Updating app state repeatedly from main thread

[burumdev]

I have an app which launches Slint window in a sub-thread from its main thread. I use an Arc<Mutex<State>> clone in order to pass a state object to Slint UI and the values are received, I can see that from the println!() statement within the loop here:

fn main() {
.........................
        let ui_handle = thread::spawn(move || {
                let app = MainWindow::new().unwrap();
        
        ........................
        ........................
        
                let app_weak = app.as_weak();
                slint::spawn_local(async move {
                    loop {
                        let appw = app_weak.clone();
                
                        let state_lock = state.lock().unwrap();
                        println!("STATE: {:?}", *state_lock);
                
                        appw.unwrap().set_state((*state_lock).clone());
                    }
                }).unwrap();
        ......................
        ......................
        }

        if quit {
                ui_handle.join().unwrap();
        }
}

But the main window appears to be blocked by this. I only see a small black window which is unresponsive.

What would be the idiomatic and correct way to approach this?

[burumdev]

I use the Timer struct for this:

            let app_weak = app.as_weak();
            timer.start(TimerMode::Repeated, Duration::from_millis(5), move || {
                let appw = app_weak.clone();

                let state_lock = state.lock().unwrap();

                appw.unwrap().set_state((*state_lock).clone());
            });

It looks like the most idiomatic way to do it.

[ogoffart]

You loop never yields (.await) and that's why it blocks the ui thread.
perhaps this could be solved with tokio::sync::Notify

[burumdev]

Ooops I forgot an await there. You're right, the loop is unyielding. And thanks for the Notify notification. The code is much more clearer now. It uses less CPU too:

let state_notifier: Arc<Notify> = Arc::new(Notify::new());
.................
// State needs updating...
state_notifier.notify_one();
..................
..................
sn_clone = Arc::clone(&state_notifier);
let app_weak = app.as_weak();
slint::spawn_local(async move {
    let appw = app_weak.clone();
    loop {
        sn_clone.notified().await;

        let state_lock = state.lock().unwrap();
        appw.unwrap().set_state((*state_lock).clone());
    }
}).unwrap();