Deadlock when closing app, associated with Footer.recompose and focus events

[slawek-es]

A deadlock similar to the one described in #4643 occurs in a simple test case where the application is closed very soon after it gets initialized. The supposed fix for #4643 does not work for this case, and the deadlock is still reproducible with textual version 0.70.0.

The issue seems to again be a bad interaction between the Footer.recompose call run as the response to the bindings_updated signal and the procedure of closing the entire application. The Footer.recompose enqueues an AwaitRemove callback while the _dom_lock is already held by _close_all, and closing the Footer requires completing the AwaitRemove future, leading to a deadlock. The issue seems to be triggered by set_focus calls which we do from a background task.

Minimal Reproduction Environment

Run pytest editshare_system_upgrade/textual_ui/repro_app.py to see the TimeoutError:

import asyncio

from textual import work
from textual.app import App, ComposeResult
from textual.widgets import Header, Footer, Input
from textual.screen import Screen


class ReproScreen(Screen[None]):
    def __init__(self) -> None:
        super().__init__()
        self._input = Input()

    def on_mount(self) -> None:
        """Start a background refresh loop."""
        self.refresh_state()

    def compose(self) -> ComposeResult:
        yield Header()
        yield self._input
        yield Footer()

    @work
    async def refresh_state(self) -> None:
        """This stands for a more complicated refresh state loop."""
        while True:
            self.set_focus(self._input)
            await asyncio.sleep(0.1)


class ReproApp(App[None]):

    AUTO_FOCUS = None  # Important for reproduction!

    def __init__(self) -> None:
        super().__init__()

    async def on_mount(self) -> None:
        self.initialize_welcome_screen()

    @work
    async def initialize_welcome_screen(self) -> None:
        await self.push_screen(ReproScreen())


async def test_repro_app() -> None:
    app = ReproApp()
    async with app.run_test():
        pass


if __name__ == "__main__":
    asyncio.run(ReproApp().run_async())

Output from `textual diagnose`

``` # Textual Diagnostics

Versions

Name	Value
Textual	0.70.0
Rich	13.7.1

Python

Name	Value
Version	3.12.1
Implementation	CPython
Compiler	GCC 9.4.0
Executable	/home/saf/code/es/editshare-system-upgrade/.venv/bin/python3

Operating System

Name	Value
System	Linux
Release	5.4.0-186-generic
Version	#206-Ubuntu SMP Fri Apr 26 12:31:10 UTC 2024

Terminal

Name	Value
Terminal Application	vscode (1.90.2)
TERM	xterm
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=169, height=18
legacy_windows	False
min_width	1
max_width	169
is_terminal	False
encoding	utf-8
max_height	18
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

</details>

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[willmcgugan]

Have you managed to reproduce this outside of pytest?

[slawek-es]

Have you managed to reproduce this outside of pytest?

Well, if you change the reproduction module to say:

if __name__ == "__main__":
    asyncio.run(test_repro_app())

then the issue technically happens outside of pytest, but it still uses App.run_test. Do you think this is a deciding factor here?

Apart from this, I have been unable to reproduce this issue by running the application normally.

[willmcgugan]

Fixed in main.

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