[hayley-patton]

> imho the issue isn't function coloring, threads, whatever. It's a compiler that defaults to async code in the calling convention and then optimization passes to de-async-ify (remove unnecessary yield points) the code at compile time. The result would be code that looks synchronous but is async where it matters (i/o).

Safepoints for garbage collection are somewhat similar, but for preemption one wants to interrupt threads on a timer, rather than before the collector takes over. Despite occurring very frequently (at around 100 _million_ checks per second), the time overhead is only about 2.5% or so, according to a study by Blackburn et al [0]. It appears, I think, that as long as the fast not-interrupting path is fast enough, eliminating safepoints isn't too important.

[0] Stop and Go: Understanding Yieldpoint Behaviour <https://users.cecs.anu.edu.au/~steveb/pubs/papers/yieldpoint...>