Rustgo: Calling Rust from Go with near-zero overhead (2017)(words.filippo.io)
words.filippo.io
Rustgo: Calling Rust from Go with near-zero overhead (2017)
https://words.filippo.io/rustgo/
79 comments
That exist(ed)! c2goasm would compile C and then decompile it into Go asm.
https://github.com/minio/c2goasm
https://github.com/minio/c2goasm
Imagine picking a language with terrible FFI overhead and weak compiler only to fight these two worsts aspects of it in an attempt to fix them.
C# with zero-cost FFI, none of the performance penalty and ability to statically link everything together is a strictly better choice. Saner type system and syntax too.
C# with zero-cost FFI, none of the performance penalty and ability to statically link everything together is a strictly better choice. Saner type system and syntax too.
C#'s FFI is kind of zero-cost with blittable types (int, float). You still need to do marshalling for anything more complex (strings was a common issue on Linux, UTF8<=>UTF16), also memory pinning. Last time I checked, it also notifies the GC the thread entered native code (can't be preempted, the stack needs to be scanned conservatively etc.) After exiting a native function IIRC there's a safepoint check. I remember years ago it was common knowledge that P/Invoke is not suitable for calling hot functions in a loop, you had to create native helper functions which make all the calls in one go.
Maybe it has changed?
Memory pinning is practically free and GC does quite a bit of work to further minimize its impact on throughput, common practice is to use stack buffers or natively allocated memory for marhsalled or other data anyway (remember - free FFI, so you can always do malloc and free which marshallers do). In practice UTF-16<->UTF-8 conversion rarely shows up on flamegraph as it turns out built-in transcoding is very fast and does not leave dangling data that GC needs to clean up. It is also not as frequently needed - you can just get a byte* for free out of "hello, world"u8 and pass it without any extra operations (the binding generator will do that for you).
On top of that, complex blittable structures are first and foremost expressible in C# - you can easily have C binary tree, or an array of arrays with byte**. Performance-sensitive code that does interop heavily exploits that to give actual C-like experience.
Also short-lived FFI calls do not need to notify GC (which is also cheap it toggles a boolean), libraries that care about extra last nanosecond annotate them with `[SuppressGCTransition]` which further streamlines assembly around FFI call.
For performing FFI in a loop - the cost comes from the same reason a non-inlineable cross-compilation-unit calls are expensive within C++. Because we're talking plain call level of overhead, which is by definition as cheap as FFI gets. Of course that can still be a bottleneck if you have a small function beyond FFI boundary within a hot loop. In that case you might as well port it to C# to make it inlineable which is going to be faster, or have an FFI call for a batched operation.
Try `dotnet publish -o . -p:StripSymbols=false`ing this: https://github.com/U8String/U8String/tree/main/Examples/Inte... and then disassembling it with Ghidra. You will be positively impressed with how codegen looks - there will be simple direct calls into Rust with single bool checks for a potential GC poll after them (and compiler will merge those too after multiple consecutive calls).
On top of that, complex blittable structures are first and foremost expressible in C# - you can easily have C binary tree, or an array of arrays with byte**. Performance-sensitive code that does interop heavily exploits that to give actual C-like experience.
Also short-lived FFI calls do not need to notify GC (which is also cheap it toggles a boolean), libraries that care about extra last nanosecond annotate them with `[SuppressGCTransition]` which further streamlines assembly around FFI call.
For performing FFI in a loop - the cost comes from the same reason a non-inlineable cross-compilation-unit calls are expensive within C++. Because we're talking plain call level of overhead, which is by definition as cheap as FFI gets. Of course that can still be a bottleneck if you have a small function beyond FFI boundary within a hot loop. In that case you might as well port it to C# to make it inlineable which is going to be faster, or have an FFI call for a batched operation.
Try `dotnet publish -o . -p:StripSymbols=false`ing this: https://github.com/U8String/U8String/tree/main/Examples/Inte... and then disassembling it with Ghidra. You will be positively impressed with how codegen looks - there will be simple direct calls into Rust with single bool checks for a potential GC poll after them (and compiler will merge those too after multiple consecutive calls).
So it's actually about the same situation in Go from what I can understand.
The only significant conceptual difference between Go's and C#'s FFI mechanisms when it comes to call overhead that I can think of is the fact that Go has to switch the current stack to a special C stack. In C#, it runs on the same stack.
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No, Go FFI is so slow it makes Python look fast which has great FFI performance, just being an interpreted language hurts. It needs to perform stack switching and worker thread pinning, and for some reason even that is slow. I don't know why.
Note on tinygo as I've been put in the jail heh:
Realistically no one runs TinyGo in production as in back-end workloads or larger user-facing applications. And when you do run it, at most you match pre-existing FFI performance of .NET which ranges at 0.5-2ns at throughput (which I assume how you are testing it) depending on flags and codegen around specific arguments. Up to 50 times difference with a standard Go, that is a lot, isn't it? All custom runtime flavours in Go usually come with significant performance issues or other tradeoffs. Something I never need to deal with when I solve the same problems with .NET, maybe occasionally addressing compatibility with AOT for libraries that have not been updated if it's a desired deployment mode.
Note on tinygo as I've been put in the jail heh:
Realistically no one runs TinyGo in production as in back-end workloads or larger user-facing applications. And when you do run it, at most you match pre-existing FFI performance of .NET which ranges at 0.5-2ns at throughput (which I assume how you are testing it) depending on flags and codegen around specific arguments. Up to 50 times difference with a standard Go, that is a lot, isn't it? All custom runtime flavours in Go usually come with significant performance issues or other tradeoffs. Something I never need to deal with when I solve the same problems with .NET, maybe occasionally addressing compatibility with AOT for libraries that have not been updated if it's a desired deployment mode.
