It isn't the fault of the group that suggests and standardizes protocols, it is everyone thinking they are smarter and they can do it better is the problem.

Further to this, my (very basic) understanding is that the actual threading implementation will be left up to the integrator, so some implementations may not actually implement any concurrency (a little like the Python GIL in a way), while others may implement real concurrency, therefore meaning that subtle threading bugs could be introduced that wouldn't be seen until you run in other environments.

> Correct me if I’m wrong, but that’s only possible if you separate runtime threads from OS threads, which sounds straightforward but introduces problems relating to stack-lifetimes in continuations so it introduces demands on the compiler and/or significant runtime memory overhead - which kinda defeats the point of trying to avoid blocking OS threads in the first place.

Correct -- note that the async implementation does not address parallelism (i.e. threading) -- it's a language +/- runtime level distinction.

The overhead is already in the languages that choose to support -- tokio in rust, asyncio in python, etc etc. For those that don't want to opt in, they can keep to synchronous functions + threads (once WASI threads are reimagined, working and stable!)

You can actually solve this problem with both multiple stacks and a continuation based approach, with different tradeoffs.

> I’m not belittling the achievement there - I’m just saying (again, correct me if I’m wrong) there’s a use-case for function-colouring in high-thread, high-memory applications. > > …but if WASI is simply adding more options without taking anything away then my point above is moot :)

Didn't take it as such! The ability to avoid function coloring does not block the implementations of high-threads/high-memory applications, once an approach to threading is fully reconsidered. And adding more options while keeping existing workflows in place is definitely the goal (and probably the only reasonable path to non-trivial adoption...).

How to do it is quite involved, but there are really smart people thinking very hard about it and trying to find a cross-language optimal approach. For example, see the explainer for Async:

https://github.com/WebAssembly/component-model/blob/main/des...

There are many corners (and much follow up discussion), but it's shaping up to be a pretty good interface, and widely implementable for many languages (Rust and JS efforts are underway, more will come with time and effort!).