改天介紹一下啊

Indeed, the main thread doesn’t know which tasklets are blocked for IO event. The back-end of gevent is libevent, there is a greenlet named Hub which runs the event loop. You can find the Hub.run here:

http://bitbucket.org/denis/gevent/src/tip/gevent/hub.py

Every IO function in gevent, use some methods like core.read_event to register a callback and switch back to the hub by get_hub().switch(), namely, fall back to the event iteration. When the IO event is done, then switch back to original tasklet and continue its task. It works just like event-driven network model, but with additional coroutine feature.

It is possible to mark greenlet as halted, but it is not necessary, libevent knows nothing about coroutine. But however, you can implement your scheduling model if you like to :)