Commands and async

update is synchronous on purpose. Background work flows in through the command proxy:

impl App for Clock {
    type Msg = Msg;

    fn init(&mut self, proxy: Proxy<Msg>) {
        std::thread::spawn(move || loop {
            std::thread::sleep(Duration::from_secs(1));
            proxy.send(Msg::Tick);
        });
    }
    // ...
}

Proxy<Msg> is cloneable and thread-safe; sends wake the event loop, apply through update, and repaint. After the window closes, sends drop silently. (A::Msg: Send — messages cross threads.)

This composes with anything async: spawn a tokio runtime in init, keep the proxy in your tasks; or pair with rfd’s file dialogs (examples/file_dialog.rs). Headlessly, render_app drains proxied messages at deterministic points, so init-time sends are testable.

Toast auto-dismiss is the canonical pattern: push the toast, spawn a timer thread, send the removal message (examples/toasts.rs).