[lelanthran]

> Said another way, explain how you solved the problems of just synchronously waiting for async.

Why? It isn't solved for async functions, is it? Just because the async is propagated up the call-stack doesn't mean that the call can't deadlock, does it?

Deadlocks aren't solved for a purely synchronous callstack either - A grabbing a resource, then calling B which calls C which calls A ...

Deadlocks are potentially there whether or not you mix sync/async. All that colored functions will get you is the ability to ignore the deadlock because that entire call-stack is stuck.

> If that just worked then we wouldn't need to proliferate the async/await through the stack.

It's why I called it a leaky abstraction.

[jayd16]

Yes actually it is solved. If you stick to async then it cannot deadlock (in this way) because you yield execution to await.

[lelanthran]

> Yes actually it is solved. If you stick to async then it cannot deadlock (in this way) because you yield execution to await.

Maybe I'm misunderstanding what you are saying. I use the word "_implementation_type_" below to mean "either implemented as option 1 or option 2 from my post above."

With current asynchronous implementations (like JS, Rust, etc), any time you use `await` or similar, that statement may never return due to a deadlock in the callstack (A is awaiting B which is awaiting C which is awaiting A).

And if you never `await`, then deadlocking is irrelevant to the _implementation_type_ anyway.

So I am trying to understand what you mean by "it cannot deadlock in this way" - in what way do you mean? async functions can accidentally await on each other without knowing it, which is the deadlock I am talking about.

I think I might understand better if you gave me an example call-chain that, in option 1, sidesteps the deadlock, and in option 2, deadlocks.

[jayd16]

I'm referring to the situation where a synchronous wait consumes the thread pool, preventing any further work.

A is sychrounously waiting B which is awaiting C which could complete but never gets scheduled because A is holding onto the only thread. Its a very common situation when you mix sync and async and you're working in a single threaded context, like UI programming with async. Of course it can also cause starvation and deadlock in a multithreaded context as well but the single thread makes the pitfall obvious.

[lelanthran]

That's an implementation problem, not a problem with the concept of asynchronous execution, and it's specifically a problem in only one popular implementation: Javascript in the browser without web-workers.

That's specifically why I called it a Leaky Abstraction in my first post on this: too many people are confusing a particular implementation of asynchronous function calls with the concept of asynchronous function calls.

I'm complaining about how the mainstream languages have implemented async function calls, and how poorly they have done so. Pointing out problems with their implementation doesn't make me rethink my position.

[jayd16]

I don't see how it can be an implementation detail when fundamentally you must yield execution when the programmer has asked to retain execution.

Besides Javascript, its also a common problem in C# when you force synchronous execution of an async Task. I'm fairly sure its a problem in any language that would allow an async call to wait for a thread that could be waiting for it.

I really can't imagine how your proposed syntax could work unless the synchronous calls could be pre-empted, in which case, why even have async/await at all?

But I look forward to your implementation.

[lelanthran]

> I don't see how it can be an implementation detail when fundamentally you must yield execution when the programmer has asked to retain execution.

It's an implementation issue, because "running on only a single thread" is an artificial constraint imposed by the implementation. There is nothing in the concept of async functions, coroutines, etc that has the constraint "must run on the same thread as the sync waiting call".

An "abstraction" isn't really one when it requires knowledge of a particular implementation. Async in JS, Rust, C#, etc all require that the programmer knows how many threads are running at a given time (namely, you need to know that there is only one thread).

> But I look forward to your implementation.

Thank you :-)[1]. I actually am working (when I get the time, here and there) on a language for grug-brained developers like myself.

One implementation of "async without colored functions" I am considering is simply executing all async calls for a particular host thread on a separate dedicated thread that only ever schedules async functions for that host thread. This sidesteps your issue and makes colored functions pointless.

This is one possible way to sidestep the specific example deadlock you brought up. There's probably more.

[1] I'm working on a charitable interpretation of your words, i.e. you really would look forward to an implementation that sidesteps the issues I am whining about.