cppcoro VS C-Coroutines

PS: Take a look at cppcoro; this might help as well, especially generator<>, if you're looking to generate numbers, and stuff;

This is the only viable implementation.

Kind of sounds like whatever library you were using provided leaky abstractions. Something like cppcoro provides really good abstractions for coroutines, the user really doesn't need to understand why any of it works.

Is there a usecase for copying/serializing such coroutines? If not, I would use the normal C++20 coroutines (cppcoro?).

C++ has the popular CppCoro library. Async_mutex is its equivalent of Tokio::sync::Mutex, providing exclusive access to data shared between tasks.

Because the whole application is running under a single thread there is no need for atomic operations in synchronization primitives(which most of the time requires seq_cst memory order and CMPXCHG which is an expensive instruction in CPU). for example what async_mutex would look like if it knows it's running in a single-threaded scheduler (a non-atomic state variable and waiters queue).

Maybe not old, but I wish cppcoro was still updated. It was such a nice start!

You can get generator<> from https://github.com/lewissbaker/cppcoro

It is possible to compose them more easily than described in the article; Lewis Baker's cppcoro library for example provides a recursive_generator<> type[0] that allows this without using any macros. It's up to the library part of coroutines to make things easy, end users are not expected to write low-level coroutine code themselves.

I wonder about the allocation elision. Return value optimization became mandatory, and some compilers can already elide calls to new/delete and malloc()/free() in normal code, so perhaps it will be possible to guarantee allocation elision in the future in the most used cases.

[0]: https://github.com/lewissbaker/cppcoro#recursive_generatort

A coroutine is an execution context + all necessary data for restoring the execution context. This includes a place for saving/restoring the stack and the registers. I always loved the simplicity and beauty of the coroutine_yield32: assembly implementation of this library. It's literally just swapping out stack and registers with another context in userspace. Async-await patterns are an abstraction around this to decide when to switch and when not to switch. Note that at no point a thread is started or stopped, or communicated with other threads/cores. Yielding is literally a series of unconditional moves.

Or take advantage of the ABI of the runtime, and use assembly. [1] Yeah, not portable. But using setjmp()/longjmp() has issues as well (way too easy to mess it up because it doesn't do what you think it's doing).

[1] https://github.com/spc476/C-Coroutines