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Comment by pushtheenvelope | Hacker News Reader

I'm curious how they solve garbage-collection, since last time I checked WebAssembly doesn't yet support that?

Hi, asterius main dev here. Garbage collection support is near; we're working actively on it, and after a few regressions are fixed it'll be available on master.

It'll be a copying GC, with builtin support to automatically free unused JavaScript references in the Haskell heap. It's also possible to plug in more fancy gc algorithms later (e.g. generational, or concurrent ones with read barriers).

To be clear, this will be your own GC bundled with each application, not an interface to the host browser's GC?

Indeed it's not an interface to the browser's gc.

There does exist a wasm anyref proposal which enables manipulating opaque references in wasm and a gc proposal for further allocating/using such garbage collected objects. However, basing our gc on those is currently less pragmatic than rolling our own :)

The consensus of "the same way they do in native code" is a probable approach, but it's worth calling out an additional complication in this setting: you might wind up working with two garbage collectors, with references in one keeping objects in the other alive. This isn't intractable, but it is messy.

Yes, like the IE memory leaks (and early Mozilla leaks) where DOM and JavaScript objects are collected in a different way, so can easily get stuck in unfreeable reference cycles.

Old Frameworks have to do perverse things to break those cycles, and if they don't, the browsers leaked memory over time.

It would be sad if that came back to modern browsers, due to WASM and DOM using separate collectors. Or worse, multiple WASM components, (perhaps in different languages, perhaps not, but all different collectors), holding indirect, accidental references to each other because someone decided to use the components in the same DOM.

So far they use the "don't" approach to garbage collection. It would have to be implemented.like the rest of the rts.

I guess parts of the c code could be transpiled but something low-level like the gc relies on details like register pinning.

C and ASM don't have a GC either, and yet we can build GC collected languages on top of them. So it will be eventually be solved in the same fashion: By building a runtime environment on top of the underlying machine, which performs memory management incl. garbage collection.

Depending on how the runtime for "native Haskell" is implemented, the effort might be everything from just cross-compile it to building a completely separate runtime.

In assembly language, you can build an accurate garbage collector for your assembly language application. There are no hidden "not user servicable" areas in the run-time, like in C. You can set up your calling and framing conventions so the GC can trace the stack and know exactly where the root pointers are.

Most likely the same way as in any hardware CPU without support for GC memory tagging.

What is hw support for GC mem tagging? I didnt realize such a thing existed.

It's something that has been researched, but not deployed. It would implement GC memory tagging in the CPU or even the memory controller. Google Scholar should produce some good hits.

Surely it was deployed, in the original Lisp Machines hardware.

Right. I forgot about those.

It existed on Lisp machines.

https://en.wikipedia.org/wiki/Lisp_machine

"Lisp Hardware Architecture: The Explorer II and beyond"

https://3e8.org/pub/scheme/doc/lisp-pointers/v1i6/p13-dussud...

"Garbage collection in a large LISP system"

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.125....

"KIM 20 : A SYMBOLIC RISC MICROPROCESSOR FOR EMBEDDED ADVANCED CONTROL "

https://www.computer.org/csdl/proceedings/easic/1990/2066/00...

The failed iAPX 432 processor from Intel also supported it.

https://en.wikipedia.org/wiki/Intel_iAPX_432#Garbage_collect...