Awaiting pop_screen in @on causes app to freeze #5008

mzebrak · 2024-09-16T11:09:42Z

Version: 0.79.1

Adding await to self.app.pop_screen causes app to freeze when triggered via button, but works fine when triggered via key binding.

from __future__ import annotations

from typing import cast

from textual import on
from textual.app import App, ComposeResult
from textual.binding import Binding
from textual.screen import Screen
from textual.widgets import Button, Footer, Header, Label


class FirstScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Label("this is the first screen")
        yield Footer()


class SecondScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Label("this is the second screen")
        yield Button("Pop back to first screen")
        yield Footer()

    @on(Button.Pressed)
    async def pressed(self) -> None:
        app = cast(MyApp, self.app)
        app.notify("Going back to first screen...")
        await app.action_pop_current_screen()


class MyApp(App):
    BINDINGS = [
        Binding("a", "pop_current_screen", "Pop screen"),  # key binding works just fine with await
        Binding("d", "push", "Push screen"),
    ]

    async def on_mount(self) -> None:
        await self.push_screen(FirstScreen())

    async def action_pop_current_screen(self) -> None:
        while not isinstance(self.screen, FirstScreen):
            await self.pop_screen()  # awaiting causes the bug, removing await fixes it in case of pressing the button

    async def action_push(self) -> None:
        await self.push_screen(SecondScreen())


MyApp().run()

The text was updated successfully, but these errors were encountered:

willmcgugan · 2024-09-16T13:08:56Z

By awaiting the pop_screen, you are waiting for all its messages to be processed. But your button.pressed message handler will never return, because it is waiting for itself to be popped. In other words, a deadlock.

I suspect the best thing for us to do is make it error / warning. To fix it, you can add @work to your action.

mzebrak · 2024-09-16T13:27:29Z

Putting @work over MyApp.action_pop_current_screen solves the case here. I thought it would be the same as
self.run_worker(app.action_pop_current_screen()) in SecondScreen.pressed, however the second one crashes without any error.

Because real scenario is something more like: #5009
so putting @work over such an App method is a no-go for me.

By awaiting the pop_screen, you are waiting for all its messages to be processed

But in the case of pop_screen, there is no need to wait for all the screen messages to be processed I think? Because this call will destroy this screen anyway, so shouldn't it prioritize it over other messages?

mzebrak · 2024-09-23T06:26:24Z

This shows the crash I've been talking about in the previous comment. Am I doing something wrong there?

TEXTUAL CONSOLE OUTPUT

[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Key(key='enter', character='\r', name='enter', is_printable=False, aliases=['enter', 'ctrl+m']) >>> Button() method=<Widget.on_key>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Key(key='enter', character='\r', name='enter', is_printable=False, aliases=['enter', 'ctrl+m']) >>> SecondScreen() method=<Widget.on_key>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Key(key='enter', character='\r', name='enter', is_printable=False, aliases=['enter', 'ctrl+m']) >>> MyApp(title='MyApp', classes={'-dark-mode'}) method=<App.on_key>
[08:23:50] SYSTEM                                                                                                                                                                                               app.py:3444
<action> namespace=Button() action_name='press' params=()
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:749
Pressed() >>> Button() method=None
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Pressed() >>> SecondScreen() method=<SecondScreen.on_button_pressed>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:749
StateChanged(<Worker RUNNING name='action_pop_current_screen' description='<coroutine object MyApp.action_pop_current_screen at 0x7f99c3f2f0d0>'>, <WorkerState.PENDING: 1>) >>> SecondScreen() method=None
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:749
StateChanged(<Worker RUNNING name='action_pop_current_screen' description='<coroutine object MyApp.action_pop_current_screen at 0x7f99c3f2f0d0>'>, <WorkerState.RUNNING: 2>) >>> SecondScreen() method=None
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Notify(notification=Notification(message='Going back to first screen...', title='', severity='information', timeout=5, raised_at=1727072630.3777125, identity='e34262f4-1c0b-4ec1-b2ad-79a4b57ab4b4')) >>> 
MyApp(title='MyApp', classes={'-dark-mode'}) method=<App.on_notify>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:749
Pressed() >>> MyApp(title='MyApp', classes={'-dark-mode'}) method=None
[08:23:50] WORKER                                                                                                                                                                                             worker.py:366
<Worker RUNNING name='action_pop_current_screen' description='<coroutine object MyApp.action_pop_current_screen at 0x7f99c3f2f0d0>'>
[08:23:50] SYSTEM                                                                                                                                                                                               app.py:2494
FirstScreen() is active
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
ScreenResume() >>> FirstScreen() method=<Screen.on_screen_resume>
[08:23:50] SYSTEM                                                                                                                                                                                               app.py:2272
SecondScreen() SUSPENDED
[08:23:50] DEBUG                                                                                                                                                                                              screen.py:827
focus was removed
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Mount() >>> Toast() method=<Toast.on_mount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Mount() >>> Toast() method=<Widget.on_mount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
ScreenSuspend() >>> SecondScreen() method=<Screen.on_screen_suspend>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Blur() >>> Button() method=<Widget.on_blur>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Mount() >>> Toast() method=<Toast.on_mount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Mount() >>> Toast() method=<Widget.on_mount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Mount() >>> ToastHolder(id='--textual-toast-e34262f4-1c0b-4ec1-b2ad-79a4b57ab4b4') method=<Widget.on_mount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Tooltip(id='textual-tooltip') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Label() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Mount() >>> ToastHolder(id='--textual-toast-e34262f4-1c0b-4ec1-b2ad-79a4b57ab4b4') method=<Widget.on_mount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> HeaderIcon() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> HeaderTitle() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> HeaderClockSpace() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FooterKey() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FooterKey() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FooterKey() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Header() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Footer() method=<Footer.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Footer() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Button() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Toast() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> ToastHolder(id='--textual-toast-e34262f4-1c0b-4ec1-b2ad-79a4b57ab4b4') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> ToastRack(id='textual-toastrack') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> SecondScreen() method=<Widget.on_unmount>
[08:23:50] WORKER                                                                                                                                                                                             worker.py:372
<Worker CANCELLED name='action_pop_current_screen' description='<coroutine object MyApp.action_pop_current_screen at 0x7f99c3f2f0d0>'>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Tooltip(id='textual-tooltip') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Label() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> HeaderIcon() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> HeaderTitle() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> HeaderClockSpace() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FooterKey() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FooterKey() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FooterKey() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Header() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Footer() method=<Footer.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Footer() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Toast() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> ToastHolder(id='--textual-toast-e34262f4-1c0b-4ec1-b2ad-79a4b57ab4b4') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> ToastRack(id='textual-toastrack') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> FirstScreen() method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> ToastRack(id='textual-toastrack') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Tooltip(id='textual-tooltip') method=<Widget.on_unmount>
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:740
Unmount() >>> Screen(id='_default') method=<Widget.on_unmount>