> No, Go FFI is so slow it makes Python look fast
Which Python and which Go? There are so many different implementations and different versions of those implementations that this broad statement is meaningless.
From what I have installed on my machine, CPython 3.11.6 seems to take around 80ns to call a C function, gc 1.22.0 takes around 50ns to call the same C function, and tinygo 0.32.0 only takes around 1ns!
Such benchmarking is always fraught with problems, so your milage may vary, but on my machine under this particular test Go wins in both cases, and tinygo is doing so at about the same speed as C itself.
Which Python and which Go? There are so many different implementations and different versions of those implementations that this broad statement is meaningless.
From what I have installed on my machine, CPython 3.11.6 seems to take around 80ns to call a C function, gc 1.22.0 takes around 50ns to call the same C function, and tinygo 0.32.0 only takes around 1ns!
Such benchmarking is always fraught with problems, so your milage may vary, but on my machine under this particular test Go wins in both cases, and tinygo is doing so at about the same speed as C itself.
> CPython 3.11.6 seems to take around 80ns to call a C function, gc 1.22.0 takes around 50ns to call the same C function
How does this make any sense? C shares a runtime with CPython. What is it doing where it manages to be slower than go?
How does this make any sense? C shares a runtime with CPython. What is it doing where it manages to be slower than go?
I'm not familiar enough with the internals to say for sure, but I do know Python has a penchant for dicts. Perhaps it looks up the function each time, whereas Go can be made aware of the function at compile time? That wouldn't be without cost.
Part and parcel with its love for dicts, Python data structures tend to not be shaped like C typically expects. Whereas Go data structures are, at most, lightweight wrappers around C-style structures, and are often even directly equivalent, making passing data about as simple as passing a pointer. Python may be getting bogged down in some kind of marshalling operation. That isn't cost-free either.
Part and parcel with its love for dicts, Python data structures tend to not be shaped like C typically expects. Whereas Go data structures are, at most, lightweight wrappers around C-style structures, and are often even directly equivalent, making passing data about as simple as passing a pointer. Python may be getting bogged down in some kind of marshalling operation. That isn't cost-free either.
Are there some recent measurements?
All I could find is somewhat old and I think there has been some work done since.
Maybe it just looks slow to you, for example, check the raylib bindings benchmarks, Go is usually at the top, together with Rust, C#, etc. and Python is at the very bottom. Perhaps not the best way to benchmark FFI but it shows that Python is not even usable besides playing.
In Go, once you've FFI'd, you're likely to be able to use the Go data directly in C. In Python, you generally have to crawl over the Python-based data at Python speeds, converting it into data that your C library can understand, and then when C is done, convert it back into a Python data type at, again, effectively Python speeds. Unless you're willing for it to just be opaque data that Python effectively can route, but not manipulate. (This works, but is distinctly less useful. Of course sometimes, like for image data, it's the best option.) Combined with the sibling comment that actually times calls and finds Go is faster anyhow, even if it is a microbenchmark, I don't think your argument carries water.
It sounds to me like you've latched on to some propaganda that you like and are happy to share but don't have any personal experience with. Go's FFI is relatively slow for a compiled language, but it isn't even remotely uniquely slow. Many languages have a C FFI with some sort of relatively expensive C conversion operation, and as I point out here, that actually includes Python in many, if not most, uses (it's pretty rare to want to write code to bind to C that just ships over two integers and returns another integer or something, usually we're doing something interesting). It is the languages like Rust or Zig that can do it for effectively free that are the exception, not the rule. Go's FFI costs are not all that expensive compared to programming languages in general, and if you're worried about the FFI performance, Go also generally needs FFI less in the first place than Python because it's a fast language (not the fastest by any means, but fast), and the higher proportion of Go code will generally smoke Python anyhow. Unless you foolishly write a very tight loop of C FFI code in Go, which is a bad idea in most langauges anyhow (again excepting the exceptions like Rust and Zig), Go's going to outpace a Python program that is mostly Python but uses a bit of FFI here and there by a lot anyhow.
The idea that Go is brought to its knees by a single C call that takes 100ms or something reminds me of the people who think that as soon as you use a garbage collected language you've signed up for a guaranteed 250ms stop-the-world pause every three seconds or something. Is it free? No. Is it expensive? In relative terms maybe. In absolute terms, not really. Most programs, most of the time you won't notice, and if you are in a situation where Python is even a performance option virtually by definition you're in a situation where it won't be a problem for Go.
This is not rah-rah for Go or slagging on Python. This is just stuff engineers need to know. Python is a very capable language, but you definitely pay for it. It is not free. Every greenfield project, you need to sit down and calculate the costs and pick a good tool, but you're going to make dumb, project-killing decisions if you're using costs that are multiple orders of magnitude off of reality. I've seen it kill projects, it's not just theory.
It sounds to me like you've latched on to some propaganda that you like and are happy to share but don't have any personal experience with. Go's FFI is relatively slow for a compiled language, but it isn't even remotely uniquely slow. Many languages have a C FFI with some sort of relatively expensive C conversion operation, and as I point out here, that actually includes Python in many, if not most, uses (it's pretty rare to want to write code to bind to C that just ships over two integers and returns another integer or something, usually we're doing something interesting). It is the languages like Rust or Zig that can do it for effectively free that are the exception, not the rule. Go's FFI costs are not all that expensive compared to programming languages in general, and if you're worried about the FFI performance, Go also generally needs FFI less in the first place than Python because it's a fast language (not the fastest by any means, but fast), and the higher proportion of Go code will generally smoke Python anyhow. Unless you foolishly write a very tight loop of C FFI code in Go, which is a bad idea in most langauges anyhow (again excepting the exceptions like Rust and Zig), Go's going to outpace a Python program that is mostly Python but uses a bit of FFI here and there by a lot anyhow.
