The Distinguishment Between Async and Threadmod

Multi-level threading is a historical accident, first and foremost. I think that a lot of that actually comes from people having operating systems in which multiple threads are not supported. And if you have an operating system that only supports a single thread of control, you can implement what threads on top of that single kernel-level entity. It's hard to unpack the arguments for having these different levels of control. You're going to reserve these for your relatively longer operations. How do you kind of keep track of the state that you've got while you're waiting for this thing?