Comment by thesuperbigfrog

3 years ago

"The top three challenging areas of Rust for current Google developers were:

  * Macros
  * Ownership and borrowing
  * Async programming

"

Async programming is the area I would like to see the most improvement, especially in the standard library.

So much concurrent and parallel Rust code relies on third-party libraries because the standard library offers primitives that work but lack the "creature comforts" that developers prefer.

It would be really nice if the Rust standard library were to get structured concurrency similar to what Ada has:

https://en.wikibooks.org/wiki/Ada_Style_Guide/Concurrency

https://learn.adacore.com/courses/Ada_For_The_CPP_Java_Devel...

54 comments

thesuperbigfrog

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no_wizard  3 years ago

Color functions are just not the right road to go down. Something akin to Javas new green threads would be better, or Go style coroutines.

The path Rust is going means async becomes viral, and is something I dislike a lot about JavaScript[0] and other languages I’ve worked in[1].

I’d love to see Rust avoid this trap.

[0]: I work in TypeScript in actuality not sure which to use here. It’s certainly by far the language I’ve used the most in my career now.

[1]: I remember it infected Python too and it was a pain as well when I did Python development years ago.

  • steveklabnik  3 years ago

    Do you have a way to accomplish this while still staying within the other various constraints that Rust's async is under? I don't believe it is reconcilable.

    For those not aware of the history and looking for background, I laid it out here: https://www.infoq.com/presentations/rust-2019/ and here https://www.infoq.com/presentations/rust-async-await/

    Those style systems are useful and have advantages, but they also have disadvantages. Not every tradeoff is a good call for every system, and that goes both ways in this scenario.

  • littlestymaar  3 years ago

    I really wish people stopped using this concept of “function colors”, especially in the context of Rust because the `async fn`/“regular function” split is strictly equivalent to the `try_something()`/`something()` split (the first one being fallible and returning a `Result` in case of failure). `Result`s and `Option`s are coloring the stack in exactly the same way a `Future` does (and `async` is pure syntactic sugar on top of future).

    So, someone may like exceptions and green threads more than `Result` and `async` (and this is a completely valid PoV, even though I personally like the explicitness better), but thinking `async` is somehow special is just a conceptual mistake.

    Edit to give an little more substance to the parallelism:

    If you want to call a fallible function inside an infallible one, you MUST handle the result. If you want to use `?` then your function MUST return a Result.

    Symmetrically, if you want to call an async function from a non-async one, you MUST `spawn` the future. If you want to use `await` then your function MUST be async.

    The only practical difference between async functions and functions returning a `Result` is that `Future` is a trait, not a struct like `Result` (and that means that your future may have a lifetime that's not visible in your function definition, which is an endless source of confusion for beginners).

    • kaba0  3 years ago

      While you are technically right, one area where the two are unlike is that you want to be polymorph with regards to async/non-async, while it is less often the case for error handling. That exact same sleep implementation, or db query should be usable both as an async call, as well as a blocking one and it is the caller that wants to decide that. Which is not trivial to do on the calling side from a language perspective as it then has to recursively decide the same for all its subcalls.

      The new experimental languages with effect types might be able to give us the best of both as they actually expose what you are talking about as an abstraction at the type level. We will see.

      8 replies →

    • valzam  3 years ago

      The main difference to me is that Async/await tends to permeate your whole codebase. Once one part of the system is Async/await everything is. With Go I can write most of my code synchronously and maybe somewhere down the stack make 3 HTTP calls in parallel without having to change anything about the calling functions.

      2 replies →

  • shellac  3 years ago

    For many languages I absolutely agree: stackful coroutines are the way to go since the programmer experience is much smoother, with fewer hiccups like having different kinds of functions, or being unable to yield in loops. Lua, Go, and now Java got this right; python, javascript, and c# have to live with a bit of a mess.

    But Rust is not a language which can dictate its execution environment. It needs to be able to exist in a C-ish world, and that's not something that supports yielding. It's a shame, but at least you can write kernel modules in Rust.

  • kaba0  3 years ago

    > Color functions are just not the right road to go down. Something akin to Javas new green threads would be better, or Go style coroutines

    I agree with you on this in case of high-level languages. Rust is not that, and wouldn’t be half as interesting that way — but by going the system/low-level language route it does have to make certain design decisions that are not ideal. They can’t do what java’s loom does as it requires knowing every method implementation, which is fine with a fat runtime, but is not possible in case of Rust, with plenty FFI boundaries, etc.

  • nu11ptr  3 years ago

    While I agree and would prefer green threads to async myself, I believe Rust chose async/await because it was shown the former could not be done as a "zero cost" abstraction and didn't interop with C well (somebody correct me if I'm wrong on that).

  • shadowgovt  3 years ago

    At this time, I believe Rust's approach is complicated but that's because correctly using "bare" threads is complicated. Goroutines simplify the problem but introduce runtime performance overhead that may not be suitable for applications Rust is used for.

    (Generally, I avoid this problem these days by avoiding threads in favor of other abstractions or multiple processes communicating over an RPC channel).