The idea that Go is brought to its knees by a single C call that takes 100ms or something reminds me of the people who think that as soon as you use a garbage collected language you've signed up for a guaranteed 250ms stop-the-world pause every three seconds or something. Is it free? No. Is it expensive? In relative terms maybe. In absolute terms, not really. Most programs, most of the time you won't notice, and if you are in a situation where Python is even a performance option virtually by definition you're in a situation where it won't be a problem for Go.
This is not rah-rah for Go or slagging on Python. This is just stuff engineers need to know. Python is a very capable language, but you definitely pay for it. It is not free. Every greenfield project, you need to sit down and calculate the costs and pick a good tool, but you're going to make dumb, project-killing decisions if you're using costs that are multiple orders of magnitude off of reality. I've seen it kill projects, it's not just theory.
> but it isn't even remotely uniquely slow.
Most languages share a runtime and stack model with C. Go is "unique" among popular languages in that it decided to do its own thing, which results in much slower FFI calls. Like sure, so did GHC, but most people don't expect GHC to behave like C.
TBH it's enough to put me off of the language outside of writing servers. There's just too much to draw from in terms of libc-based libraries and the drawbacks in Go are too severe to make its interesting concurrency ideas generally worth it.
EDIT: Not to mention if you have WASI as a target go is a terrible choice for the exact same reasons—it has its unique memory and stack model that don't work well with web assembly.
Most languages share a runtime and stack model with C. Go is "unique" among popular languages in that it decided to do its own thing, which results in much slower FFI calls. Like sure, so did GHC, but most people don't expect GHC to behave like C.
TBH it's enough to put me off of the language outside of writing servers. There's just too much to draw from in terms of libc-based libraries and the drawbacks in Go are too severe to make its interesting concurrency ideas generally worth it.
EDIT: Not to mention if you have WASI as a target go is a terrible choice for the exact same reasons—it has its unique memory and stack model that don't work well with web assembly.
Again, people throw around "much slower" and it comes off like it's 100ms or something. It's not that much slower, it's not even close.
It's only an issue if you're planning on making tens or hundreds of thousands of FFI calls per second, routinely. That describes a non-zero set of software people may want to write. If you are writing one of them, you need to know that. But it doesn't describe anything like a majority of software cases in general.
It is one of the things you need to know, but you need to have a correct view of the costs to make correct decisions, or, at least, not one that's off by orders of magnitude and leads to people running around claiming Go is "uniquely slow" at FFI and bragging about how much faster Python is when it turns out "uniquely slow" Go is actually faster than Python. Costs aren't a matter of feelings or what reinforces your decisions about what language to use or how much you hate that Go doesn't have sum types. Costs are what they are.
My personal favorite, and bear with me because this is going to be generally a negative for Go, is the number of databases that for some reason are getting written in Go. My rule of thumb is that Go is 2-3x slower than C/C++ (and, increasingly in that set, Rust). On the grand landscape of programming languages, this puts it distinctly towards the faster end in a general sense; there are very popular languages clocking in at "generally 40x-50x slower and also can't use more than one CPU at a time". But if you're writing a database, you're going into a market where it's virtually guaranteed that's going to be a problem. Maybe don't do that. But then deciding that you aren't going to use Go to write your command-line app to hit an HTTP API because it's not the fastest language for databases is not a correct engineering conclusion to draw.
It's only an issue if you're planning on making tens or hundreds of thousands of FFI calls per second, routinely. That describes a non-zero set of software people may want to write. If you are writing one of them, you need to know that. But it doesn't describe anything like a majority of software cases in general.
It is one of the things you need to know, but you need to have a correct view of the costs to make correct decisions, or, at least, not one that's off by orders of magnitude and leads to people running around claiming Go is "uniquely slow" at FFI and bragging about how much faster Python is when it turns out "uniquely slow" Go is actually faster than Python. Costs aren't a matter of feelings or what reinforces your decisions about what language to use or how much you hate that Go doesn't have sum types. Costs are what they are.
My personal favorite, and bear with me because this is going to be generally a negative for Go, is the number of databases that for some reason are getting written in Go. My rule of thumb is that Go is 2-3x slower than C/C++ (and, increasingly in that set, Rust). On the grand landscape of programming languages, this puts it distinctly towards the faster end in a general sense; there are very popular languages clocking in at "generally 40x-50x slower and also can't use more than one CPU at a time". But if you're writing a database, you're going into a market where it's virtually guaranteed that's going to be a problem. Maybe don't do that. But then deciding that you aren't going to use Go to write your command-line app to hit an HTTP API because it's not the fastest language for databases is not a correct engineering conclusion to draw.
The idea that a feature isn't that slow if you don't use it much isn't very persuasive.
You could also flip this argument on its head. What is go good at? Writing evented servers. If you're writing one of these you'll know it.
Also, I admit I was wrong; go doesn't have uniquely bad ffi. It's just worse than C++, rust, D, jvm, .net, and any compiler lisp I've ever used. Perhaps go is uniquely well suited to writing stuff other than evented servers in way I just can't see yet.
(And FWIW I am still baffled how python managed to be this slow without needing to switch stacks.)
