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Why has Rust struggled so much with this, where Go has succeeded from the start with its language-level “goroutine” concept and runtime? Maybe it just wasn’t a

Why has Rust struggled so much with this, where Go has succeeded from the start with its language-level “goroutine” concept and runtime? Maybe it just wasn’t a focal area for the original Rust designers?

cute_boi 5y ago
zero cost abstraction and no gc
- pjmlp 5y ago
  Same could be said for C++, and yet while C++20 also doesn't have an official runtime on std (C++23 will fix that assuming executors land), the vocabulary types required for interoperability across runtimes are part of the co-routines design.
  - varajelle 5y ago
    Rust also has the vocabulary types required for interoperability, such as Future and Waker. Or what exactly make C++ more interoperable?
    - pjmlp 5y ago
      Does it? https://book.async.rs/overview/std-and-library-futures.html https://book.async.rs/overview/std-and-library-futures.html C++ ones can interoperate with any type that plugs into the compiler magic expected by the co-routines code rewrite. If you want to deep dive into how Visual C++ does it, and how WinRT gets plugged into C++ co-routines, here is a very lengthy set of blog posts. https://devblogs.microsoft.com/oldnewthing/20210504-01/?p=105178 https://devblogs.microsoft.com/oldnewthing/20210504-01/?p=10... Now back to Rust, how can I interoperate across tokio, async-std, smol and fuchsia-std, as easy as I can between WinRT, and others?
      - varajelle 5y ago
        The std::future::Future from the rust standard library works with every runtime. Not sure I understand, what kind of interoperability you are talking about. What kinds of code works in C++ across runtimes, for which the equivalent in Rust doesn't?
        pjmlp 5y ago
        In C++ you don't have the scenario like in Rust, where one is forced to use a specific async runtime for library xyz, because it depends on having tokio as runtime. Or has that situation been sorted out by now?
        varajelle 5y ago
        In Rust you only are forced to use a specific runtime if you want to use its API. For example to spawn new tasks, or to block on a future. I believe that would be the same in C++. In Rust, you don't need to use a specific runtime if you just want to use async function in your library.
- mseepgood 5y ago
  All design trade-offs have a cost. In this case the costs are reduced usability and async struggles.
  - carlmr 5y ago
    Zero-cost abstractions is used to mean zero runtime cost (in release builds), so if an abstraction would break that it wouldn't be suitable for this goal. Like adding a GC for the async feature.
tcoff91 5y ago
Go is a very different language than rust. Go has automatic memory management & garbage collection. This automatically disqualifies it from being used in many scenarios that rust is designed to support, like embedded systems. Go’s runtime model just makes stuff like this vastly simpler. Rust can’t impose the same kind of runtime model that go has.
- IceWreck 5y ago
  While Go isn't designed for embedded systems, it can run on them. TinyGo is another Go compiler intended for embedded systems. And now its officially sponsored by Google. https://tinygo.org/docs/reference/microcontrollers/ https://tinygo.org/docs/reference/microcontrollers/
  - mseepgood 5y ago
    TinyGo is awesome.
  - pjmlp 5y ago
    TamaGo is another example, https://www.f-secure.com/en/consulting/foundry/usb-armory https://www.f-secure.com/en/consulting/foundry/usb-armory
- fulafel 5y ago
  Lots of embedded systems are very happy using garbage collection and languages with runtimes.
swiftcoder 5y ago
It's extremely challenging to make async that is usable without introducing a garbage collector or a whole lot of runtime overhead. A better comparison would be between the Rust and C++ paths to async - C++ also spent years designing their async system, and the end result is divisive at best.
- dxuh 5y ago
  And we are not even done yet. The Networking TS seems to have fallen out of favor and now it seems we are going to get executors + senders/receivers, which I personally think is pretty cool actually.
  - jabl 5y ago
    Wonder if the Rust team is aware of the work on the C++ side of the fence on the executors+senders/receivers approach: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2300r1.html http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p230... Not saying that is the ultimate answer to building async and/or parallel algorithms, but being aware of what others in the same space are doing is certainly useful.
- pjmlp 5y ago
  True, and as the sibling comment notes it is still not fully there, yet as the vocabulary types are part of the standard library, it means what I have coded running on top of C++/WinRT, might equally work on top of HPX or cppcoro, just by changing includes and library being linked.
stubish 5y ago
