An idea; Coroutines

[Richard Andrew Cattermole (Rikki)]

On Tuesday, 16 January 2024 at 14:46:03 UTC, Stefan Koch wrote:
> We have fibers in the runtime; why would we need the coroutines 
> you propose and what's the difference to the fibers we already 
> have?

To quote: 
https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2018/p1364r0.pdf

Which comes from Microsoft: 
https://devblogs.microsoft.com/oldnewthing/20191011-00/?p=102989

> We have accumulated more than a quarter century of experience 
> with  fibers across variety of programming languages and 
> platforms. In the 90s fibers and N : M scheduling looked 
> promising, now, with improvements in hardware, operating system 
> kernel and painful experience of trying to make the fibers work 
> has resulted in a recommendation: **DO NOT USE FIBERS!** Use 
> threads instead and/or write your code using asynchronous APIs 
> with hand-crafted state machines.

Fibers as we have them are a runtime hack using inline assembly. 
Microsoft had to add them to WinAPI specifically because people 
kept messing up their implementation with the calling conventions.

Ours on OSX broke a few years ago too (was fixed quickly).

But the key difference to understand about stackless coroutines 
instead of fibers, coroutines understand the dependency that a 
coroutine that has yielded has, a fiber does not.