You could also flip this argument on its head. What is go good at? Writing evented servers. If you're writing one of these you'll know it.
Also, I admit I was wrong; go doesn't have uniquely bad ffi. It's just worse than C++, rust, D, jvm, .net, and any compiler lisp I've ever used. Perhaps go is uniquely well suited to writing stuff other than evented servers in way I just can't see yet.
(And FWIW I am still baffled how python managed to be this slow without needing to switch stacks.)
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Thank you for responding. Indeed, it's not quite as bad as Python in overall performance. But I'm happy it brought attention to the fact that Go is still pretty inadequate at this.
My main point is engineers keep trying to shoehorn it in domains, where, should they not want to use Rust or Zig as you mentioned (which are great), they should have chosen C# (which is also great for FFI, look at Stride3D, Ryujinx or even its Sqlite driver speed, all of which are FFI heavy), but instead they keep attempting to use Go where they have to work hard to counteract its inadequacy, instead of using a platform where their solution would perform great not despite the tool but because of it.
My main point is engineers keep trying to shoehorn it in domains, where, should they not want to use Rust or Zig as you mentioned (which are great), they should have chosen C# (which is also great for FFI, look at Stride3D, Ryujinx or even its Sqlite driver speed, all of which are FFI heavy), but instead they keep attempting to use Go where they have to work hard to counteract its inadequacy, instead of using a platform where their solution would perform great not despite the tool but because of it.
The biggest problem with FFI in Go (gc, at least) isn't in the FFI operation itself, rather FFI functions that block for a long time mess with the scheduler.
It seems C# suffers the same problem as real-world benchmarks often show it to be slower than Go when performing FFI, even if it should be theoretically faster.
As usual, performance can be hard to predict. Benchmarking the actual code you intend to use is the only way to ensure that what you think is true actually is. If you aren't measuring, you aren't engineering.
It seems C# suffers the same problem as real-world benchmarks often show it to be slower than Go when performing FFI, even if it should be theoretically faster.
As usual, performance can be hard to predict. Benchmarking the actual code you intend to use is the only way to ensure that what you think is true actually is. If you aren't measuring, you aren't engineering.
Do you have any example of code that can demonstrate how it is possible to meaningfully slow down .NET and its threadpool and GC when performing FFI where Go does not suffer to a significantly greater extent?
(if you fashion a Go example - that'll be enough and I'll make a C# one)
.NET's threadpool is specifically made with the consideration of worker threads being potentially blocked in mind, and has two mechanisms to counteract it - hill-climbing algorithm that grows and shrinks the active number of threads to minimize task wait time in queues, and another mechanism to actively detect blocked threads (like system sleep or blocked by synchronous network read) and inject additional workers without waiting for hill-climbing to kick in. It is a very resilient design. Go's and Tokio threadpool are comparatively lower effort - both are work-stealing designs but neither has the active scaling mechanism .NET has already had since .NET Framework days.
GC implementation at the same time is pinning-aware and can shuffle around memory in such a way to allow other objects to participate in collection or promotion to older generations while keeping the pinned memory where it is. There have been years of work towards improving this, and there is also an additional pinned memory heap for long-lived pinned allocations on the rare occasion where just performing malloc is not appropriate.
I doubt there is any other high-level language or platform that can compete on FFI with .NET, something that has been considered as a part of its design since the very first version. If you want better experience your main upgrade options are literally C, C++, Zig, Rust, and honorable mention Swift (it is mostly a side-grade, with the heavy lifting done by LLVM).
(if you fashion a Go example - that'll be enough and I'll make a C# one)
.NET's threadpool is specifically made with the consideration of worker threads being potentially blocked in mind, and has two mechanisms to counteract it - hill-climbing algorithm that grows and shrinks the active number of threads to minimize task wait time in queues, and another mechanism to actively detect blocked threads (like system sleep or blocked by synchronous network read) and inject additional workers without waiting for hill-climbing to kick in. It is a very resilient design. Go's and Tokio threadpool are comparatively lower effort - both are work-stealing designs but neither has the active scaling mechanism .NET has already had since .NET Framework days.
GC implementation at the same time is pinning-aware and can shuffle around memory in such a way to allow other objects to participate in collection or promotion to older generations while keeping the pinned memory where it is. There have been years of work towards improving this, and there is also an additional pinned memory heap for long-lived pinned allocations on the rare occasion where just performing malloc is not appropriate.
I doubt there is any other high-level language or platform that can compete on FFI with .NET, something that has been considered as a part of its design since the very first version. If you want better experience your main upgrade options are literally C, C++, Zig, Rust, and honorable mention Swift (it is mostly a side-grade, with the heavy lifting done by LLVM).
> Do you have any example of code
No better than your own code. Why not put it to the test? In the end you will either know that you made the right choice, or have the better solution ready to swap in. You can't lose.
The key takeaway from the previous comment isn't some pointless C# vs Go comparison, it is that performance can be hard to predict. Someone else's code isn't yours. It won't tell you anything about yours. Measure and find out!
No better than your own code. Why not put it to the test? In the end you will either know that you made the right choice, or have the better solution ready to swap in. You can't lose.
The key takeaway from the previous comment isn't some pointless C# vs Go comparison, it is that performance can be hard to predict. Someone else's code isn't yours. It won't tell you anything about yours. Measure and find out!
You did mention there exists an FFI scenario where Go supposedly performs better. It would be interesting to look at it, given the claim.
Could it be that Go has other benefits that outweigh ffi being a little slower?
This is _hacker_ news, doing the thing it wasn’t designed to do is the point. The harder the challenge, the better.
