"Tight control over memory use" sounds wrong considering every single allocation in rust is done through the global allocator. And pretty much everything in rust async is put into an Arc.
I don't understand what kind of use case they were optimizing for when they designed this system. Don't think they were optimizing only for embedded or similar applications where they don't use a runtime at all.
Using stackfull coroutines, having a trait in std for runtimes and passing that trait around into async functions would be much better in my opinion instead of having the compiler transform entire functions and having more and more and more complexity layered on top of it solve the complexities that this decision created.
> "Tight control over memory use" sounds wrong considering every single allocation in rust is done through the global allocator.
In the case of Rust's async design, the answer is that that simply isn't a problem when your design was intentionally chosen to not require allocation in the first place.
> And pretty much everything in rust async is put into an Arc.
IIRC that's more a tokio thing than a Rust async thing in general. Parts of the ecosystem that use a different runtime (e.g., IIRC embassy in embedded) don't face the same requirements.
I think it would be nice if there were less reliance on specific executors in general, though.
> Don't think they were optimizing only for embedded or similar applications where they don't use a runtime at all.
I would say less that the Rust devs were optimizing for such a use case and more that they didn't want to preclude such a use case.
> having a trait in std for runtimes and passing that trait around into async functions
Yes, the lack of some way to abstract over/otherwise avoid locking oneself into specific runtimes is a known pain point that seems to be progressing at a frustratingly slow rate.
I could have sworn that that was supposed to be one of the improvements to be worked on after the initial MVP landed in the 2018 edition, but I can't seem to find a supporting blog post so I'm not sure I'm getting this confused with the myriad other sharp edges Rust's sync design has.
> > And pretty much everything in rust async is put into an Arc.
> IIRC that's more a tokio thing than a Rust async thing in general. Parts of the ecosystem that use a different runtime (e.g., IIRC embassy in embedded) don't face the same requirements.
Well, if you're implementing an async rust executor, the current async system gives you exactly 2 choices:
1) Implement the `Wake` trait, which requires `Arc` [1], or
2) Create your own `RawWaker` and `RawWakerVTable` instances, which are gobsmackingly unsafe, including `void*` pointers and DIY vtables [2]
Sure, but those are arguably more like implementation details as far as end users are concerned, aren't they? At least off the top of my head I'd imagine tokio would require Send + Sync for tasks due to its work-stealing architecture regardless of whether it uses Wake or RawWaker/RawWakerVTable internally.
I find it interesting that there's relatively recent discussion about adding LocalWaker back in [0] after it was removed [1]. Wonder what changed.
I don't understand what kind of use case they were optimizing for when they designed this system. Don't think they were optimizing only for embedded or similar applications where they don't use a runtime at all.
Using stackfull coroutines, having a trait in std for runtimes and passing that trait around into async functions would be much better in my opinion instead of having the compiler transform entire functions and having more and more and more complexity layered on top of it solve the complexities that this decision created.