Reload slow, no response to ctrl-C on Windows

[superlou]

Description

A simple application starts up in a second or two, but on making a change, reloading may take 10 seconds or more and may hang. Additionally, when hung, the terminal (both PowerShell and CMD) has no response to ctrl-c or clicking the close button. It's been about a year since I've used NiceGUI on Windows (I mostly use Linux) and I don't remember this behavior before.

It sounds a bit like #3344, but this isn't in PyCharm. There are also some issues in uvicorn like encode/uvicorn#1972 that sound related, but I know enough about the NiceGUI stack to know if that could be the root cause.

My test script is:

from nicegui import ui

ui.button("Button 1")
ui.button("Button 2")
ui.button("Button 3")

ui.run()

Steps to recreate:

1. Make a simple NiceGUI script like the above named simple.py.
2. Run python simple.py in a Windows terminal.
3. Comment out one of the ui.button(...) calls and save the file.
4. Wait for "... Reloading..." to complete and show "NiceGUI ready to go..."

Environment:

• Windows 11 (also Windows 10, but mostly testing on Windows 11)
• Python 3.12.4 (x64)
• nicegui 1.4.37
• uvicorn 0.30.6
• fastapi 0.109.2

Edit: I tried the same test in WSL2 on the same computer and reloads are very fast, under a second.

[rodja]

Wow. That sounds serious. We aim for a super fast reload. Can anyone else with Windows reproduce this?

[python-and-novella]

@superlou do you test it in pure termial or in ide's integrated terminal? It soulds like similar bug in pycharm or in vscode i met.

[superlou]

I was testing in a pure terminal, both Powershell and CMD had similar behavior (as well as Microsoft Terminal running Powershell).

[frankhuurman]

@superlou
This might be a bit skewed because I'm using Windows 10 in a VM but for me with the nicegui version you specified and running your code example in cmd.exe it takes about 5 seconds on average to reload the page during file saves.
Using Git Bash takes about 4 seconds on average though it has trouble handling Ctrl + C for me as well.

On Linux it's nearly instant for me so seems to be a very Windows-y problem.

Upgrading to the latest NiceGUI version doesn't seem to change anything speed-wise either so it might be related to the way filewatcher picks up on filechanges on Windows in comparison to the other OS-es?

[superlou]

@frankhuurman, I don't think it's filewatcher, only because when I save, it immediately pops up with the notification that a file changed. The issues happen in the delay after.

Does nicegui use uvicorn logging? This comment describes my ctrl-c behavior.

[rodja]

Interesting @superlou! Uvicorn logging can be disabled with ui.run(uvicorn_logging_level='critical').

[superlou]

Just got a chance to try it with logging disabled. No change unfortunately. Was really hoping it was something straightforward.

from nicegui import ui

ui.button("Button 1")
ui.button("Button 2")
ui.button("Button 3")

ui.run(uvicorn_logging_level='critical')

It's still 5 to 10 seconds to reload (if it does) when commenting and uncommenting buttons. I'm pretty sure it's reacting to uvicorn_logging_level, since I don't get the "WARNING: WatchFiles detected changes in 'main.py'. Reloading..." message with the logging level set to critical.

[frankhuurman]

Just noticed that you're using Python 3.12.
I opened a NiceGUI issue a while back that's related to the Python 3.12 and Windows combination that might be similar to your issue: #2138

Could you try your same code using Python 3.11 on Win 11?

Back then it seemed to be an upstream problem that needed to be fixed but I assumed that would've been done by now, but I'm curious if downgrading your Python version solves the issue for now.

[superlou]

I used uv to test with Python 3.11.9, and it's the same behavior. WatchFiles detects changes immediately, but it takes about 15 seconds to respond in the browser.

[NebularNerd]

I'm just starting out with NiceGUI on Win11 running Python 3.10 and have had similar issues. Same as @superlou I'll start the server, make a change in VSCODE and it sometimes will reload ok, but it's 50/50 between that or just locking up and needing me to kill Python in the task manger.

Running it via Powershell in Microsoft Terminal if that helps.

[genotrance]

I'm seeing the same issue on Windows - reloads (and loads) are super slow and frustrating.

Python 3.12.7
nicegui 2.5.0
fastapi 0.115.4
uvicorn 0.32.0

[superlou]

I'm not sure this is the root cause, but is there a way to try the solution suggested in encode/uvicorn#1972 (comment) to see if it's something related to filewatches in uvicorn? I'm not sure how to configure nicegui to test that.

[falkoschindler]

@superlou This works for me on Mac:

watchfiles --filter python "python main.py"

[superlou]

Unfortunately, when I edit the test file (same process as earlier by commenting/un-commenting buttons) on Windows, either the page doesn't update or I get a permissions error:

PS C:\workspace\nicegui-test> watchfiles --filter python "python main.py"
[08:27:34] watchfiles v0.24.0 👀  path="C:\workspace\nicegui-test" target="python main.py" (command) filter=PythonFilter...
NiceGUI ready to go on http://localhost:8080, http://192.168.40.71:8080, and http://192.168.56.1:8080
[08:27:40] 1 change detected
NiceGUI ready to go on http://localhost:8080, http://192.168.40.71:8080, and http://192.168.56.1:8080
[08:27:48] 1 change detected
NiceGUI ready to go on http://localhost:8080, http://192.168.40.71:8080, and http://192.168.56.1:8080
[08:27:53] 1 change detected
NiceGUI ready to go on http://localhost:8080, http://192.168.40.71:8080, and http://192.168.56.1:8080
WARNING:  WatchFiles detected changes in 'main.py'. Reloading...
[08:28:05] 1 change detected
Traceback (most recent call last):
  File "C:\Users\lsimons\AppData\Local\Programs\Python\Python312\Lib\site-packages\watchfiles\run.py", line 149, in run_process
    process.stop(sigint_timeout=sigint_timeout, sigkill_timeout=sigkill_timeout)
  File "C:\Users\lsimons\AppData\Local\Programs\Python\Python312\Lib\site-packages\watchfiles\run.py", line 327, in stop
    os.kill(self.pid, signal.SIGINT)
KeyboardInterrupt

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\lsimons\AppData\Local\Programs\Python\Python312\Scripts\watchfiles.exe\__main__.py", line 7, in <module>
  File "C:\Users\lsimons\AppData\Local\Programs\Python\Python312\Lib\site-packages\watchfiles\cli.py", line 171, in cli
    run_process(
  File "C:\Users\lsimons\AppData\Local\Programs\Python\Python312\Lib\site-packages\watchfiles\run.py", line 153, in run_process
    process.stop()
  File "C:\Users\lsimons\AppData\Local\Programs\Python\Python312\Lib\site-packages\watchfiles\run.py", line 327, in stop
    os.kill(self.pid, signal.SIGINT)
PermissionError: [WinError 5] Access is denied