Yes there are tons of better choices for rust interop. Any LLVM language will work. That’s not interesting.
Yes there are tons of better choices for rust interop. Any LLVM language will work. That’s not interesting.
lol I remember looking at this when doing our major port from Go to Rust. I noped out once I saw the raw assembly portion. Great for a side project but probably not the move for a cross platform binary run by thousands of people. Still a very cool post and the literature for Go/Rust interop is def lacking
https://github.com/petermattis/fastcgo, which is now 7 years old seems to do something similar without the need to about obscure CGO FFI configuration. It also seems to be more generally applicable for any language with C interop.
There had been an issue for having something similar in the language itself - https://github.com/golang/go/issues/42469, but the Golang compiler team rejected it. If you have followed similar discussions around this with the Golang compiler team, you will notice a pattern of interaction that strongly indicates that they are very much opposed to ever accepting this into the compiler.
There had been an issue for having something similar in the language itself - https://github.com/golang/go/issues/42469, but the Golang compiler team rejected it. If you have followed similar discussions around this with the Golang compiler team, you will notice a pattern of interaction that strongly indicates that they are very much opposed to ever accepting this into the compiler.
fastcgo links to rustgo
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Does this mean you could now use gokrazy to run rust apps on an sbc with better startup speeds than linux??
If you're calling rust from go, wouldn't you still have the go startup time before you could call the rust code?
This is totally sick! I can't wait to go through these repro steps using new versions.
it makes me think about https://news.ycombinator.com/item?id=41117749 it is the mirror of this project: effient wal to call Go from Rust
What is the benefit of this?
I was under the impression that go isn't that far off from rust on most speed metrics being both compiled. So this adds complexity for what gain?
I was under the impression that go isn't that far off from rust on most speed metrics being both compiled. So this adds complexity for what gain?
Allocating is much easier in Go and much harder to eliminate in it, for example.
Also, for some kinds of code (usually not CRUD), LLVM does better job than the Go compiler.
And if you do concurrency, Rust's async await can be faster than Go's approach (but it is a lot more complicated, and the perf gain usually doesn't matter).
Also, for some kinds of code (usually not CRUD), LLVM does better job than the Go compiler.
And if you do concurrency, Rust's async await can be faster than Go's approach (but it is a lot more complicated, and the perf gain usually doesn't matter).
Libraries can be written once and then used in both languages.
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In benchmarks I've seen, Go is ~6 times slower.
But generally speaking, the reason I prefer Rust to Go for most developments is its type system. I could see myself using Rust to handle business-specific/safety-critical logic and Go as a fast prototyping language to assemble them.
But generally speaking, the reason I prefer Rust to Go for most developments is its type system. I could see myself using Rust to handle business-specific/safety-critical logic and Go as a fast prototyping language to assemble them.
What part of the Go typing system is lacking for "business-specific/safety-critical logic"?
I wasn't planning to turn this into a language flame war, so I'm not going to give details.
Let's just say that the designers of Rust and Go have prioritized very different feature sets when designing their type systems. If you develop in Rust, it's typically because you want to write "fearless code", i.e. attach sophisticated invariants to types to avoid safety issues later in development/coming from client code. If you develop in Go, it's typically because you want "productivity", i.e. reach quickly a point where you code can run and you can start testing it.
As usual, it's a tradeoff. For most tasks, I happen to click better with the former. YMMV
Let's just say that the designers of Rust and Go have prioritized very different feature sets when designing their type systems. If you develop in Rust, it's typically because you want to write "fearless code", i.e. attach sophisticated invariants to types to avoid safety issues later in development/coming from client code. If you develop in Go, it's typically because you want "productivity", i.e. reach quickly a point where you code can run and you can start testing it.
As usual, it's a tradeoff. For most tasks, I happen to click better with the former. YMMV
Go doesn't have any closed or sealed types. An "enum" is just a subtype and subtypes can't restrict the range of their values. It's possible to have something like a closed tagged union using an interface with an unexported method and type-switching, but the language won't understand this for e.g. detecting whether a switch without default is exhaustive.
There's also no way to declare a non-nil pointer nor to work cleanly with nested nil-able struct fields.
There's also no way to declare a non-nil pointer nor to work cleanly with nested nil-able struct fields.
Go's enums aren't even something to talk about when compared with classical Pascal enumerations.
Naturally this is much better to type,
Naturally this is much better to type,
type Weekdays int
const (
Monday Weekdays = iota
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
)
type Weekdays = (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday)
It lacks expressiveness, which means you actually have to put some thought into your design to avoid butting heads with it. You can't throw up garbage and then keep massaging the types until you can make whatever gobbledygook you came up with fit.
Business/safety critical logic tends to get complicated, and, at least in the case of business software, is more than likely is venturing into unexplored territory, so when you're not very skilled at programming finding the right design can become an insurmountable challenge. A more expressive type system offers a bandaid to work around that.
Business/safety critical logic tends to get complicated, and, at least in the case of business software, is more than likely is venturing into unexplored territory, so when you're not very skilled at programming finding the right design can become an insurmountable challenge. A more expressive type system offers a bandaid to work around that.
A bit of cart-horse-y reasoning…. An expressive type system helps me to model the nuances that are actually present in the business logic. If I simplify or restructure my model more than real life allows for I would say that causes much more trouble than actually modeling what’s happening on the ground.
Yes, when I’m behind my desk I always find ways to make the business logic better and simpler and more fitting. But those damn humans never follow my rules.
Yes, when I’m behind my desk I always find ways to make the business logic better and simpler and more fitting. But those damn humans never follow my rules.
mr90210(1)
That's widely incorrect, Rust and C are like 2-5x faster than Go?