  • gpderetta  3 years ago

    I vastly prefer stackful coroutines than stackless, but of all the languages, rust is probably the one that can justify that decision the most.

  • hgomersall  3 years ago

    "Color" in this case just means signature. Of course you can't mix signatures - why would you want to? You might as well argue that Rust shouldn't have had any more than a single integer argument to every function. Async in rust essentially desugars to a return trait impl.

    • zaphar  3 years ago

      That isn't quite true. An async signature forces it's caller to be async as well. This is because of it's semantics. Most signatures don't infect their callers signatures like that. async is qualitatively different in this regard.

      4 replies →

mjhay  3 years ago

> Async programming is the area I would like to see the most improvement, especially in the standard library.

> So much concurrent and parallel Rust code relies on third-party libraries because the standard library offers primitives that work but lack the "creature comforts" that developers prefer.

This seems to be an repeated antipattern with a lot of languages/ecosystems, resulting in fragmented and half-baked solutions. A fully-featured async standard library involves making a lot of opinion-based decisions, and not everyone will be happy. But it's better for 80% of people who probably don't care that much, and nothing stops the other 20% from implementing libraries for their use-cases.

  • pie_flavor  3 years ago

    As news of Rust's decisions several years ago reaches people only now, it is fun to watch people make predictions about 'the future' that have not been borne out in reality one smidgen. Just using the library everyone else uses has also worked for 80% of people that don't care that much.

jimbob45  3 years ago

Is there any Rust outfit out there that doesn't discourage macro use? For that matter, is there any team with a language out there that encourages macro use when working as a team?

  • giraffe_lady  3 years ago

    I've never seen a team that encouraged writing new macros to solve routine problems. But I've certainly been on teams that made heavy use of a few carefully deployed macros to solve recurring problems specific to that codebase.

    I think elixir's sigils are probably the closest thing I've seen to "routine, encouraged macro use." Since almost every application will end up with a bit of template lite almost-dsl pseudo language for something or other. They're simpler than defining a grammar & writing a parser and more maintainable than regex.

    • 59nadir  3 years ago

      I think Elixir is a bad example here because it's one of the eco systems that, while they preach "Use a function if you can!" very loudly, use macros much more heavily than other eco systems, often in places where they don't have to. Phoenix, the (unfortunate) flagship library, abuses macros all over the place where even relative beginners can see that they didn't need to (see [0] for example). It's incredibly badly designed overall and these things have set the tone (especially since a lot of Elixir programmers are in reality just Phoenix programmers).

      So, while macros are "discouraged" in Elixir, in practice they are very much encouraged by several prominent libraries. Picking on Phoenix is very easy because it's so blatantly bad in this regard (and others) but it's almost impossible to do useful things with Ecto if you go outside the macro bubble, etc., as well.

      Example that shows how an eco system that definitely could have done stuff with macros (Clojure) has correctly decided that writing functions that take data is better than using macros:

      Elixir and `Plug.Router`:

          defmodule MyRouter do
      use Plug.Router
    
      plug :match
      plug :dispatch
    
      get "/hello" do
        send_resp(conn, 200, "world")
      end
    
      forward "/users", to: UsersRouter
    
      match _ do
        send_resp(conn, 404, "oops")
      end
    end

      Clojure and `reitit` (https://github.com/metosin/reitit):

          (def router
      (r/routes
        [["/hello" {:get (fn [r] {:status 200 :body "world"})}]
         ["/users" {:name :users
                    :router users-router}]
         ["*" {:get (fn [r] {:status 404 :body "oops"})}]]))

      P.S. I've used Elixir since 2015, this is not an opinion I've developed at a glance.

  • rockemsockem  3 years ago

    So far I've only written rust on solo projects, why is macro use often discouraged? Does that discouragement extend to little things like derive?

VWWHFSfQ  3 years ago

rust team needs to abandon their own execution runtime and just bless tokio and pull it into std. They're doing nobody any favors right now

  • Animats  3 years ago

    I'm struggling to get tokio out of my executable. I'm not using it, but stuff keeps pulling it in. Async contamination is a huge problem. For highly concurrent code with threads running at different priority levels, if async gets in there it makes a mess.

    • jrockway  3 years ago

      You know what they say about libraries; if you're not having problems, you're not using enough of them.

      On a more serious note, "I want other people to write my code, but they're not following my standards" is rarely a sympathetic point of view.

    • arijun  3 years ago

      Sorry if this is ignorant, but what’s the difference between async and concurrent? Is the problem that async schedules everything itself?

      6 replies →

  • estebank  3 years ago

    The Rust team doesn't have its own execution runtime. Tokio is certainly the closest thing to the "default".

  • sanxiyn  3 years ago

    Given that Linux kernel is using async Rust which is implemented on top of kernel workqueue, and tokio won't be usable in kernel, it is a good thing tokio is not blessed. That's what enables both userland and kernel to use async Rust.

    • jenadine  3 years ago

      There can be both a "blessed" executor, while staying optional for such cases.

      For example, Rust std lib has blessed Mutex. Even though these can't be used in the kernel, it is still good to have them in the std lib for >90% of normal crates.