Briefcase not closing down cleanly

[JDarsley]

Describe the bug

On Windows, when using the default menu option File | Exit, or the standard window close button, while running a Toga app under Briefcase, the application crashes, reporting that there are still pending operations.

Steps to reproduce

1. Set up a virtual environment, and create a new project called "jotter".
2. Copy the two Python files into the src\jotter folder, as app.py and main.py (with a pair of double underscores - they appear to have been formatted out of the latter file name).
3. briefcase dev
4. See error messages in console (attached).

app.py

import toga

class Jotter(toga.App):

    def startup(self):
        self.main_window = toga.MainWindow()
        self.main_window.content = toga.Box()

        lstDetail = [
            {"Detail": "Subject Heading"},
            {"Detail": "Date and time"},
            {"Detail": "Note text"}
        ]

        self.tblNoteDetails = toga.Table(
            headings=None,
            accessors=["Detail"],
            data=lstDetail,
            on_select=self.onSelect,
            flex=1
        )

        self.countOnSelect = 0

        self.main_window.content.add(self.tblNoteDetails)
        
        self.main_window.show()

    def onSelect(self, widget, **kwargs):
        self.countOnSelect += 1
        print(f"\nSelect handler - call {self.countOnSelect}")
        print({widget.data[0]})
        print({widget.data[1]})
        print({widget.data[2]})

(Am I doing something wrong with the code formatting? It won't come out right.)

main.py

from jotter.app import Jotter

if __name__ == "__main__":
    app = Jotter()
    app.main_loop()

Expected behavior

Closing the app shouldn't generate error messages. I was previously running an older version of Toga, and didn't get those errors.

Screenshots

Error messages on exit from the app.

Environment

• Operating System: Windows 11 24H2
• Python version: 3.12.6
• Software versions:
  • Briefcase: 0.3.22
  • Toga: 0.5.0
  • ...

Logs

Additional context

No response

[HalfWhitt]

(Am I doing something wrong with the code formatting? It won't come out right.)

It looks like you're using one backtick(`) before and after your code blocks; you should use three instead (```). Alternatively, indent the whole code block by four spaces instead, with no backticks. (This is why everything in your code that's indented once or more currently displays as a code block, with one layer of indentation removed.)

An advantage of using backticks instead of indentation is that you can specify the language and get syntax highlighting, e.g. in this case open a code block with ```python.

[JDarsley]

Thanks Charles, that's useful to know.

[HalfWhitt]

I don't have my hands on Windows at the moment to look into this. But if you have the time, here are some things that would help narrow down the source. Do you get the same crash...

• With one of the Toga example apps (in /examples in the repo)?
• When running the Python module directly, rather than from Briefcase?
• With Toga 0.4.9 instead of 0.5.0?

[freakboy3742]

Thanks for the report - I've been able to reproduce this using Toga Tutorial 0 on Windows 10. It only occurs with briefcase dev. I don't see the problem on Toga 0.4.9.

I don't see the problem with python -m tutorial; but if I set PYTHODNEVMODE=1 in the environment, I can reproduce the messages. They appear to be a combination of warnings, and asyncio cleanup errors.

The good news is that they're not a problem per se - they're obviously undesirable, but they're not an indication that anything is actually broken. The issues being reported are all things that will be cleaned up automatically when the app exits.

They seem to stem from the end-of-life of the Windows Proactor - that proactor isn't being explicitly shut down, and Python's asyncio cleanup warnings are being triggered as a result. From the look of it, the "run_forever_cleanup" portion of the event loop is not being executed... but that isn't a change since 0.4.9, so I can't work out why this has become a problem. More investigation is required.

[JDarsley]

I don't have my hands on Windows at the moment to look into this. But if you have the time, here are some things that would help narrow down the source. Do you get the same crash...

* With one of the Toga example apps (in `/examples` in the repo)?

* When running the Python module directly, rather than from Briefcase?

* With Toga 0.4.9 instead of 0.5.0?

Hi Charles. I think Russell's reply probably covers these points, but if not, let me know if there's anything you'd still like me to try.

[freakboy3742]

@JDarsley I think I've found a fix for this; if you're able to try out the patch on #3270 that would be very helpful. If you've got a Briefcase project, you can replace the references to toga-core==0.5.0 and toga-winforms==0.5.0 with git+https://github.com/freakboy3742/toga.git@proactor-exit#egg=toga-core&subdirectory=core and git+https://github.com/freakboy3742/toga.git@proactor-exit#egg=toga-winforms&subdirectory=winforms respectively, then running briefcase dev -r to get the updated version installed.

