[quotemstr]

Huh? It doesn't follow that forbidding blocking IO is either necessary or sufficient for concurrency safety, at least under any definition of "safety" I can imagine. What do you mean? You mean async-not-blocking-event-loop stuff? That's not the only way to do more than one IO at a time.

[rurban]

Non-blocking IO is only one part to provide concurrency safety. Process locks are even worse. All locks are forbidden to avoid dead-locks.