After changing a RwSignal from an OS callback, the UI is not updated until focused/hovered

[kaivol]

On Windows, I'm using a RwSignal to store (and show) the system's current accent color.
Further, I register a SUBCLASSPROC callback using SetWindowSubclass to get notified when the accent color is changed: In the callback, I update the value in the RwSignal.

If I now change the accent color in the Windows settings the callback is invoked immediately, but the UI does not show this change until I hover the window with the mouse or focus the window.
A workaround that I have found is calling

floem::ext_event::register_ext_trigger(Trigger::new());

after changing the RwSignal. This causes the UI to be updated immediately.

Is this the expected/desired behavior, and if so, what would be the best way to solve the problem?

Thanks!

[panekj]

That's because almost every Windows API is async. This is the expected behaviour.

[kaivol]

Could you elaborate on what you mean by “async” in this context?
As far as I understand it, SetWindowSubclass registers an ordinary callback which gets invoked in the main thread.