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Comment by lixiasky | Hacker News Reader

That is a fascinating comparison! History really does rhyme. What you described—suspending with a flag and resuming with new values—is surprisingly similar to how the C++20 compiler transforms coroutines into a state machine under the hood. In tiny_coro, the promise_type essentially manages that "inversion of control" you mentioned, but hides the manual state management behind the co_await syntax. It's really cool to see that these fundamental patterns for "stopping and resuming" computation have existed for so long, just in different forms.

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Coroutine idea is very old. I am not 100% sure but they were heavily used in Telecom applications.

It's easier in C and old C++ if one can drop down to assembly to switch between different call stacks.

Among modern languages there is Lua. Take a look at Felix too.

https://felix-tutorial.readthedocs.io/en/latest/tut110.html

https://felix.readthedocs.io/en/latest/fibres.html

You are absolutely right about the history (Conway coined the term in '63!). The assembly stack-switching you mentioned is the classic "Stackful" approach (like Fibers or Boost.Context). C++20 went the "Stackless" route (compiler-generated state machines) to avoid the per-stack memory overhead, though it certainly makes the implementation mechanics trickier. Lua is definitely a gold standard for asymmetric coroutines. As for Felix—I actually wasn't familiar with it until you mentioned it. Thanks for the pointer! I'll definitely dig into their docs to see how they handle scheduling compared to the C++20 approach.

BTW what happened to your baby wireshark ?

Also, do you use ChatGPT to frame your responses ? Nothing wrong if you do, but people might notice the tone and wonder.

Haha, you have a really sharp eye! 1. The Baby Wireshark: Unfortunately, my previous GitHub account got flagged/shadowbanned (still not sure why, and the appeal didn't work), so I lost access to that repo. I had to start fresh with this new account. 2. The Tone: You caught me! English is not my first language. I do use LLMs to help polish my grammar because I want to ensure my technical points are clear and I don't accidentally sound rude due to language barriers. Also, I learned most of my English from reading technical documentation and watching TED talks, so my "default" style tends to be a bit formal—just like an AI! :)

> Unfortunately, my previous GitHub account got flagged/shadowbanned

Oh! That sucks big time. Hope you had a local repo of everything.

BTW I don't think your tone is formal, just suspiciously congratulatory and polite :)

Do checkout Felix when you get time. It has done a lot with coroutines. You were asking about scheduling, it allows you to create more schedulers within the language.

Haha, point taken! I will try to dial down the "customer service mode" :) Re: GitHub: Yeah, thankfully I had the local git history, so the code was safe. Just lost the community interactions (stars/issues), which was a bummer. Re: Felix: That sounds exactly like what I need. Being able to define custom schedulers within the language is pretty much the holy grail I'm chasing here. I'll put it on my reading list for tonight.

Also look at Protothreads :)

Oh absolutely! Adam Dunkels' work is legendary. It's kind of poetic that Protothreads achieved stackless concurrency via C preprocessor macros and Duff's device tricks, and now years later, C++20 finally baked that exact same "state machine via switch-case" logic directly into the compiler. Same spirit, just less macro magic! :)

Simon Tatham and Tom Duff too.

https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html

The legendary "Coroutines in C" article!

Thanks for the reference—I learned a lot from his work. His use of macros to hide the switch statement is basically the spiritual ancestor of co_await. It is wild to think that C++20 essentially standardized that exact pattern, just moving the "state machine generation" from the preprocessor hacks to the compiler itself.

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