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Comment by groundzeros2015 | Hacker News Reader

groundzeros2015

In that sentence I’m referring to the abstract idea of a thread of execution as a model of programming, not OS threads. A green thread implementation could do it too.

But what you said about kernel implementation is true. But are we really saying that the primary motivation for async/await is performance? How many programmers would give that answer? How many programs are actually hitting that bottleneck?

Doesn’t that buck the trend of every other language development in the past 20 years, emphasizing correctness and expressively over raw performance?

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> But are we really saying that the primary motivation for async/await is performance?

Of course - what else would it be? The whole async trend started because moving away from each http request spawning (or being bound to) an OS thread gave quite extreme improvements in requests/second metrics, didn't it?

I agree. Managing many http requests or responses was a motivating problem.

What I question is whether 1. Most programs resemble that, so that they make it an invasive feature of every general purpose language. 2. Whether programmers are making a conscious choice because they ruled out the perf overhead of the simpler model we have by default.

That is why we have the function colouring problem and a split ecosystem in the first place - if it were obviously better in all cases, we'd make async the default, and get rid of the split altogether (and there are languages, like Erlang, that fall on this side of the fence)

It was not for performance reasons, but for scaling up.

That's the same thing?

> But are we really saying that the primary motivation for async/await is performance?

The original motivation for not using OS threads was indeed performance. Async/await is mostly syntax sugar to fix some of the ergonomic problems of writing continuation-based code (Rust more or less skipped the intermediate "callback hell" with futures that Javascript/Python et al suffered through).

In some languages, yes, in others (js/python) async is just workaround about not having proper threading.

Python used multiple threads to handle I/O long before async/await was a glimmer in anyone's mind (despite the GIL). nodejs is one of the very few languages I can think of that was born single-threaded and used an asynchronous runtime from the get-go

Importantly though, performance might be worse depending on use case and program. Specifically with scheduling in user space it can negatively impact branch prediction as your CPU is already hyper optimized for doing things differently.

It's all nuanced and what to choose requires careful evaluation.

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