There is a very big difference between implicit flow control, that you have with green threads and explicit one, that you have with "reinvented green threads",

There is a very big difference between implicit flow control, that you have with green threads and explicit one, that you have with "reinvented green threads", as you call them. First one will force you to think about synchronization to access your memory, but the second one - won't. It will also let you do clean cancellation, etc., that you won't be able to do with green thread.