on_shutdown callback not called on Windows 10

[chhinze]

Description

Hi all,

thanks for this awesome project.

Registering a callback with app.on_shutdown should lead to the callback to be called during hot reloading (described in https://nicegui.io/documentation#events). This worked on a machine with Ubuntu 23.04 as expected, but on Windows 10 it is not called.

Minimal example to reproduce:

from nicegui import app, ui

app.on_shutdown(lambda: print("Shutdown called"))
app.on_startup(lambda : print("Startup called"))

ui.markdown("# Title")
ui.run(title="Does not call shutdown on Win10 Demo")

On Windows 10 the console Output is

Startup called
NiceGUI ready to go in http://...
?[33mWARNING?[0m: Watch files detected changes in ...

[here is, where the reload happens, triggered by Ctrl+S in the file.]

Startup called
NiceGUI ready to go in http://...

In Ubuntu I see a line Shutdown called before the second startup called, this is also what I would expect reading the documentation.

Am I using it wrong?
Is this related to #604 i.e., the Ctrl handler is not set properly?

Best regards
Chris

[falkoschindler]

Thanks for reporting this issue, @chhinze! This is definitely unexpected.

NiceGUI's lifecycle hooks like on_startup and on_shutdown rely on FastAPI. Can you, please, check if the following pure FastAPI example has the same problem on Windows 10?

main.py:

import uvicorn
from fastapi import FastAPI

app = FastAPI()

@app.on_event("startup")
async def startup_event():
    print("Application startup")

@app.on_event("shutdown")
async def shutdown_event():
    print("Application shutdown")

@app.get("/")
def read_root():
    return {"Hello": "World"}

if __name__ == "__main__":
    uvicorn.run('main:app', host="0.0.0.0", port=8000, reload=True)

[chhinze]

Thank you a lot for the quick response, @falkoschindler.

I just tested your code. The problem persists also with the pure FastAPI example you provided. The output is:

INFO:     Will atch for changes in these directories: ['...']
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [3644] using WatchFiles
INFO:     Started server process [7404]
INFO:     Waiting for application startup.
Application startup
INFO:     Application startup complete.
WARNING:  WatchFiles detected changes in 'main.py'. Reloading...
INFO:     Started server process [5596]
INFO:     Waiting for application startup.
Application startup
INFO:     Application startup complete.

On Linux, after the line WARNING: WatchFiles detected changes in 'main.py'. Reloading... I get the additional lines

INFO:   Shutting down
INFO:   Waiting for application shutdown.
Application shutdown 
INFO:   Application shutdown complete
INFO:   Finished server process [ProcessNo]

Thanks to your information that it is related to FastAPI I now found the open issues fastapi#6026 and fastapi#6391. A fix seems to be merged already back in April and is scheduled for uvicorn release 0.22.0.

I guess the best option is to just wait for this release of FastAPI.
Or is there a workaround to register a callback before reloading?

Edit: Clarified that the fix is in uvocorn (not fastapi).

[rodja]

Or is there a workaround to register a callback before reloading?

Unfortunately not. Or none that we are aware of. We would really much like to execute some code before uvicorn reloads, but we have not found a way yet.

[falkoschindler]

Ok, we'll wait for encode/uvicorn#1584 to be released.

[firai]

Ok, we'll wait for encode/uvicorn#1584 to be released.

It seems like this was already released in uvicorn 0.22.0 in April (https://github.com/encode/uvicorn/releases/tag/0.22.0)? However, uvicorn seems to be pinned to 0.20.0 in NiceGui.

[chhinze]

Yes, you are right. I was misguided by the milestone progress bar in the issue (encode/uvicorn#1584). Sorry for the confusion.
I also tested manually upgrading uvicorn: on_shutdown callbacks work as expected now.

[firai]

@falkoschindler Can uvicorn be upgraded to 0.22.0? Or would there be blocking conflicts from changes in uvicorn 0.21.0 or 0.22.0?

[rodja]

@firai thanks for asking. We will use uvicorn 0.22.0 in our upcoming 1.3 release. It would be great if you could try it out and tell us if it works for you.

[firai]

Ah, I assumed that development was on main without looking. Didn't realize that it's already changed on the 1.3 branch. Thanks!

[rodja]

Yea, we normally do everything on main. But breaking changes have accumulated on the v1.3 branch and is almost ready to be released.

[falkoschindler]

Ok, uvicorn has been updated in commit 578de6a. It will be released with NiceGUI 1.3.0. Therefore I'll close this issue.