also, there's been work to make for-loops preemptible:

- https://github.com/golang/go/issues/10958

- https://go-review.googlesource.com/c/go/+/33910

- https://go-review.googlesource.com/c/go/+/36206

- https://go-review.googlesource.com/c/go/+/46410

- https://go-review.googlesource.com/c/go/+/43050