4 ms·

Sorry, but it really sounds to me like you're repeating something from theorical research on GCs, best cases, and cherry-picking counter-examples. * ARCs non-d

Sorry, but it really sounds to me like you're repeating something from theorical research on GCs, best cases, and cherry-picking counter-examples. * ARCs non-determinism doesn't matter outside of contrived cases. In practical use it's as deterministic as expected. * The runtime overhead of modern GC algorithms might have been proven formally to have a "lower bound than ARC", but like many things proven formally, it's seldom the case in practice. And this isn't also counting the memory overhead from using GC. Just like the oft-repeated "JIT can be faster than compiled because it has knowledge of the runtime" but in practice that only happens on special cases, and compiled C/C++/Rust still beats its ass. As for the runtime overhead of deferred GC happing "outside of the hot path", and yet every domain with a GC and high load/low latency has historically suffered GC pauses, and GCs have to be reworked to ever more complex byzantine schemes to try to reduce the issue. >*ARC is in fact a GC strategy. E.g. obj-c has autorelease pools that postpone deletion until later, so the hot path doesn't get interrupted if reference count of something reaches zero early. These things are a spectrum. Yes, like cars and 18-wheelers are a spectrum. And C++/Rust is on the other side of that spectrum compared to Java and Go.

bencyoung 3y ago
The worst memory performance bug I ever saw turned out to be heap fragmentation in a non-GC system. There are memory allocators that solve this like https://github.com/jemalloc/jemalloc/tree/dev https://github.com/jemalloc/jemalloc/tree/dev but ... they do it by effectively running a GC at the block level As soon as you use atomic counters in a multi-threaded system you can wave goodbye to your scalability too!
deleted 3y ago
[deleted]
t8sr 3y ago
As you point out, the use of ARC is correlated with languages used in high-performance code. You think it's because ARC is a better way of managing memory, but that's false. Rust is not fast because it uses ARC, it uses ARC because Rust is fast. Rust is fast because it has a good ownership model for memory, because it encourages patterns that mostly get rid of the need to dynamically manage lots of heap objects. These qualities make it cache-friendly, among other things. What's left is generally small enough that even a poor GC strategy like ARC is good enough. A state-of-the-art GC wouldn't be worth the extra complexity in Rust. (And would probably conflict with other features.) Go needs a state of the art GC, because it wants to hide "stack vs heap" from the programmer, and so it puts a lot of things on the heap. If it used ARC, it would be unusable. To people who have worked on programming languages, saying "ARC is good, actually" is either a sign that you're about to present a very nuanced argument informed by decades of experience, or, more likely, that you have no idea what you're talking about. If you're going to make a claim that lies this far outside the mainstream, I'd say the onus to present a good argument is on you, not me. With age, I've found it good to moderate my fervor in proportion to how much I know about a subject. If people learn that you're someone who talks with confidence only about things you know, you'll have an easier time getting them to listen.
- kaba0 3y ago
  > Go needs a state of the art GC It needs, but unfortunately it doesn’t have. That category is won by Java multiple times.
  - t8sr 3y ago
    Interesting - I would be really interested in an apples-to-apples comparison between the two of them, but such a thing must be hard to do. I'd fully expect the amount of investment in JVM to have produced a way better result, but I can't find any good articles about it.
    - kaba0 3y ago
      Not an article, but a good “measuring stick” might be the binary trees benchmark: https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/binarytrees.html https://benchmarksgame-team.pages.debian.net/benchmarksgame/... This one stresses the GC quite a bit (so it doesn’t make much sense for non-managed languages that can “cheat”), and there is only Haskell as a managed language that could get ahead of Java (but it is not really apples to oranges due to the different execution model), and in other’s case it is not even close. Go is particularly bad in this benchmark, though it sort of makes sense as it optimizes for low latency, which is fundamentally at odds with throughput.
      - neonsunset 3y ago
        Also the cost of write barriers. Looking at the benchmark code, it may actually benefit the languages with non-moving, simpler GC implementations because they would have cheaper write barriers or complete lack of thereof. With that said, it's a good demonstration of the quality of OpenJDK HotSpot JIT and GC. This is an area where .NET has still some ways to go - it has precise write barriers but they are not inlined so performance in scenarios bottlenecked by the cost of assigning object reference to a new heap location will vary a lot depending on WKS vs SRV GC and its configuration + exact CPU model and arch being used (more so than regular code). It does, however, use .NET 7 which is a shame.
pjmlp 3y ago
And yet no one is rewriting either Android (outside kernel services) or Kubernetes in C++/Rust. Apparently after the whole WinRT/UWP mess, C++ is now left for writing low level stuff, with everything else on WinUI 3.0/WinAPPSDK being done in C#. Devil May Cry 5 on PlayStation 5 seems to be doing quite alright with Campcon's in-house fork from .NET. So in the end, other than some corner cases where no kind of automated memory management is at all allowed, people will rather take a regular car instead of a F1.