───────────────────────────────────────────────────────────────────────────────────────────── Client '127.0.0.1' disconnected ─────────────────────────────────────────────────────────────────────────────────────────────
[08:23:50] EVENT                                                                                                                                                                                        message_pump.py:749
Unmount() >>> MyApp(title='MyApp', classes={'-dark-mode'}) method=None

from __future__ import annotations

from typing import cast

from textual import on
from textual.app import App, ComposeResult
from textual.binding import Binding
from textual.screen import Screen
from textual.widgets import Button, Footer, Header, Label


class FirstScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Label("this is the first screen")
        yield Footer()


class SecondScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Label("this is the second screen")
        yield Button("Pop back to first screen")
        yield Footer()

    @on(Button.Pressed)
    async def pressed(self) -> None:
        app = cast(MyApp, self.app)
        app.notify("Going back to first screen...")
        self.run_worker(app.action_pop_current_screen())  # causes app closure


class MyApp(App):
    BINDINGS = [
        Binding("a", "pop_current_screen", "Pop screen"),  # key binding works just fine with await
        Binding("d", "push", "Push screen"),
    ]

    async def on_mount(self) -> None:
        await self.push_screen(FirstScreen())

    async def action_pop_current_screen(self) -> None:
        while not isinstance(self.screen, FirstScreen):
            await self.pop_screen()  # awaiting causes the bug, removing await fixes it in case of pressing the button

    async def action_push(self) -> None:
        await self.push_screen(SecondScreen())


MyApp().run()

mzebrak · 2024-09-26T07:58:31Z

I investigated a bit and found out that when the app closure happens, there is asyncio.CancelledError being raised from this line: https://github.com/Textualize/textual/blob/main/src/textual/worker.py#L339

After adding a wrapper to log cancellation inspired by https://stackoverflow.com/a/71356489 and some more logging looks like it comes from await_prune of AwaitRemove:

