[zelly]

These are cooperative threads, not kernel threads which can actually run at the same time. It uses threads for its abstraction as a concurrent task. Ruby and Python also have "Thread" classes which don't make system calls and are just useful as a programming pattern. Maybe one day Emacs (and Python and Ruby) will have real threads, so the idea might be to switch the implementation over to real threads without requiring any client code to be rewritten since it follows the same API as real threads.