Go has arguably a better concurrency model, so for some usecases it can work much better, but for some realtime programming stuff, Go is a no-go ba-dum-tss.
For webdev I would never chose Rust over Go, each language has their own advantage.
Go has arguably a better concurrency model, so for some usecases it can work much better, but for some realtime programming stuff, Go is a no-go ba-dum-tss.
For webdev I would never chose Rust over Go, each language has their own advantage.
> Go has arguably a better concurrency model
Go might have a better concurrency implementation, Go’s concurrency model is pretty much just threads and telling you to git gud scrub.
Go might have a better concurrency implementation, Go’s concurrency model is pretty much just threads and telling you to git gud scrub.
That's true, it's more precise to say that it's an implementation. I'm happy you understood what I meant though.
The developer experience on using it is much better than using coroutines in another lang.
The developer experience on using it is much better than using coroutines in another lang.
Go's concurrency model lets you just access the same mutable variable from multiple goroutines - that kind of "good model" you can also get with C and some implementation of channels and green threads.
Yes, but having coded in both languages you can see how Go's concurrency system works well with it and fits neatly.
Try using async in Rust and you'll see what I mean, it sucks to use it.
The same applies to cpp, you'll need years and years of experience to write somewhat decent cpp what you can write in Go with a few weeks learning coroutines, and will still be prone to make mistakes. I've done lots of cpp and can affirm that after decades I'm still not sure if my concurrent solution will run as well as my half-assed Go coroutine code.
Go coroutines is a good abstraction that is very fitting to the language, similar to the actor model and the BEAM VM (erlang/elixir).
Use the same abstraction in another language (like JVM or C) and you'll see how the devex makes a huge difference.
Try using async in Rust and you'll see what I mean, it sucks to use it.
The same applies to cpp, you'll need years and years of experience to write somewhat decent cpp what you can write in Go with a few weeks learning coroutines, and will still be prone to make mistakes. I've done lots of cpp and can affirm that after decades I'm still not sure if my concurrent solution will run as well as my half-assed Go coroutine code.
Go coroutines is a good abstraction that is very fitting to the language, similar to the actor model and the BEAM VM (erlang/elixir).
Use the same abstraction in another language (like JVM or C) and you'll see how the devex makes a huge difference.
I'd chose async/await over threads any day, and many people do too, that's why this construct has gained so much popularity in many different languages. Async/await is a rare example in PL design where a new concept is implemented in one language and then adopted by many in the following years.
In fact, the “threads are more ergonomic than async/await” seems to be more of an HN meme than a popular opinion in the wild. (And please don't quote What color is your function since it's mostly a rant about callback-based concurrency which everyone agree it sucks).
In fact, the “threads are more ergonomic than async/await” seems to be more of an HN meme than a popular opinion in the wild. (And please don't quote What color is your function since it's mostly a rant about callback-based concurrency which everyone agree it sucks).
> since it's mostly a rant about callback-based concurrency which everyone agree it sucks
It really isn’t, it’s a rant about there being two worlds (colors) of functions - async and not async, which don’t compose that well together. I believe Rust is exploring the ability to genericize functions over their asyncness, and I wish them luck in that endeavor.
Async/await is, if anything, a tradeoff for performance and ffi over usability. As they are generally stackless and in the case of rust don’t need allocations.
With green threads like in Go you’ll generally have to allocate at least a small stack for each goroutine, and you’ll have to fix up things for ffi, but it’s much more straightforward, all functions have the same color (you just write “blocking” code, but the underlying implementation is async), you don’t have an ecosystem split, and you don’t have to war with the type system every other day (as many feel like they’re doing in Rust when writing async).
It’s a pretty good point in case that Java just spent a few years making project loom happen, which effectively brings the Go approach to Java.
Async/await has its place, especially in very performance-critical code, but its usability is, IMO, miles behind threads.
Of course, an ideal world would be green threads with rusts compile-time checking of concurrency safety…
It really isn’t, it’s a rant about there being two worlds (colors) of functions - async and not async, which don’t compose that well together. I believe Rust is exploring the ability to genericize functions over their asyncness, and I wish them luck in that endeavor.
Async/await is, if anything, a tradeoff for performance and ffi over usability. As they are generally stackless and in the case of rust don’t need allocations.
With green threads like in Go you’ll generally have to allocate at least a small stack for each goroutine, and you’ll have to fix up things for ffi, but it’s much more straightforward, all functions have the same color (you just write “blocking” code, but the underlying implementation is async), you don’t have an ecosystem split, and you don’t have to war with the type system every other day (as many feel like they’re doing in Rust when writing async).
It’s a pretty good point in case that Java just spent a few years making project loom happen, which effectively brings the Go approach to Java.
Async/await has its place, especially in very performance-critical code, but its usability is, IMO, miles behind threads.
Of course, an ideal world would be green threads with rusts compile-time checking of concurrency safety…
I'm not sure what you mean by "don't compose well".
You can call sync code from an async function perfectly well. Going the other way around is either very simple in a throwaway code (just use pollster or tokio's block_on), or requires appropriate care (because async means IO and calling a function doing IO means your function now does IO too).
I believe what most people are struggling with is having to think about doing IO instead of just doing IO wherever. But that's a feature, not a bug, and an overarching theme in Rust: you need to think what you're doing and how everything will work together. Yes you can't just put an async call somewhere down the stack without changing the signatures, but that's a good thing.
You can call sync code from an async function perfectly well. Going the other way around is either very simple in a throwaway code (just use pollster or tokio's block_on), or requires appropriate care (because async means IO and calling a function doing IO means your function now does IO too).
