How to Draw To Two Canvases (One layer being always background) with different threads?

aarondbaron

In this example , the author shows a way to ensure that you can always draw certain objects behind or in front of other objects. He does this using layers, where you draw to each pgraphics object the thing you want (in his example, letters in one layer, rects in another).

Is it possible to do this in a threaded way too? In his example, still we write sequentially to one pgraphics object and then another. Is there a way to write my letters and rects simultaneously with threads, and still ensure that they will appear one after the other?