Python 3.12: Shiny refuses to shut down until all network connections are closed

[daattali]

I just installed py-shiny on a fresh Windows installation. I'm getting an issue where any time the shiny app is killed, the terminal freezes. If I run a shiny app with shiny run, then when I press ctrl+C I see messages saying that the shiny app is attempting to shut down, but the terminal gets stuck and never returns to the prompt.

If I run in --reload mode, then the moment I change a file and save it, the terminal gets to the same state.

This happens in the command line and also in VSCode.

(venv) C:\Users\Dean\Documents\R\python\shinytest>shiny run
←[32mINFO←[0m:     Started server process [←[36m16176←[0m]
←[32mINFO←[0m:     Waiting for application startup.
←[32mINFO←[0m:     Application startup complete.
←[32mINFO←[0m:     Uvicorn running on ←[1mhttp://127.0.0.1:8000←[0m (Press CTRL+C to quit)
←[32mINFO←[0m:     127.0.0.1:49687 - "←[1mGET / HTTP/1.1←[0m" ←[32m200 OK←[0m
←[32mINFO←[0m:     ('127.0.0.1', 49689) - "WebSocket /websocket/" [accepted]
←[32mINFO←[0m:     connection open
←[32mINFO←[0m:     127.0.0.1:49688 - "←[1mGET / HTTP/1.1←[0m" ←[32m200 OK←[0m
←[32mINFO←[0m:     connection closed
←[32mINFO←[0m:     ('127.0.0.1', 49695) - "WebSocket /websocket/" [accepted]
←[32mINFO←[0m:     connection open
←[32mINFO←[0m:     Shutting down

[daattali]

(As you can see from the logs, it would also be nice to fix #162 because this is a terrible experience on Windows, it gives me the feeling that Windows users are not meant to use py-shiny)

[j-lim-sigma]

Hi, I experienced the same thing using python 3.12 on MacOS. It works fine with 3.11 though, both with --reload and without.

[jcheng5]

@j-lim-sigma Thank you, I'm installing 3.12 now to try to repro.

@daattali Any chance you're on Python 3.12 as well?

[daattali]

Yes I am indeed on 3.12. I can try to install 3.11 later if I find very simple instructions for it :)

[jcheng5]

I can repro on macOS 3.12 if I still have a connected browser. Once I close the browser, the command line returns. I get the same thing if I run the command uvicorn app:app instead of shiny run.

Edit: on Windows, it stays hung even after the browser closes.

Edit 2: on Windows, the command line returns if I close the whole browser. It's like an open socket is keeping Python alive.

[jcheng5]

Here is a discussion on Uvicorn and a suggested fix, no response yet: encode/uvicorn#2122

[jcheng5]

FWIW, I tried daphne (daphne app:app) and hypercorn (hypercorn app:app) under Python 3.12 and they both served up my app fine and exited cleanly. So this appears to be specific to uvicorn.

[daattali]

Here is a discussion on Uvicorn

Maybe it should be upgraded to an "Issue" in oder for the uvicorn team to notice?

[daattali]

I can confirm that downgrading to python 3.11 fixes this

[jcheng5]

This PR contains the fix. Thanks for your patience! encode/uvicorn#2145

[ME-researchgroup]

I am experiencing this issue using python 3.10.4 on windows.
I have to kill the terminal to stop shiny from running after hitting ctrl+c

[corey-dawson]

Similar issue on python 3.10.13. Sometimes the process shuts down normally, sometimes the terminal freezes. for me. Have to close the terminal and reopen a new one. this is where mine gets stuck, but only maybe half the time:

[jcheng5]

@corey-dawson Does it happen even with the simplest Shiny app?

from shiny.express import input, render, ui

ui.input_slider("n", "N", 0, 100, 20)


@render.text
def txt():
    return f"n*2 is {input.n() * 2}"