I believe what most people are struggling with is having to think about doing IO instead of just doing IO wherever. But that's a feature, not a bug, and an overarching theme in Rust: you need to think what you're doing and how everything will work together. Yes you can't just put an async call somewhere down the stack without changing the signatures, but that's a good thing.
Rust doesn’t model IO in terms of types though, does it? Sure, an async function likely does IO, but maybe it’s just receiving from a channel? At the same time 90% (completely made up number) of Rust just does plain blocking IO and you absolutely won’t get that in the signature either (other than looking into error types, that is). We’re not in Haskell here. You can just make a blocking call in your async code, not notice it does IO (or you’re just not proficient in async), and it falls to pieces, your runtime just hung.
While “you can just use pollster” means you now have to wrap every function call to an async-first library in your async-less codebase. Again, this isn’t “composing well” in my book, it absolutely does create a divide in the ecosystem.
While in Go all code is written in a blocking fashion, but all IO is done async (either via threadpool or non-blocking syscalls), handled by the runtime, because the threads are green. Of course, that’s less performant and falls apart if you start using C libraries that do blocking IO (but it’s not like Rust would do better in that latter case).
At the same time, whether modeling IO in the type system is good or not, is I think something where opinions very much differ.
To be clear, again, I’m not bashing Rust async in general, I just think it’s a tradeoff and I very much think its usability is worse than just writing straightforward blocking code.
While “you can just use pollster” means you now have to wrap every function call to an async-first library in your async-less codebase. Again, this isn’t “composing well” in my book, it absolutely does create a divide in the ecosystem.
While in Go all code is written in a blocking fashion, but all IO is done async (either via threadpool or non-blocking syscalls), handled by the runtime, because the threads are green. Of course, that’s less performant and falls apart if you start using C libraries that do blocking IO (but it’s not like Rust would do better in that latter case).
At the same time, whether modeling IO in the type system is good or not, is I think something where opinions very much differ.
To be clear, again, I’m not bashing Rust async in general, I just think it’s a tradeoff and I very much think its usability is worse than just writing straightforward blocking code.
I disagree with your "just" in "just receiving from a channel". Receiving from a channel is hardly distinguishable from IO, since it can take an arbitrary amount of time and the receiver needs to handle external resource failures (ie the other side of the channel getting dropped). That's very different from normal sync functions parsing JSON, adding matrices, or doing date math. Also note how functions that can't block are still sync, like tokio::sync::oneshot::Sender::send.
I also can't agree with the argument that if it's possible to hang the runtime there's no point in explicit async. Yes people can still make mistakes, but it's better when it's explicitly a mistake and not just haphazard IO everywhere being the norm.
What is the "async-less" codebase for? Why does it have to be "async-less"? A Go codebase is fully async at all times, so why shouldn't a Rust system extend async up to main() (or at least encapsulate IO-heavy parts in a separate async part)?
Runtime behaviour of async rust is ~equivalent to Go, so coming back to my original point, the difference is that 1) Rust allows to have non-async, predictable functions, async is opt-in 2) the opt-in must be explicit 3) you have more choice between intra- and inter-future concurrency (select! vs spawn). All those points are important and empowering, they aren't problems to be solved.
I agree that the flip side is that Rust forces explicit decisions upfront, but that's one of the core premises of Rust.
I also can't agree with the argument that if it's possible to hang the runtime there's no point in explicit async. Yes people can still make mistakes, but it's better when it's explicitly a mistake and not just haphazard IO everywhere being the norm.
What is the "async-less" codebase for? Why does it have to be "async-less"? A Go codebase is fully async at all times, so why shouldn't a Rust system extend async up to main() (or at least encapsulate IO-heavy parts in a separate async part)?
Runtime behaviour of async rust is ~equivalent to Go, so coming back to my original point, the difference is that 1) Rust allows to have non-async, predictable functions, async is opt-in 2) the opt-in must be explicit 3) you have more choice between intra- and inter-future concurrency (select! vs spawn). All those points are important and empowering, they aren't problems to be solved.
I agree that the flip side is that Rust forces explicit decisions upfront, but that's one of the core premises of Rust.
> It really isn’t, it’s a rant about there being two worlds (colors) of functions - async and not async, which don’t compose that well together.
Except the composition problem only manifests itself badly when your “red function” is callback-based. Re-read the blog post and you'll see that the fundamental problem is that red functions are unwieldy (which it really is when you have callbacks, but not when you have async/await).
In Rust async/await is exactly as contaminating as `Option` or `Result`, or “error as return values” in Go or C, which creates the same split (functions which can propagate an error and the ones which don't), but it's almost never being discussed in terms of “function color” because it's not in fact such a big deal.
> I believe Rust is exploring the ability to genericize functions over their asyncness
In fact they (well, in practice mostly Yoshua) would like to genericize over all effects including fallibility because they are well aware that the problems are equivalent. The biggest problem in Rust's case being the combinatory explosion between different effects.
> Async/await has its place, especially in very performance-critical code, but its usability is, IMO, miles behind threads.
> Of course, an ideal world would be green threads with rusts compile-time checking of concurrency safety…
This is entirely subjective: as I said above I would never willingly works with threads if I can use async/await instead. It's not just a performance thing at all. For many people async/await is just a superior user experience.
In fact it's exactly the same as exceptions vs `Result`: (unchecked) exceptions don't make colored functions whereas `Result` does, but exceptions, like threads hide where something can fail on your code (resp. when your code can get stuck waiting for IO) and this explicitness has value even if it comes with a cost in terms on annotation effort.