[JDarsley]

@freakboy3742 I'm not entirely clear on this. When you refer to the "Briefcase project", I'm guessing that would essentially be the pyproject.toml file? If so, I have a reference in there to toga-winforms:

[tool.briefcase.app.jotter.windows]
requires = [
    "toga-winforms~=0.4.7",
]

No reference to toga-core though. So I'm not sure what changes are needed. I did try simply replacing the toga-winforms requirement with your new version, but predictably, on its own that's clearly not ok.

I've attached the full file, in case that helps (I've given it a .txt extension, as the attachment mechanism here won't allow .toml).

pyproject.toml.txt

As an aside (and nothing to do with attempting to upgrade), the very first run of version 0.3.22 of briefcase dev actually downgrades a number of components - toga-core from 0.5.0 to 0.4.9, toga-winforms the same, and travertino from 0.5.0 to 0.3.0.

[mhsmith]

No reference to toga-core though. So I'm not sure what changes are needed. I did try simply replacing the toga-winforms requirement with your new version, but predictably, on its own that's clearly not ok.

Try replacing the toga-winforms requirement with both the toga-core and toga-winforms URLs above.

the very first run of version 0.3.22 of briefcase dev actually downgrades a number of components - toga-core from 0.5.0 to 0.4.9, toga-winforms the same, and travertino from 0.5.0 to 0.3.0.

Yes, that will be because of the ~=0.4.7 requirement. You can update that to 0.5.0 now that it's been released.

[freakboy3742]

@freakboy3742 I'm not entirely clear on this. When you refer to the "Briefcase project", I'm guessing that would essentially be the pyproject.toml file? If so, I have a reference in there to toga-winforms:

Apologies - I forgot the content that Briefcase generates by default. I've been using tutorial0 as a demo, and it has a slightly different setup.

If you modify the windows section of your pyproject.toml to read:

[tool.briefcase.app.jotter.windows]
requires = [
    "git+https://github.com/freakboy3742/toga.git@proactor-exit#egg=travertino&subdirectory=travertino",
    "git+https://github.com/freakboy3742/toga.git@proactor-exit#egg=toga-core&subdirectory=core",
    "git+https://github.com/freakboy3742/toga.git@proactor-exit#egg=toga-winforms&subdirectory=winforms",
]

then run briefcase dev -r, that should be everything you need to test the new code.

[JDarsley]

Thanks @mhsmith and @freakboy3742. I can confirm that after making those changes, the error messages no longer appear when closing the app.

However, a number of console messages caught my eye. Is there anything here that looks wrong?

Installing collected packages: travertino, toga-core, toga-winforms
  Attempting uninstall: travertino
    Found existing installation: travertino 0.5.0
    Uninstalling travertino-0.5.0:
      Successfully uninstalled travertino-0.5.0
  Attempting uninstall: toga-core
    Found existing installation: toga-core 0.5.0
    Uninstalling toga-core-0.5.0:
      Successfully uninstalled toga-core-0.5.0
  Attempting uninstall: toga-winforms
    Found existing installation: toga-winforms 0.5.0
    Uninstalling toga-winforms-0.5.0:
      Successfully uninstalled toga-winforms-0.5.0
ERROR: pip's dependency resolver does not currently take into account all the packages that are installed. This behaviour is the source of the following dependency conflicts.
toga 0.5.0 requires toga-winforms==0.5.0; sys_platform == "win32", but you have toga-winforms 0.4.5.dev1514+gdd979716c which is incompatible.
Successfully installed toga-core-0.4.5.dev1514+gdd979716c toga-winforms-0.4.5.dev1514+gdd979716c travertino-0.4.5.dev1514+gdd979716c
Installing dev requirements... done

Obviously, pip is complaining. However, the question for me is whether those versions 0.4.5.dev are correct - as in lower version numbers than the 0.5.0 I was previously running? I'm guessing it's probably the way dev versions feed into the main branch, so probably nothing.

Will it be obvious, when the time comes, when I should update pyproject.toml back to main release versions?

[mhsmith]

Obviously, pip is complaining. However, the question for me is whether those versions 0.4.5.dev are correct - as in lower version numbers than the 0.5.0 I was previously running? I'm guessing it's probably the way dev versions feed into the main branch, so probably nothing.

Yes, this is fine. It's because the freakboy3742/toga fork doesn't automatically get copies of new version tags from the main repository.

Will it be obvious, when the time comes, when I should update pyproject.toml back to main release versions?

The fix will be included in the next Toga release. You can be notified of this by watching the project on GitHub – select "Custom" mode to be notified only of releases and not other activity.

[JDarsley]

Thanks @mhsmith - I'll watch for the release.