The saddest part of learning Rust was discovering that there are no goroutines and that async works like Python and everything needs to be written twice to support both async and blocking styles. Like it was 20 years ago all over again and I'm still trying to mix Twisted and stdlib Python. I got all excited thinking of how the borrow checker would work so well with coroutines, only to discover it got nobbled because Rust's use cases include embedded systems and no runtime (like in a golang 9MB hello_world.exe). I have no idea if Rust could evolve its concurrent programming support to something better than Go's, even if it did drop some of its shackles.
- wongarsu 5y ago
  I find traditional multi threading a pleasure in Rust, and it works really well with the borrow checker and how the type system is designed (like the Send and Sync traits). On the semantic side, extending it to a N:M threading model like Erlang or Go would work great. But that model only seems to work well if you basically make the entire language async, which is in conflict with too many of rust's goals. So we are left with the somewhat awkward state of async as a second class citizen.
- KingOfCoders 5y ago
  I only have rudimentary knowledge of Golang (but think the blocked/green automatic scheduling is excellent). How does go nest aync calls? func f() { } func g() { } func h() { go g() go f() } What happens on f() Are the g() and f() calls inside h() blocking? Or are they async and the block happens at the point of return? Which would be the main difference to languages with an async keyword, were you need to be explicit about blocking.
  - zaphar 5y ago
    The go keyword executes the called function asynchronously so g() and f() won't block h(). If you need a computed result from g() or f() then you'll need to use a channel or a shared mutex guarded value to get it. A channel is the correct default choice and the mutex should only be used if you need it for performance or other reasons.
npigrounet 5y ago
Rust never struggles! It just takes its time to be perfect <3
exDM69 5y ago
Early on in Rust's history, it had something similar to Go's goroutines with n:m green thread scheduling and libuv for async everything. Some other languages (e.g. Haskell/GHC) also have this kind of system. But this practically requires some kind of garbage collection and a fat runtime. I think it was a good decision on the Rust team to abandon this and go for a low level systems programming language. Otherwise it would've been just another Go-like language that isn't really usable in low level systems programming. Implementing portable async language features without a fat runtime or garbage collection is novel work so it's no wonder that it's taking its own sweet time to reach maturity.
jasode 5y ago
>Why has Rust struggled so much with this, where Go has succeeded from the start with its language-level “goroutine” concept and runtime? Rust made the deliberate decision to avoid the heavier Go goroutines runtime model after early alpha/beta experiments showed it conflicted with Rust's low-level design. I found 3 links to some history of that rationale in a previous comment: https://news.ycombinator.com/item?id=28660089 https://news.ycombinator.com/item?id=28660089 And some more links: https://stackoverflow.com/questions/29428318/why-did-rust-remove-the-green-threading-model-whats-the-disadvantage https://stackoverflow.com/questions/29428318/why-did-rust-re... https://github.com/rust-lang/rfcs/blob/master/text/0230-remove-runtime.md https://github.com/rust-lang/rfcs/blob/master/text/0230-remo... And lots of debate in this previous thread: https://news.ycombinator.com/item?id=10225903 https://news.ycombinator.com/item?id=10225903
jayflux 5y ago
> Why has Rust struggled so much with this, where Go has succeeded from the start with its language-level “goroutine” concept and runtime? It’s not that Rust has struggled, it was never Rust’s priority to have a runtime or high level async code. It had very different goals to Go. It’s like asking “why has C struggled to implement Promises like JavaScript”? The languages serve different purposes. You’re right it wasn’t their initial focal point but later on Rust wanted to offer the chance of having a go-like runtime without destabilising the low-level performance at the core level. I.E only those that use it pay for it and those that don’t use it aren’t affected. Offering “zero cost” futures etc is very difficult to do. See https://aturon.github.io/blog/2016/08/11/futures/ https://aturon.github.io/blog/2016/08/11/futures/ for more info, old but still relevant (including the chart)
skohan 5y ago