bencyoung 3y ago

The worst memory performance bug I ever saw turned out to be heap fragmentation in a non-GC system. There are memory allocators that solve this like https://github.com/jemalloc/jemalloc/tree/dev https://github.com/jemalloc/jemalloc/tree/dev but ... they do it by effectively running a GC at the block level As soon as you use atomic counters in a multi-threaded system you can wave goodbye to your scalability too!

deleted 3y ago

[deleted]

t8sr 3y ago

As you point out, the use of ARC is correlated with languages used in high-performance code. You think it's because ARC is a better way of managing memory, but that's false. Rust is not fast because it uses ARC, it uses ARC because Rust is fast. Rust is fast because it has a good ownership model for memory, because it encourages patterns that mostly get rid of the need to dynamically manage lots of heap objects. These qualities make it cache-friendly, among other things. What's left is generally small enough that even a poor GC strategy like ARC is good enough. A state-of-the-art GC wouldn't be worth the extra complexity in Rust. (And would probably conflict with other features.) Go needs a state of the art GC, because it wants to hide "stack vs heap" from the programmer, and so it puts a lot of things on the heap. If it used ARC, it would be unusable. To people who have worked on programming languages, saying "ARC is good, actually" is either a sign that you're about to present a very nuanced argument informed by decades of experience, or, more likely, that you have no idea what you're talking about. If you're going to make a claim that lies this far outside the mainstream, I'd say the onus to present a good argument is on you, not me. With age, I've found it good to moderate my fervor in proportion to how much I know about a subject. If people learn that you're someone who talks with confidence only about things you know, you'll have an easier time getting them to listen.

kaba0 3y ago
> Go needs a state of the art GC It needs, but unfortunately it doesn’t have. That category is won by Java multiple times.
- t8sr 3y ago
  Interesting - I would be really interested in an apples-to-apples comparison between the two of them, but such a thing must be hard to do. I'd fully expect the amount of investment in JVM to have produced a way better result, but I can't find any good articles about it.
  - kaba0 3y ago
    Not an article, but a good “measuring stick” might be the binary trees benchmark: https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/binarytrees.html https://benchmarksgame-team.pages.debian.net/benchmarksgame/... This one stresses the GC quite a bit (so it doesn’t make much sense for non-managed languages that can “cheat”), and there is only Haskell as a managed language that could get ahead of Java (but it is not really apples to oranges due to the different execution model), and in other’s case it is not even close. Go is particularly bad in this benchmark, though it sort of makes sense as it optimizes for low latency, which is fundamentally at odds with throughput.
    - neonsunset 3y ago
      Also the cost of write barriers. Looking at the benchmark code, it may actually benefit the languages with non-moving, simpler GC implementations because they would have cheaper write barriers or complete lack of thereof. With that said, it's a good demonstration of the quality of OpenJDK HotSpot JIT and GC. This is an area where .NET has still some ways to go - it has precise write barriers but they are not inlined so performance in scenarios bottlenecked by the cost of assigning object reference to a new heap location will vary a lot depending on WKS vs SRV GC and its configuration + exact CPU model and arch being used (more so than regular code). It does, however, use .NET 7 which is a shame.

pjmlp 3y ago

And yet no one is rewriting either Android (outside kernel services) or Kubernetes in C++/Rust. Apparently after the whole WinRT/UWP mess, C++ is now left for writing low level stuff, with everything else on WinUI 3.0/WinAPPSDK being done in C#. Devil May Cry 5 on PlayStation 5 seems to be doing quite alright with Campcon's in-house fork from .NET. So in the end, other than some corner cases where no kind of automated memory management is at all allowed, people will rather take a regular car instead of a F1.