[tomck]

> I do fully understand people who can't get their heads around threads and prefer async

This is a bizarre remark

Async/await isn't "for when you can't get your head around threads", it's a completely orthogonal concept

Case in point: javascript has async/await, but everything is singlethreaded, there is no parallelism

Async/await is basically just coroutines/generators underneath.

Phrasing async as 'for people who can't get their heads around threads' makes it sound like you're just insecure that you never learned how async works yet, and instead of just sitting down + learning it you would rather compensate

Async is probably a more complex model than threads/fibers for expressing concurrency. It's fine to say that, it's fine to not have learned it if that works for you, but it's silly to put one above the other as if understanding threads makes async/await irrelevant

> The stdlib isn't too bad but last time I checked a lot of crates.io is filled with async functions for stuff that doesn't actually block

Can you provide an example? I haven't found that to be the case last time I used rust, but I don't use rust a great deal anymore

[dang]

> This is a bizarre remark

> makes it sound like you're just insecure

> instead of just sitting down + learning it you would rather compensate

Can you please edit out swipes like these from your HN posts? This is in the site guidelines: https://news.ycombinator.com/newsguidelines.html.

Your comment would be fine without those bits.

[ksec]

>Case in point: javascript has async/await, but everything is singlethreaded, there is no parallelism, Async/await is basically just coroutines/generators underneath.

May be I just wish Zig dont call it async and use a different name.

[vjerancrnjak]

It's more about how the code ends up evolving.

Async-await in JS is sometimes used to swallow exceptions. It's very often used to do 1 thing at a time when N things could be done instead. It serializes the execution a lot when it could be concurrent.

    if (await is_something_true()) {
      // here is_something_true() can be false
    }

And above, the most common mistake.

Similar side-effects happen in other languages that have async-await sugar.

It smells as bad as the Zig file interface with intermediate buffers reading/writing to OS buffers until everything is a buffer 10 steps below.

It's fun for small programs but you really have to be very strict to not have it go wrong (performance, correctness).

[tomck]

I think you replied to the wrong person.

That being said, I don't understand your `is_something_true` example.

> It's very often used to do 1 thing at a time when N things could be done instead

That's true, but I don't think e.g. fibres fare any better here. I would say that expressing that type of parallel execution is much more convenient with async/await and Promise.all() or whatever alternative, compared to e.g. raw promises or fibres.

[vjerancrnjak]

I replied directly to you. There are valid arguments as to why async-await sucks, even after you're deeply familiar with how it works. Even though it's just generators/coroutines beneath, async-await pollutes the code completely if you're not strict about its usage.

`is_something_true` is very simple, if condition is true, and then inside the block, if you were to check again it can be false, something that can't happen in synchronous code, yet now, with async-await, it's very easy to get yourself into situations like these, even though the code seems to yell at you that you're in the true branch. the solution is adding a lock, but with such ease to write async-await, it's rarely caught

[tomck]

> I replied directly to you

My comment was responding only to the person who equated threads and async. My comment only said that async and threading are completely orthogonal, even though they are often conflated

> `is_something_true` is very simple, if condition is true, and then inside the block, if you were to check again it can be false, something that can't happen in synchronous code

It can happen in synchronous code, but even if it couldn't - why is async/await the problem here? what is your alternative to async/await to express concurrency?

Here are the ways it can happen:

1. it can happen with fibers, coroutines, threads, callbacks, promises, any other expression of concurrency (parallel or not!). I don't understand why async/await specifically is to blame here.

2. Even without concurrency, you can mutate state to make the value of is_something_true() change.

3. is_something_true might be a blocking call to some OS resource, file, etc - e.g. the classic `if (file_exists(f)) open(f)` bug.

I am neutral on async/await, but your example isn't a very good argument against it

Seemingly nobody ever has any good arguments against it

> async-await pollutes the code completely if you're not strict about its usage

This is a good thing, if a function is async then it does something that won't complete after the function call. I don't understand this argument about 'coloured functions' polluting code. if a function at the bottom of your callstack needs to do something and wait on it, then you need to wait on it for all functions above.

If the alternative is just 'spin up an OS thread' or 'spin up a fiber' so that the function at the bottom of the callstack can block - that's exactly the same as before, you're just lying to yourself about your code. Guess what - you can achieve the same thing by putting 'await' before every function call

Perhaps you have convinced me that async/await is great after all!

[vjerancrnjak]

Async and threading are applied to similar problems, that's how I understood OP.

`if (file_exists(f))` is misuse of the interface, a lesson in interface design, and a faulty pattern that's easy to repeat with async-await.

> I don't understand this argument about 'coloured functions' polluting code.

Let's say you have some state that needs to be available for the program. What happens in the end game is that you've completely unrolled the loads and computation because any previous interface sucks (loading the whole state at the beginning which serializes your program and makes it slower, or defining `async loadPartial` that causes massive async-await pollution at places where you want to read a part of the state, even if it is already in cache).

Think about it, you can't `await` on part of the state only once and then know it's available in other parts of code to avoid async pollution. When you solve this problem, you realize `await` was just in the way and is completely useless and code looks exactly like a callback or any other more primitive mechanism.

A different example is writing a handler of 1 HTTP request. People do it all the time with async-await, but what to do when you receive N HTTP requests? The way to make code perform well is impossible with the serial code that deals with 1 request, so async-await just allowed you to make something very simple and in an easy way, but then it falls apart completely when you go from 1 to N. Pipelining system won't really care for async-await at all, even though it pipelines IO in addition to compute.

I think "how to express concurrency" is a question I'm not even trying to answer, although I could point to approaches that completely eliminate pollution and force you to write code in that "unrolled" way from start, something like Rx or FRP where time is exactly the unit they're dealing with.

[tomck]

> `if (file_exists(f))` is misuse of the interface, a lesson in interface design, and a faulty pattern that's easy to repeat with async-await.

It's even easier to repeat without async-await, where you don't need to tag the function call with `await`!

> Think about it, you can't `await` on part of the state only once and then know it's available in other parts of code to avoid async pollution. When you solve this problem, you realize `await` was just in the way and is completely useless and code looks exactly like a callback or any other more primitive mechanism.

I don't understand why you can't do this by just bypassing the async/await mechanism when you're sure that the data is already loaded

```

data = null

async function getDataOrWait() { await data_is_non_null(); // however you do this return data }

function getData() { if (data == null) { throw new Error('data not available yet'); } return data; }

```

You aren't forced into using async/await everywhere all the time. this sounds like 'a misuse of the interface, a lesson in interface design', etc

> I think "how to express concurrency" is a question I'm not even trying to answer

You can't criticise async/await, which is explicitly a way to express concurrency, if you don't even care to answer the question - you're just complaining about a solution that solves a problem that you clearly don't have (if you don't need to express concurrency, then you don't need async/await, correct!)

> point to approaches that completely eliminate pollution and force you to write code in that "unrolled" way from start, something like Rx or FRP where time is exactly the unit they're dealing with.

So they don't 'eliminate pollution', they just pollute everything by default all the time (???)