Help needed with running the backend of the application

[Ruulul]

I want to use a module that uses the signal module internally;
I need to have access to app.paths before instanciating it, in order to have the proper paths to write data to;
But I cant instanciate it on the app's startup because the app's main loop apparently is not on the main thread of the main interpreter...

I have no clue in how to handle this dilemma

Traceback (most recent call last):
  File "threading.py", line 1041, in _bootstrap_inner
  File "threading.py", line 992, in run
  File "...\reticulumsocial\backend\__main__.py", line 37, in main_loop
    router = LXMF.LXMRouter(id, paths['data'].__str__())
  File "...", line 270, in __init__
    signal.signal(signal.SIGINT, self.sigint_handler)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "signal.py", line 58, in signal
ValueError: signal only works in main thread of the main interpreter

[freakboy3742]

A fix for this is going to be very specific to your app's circumstances, but I can try and fill in some of the background here.

The main loop handling is platform-specific. Based on the error you're reporting, I'm guessing you're on Windows - and on Windows, the app's main thread isn't the GUI loop. There's nothing that can be done to avoid that; it's a feature of how Winforms works.

However, you can differentiate between instantiating the app, and starting the main loop. The code to start a Toga app is very explicitly:

app = MyApp(...)
app.main_loop()

After the first line has executed, the app exists, but isn't running. The second lines starts the GUI main loop, which creates the second (GUI) thread. Any user actions that occur after that point in response to GUI events are occurring on the GUI thread.

So - if you need to do something with signals... do it before you start the main loop. You can still have access to the app (and thus to app.paths and similar properties) - but you can't assume you can display a GUI or anything like that.

[Ruulul]

I was trying out to use the multiprocessing library, which I am not entirely sure it will work, but I stepped back and tried that - at least it gives me a new error:

Traceback (most recent call last):
  File "\app\reticulumsocial\__main__.py", line 8, in <module>
    app: toga.App = main()
                    ~~~~^^
  File "\app\reticulumsocial\app.py", line 54, in main
    return ReticulumSocial()
  File "\app_packages\toga\app.py", line 310, in __init__
    self.factory = get_platform_factory()
                   ~~~~~~~~~~~~~~~~~~~~^^
  File "\app_packages\toga\platform.py", line 114, in get_platform_factory
    factory = importlib.import_module(f"{backend.value}.factory")
  File "importlib\__init__.py", line 88, in import_module
  File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1310, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1331, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 935, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 1022, in exec_module
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "\app_packages\toga_winforms\__init__.py", line 1, in <module>
    import clr
  File "\app_packages\clr.py", line 5, in <module>
    from pythonnet import load
  File "\app_packages\pythonnet\__init__.py", line 10, in <module>
    _RUNTIME: Optional[clr_loader.Runtime] = None
                       ^^^^^^^^^^^^^^^^^^
AttributeError: module 'clr_loader' has no attribute 'Runtime'

So... is this supposed to happen?

[freakboy3742]

Without knowing what it is you've done, it's very difficult to say whether it should or shouldn't happen. That error definitely shouldn't happen in "normal" usage. It seems to indicate that either you've got the wrong version of .NET available, or you've interrupted the initialisation of Toga (or python.net) in some way. Knowing whether a "hello world" app works, without any special modifications that might be interfering, is an important first diagnosis step here.

As for multiprocessing - it will work in an app you're starting with python -m myapp (or similar), but it won't work in the context of an app packaged with Briefcase. This is a known limitation of the stub binary approach used by Briefcase.

[Ruulul]

thats good to know about the multiprocessing

I did a clean briefcase project and just changed the main to separate them, and it seems it works on dev but I am again running into issues when going to the other modes, but at this point this is not a Toga issue anymore

Thanks for the pointers, I will be closing this for now