I think part of it is because computer science hasn't really nailed the right abstraction for concurrent code execution. For instance, C is a great abstraction. You take assembly language, abstract away manual management of registers with variables and pointers, add structured types to describe memory layout, standardize flow of control operations, and add functions to enable code reusability, and you have something which is very easy to work with and also to understand. It's not 100% on par with assembly in terms of performance, but it's pretty darned close, and with a little bit of practice it's very easy to look at a block of C code and basically understand what equivalent assembly it compiles to. It's a great abstraction, and it's no wonder that a vast majority of the languages which have come after it have borrowed most of its major features. I would argue we haven't really had a "great abstraction" to the same level since then*. There have been efforts to abstract away memory management the way register management has been abstracted away, and many of them have been successful for a lot of use-cases, but not to the point that everyone can forget about memory management the way the vast majority of us can forget about register management. Garbage collectors can be too slow or too wasteful for a lot of use-cases, and you need essentially another program you didn't write to pull it off. In a GC'd language it's not so trivial to look at a block of high-level code and predict what your CPU will do. There are other approaches: like the structured approaches of Rust and Swift which are quite interesting, but they're far from proven at this point. Similarly I think we're not quite there yet with concurrent programming. As far as the transparency topic, a lot of async implementations are more in the direction of garbage collectors, where the compiler rips apart your code and builds a state machine in its place. It's not hard to believe that the result will be difficult to work with and reason about in some cases. And maybe the problem is that most approaches to async are trying to cram concurrent execution into that C-like abstraction, which is such an elegant abstraction for single-threaded execution exactly. Maybe concurrent programming needs to be re-thought from first principals, with different primitives involved. *Aside: if there is another "great abstraction" on the horizon, I believe it to be ADT's. That is a feature of programming which feels like a clear step forward with no clear downsides. It's a shame that they haven't been included in Zig.
- c-cube 5y ago
  Zig has tagged unions and the corresponding switch expressions, is that not equivalent?
shellac 5y ago
Sibling comments have explained the detail. The pithier explanation perhaps is that rust is intended as a 'systems language', and it interprets that as meaning there should be no runtime. Or, more simply, it ought to be possible to call a rust function from C without providing an additional argument that encapsulates rust 'environment'. (C effectively defining this area) Go and Java (with Loom) have these lovely facilities, but it is hard to interface with them if your language lacks these features. I find it odd that C#, javascript, and python don't provide the smoother async Go experience despite having runtimes / VMs.
ezekiel68 5y ago
Funny you should ask that... about 6 years ago, Mozilla released an event-handling library written in go named Heka. It made use of go's built-in goroutines and channels and what made it really cool was that it had an embedded lua interpreter so people could update lua scripts in their event processing systems to alter the behavior (such as reformatting dates, etc) without needing to re-compile the solution. It got pretty popular and you can still find YouTube tutorials on using it to this day. Unfortunately, according to one of the lead developers, the system couldn't keep up with Mozilla's throughput and reliability requirements due to limitations of go's built-in features.[0] They announced they would re-write a new solution in c ("Hindsight") and they basically left an entire community of users high and dry due to not being able to salvage the go-based project, since it relied so heavily on the built-in features. [0] https://heka.mozilla.narkive.com/9heQ11hz/state-and-future-of-heka https://heka.mozilla.narkive.com/9heQ11hz/state-and-future-o...
pornel 5y ago
Rust doesn't want to impose its own one-size-fits-all runtime on all users of the language, because Rust wants to work in places where Go isn't a good fit, e.g. microcontrollers, kernels, or seamlessly on top of other languages' runtimes. Architecture of an efficient async runtime is going to be different for 128-core server vs single-threaded chip with barely any RAM. In Rust you can write your own runtime to your needs, rather than fight overhead of a big runtime on a small device, or struggle to scale a dumb runtime to complex workloads.
nextaccountic 5y ago
Go has a single runtime, Rust supports multiple async runtimes. Rust needs to support multiple runtimes because in low level space there is no one size fits all solution. For example, Go runtime imposes unavoidable overhead in memory usage, because each goroutine must have its own allocated stack (Rust futures, on the other hand, are stackless). Rust runs on low memory platforms where Go isn't really suitable.

