Window does not close when stopping native mode with Ctrl-C on Windows

[falkoschindler]

As already mentioned on #584, the native application does not terminate correctly with Ctrl-C on Windows.

[al-eax]

uvicorn has similar issues:
encode/uvicorn#1872

[rodja]

We will wait a bit longer for the uvicorn issue to evlolve.

[falkoschindler]

@rodja Issue encode/uvicorn#1872 is from Feb 21 and still tagged as "needs confirmation". Anyway, I'll tag our issue as "waiting" and move it to "Later". Feel free to revert.

[ItsCubeTime]

Hai, you can implement a fix for this yourself!

if sys.platform == "win32":
    import win32api
    import os
    win32api.SetConsoleCtrlHandler(lambda a=None: os.kill(os.getpid(), 15)) # Enables ctrl+C to kill the terminal on Windows. 15 == signal.SIGTERM

[rodja]

@ItsCubeTime cool. Would you care to create a pull request to close this bug?

[falkoschindler]

Good news for encode/uvicorn#1872:

xiaotushaoxia closed this as completed yesterday

So maybe we can resolve our issue soon by updating uvicorn.

[falkoschindler]

Looks like encode/uvicorn#1872 has been closed based on PR encode/uvicorn#1584 which was merged already on April 13. According to the milestone and the release notes, it should have been released on April 28 with uvicorn 0.22.0.

@al-eax and @ItsCubeTime, can you check if the issue is gone with uvicorn 0.22.0? Thanks!

[falkoschindler]

Nope, the problem remains with uvicorn 0.22.0 and NiceGUI 1.3.5 on Windows. 😕

[falkoschindler]

Looks like a pywebview issue. The example from https://pywebview.flowrl.com/#hello-world has the same problem:

import webview
webview.create_window('Hello world', 'https://pywebview.flowrl.com/')
webview.start()

[miningmanna]

As far as I understand, pywebview needs to run in the main thread, therefore eating the SIGINT/SIGTERM signal.
In nicegui it is already running in a different process. The uvicorn server also exits when you press ctrl-c in the console.
From my (maybe limited) testing, it could be as simple to fix as setting the pywebview process to be a daemon process.

native_mode.py (line 109)
process = mp.Process(target=open_window, args=args, daemon=True)

or have some kind of message one could send to the pywebview process, similar to how get_size and so on work, in order to cleanly terminate the process.

[falkoschindler]

@miningmanna Have you tried setting daemon=True? If it worked, a pull request would be very welcome. We just can't test it ourselves, since we have no Windows machine at hand.

[miningmanna]

@falkoschindler I tried it on a Windows 10 and Windows 11 machine. It works on both.
I will create a pull request.

[falkoschindler]

Amazing! The argument daemon=False has been added to the code in the very first commit regarding native mode: c734cab#diff-e16537d6af67de700fc23c3bd55c1eb27592a57962272242cb148bae23275af0. Somehow it was never questioned.

For a bit more context, this is how ChatGPT describes its function:

The multiprocessing.Process with daemon=False means that the main program will wait for the open_window function to complete its execution in the separate process before the main program finishes.

So since the window process shouldn't run without the main process, setting daemon=True seems to be absolutely correct. 👍🏻