For parallelism I'd expect something like Cilk (or Rayon, which was inspired by it), where there's some syscalls for spawning and then joining on tasks, but the

For parallelism I'd expect something like Cilk (or Rayon, which was inspired by it), where there's some syscalls for spawning and then joining on tasks, but the VM handles starting and managing the thread pool. For concurrency it's a lot harder to make a good interface