cute_boi 5y ago

zero cost abstraction and no gc

pjmlp 5y ago
Same could be said for C++, and yet while C++20 also doesn't have an official runtime on std (C++23 will fix that assuming executors land), the vocabulary types required for interoperability across runtimes are part of the co-routines design.
- varajelle 5y ago
  Rust also has the vocabulary types required for interoperability, such as Future and Waker. Or what exactly make C++ more interoperable?
  - pjmlp 5y ago
    Does it? https://book.async.rs/overview/std-and-library-futures.html https://book.async.rs/overview/std-and-library-futures.html C++ ones can interoperate with any type that plugs into the compiler magic expected by the co-routines code rewrite. If you want to deep dive into how Visual C++ does it, and how WinRT gets plugged into C++ co-routines, here is a very lengthy set of blog posts. https://devblogs.microsoft.com/oldnewthing/20210504-01/?p=105178 https://devblogs.microsoft.com/oldnewthing/20210504-01/?p=10... Now back to Rust, how can I interoperate across tokio, async-std, smol and fuchsia-std, as easy as I can between WinRT, and others?
    - varajelle 5y ago
      The std::future::Future from the rust standard library works with every runtime. Not sure I understand, what kind of interoperability you are talking about. What kinds of code works in C++ across runtimes, for which the equivalent in Rust doesn't?
      - pjmlp 5y ago
        In C++ you don't have the scenario like in Rust, where one is forced to use a specific async runtime for library xyz, because it depends on having tokio as runtime. Or has that situation been sorted out by now?
        varajelle 5y ago
        In Rust you only are forced to use a specific runtime if you want to use its API. For example to spawn new tasks, or to block on a future. I believe that would be the same in C++. In Rust, you don't need to use a specific runtime if you just want to use async function in your library.
mseepgood 5y ago
All design trade-offs have a cost. In this case the costs are reduced usability and async struggles.
- carlmr 5y ago
  Zero-cost abstractions is used to mean zero runtime cost (in release builds), so if an abstraction would break that it wouldn't be suitable for this goal. Like adding a GC for the async feature.

tcoff91 5y ago

Go is a very different language than rust. Go has automatic memory management & garbage collection. This automatically disqualifies it from being used in many scenarios that rust is designed to support, like embedded systems. Go’s runtime model just makes stuff like this vastly simpler. Rust can’t impose the same kind of runtime model that go has.

IceWreck 5y ago
While Go isn't designed for embedded systems, it can run on them. TinyGo is another Go compiler intended for embedded systems. And now its officially sponsored by Google. https://tinygo.org/docs/reference/microcontrollers/ https://tinygo.org/docs/reference/microcontrollers/
- mseepgood 5y ago
  TinyGo is awesome.
- pjmlp 5y ago
  TamaGo is another example, https://www.f-secure.com/en/consulting/foundry/usb-armory https://www.f-secure.com/en/consulting/foundry/usb-armory
fulafel 5y ago
Lots of embedded systems are very happy using garbage collection and languages with runtimes.

swiftcoder 5y ago

It's extremely challenging to make async that is usable without introducing a garbage collector or a whole lot of runtime overhead. A better comparison would be between the Rust and C++ paths to async - C++ also spent years designing their async system, and the end result is divisive at best.

dxuh 5y ago
And we are not even done yet. The Networking TS seems to have fallen out of favor and now it seems we are going to get executors + senders/receivers, which I personally think is pretty cool actually.
- jabl 5y ago
  Wonder if the Rust team is aware of the work on the C++ side of the fence on the executors+senders/receivers approach: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2300r1.html http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p230... Not saying that is the ultimate answer to building async and/or parallel algorithms, but being aware of what others in the same space are doing is certainly useful.
pjmlp 5y ago
True, and as the sibling comment notes it is still not fully there, yet as the vocabulary types are part of the standard library, it means what I have coded running on top of C++/WinRT, might equally work on top of HPX or cppcoro, just by changing includes and library being linked.

