Getting a "connection lost" error when trying to use the file picker in native mode

[varchasgopalaswamy]

Description

I'm trying to use the example case provided in https://github.com/zauberzeug/nicegui/discussions/283

from nicegui import app, ui

async def choose_file():
    files = await app.native.main_window.create_file_dialog(allow_multiple=True)
    for file in files:
        ui.notify(file)

ui.button('choose file', on_click=choose_file)

ui.run(native=True)

but when I try to run this, I get a message "Connection lost", and the file browser doesn't show up.

[rodja]

The posted code is working for me. Maybe its an operating system issue? I'm on Mac OS with Chrome.

[varchasgopalaswamy]

Interesting. I'm on RHEL 9 and using GTK for Webview. I found QT did not work (I was getting a white blank screen). I am able to launch the file browser using Webview, e.g.

import webview

def open_file_dialog(window):
    file_types = ('Image Files (*.bmp;*.jpg;*.gif)', 'All files (*.*)')

    result = window.create_file_dialog(webview.OPEN_DIALOG, allow_multiple=True, file_types=file_types)
    print(result)

if __name__ == '__main__':
    window = webview.create_window('Open file dialog example', 'https://pywebview.flowrl.com/hello')
    webview.start(open_file_dialog, window)

so I guess it's not an issue with Webview?

[varchasgopalaswamy]

I turned on uvicorn_debug and got

DEBUG: < TEXT '42["event",{"id":12,"listener_id":"a96b632f-5e0...3cfa3ff0eb","args":[]}]' [84 bytes]

when I clicked on the "open file" dialog. I guess it's not able to get a connection to something since there's no reply?

[rodja]

It may be some code is blocking the main thread. Can anyone on Linux with GTK confirm this issue?

[falkoschindler]

@NiklasNeugebauer, @JensOgorek, I already tried to reproduce this issue with @denniswittich, but we couldn't get GTK running. Could one of you, please, try to run the code from the original post and see if the file dialog works? Thanks!

[JensOgorek]

I can confirm the error. Tried the code above, clicked on "Choose File" and connection is lost.

[Liquidmasl]

to add some info, for me it works fine if I am in debug mode (pytorch) but i get the same issue when i am in run mode.

[falkoschindler]

I just reproduced the issue on an Ubuntu machine, but I have no clue why the dialog doesn't open.

I thought it might have to do with the button click, but this minimal pywebview example works perfectly fine:

import webview

class Api:
    def open_file_dialog(self):
        print(window.create_file_dialog(webview.OPEN_DIALOG, allow_multiple=True, file_types=()))

api = Api()
window = webview.create_window('Test', html='<button onclick="pywebview.api.open_file_dialog()">open dialog</button>', js_api=api)
webview.start()

Are we doing something wrong when sending the request to the other process? https://github.com/zauberzeug/nicegui/blob/460dbc1f1549bfc35cace6cdb76d7402762ae9a8/nicegui/native/native.py#L114-L123

Should we set block or timeout differently when calling get()? I don't have my dev environment on this Linux machine, so it's a bit cumbersome to play around with the source code. Can anyone step in?

[JensOgorek]

@falkoschindler I changed the code of native.py, but it seems it already get stuck at method_queue.put((name, args, kwargs)) for me.

[gsal]

I am trying nicegui and native=True, but things are not working for me.

If I try the code at the top from the OP:

from nicegui import app, ui

async def choose_file():
    files = await app.native.main_window.create_file_dialog(allow_multiple=True)
    for file in files:
        ui.notify(file)

ui.button('choose file', on_click=choose_file)
ui.run(native=True)

The final error message is as follows:

File "/home/gsal/.conda/envs/py311nice/lib/python3.11/multiprocessing/synchronize.py", line 107, in __getstate__
    raise RuntimeError('A SemLock created in a fork context is being '
RuntimeError: A SemLock created in a fork context is being shared with a process in a spawn context. This is not supported. Please use the same context to create multiprocessing objects and Process.

I am in Rocky9 and using a conda environment that I created (in the last 48 hours) with the latest nicegui