Firstly, thank you. Your comment is relating a couple of distinct ideas together in a way that is very helpful.

>Then your code can run till it's done, making system calls if it needs to, and potentially being preemptively multitasked, but that's all invisible to your code, black box in terms of how it's implemented.

I'm realizing that I don't actually understand how pre-emptive multi-tasking is implemented at the VM level, and I think this is perhaps what I actually want. Can you elaborate and/or suggest any articles/video-lectures on the subject?

Maybe what I need is an operating-systems course...