app.py

# This takes a lot of time (compute heavy).
async def blocking_function(q: Q):
    count = 0
    total = 20
    while count < total:
        # Check if cancelled.
        if q.client.event.is_set():
            await show_cancel(q)
            return 
        # This blocks the main thread and prevents any other execution.
        # This would be a heavy compute job in the real world.
        time.sleep(1)
        count += 1
        # Assume you are able to emit some kind of progress.
        await update_ui(q, count / total)

    # Show a notification at the end.
    await show_notification(q)