CODEWITHSUNDEEP
c++linuxwindowsmultithreadingfiber
DontCareBear
DontCareBear

Reputation: 834

Can fibers migrate between threads?

Can a fiber created in thread A switch to another fiber created in thread B? To make the question more specific, some operating systems have fibers natively implemented (windows fibers),
other need to implement it themselves (using setjump longjump in linux etc.).

Libcoro for example wraps this all up in a single API (for windows it’s just a wrapper for native fibers, for Linux it implements it itself etc.)

So, if it's possible to migrate fibers between threads, can you give me an example usage in windows (linux) in c/c++?

I found something about fiber migration in the boost library documentation, but it's not specific enough about it's implementation and platform dependence. I still want to understand how to do it myself using only windows fibers for example (or using Libcoro on linux).

If it's not possible in a general way, why so?

I understand that fibers are meant to be used as lightweight threads for cooperative multitasking over a single thread, they have cheap context switching compared to regular threads, and they simplify the programming. An example usage is a system with several threads, each having several fibers doing some kind of work hierarchy on their parent thread (never leaving the parent thread).

Even though it's not the intended use I still want to learn how to do it if it's possible in a general way, because I think I can optimize the work load on my job system by migrating fibers between threads.

Upvotes: 2

Views: 1070

Answers (1)

xlrg
xlrg

Reputation: 2109

The mentioned boost.fiber uses boost.context (callcc/continuation) to implement context switching. Till boost-1.64 callcc was implemented in assembler only, boost-1.65 enables you to choose between assembler, Windows Fibers (Windows) or ucontext (POSIX if available; deprecated API by POSIX). The assembler implementation is faster that the other two (2 orders of magnitude compared to ucontext).

boost.fiber uses callcc to implement lightweight threads/fibers - the library provides fiber schedulers that allow to migrate fibers between threads. For instance one provided scheduler steals fibers from other threads if its run-queue goes out of work (fibers that are ready/that can be resumed).

(so you can choose Windows Fibers that get migrated between threads).

Upvotes: 2

Related Questions