How to implement a practical fiber scheduler?

Question

I know the very basics about using coroutines as a base and implementing a toy scheduler. But I assume it's oversimplified view about asynchronous schedulers in whole. There are whole set of holes missing in my thoughts.

How to keep the cpu from running a scheduler that's running idle/waiting? Some fibers just sleep, others wait for input from operating system.

Answer 1

You'd need to multiplex io operations into an event based interface(select/poll), so you can leverage the OS to do the waiting, while still being able to schedule other fibers. select/poll have a timeout argument - for fibers that want to sleep, you can create a priority queue that uses that option of select/poll to emulate a sleep call.

Trying to serve fibers that does blocking operations (call read/write/sleep etc). directly won't work unless you schedule each fiber in a native thread - which kind of beats the purpose.

See http://swtch.com/libtask/ for a working implementation.