[jpc0]

I agree with many of your points, including coroutines being a good abstraction.

The reality is though that you are directly fighting or reimplementing the OS scheduler.

I haven’t found an abstraction that does exactly what I want but unfortunately any sort of structured concurrency tends to end up with coloured functions.

Something like C++ stdexec seems interesting but there are still elements of function colouring in there if you need to deal with async. The advantage is that you can compose coroutines and synchronous code.

For me I want a solution where I don’t need to care whether a function is running on the async event loop, a separate thread, a coprocessor or even a different computer and the actor/CSP model tends to model that the best way. Coroutines are an implementation detail and shouldn’t be exposed in an API but that is a strong opinion.