You're describing exactly why it's painful for threads. If you only cancel co-routines at yield points (which unless you do dark magic is the only time you can

You're describing exactly why it's painful for threads. If you only cancel co-routines at yield points (which unless you do dark magic is the only time you can cancel them) is always safe. A co-routine that yields in the middle of an atomic operation is an oxymoron. Anything can happen before you're scheduled again.