stubish 5y ago

The saddest part of learning Rust was discovering that there are no goroutines and that async works like Python and everything needs to be written twice to support both async and blocking styles. Like it was 20 years ago all over again and I'm still trying to mix Twisted and stdlib Python. I got all excited thinking of how the borrow checker would work so well with coroutines, only to discover it got nobbled because Rust's use cases include embedded systems and no runtime (like in a golang 9MB hello_world.exe). I have no idea if Rust could evolve its concurrent programming support to something better than Go's, even if it did drop some of its shackles.

wongarsu 5y ago
I find traditional multi threading a pleasure in Rust, and it works really well with the borrow checker and how the type system is designed (like the Send and Sync traits). On the semantic side, extending it to a N:M threading model like Erlang or Go would work great. But that model only seems to work well if you basically make the entire language async, which is in conflict with too many of rust's goals. So we are left with the somewhat awkward state of async as a second class citizen.
KingOfCoders 5y ago
I only have rudimentary knowledge of Golang (but think the blocked/green automatic scheduling is excellent). How does go nest aync calls? func f() { } func g() { } func h() { go g() go f() } What happens on f() Are the g() and f() calls inside h() blocking? Or are they async and the block happens at the point of return? Which would be the main difference to languages with an async keyword, were you need to be explicit about blocking.
- zaphar 5y ago
  The go keyword executes the called function asynchronously so g() and f() won't block h(). If you need a computed result from g() or f() then you'll need to use a channel or a shared mutex guarded value to get it. A channel is the correct default choice and the mutex should only be used if you need it for performance or other reasons.

npigrounet 5y ago

Rust never struggles! It just takes its time to be perfect <3

exDM69 5y ago

Early on in Rust's history, it had something similar to Go's goroutines with n:m green thread scheduling and libuv for async everything. Some other languages (e.g. Haskell/GHC) also have this kind of system. But this practically requires some kind of garbage collection and a fat runtime. I think it was a good decision on the Rust team to abandon this and go for a low level systems programming language. Otherwise it would've been just another Go-like language that isn't really usable in low level systems programming. Implementing portable async language features without a fat runtime or garbage collection is novel work so it's no wonder that it's taking its own sweet time to reach maturity.

jasode 5y ago

>Why has Rust struggled so much with this, where Go has succeeded from the start with its language-level “goroutine” concept and runtime? Rust made the deliberate decision to avoid the heavier Go goroutines runtime model after early alpha/beta experiments showed it conflicted with Rust's low-level design. I found 3 links to some history of that rationale in a previous comment: https://news.ycombinator.com/item?id=28660089 https://news.ycombinator.com/item?id=28660089 And some more links: https://stackoverflow.com/questions/29428318/why-did-rust-remove-the-green-threading-model-whats-the-disadvantage https://stackoverflow.com/questions/29428318/why-did-rust-re... https://github.com/rust-lang/rfcs/blob/master/text/0230-remove-runtime.md https://github.com/rust-lang/rfcs/blob/master/text/0230-remo... And lots of debate in this previous thread: https://news.ycombinator.com/item?id=10225903 https://news.ycombinator.com/item?id=10225903

jayflux 5y ago

> Why has Rust struggled so much with this, where Go has succeeded from the start with its language-level “goroutine” concept and runtime? It’s not that Rust has struggled, it was never Rust’s priority to have a runtime or high level async code. It had very different goals to Go. It’s like asking “why has C struggled to implement Promises like JavaScript”? The languages serve different purposes. You’re right it wasn’t their initial focal point but later on Rust wanted to offer the chance of having a go-like runtime without destabilising the low-level performance at the core level. I.E only those that use it pay for it and those that don’t use it aren’t affected. Offering “zero cost” futures etc is very difficult to do. See https://aturon.github.io/blog/2016/08/11/futures/ https://aturon.github.io/blog/2016/08/11/futures/ for more info, old but still relevant (including the chart)