272 │ 2024-09-26 10:35:07.036 | ❌ ERROR    | textual.worker:_run:380 - In worker run of: action_pop_current_screen
 273 │ 2024-09-26 10:35:07.037 | ❌ ERROR    | textual.worker:_run_async:338 - In _run_async of: action_pop_current_screen
 274 │ 2024-09-26 10:35:07.037 | ❌ ERROR    | textual.worker:_run_async:339 - self._work is <coroutine object MyApp.action_pop_current_screen at 0x7f13aa1a78b0>
 275 │ 2024-09-26 10:35:07.037 | ❌ ERROR    | textual.worker:_run_async:348 - awaiting self._work
 276 │ 2024-09-26 10:35:07.064 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function sleep at 0x7f13aefa4e50>
 277 │ 2024-09-26 10:35:07.064 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function Timer._run at 0x7f13aee51fc0>
 278 │ 2024-09-26 10:35:07.064 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function sleep at 0x7f13aefa4e50>
 279 │ 2024-09-26 10:35:07.065 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function Timer._run at 0x7f13aee51fc0>
 280 │ 2024-09-26 10:35:07.067 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function sleep at 0x7f13aefa4e50>
 281 │ 2024-09-26 10:35:07.068 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function Timer._run at 0x7f13aee51fc0>
 282 │ 2024-09-26 10:35:07.069 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function sleep at 0x7f13aefa4e50>
 283 │ 2024-09-26 10:35:07.069 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function Timer._run at 0x7f13aee51fc0>
 284 │ 2024-09-26 10:35:07.070 | ❌ ERROR    | textual.utils:wrapper:27 - Cancelled <function AwaitRemove.__await__.<locals>.await_prune at 0x7f13a9fe1360>
 285 │ 2024-09-26 10:35:07.070 | ❌ ERROR    | textual.worker:_run_async:352 - CancelledError: CancelledError()

further narrowing shows it comes from await gather(*tasks) and we can see there is <Task cancelled name='message pump SecondScreen()', ...> there

mzebrak · 2024-09-27T07:38:36Z

Created a separate issue for the self.run_worker as seems like this is a different thing than the original cause of this issue which was awaiting pop_screen in @on. See: #5064

matmaer · 2024-09-27T10:49:38Z

Adding await to self.app.pop_screen causes app to freeze when triggered via button, but works fine when triggered via key binding.

Check inheritage of classes, you are using BINDINGS. There's a lot going on when triggered, compare the objects. Hope this helps.

mzebrak · 2024-09-27T11:15:03Z

Adding await to self.app.pop_screen causes app to freeze when triggered via button, but works fine when triggered via key binding.

Check inheritage of classes, you are using BINDINGS. There's a lot going on when triggered, compare the objects. Hope this helps.

It is explained why it happens, see Will's answer above.
Workaround of running in a background worker can be used, but still, I'm not sure it should work like that.

It's just weird the bindings action is run in a safe place, and the button action/event is not, while they're defined on the same screen.

In my case it occurred in code like this:

@on(Button.pressed)
async def button_finish(self) -> None:
    await self._finish()
    
async def action_finish(self) -> None:
    await self._finish()

Very hard to get the difference from the screen's POV. (action_finish works just OK, while button_finish does not)

Workaround is:

@on(Button.pressed)
async def button_finish(self) -> None:
    self.app.run_worker(self._finish())  # has to be self.app.run_worker, not self.run_worker in some cases, see: #5064
    
async def action_finish(self) -> None:
    await self._finish()

github-actions · 2024-10-01T14:28:23Z

Don't forget to star the repository!

Follow @textualizeio for Textual updates.

See: - Textualize/textual#5008 - Textualize/textual#5064

Textualize deleted a comment from github-actions bot Sep 16, 2024

mzebrak mentioned this issue Sep 27, 2024

Running self.run_worker crashes the app with no error message #5064

Closed

willmcgugan mentioned this issue Sep 27, 2024

Add pop_until_active #5069

Merged

willmcgugan closed this as completed in #5069 Oct 1, 2024

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 10, 2024

Fix freeze after Onboarding

55ae2e1

See: - Textualize/textual#5008 - Textualize/textual#5064

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 10, 2024

Fix freeze after Onboarding

58f1e06

See: - Textualize/textual#5008 - Textualize/textual#5064

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 10, 2024

Fix freeze after Onboarding

03433c4

See: - Textualize/textual#5008 - Textualize/textual#5064

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 14, 2024

Fix freeze after Onboarding

44a4d7c

See: - Textualize/textual#5008 - Textualize/textual#5064

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 15, 2024

Fix freeze after Onboarding

3669e57

See: - Textualize/textual#5008 - Textualize/textual#5064

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 15, 2024

Fix freeze after Onboarding

c385690

See: - Textualize/textual#5008 - Textualize/textual#5064

Gandalf-the-Grey pushed a commit to openhive-network/clive that referenced this issue Oct 16, 2024

Fix freeze after Onboarding

092074d

See: - Textualize/textual#5008 - Textualize/textual#5064

mzebrak mentioned this issue Nov 28, 2024

pop_until_active does not pop screens #5166

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Awaiting pop_screen in @on causes app to freeze #5008

Awaiting pop_screen in @on causes app to freeze #5008

mzebrak commented Sep 16, 2024

willmcgugan commented Sep 16, 2024

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matmaer commented Sep 27, 2024

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Awaiting pop_screen in @on causes app to freeze #5008

Awaiting pop_screen in @on causes app to freeze #5008

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