with Flask? Any async/await tricks? Can I just
configure gunicorn to use gevent worker threads?
https://flask.palletsprojects.com/en/2.3.x/deploying/gunicorn/

Has anyone tried Quart? https://pypi.org/project/quart/

How well does gevent monkey-patch into a Flask app?

A penny for your thoughts

Thanks!

Re: Async options for flask app

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From: rosuav@gmail.com (Chris Angelico)
Newsgroups: comp.lang.python
Subject: Re: Async options for flask app
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by: Chris Angelico - Mon, 18 Sep 2023 04:17 UTC

On Mon, 18 Sept 2023 at 13:45, Rimu Atkinson via Python-list
<python-list@python.org> wrote:
>
> Hi all,
>
> I'm writing a fediverse server app, similar to kbin https://kbin.pub/en
> and lemmy https://join-lemmy.org/. It's like reddit except anyone can
> run a server in the same way email works.

And the part you didn't say: It's like Reddit but without a ridiculous
API fee. Right? :)

> The current fashion is to do this with cooperative multitasking
> (async/await/gevent/etc) to avoid the overhead associated with
> continually context switching threads and processes. Correct me if I'm
> wrong.

I wouldn't say "current fashion", but yes, there is significant
benefit in putting more than one task onto any given thread. (Most
likely, if you want maximum throughput, you'll end up wanting a
two-level multiplexer, with a pool of processes, each one managing a
pool of tasks.)

> How can I do this with Flask? Any async/await tricks? Can I just
> configure gunicorn to use gevent worker threads?
> https://flask.palletsprojects.com/en/2.3.x/deploying/gunicorn/

It's been a while since I did it, but it definitely does work, yes.

> Has anyone tried Quart? https://pypi.org/project/quart/

Not me, so I'll let someone else answer that.

> How well does gevent monkey-patch into a Flask app?
>

Here's one where I've done that: https://github.com/rosuav/mustardmine

However, it's worth noting that (a) the exact details might differ
depending on precisely what you use - this is backed by PostgreSQL and
also uses websockets; and (b) I originally did this quite a while ago,
and things may have gotten easier since then. All I know is, it works
if I do it this way, and I haven't felt the urge to mess with that
part of it. You may notice that my README mentions issues with Python
3.8 from back when that was new :)

But with all of those caveats: Yes, this absolutely does work, and I
make use of the Mustard Mine on a regular basis. It gets updates
occasionally, not often, but I bump it onto newer Pythons every now
and then, so the techniques it uses should still be valid.

ChrisA

It has just been discovered that research causes cancer in rats.

devel / comp.lang.python / Re: Async options for flask app

devel / comp.lang.python / Re: Async options for flask app

Subject	Author
Async options for flask app	Rimu Atkinson
Re: Async options for flask app	Chris Angelico