skohan 5y ago

I think part of it is because computer science hasn't really nailed the right abstraction for concurrent code execution. For instance, C is a great abstraction. You take assembly language, abstract away manual management of registers with variables and pointers, add structured types to describe memory layout, standardize flow of control operations, and add functions to enable code reusability, and you have something which is very easy to work with and also to understand. It's not 100% on par with assembly in terms of performance, but it's pretty darned close, and with a little bit of practice it's very easy to look at a block of C code and basically understand what equivalent assembly it compiles to. It's a great abstraction, and it's no wonder that a vast majority of the languages which have come after it have borrowed most of its major features. I would argue we haven't really had a "great abstraction" to the same level since then*. There have been efforts to abstract away memory management the way register management has been abstracted away, and many of them have been successful for a lot of use-cases, but not to the point that everyone can forget about memory management the way the vast majority of us can forget about register management. Garbage collectors can be too slow or too wasteful for a lot of use-cases, and you need essentially another program you didn't write to pull it off. In a GC'd language it's not so trivial to look at a block of high-level code and predict what your CPU will do. There are other approaches: like the structured approaches of Rust and Swift which are quite interesting, but they're far from proven at this point. Similarly I think we're not quite there yet with concurrent programming. As far as the transparency topic, a lot of async implementations are more in the direction of garbage collectors, where the compiler rips apart your code and builds a state machine in its place. It's not hard to believe that the result will be difficult to work with and reason about in some cases. And maybe the problem is that most approaches to async are trying to cram concurrent execution into that C-like abstraction, which is such an elegant abstraction for single-threaded execution exactly. Maybe concurrent programming needs to be re-thought from first principals, with different primitives involved. *Aside: if there is another "great abstraction" on the horizon, I believe it to be ADT's. That is a feature of programming which feels like a clear step forward with no clear downsides. It's a shame that they haven't been included in Zig.

c-cube 5y ago
Zig has tagged unions and the corresponding switch expressions, is that not equivalent?

shellac 5y ago

Sibling comments have explained the detail. The pithier explanation perhaps is that rust is intended as a 'systems language', and it interprets that as meaning there should be no runtime. Or, more simply, it ought to be possible to call a rust function from C without providing an additional argument that encapsulates rust 'environment'. (C effectively defining this area) Go and Java (with Loom) have these lovely facilities, but it is hard to interface with them if your language lacks these features. I find it odd that C#, javascript, and python don't provide the smoother async Go experience despite having runtimes / VMs.

ezekiel68 5y ago

Funny you should ask that... about 6 years ago, Mozilla released an event-handling library written in go named Heka. It made use of go's built-in goroutines and channels and what made it really cool was that it had an embedded lua interpreter so people could update lua scripts in their event processing systems to alter the behavior (such as reformatting dates, etc) without needing to re-compile the solution. It got pretty popular and you can still find YouTube tutorials on using it to this day. Unfortunately, according to one of the lead developers, the system couldn't keep up with Mozilla's throughput and reliability requirements due to limitations of go's built-in features.[0] They announced they would re-write a new solution in c ("Hindsight") and they basically left an entire community of users high and dry due to not being able to salvage the go-based project, since it relied so heavily on the built-in features. [0] https://heka.mozilla.narkive.com/9heQ11hz/state-and-future-of-heka https://heka.mozilla.narkive.com/9heQ11hz/state-and-future-o...

pornel 5y ago

Rust doesn't want to impose its own one-size-fits-all runtime on all users of the language, because Rust wants to work in places where Go isn't a good fit, e.g. microcontrollers, kernels, or seamlessly on top of other languages' runtimes. Architecture of an efficient async runtime is going to be different for 128-core server vs single-threaded chip with barely any RAM. In Rust you can write your own runtime to your needs, rather than fight overhead of a big runtime on a small device, or struggle to scale a dumb runtime to complex workloads.

nextaccountic 5y ago

Go has a single runtime, Rust supports multiple async runtimes. Rust needs to support multiple runtimes because in low level space there is no one size fits all solution. For example, Go runtime imposes unavoidable overhead in memory usage, because each goroutine must have its own allocated stack (Rust futures, on the other hand, are stackless). Rust runs on low memory platforms where Go isn't really suitable.