[chrisseaton]

> Right, but you'd still need to synchronize that with some concurrency primitives (like a mutex or semaphore)

Why? If you know your thread won't be interleaved with any other until you a well-defined point, how's that different to using a mutex or semaphore?

[MobiusHorizons]

IIUC, Loom threads can be scheduled across multiple OS threads (much like go-routines), so there is (at least the possibility of) real concurrency going on.