Comment by josephg

Comment by josephg 10 hours ago

It’s not a prerequisite for using the DOM from wasm.

See, for example, the rust web frameworks of leptos and dioxus. They’re honestly great, and usable today as replacements for react and friends. (With the single caveat that wasm bundle size is a bit bigger than .js size).

They work by exposing a number of browser methods through to wasm, and then they call them through a custom wasm/JS API bridge. All rust objects and DOM objects are completely isolated. Rust objects are allocated via an embedded malloc implementation and JS objects are managed by V8 (or whatever). but the DOM can still be manipulated via (essentially) message passing over an RPC like interface.

But the rust code needs to compile malloc specially for wasm. This is ok in rust - malloc is 75kb or something. But in languages like C#, Go or Python, the runtime GC is much bigger and harder to fit in a little wasm bundle.

The upside of wasm-gc is that this divide goes away. Objects are just objects, shared between both languages. So wasm bundles can use & reference JS/DOM objects directly. And wasm programs can piggyback on V8’s GC without needing to ship their own. This is good in rust, and great in GC languages. I saw an example with blazor where a simple C# wasm todo app went from 2mb or something to 10kb when wasmgc was used.

TLDR: wasm-gc isn’t strictly needed. You can use DOM from wasm today. It just makes wasm bundles smaller and wasm-dom interaction easier (and theoretically faster).

weinzierl 2 hours ago

That's why I wrote direct DOM access above. Sure, we can load extra JS in an addition to WASM and and funnel everything through JS. Some say, it does not matter.

I think it does, but it is hard to track the initiatives that tackle this. That's why I'm asking.

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flohofwoe 2 hours ago

WASM-GC is essentially a way to hook into an externally provided garbage collector, it doesn't help much with calling into web APIs.
The DOM has been designed as a JS API (for better or worse), accessing that from WASM will always require to go through some FFI layer (this layer may be hidden and automatically created at runtime, but it still needs to exist).
The question is just how much marshalling needs to happen in that FFI layer. Making the DOM (or other Web APIs) actually WASM friendly would require an alternative DOM API which looks more like a very low-level C API - e.g. not using Javascript objects/strings at all, but only numbers, some of them 'pointers' into an ArrayBuffer (e.g. the WASM heap).
There's also a middle-way of adding such 'garbage free' functions to web APIs which allow to be called with less overhead in the JS engine, for instance WebGPU has such functions, and they were specifically added to reduce marshalling and GC overhead when called from WASM.
E.g. GC-free Web APIs would be much more useful than GC support in WASM for interacting with the browser side. GC support in WASM is mainly useful for languages that depend on garbage collection, because those can delegate the GC runtime tasks to the JS engine's garbage collector.

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- weinzierl 15 minutes ago
  
  If I remember correctly one reason for the direct DOM initiative been held was that it depended on the WASM GC being completed.
  "The DOM has been designed as a JS API (for better or worse), accessing that from WASM will always require to go through some FFI layer (this layer may be hidden and automatically created at runtime, but it still needs to exist)."
  I don't see that. The DOM is the underlying data structure and what we need is direct access to it form WASM, without FFI or going through JS. WASM should be a first class citizen next to JS.
  
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geokon 7 hours ago

Out of curiosity, why is malloc 75kb ? That seems like an crazy amount of code (if this after linking and dead code removal for platform specific magic?)

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kvdveer 2 hours ago

Malloc can indeed be implemented in a handful of bytes, but that's nog going to perform well.
Doing malloc well is actually quite a bit of work. You need to group allocations by size, manage alignment, request and release pages from the OS/browser implement reallocate, etc. A typical malloc implementation is actually a combination of several different allocation strategies.

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- flohofwoe 2 hours ago
  
  The best solution is to reduce the amount of alloc/free calls in your code, then you can just as well use a slow-and-small allocator like emmalloc since allocator overhead doesn't matter anymore: https://github.com/emscripten-core/emscripten/blob/main/syst...
  (e.g. if memory management overhead shows up in the profiler, the proper solution is not to go looking for a faster general-purpose allocator, but to reduce the amount of calls into the allocator)
  
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quotemstr 10 hours ago

Wasm GC also solved the problem of reference cycles between objects in disparate heap managers leading to memory leaks. It's not just a performance or size win: it's a correctness win.

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