Telling someone that prefers async/await that thread is absolutely better is exactly like telling someone that dynamic typing is better than static typing because you have less things to when writing code…
Except the composition problem only manifests itself badly when your “red function” is callback-based. Re-read the blog post and you'll see that the fundamental problem is that red functions are unwieldy (which it really is when you have callbacks, but not when you have async/await).
In Rust async/await is exactly as contaminating as `Option` or `Result`, or “error as return values” in Go or C, which creates the same split (functions which can propagate an error and the ones which don't), but it's almost never being discussed in terms of “function color” because it's not in fact such a big deal.
> I believe Rust is exploring the ability to genericize functions over their asyncness
In fact they (well, in practice mostly Yoshua) would like to genericize over all effects including fallibility because they are well aware that the problems are equivalent. The biggest problem in Rust's case being the combinatory explosion between different effects.
> Async/await has its place, especially in very performance-critical code, but its usability is, IMO, miles behind threads.
> Of course, an ideal world would be green threads with rusts compile-time checking of concurrency safety…
This is entirely subjective: as I said above I would never willingly works with threads if I can use async/await instead. It's not just a performance thing at all. For many people async/await is just a superior user experience.
In fact it's exactly the same as exceptions vs `Result`: (unchecked) exceptions don't make colored functions whereas `Result` does, but exceptions, like threads hide where something can fail on your code (resp. when your code can get stuck waiting for IO) and this explicitness has value even if it comes with a cost in terms on annotation effort.
Telling someone that prefers async/await that thread is absolutely better is exactly like telling someone that dynamic typing is better than static typing because you have less things to when writing code…
> Except the composition problem only manifests itself badly when your “red function” is callback-based. Re-read the blog post and you'll see that the fundamental problem is that red functions are unwieldy (which it really is when you have callbacks, but not when you have async/await).
Not only; the problem also manifests when you interoperate with blue functions, for example because they are provided to you by libraries.
Not only; the problem also manifests when you interoperate with blue functions, for example because they are provided to you by libraries.
But even Go have a red/blue distinction (functions that return an error and the ones that don't), and in practice it's so fine it never occurred to you that it was in fact a red/blue split!
The real problem came in JavaScript with the callback hell, everything else is a minor issue that nobody really notice.
The real problem came in JavaScript with the callback hell, everything else is a minor issue that nobody really notice.
Not "threads are more ergonomic than async/await", but "threads and channels can be ergonomic".
I've been a big fan and user of async/await in various languages for over a decade now, and it can absolutely improve reading sequential asynchronous logic flow, but lets not pretend it isn't without tradeoffs. Compared to wrangling synchronization contexts and function colors, channels can be rather straightforward.
I've been a big fan and user of async/await in various languages for over a decade now, and it can absolutely improve reading sequential asynchronous logic flow, but lets not pretend it isn't without tradeoffs. Compared to wrangling synchronization contexts and function colors, channels can be rather straightforward.
Errors as return value are a “function color” too (in practice, you need to propagate it upwards the stack and it “contaminates” your code the same way as async/await). And in fact it interacts better with async/await (like in Rust) than with channels…
It still offers good structures to help you be careful in these situations, but you’re right. It’s not as complete of a concurrency model as BEAM languages.
The benefit isn't necessarily for speed there are some libraries for example available in Rust that are not in Go. This is something I am exploring at the moment rather than having to totally rewrite the library in Go
> go isn't that far off from rust on most speed metrics being both compiled
The only way I see this happening for the same code snippet is if the Rust code was being compiled in debug mode instead of release mode.
The only way I see this happening for the same code snippet is if the Rust code was being compiled in debug mode instead of release mode.
(2017) Discussions:
2017 (282 points, 68 comments) https://news.ycombinator.com/item?id=15017519
2019 (107 points, 37 comments) https://news.ycombinator.com/item?id=20600178
2017 (282 points, 68 comments) https://news.ycombinator.com/item?id=15017519
2019 (107 points, 37 comments) https://news.ycombinator.com/item?id=20600178
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There are many years since the article being written. I'm wondering if there is a better solution in 2024.
Cgo overhead was made 5-30x faster in go1.21, and it was already within noise levels in this article, so i'd use that.
Can you provide a reference for that? A quick search for me didn't bring up anything. I'm curious to read more.
> Cgo calls take about 40ns, about the same time encoding/json takes to parse a single digit integer.
As an aside, that sure feels like a lot of time to parse a single-digit integer. Not catastrophic by any means, but still, 100 to 200 cycles is a sign the program is definitely Doing Something. Perhaps that’s the memory allocator?
As an aside, that sure feels like a lot of time to parse a single-digit integer. Not catastrophic by any means, but still, 100 to 200 cycles is a sign the program is definitely Doing Something. Perhaps that’s the memory allocator?
It's probably just because it's using reflection which is pretty slow in general. Lots of conditions/branches and boxing/unboxing of values.
they changed the ABI in 1.17 to pass arguments in registers instead of the stack: https://go.dev/doc/go1.17#compiler so if you used this solution you might not need to do the fixup anymore if the ABI matches.
Doesn’t seem like there is. Probably because go developers want code to be pure go if possible
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I wonder if it would have been easier to disassemble the rust binary and turn it into Go assembly and use that.
That would need a fairly complicated program to process the binary back into assembler. Maybe getting the rust compiler to output assembly and processing into Go assembly would be the way.
Using Go assembly would save fighting with the linker, be more likely to survive upgrades and it would be cross platform (well at least on platforms with the same CPU arch).