How do you implement Coroutines in C++

Question

I doubt it can be done portably, but are there any solutions out there? I think it could be done by creating an alternate stack and reseting SP,BP, and IP on function entry

Answer 1

A new library, Boost.Context, was released today with portable features for implementing coroutines.

Answer 2

Check out my implementation, it illustrates the asm hacking point and is simple:

https://github.com/user1095108/generic/blob/master/coroutine.hpp

Answer 3

On POSIX, you can use makecontext()/swapcontext() routines to portably switch execution contexts. On Windows, you can use the fiber API. Otherwise, all you need is a bit of glue assembly code that switches the machine context. I have implemented coroutines both with ASM (for AMD64) and with swapcontext(); neither is very hard.

Answer 4

https://github.com/tonbit/coroutine is C++11 single .h asymmetric coroutine implementation supporting resume/yield/await primitives and Channel model. It's implementing via ucontext / fiber, not depending on boost, running on linux/windows/macOS. It's a good starting point to learn implementing coroutine in c++.

Answer 5

You might be better off with an iterator than a coroutine if possible. That way you can keep calling next() to get the next value, but you can keep your state as member variables instead of local variables.

It might make things more maintainable. Another C++ developer might not immediately understand the coroutine whereas they might be more familiar with an iterator.

Answer 6

Does COROUTINE a portable C++ library for coroutine sequencing point you in the right direction? It seems like an elegant solution that has lasted the test of time.....it's 9 years old!

In the DOC folder is a pdf of the paper A Portable C++ Library for Coroutine Sequencing by Keld Helsgaun which describes the library and provides short examples using it.

[update] I'm actually making successful use of it myself. Curiosity got the better of me, so I looked into this solution, and found it was a good fit for a problem I've been working on for some time!