With green threads, I think you can have async io but with threads. When your current thread is making an async call, suspend the green thread (cheap) and yield

With green threads, I think you can have async io but with threads. When your current thread is making an async call, suspend the green thread (cheap) and yield back to the event loop. Threads are woken up when their async call finishes. This avoids the overhead of real OS threads per connection.