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by kaba0 636 days ago
I did write ‘simple’, but obviously meant simpleR. A performant runtime will still require considerable complexity. Also, C# doesn’t underperform, I never said that — partially as the whole platform has access to lower level optimizations that avoid allocating in the first place, as you mention (but Span et alia does make the language considerably more complex than Java - which was my point).

But on the GC side it quite objectively has worse throughput than Java’s, one very basic data point would be the binary tree benchmark on benchmark games. This may or may not be a performance bottleneck in a given application, that’s besides the point. (As an additional data point, Swift is utterly bad on this benchmark finishing in 17sec, while java does in 2.59 and C# in 4.61), due to it having reference counting GC, which has way worse throughput than tracing GCs). But you are the one who already linked to this benchmark on this thread, so you do know it.
1 comments
neonsunset 636 days ago
Do Go slices make it more complex? :)

Span<T> makes the language simpler from both the user and C# to IL bytecode point of view, all the complexity is in the runtime (well, not exactly anymore - there's ref T lifetime analysis now). On that note, Java does not seem to have a generic slice type, like ArraySegment<T> which predates spans. I can see it has ByteBuffer, CharBuffer, IntBuffer, AbstractEnterpriseIntProviderFactoryBuffer (/s), etc from NIO as well as sub-Lists(?) and using Streams in the style of LINQ's Skip+Take.

Spans are very easy to use, and advertising them as advanced type was a short-lived mistake at their inception. Since then, they have gotten adopted prominently throughout the ecosystem.

After all, it's quite literally just

  var text = "Hello, World!".AsSpan();
  var hello = text[..text.IndexOf(','));
  var twoChars = hello[..2];
And, to emphasize, they transparently work with stack buffers, arrays, unmanaged memory and anything in-between. You can even reference a single field from an object:

    var user = (Name: "John", DoB: new DateTime(1989, 1, 1));
    ProcessStrings(new(ref user.Name));

    // Roslyn emits an inline array struct, from which a span is constructed
    // It's like T... varargs in Java but guaranteed zero-cost
    // In C# 13, this gets support of params so many existing callsites
    // that used to be params T[] start accepting spans instead,
    // completely eliding allocations or even allowing the compiler
    // to reference baked into binary constant arrays
    ProcessStrings(["hello", "world"]);

    void ProcessStrings(Span<string> values) { /* ... */ }
On binary-trees - indeed, the results are interesting and Java demonstrates consistently lower CPU time cost to achieve similar or higher throughput (look at benchmark results distribution). It is a stress-test for allocation and collection throughput, yes. However, Java benchmarks also tend to consume consistently more memory even in allocatey scenarios: https://benchmarksgame-team.pages.debian.net/benchmarksgame/...

In any case, I have asked around for more data on detailed comparison of heap profiles between G1, Zgc and Parallel and will post them here if I get a response to provide more context. It's an interesting topic.

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