add_background_task is blocked in this Situation!

[vzool]

Describe the bug

I made a loading page that works fine, but when I start using it with something, the whole UI gets blocked and stopped react until the background process finishes.

Steps to reproduce

import toga
from toga.style import Pack
from toga.style.pack import COLUMN, ROW

from zakat import ZakatTracker # pip install zakat
from time import time_ns
import asyncio

class BackgoundTasks(toga.App):
    def startup(self):
        self.main_box = toga.Box(style=Pack(direction=COLUMN))
        async def generate_records(widget, **kwargs):
            print('generate_records')
            self.goto_loading_page(widget)
            await asyncio.sleep(0.6)
            async def process(app, /, **kwargs):
                print('process')
                ZakatTracker.generate_random_csv_file('million.csv', count=1_000_000, with_rate=True) # very long process
                self.main_window.info_dialog(
                    'Message Status',
                    'Operation Accomplished Successfully',
                )
                self.goto_main_page(widget)
            self.add_background_task(process)
        self.main_box.add(toga.Button('Test Loading Page (Working Fine)', on_press=lambda e: self.goto_loading_page(e, True), style=Pack(flex=1)))
        self.main_box.add(toga.Button('Generate 1,000,000 record (UI Blocked!!!)', on_press=generate_records, style=Pack(flex=1)))
        self.main_window = toga.MainWindow(title=self.formal_name)
        self.main_window.content = self.main_box
        self.main_window.show()
    
    def goto_main_page(self, widget):
        self.main_window.content = self.main_box

    def goto_loading_page(self, widget, show_back_button=False):
        self.main_window.content = self.loading_page(widget, show_back_button)

    def loading_page(self, widget, show_back_button=False):
        print('loading_page')
        page = toga.Box(style=Pack(direction=COLUMN, flex=1, padding=(150,0)))
        animation_label = toga.Label('', style=Pack(flex=1, text_align='center', font_weight='bold', font_size=60))
        page_label = toga.Label('Loading', style=Pack(flex=1, text_align='center', font_weight='bold', font_size=21))
        timer_label = toga.Label('', style=Pack(flex=1, text_align='center', font_weight='bold', font_size=12))
        page.add(animation_label)
        page.add(page_label)
        page.add(timer_label)
        if show_back_button:
            page.add(toga.Button('Back', on_press=self.goto_main_page, style=Pack(flex=1)))
        # loading_animation
        text = ["◑", "◒", "◐", "◓"] # REF https://github.com/jaywcjlove/loading-cli
        animation_label.text = text[0]
        async def loading_animation(widget, **kwargs):
            print('loading_animation')
            i = 0
            while self.main_window.content == page:
                print('loading_animation', i)
                animation_label.text = text[i]
                i += 1
                if i >= len(text):
                    i = 0
                await asyncio.sleep(0.3)
        # timer
        start = time_ns()
        coloned_time, _ = ZakatTracker.duration_from_nanoseconds(time_ns() - start)
        timer_label.text = coloned_time
        async def timer(widget, **kwargs):
            print('timeer')
            while self.main_window.content == page:
                coloned_time, _ = ZakatTracker.duration_from_nanoseconds(time_ns() - start)
                timer_label.text = coloned_time
                await asyncio.sleep(0.1)
        self.add_background_task(loading_animation)
        self.add_background_task(timer)
        return page

def main():
    return BackgoundTasks()

Expected behavior

The UI should behave smoothly in all situations when using add_background_task.

Screenshots

Screen.Recording.1446-01-15.at.1.31.38.PM.mov

Environment

• Operating System: macOS 14.5 (23F79)
• Python version: 3.11.5
• Software versions:
  • Briefcase: 0.3.19
  • Toga: 0.4.5

Logs

Additional context

No response

[mhsmith]

add_background_task is a misleading name, which is why we're deprecating it in the next version of Toga (#2678). It doesn't actually create a background thread, so your user interface will still freeze unless the task calls await frequently enough.

If you need to run some slow code which doesn't call await frequently enough, you'll need to put it in a thread. See #2099 (comment) for examples.