Yes, it's definitely possible that a spinning virtual thread will effectively pin the current OS thread. The Loom folks could keep, say, a count of how many ins

Yes, it's definitely possible that a spinning virtual thread will effectively pin the current OS thread. The Loom folks could keep, say, a count of how many instructions the virtual thread has executed, and pre-empt it itself if it needs to. This could fight a little with the OS scheduler, so I'm not sure what the tradeoffs are, but if you absolutely cannot allow a spinning virtual thread to effectively pin an OS thread, you'd want to do this. If you're going to do a bunch of computation without blocking, I'm not sure virtual threads are the tool you want to apply in the first place. They're meant to provide cheap blocking and cheap context switching. If you've got a job that's more CPU-bound than I/O bound, it's probably worth using OS threads instead.