[grogers]

While this is technically true it's quite misleading. The VM itself uses cooperative scheduling, but the Erlang compiler emits something akin to yields appropriately, such the net effect is preemptive scheduling. You can break it by calling a NIF that doesn't do the yields appropriately, but that's not the norm.

[bjourne]

Preemptive threading means that the running thread can be paused by the system without ANY cooperation from the thread itself. Emphasis on "any". Python works roughly the same as Erlang. Every N bytecodes it checks if a thread is waiting to run and switches to that. Both are variants of cooperative threading.