How do DAW's process sends/returns with busses if they are routed to themselves?

Question

I'm looking into creating the sends/returns/busses logic for my own audio application. When checking existing DAW's (Logic Pro / Ableton Live) I noticed you can make a routing-loop by sending busses/aux to itself (depending on the DAW).

In the image below you can see a simple example. In the 'A Delay' bus is 'sent' to itself.

I was wondering if anyone has an idea how this is processed. As I would expect there to be some infinite loop or at least a very high CPU load. Or is there some other trick I might be missing?