How to prevent shiny app not showing during long global.R execution times?



Currently I use the global.R to load some global variables/datastructures that has to available in ui.R/server.R.
That can take up to 30s in which nothing is shown to the user (e.g. as ui.R is only run AFTER global.R is done) making it seem like the application is not working at all.

Is there some smart way to show the user, that something is happening already? The only other solution I could think of would be to move much data loading to server.R and fill/build many parts of ui.R dynamically - that would add some extra complexity though