WASM Garbage Collection in JSC
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The document discusses the proposal for WebAssembly (Wasm) garbage collection (GC) presented by Asumu Takikawa at the 2023 WebKit Contributors Meeting. It highlights the implementation progress in JSC, the features already developed, and the exciting implications for languages requiring GC support, enabling developers to target Wasm with languages like Java and OCaml. The proposal is at phase 4, indicating that many major browser engines will soon support Wasm GC, broadening its use cases.
WASM Garbage Collection in JSC
- 1. Wasm Garbage Collection in JSC Asumu Takikawa (Igalia) WebKit Contributors Meeting 2023 Photo credit: https://www.pexels.com/@zydeaosika-2261055/
- 3. Wasm is a target language for compiling web programs
- 5. Wasm MVP great for C/C++/Rust programs ● Works well for languages without GC/managed runtimes ● But what about programs in languages needing GC?
- 6. Key missing piece was Wasm support for allocatable memory with GC
- 7. GC Proposal enables those languages ● Supports allocatable data types like structs & arrays ● New kinds of reference types pointing to allocated values ● Type casts & advanced types ● Takes advantage of browser JS engines’ built-in GC +GC https://github.com/WebAssembly/gc/ for the nitty-gritty details
- 8. A concrete example (module (type $s (struct (field $x i32) (field $y i32)) (global (ref $s) (struct.new (i32.const 42) (i32.const 42))) (func $get-x (param (ref $s)) (result i32) (struct.get $s $x (local.get 0)))) New type declaration form
- 9. A concrete example (module (type $s (struct (field $x i32) (field $y i32)) (global (ref $s) (struct.new (i32.const 42) (i32.const 42))) (func $get-x (param (ref $s)) (result i32) (struct.get $s $x (local.get 0)))) Globals can be init with new types
- 10. A concrete example (module (type $s (struct (field $x i32) (field $y i32)) (global (ref $s) (struct.new (i32.const 42) (i32.const 42))) (func $get-x (param (ref $s)) (result i32) (struct.get $s $x (local.get 0)))) New instructions to access GC data
- 11. A concrete example (module (type $s (struct (field $x i32) (field $y i32)) (global (ref $s) (struct.new (i32.const 42) (i32.const 42))) (func $get-x (param (ref $s)) (result i32) (struct.get $s $x (local.get 0)))) Ref types let you reference GC values
- 13. We’re implementing Wasm GC for JSC ● WIP implementation underway ● Most features already implemented ● Should get to shippable state in a few months ��
- 14. What’s implemented & what’s not ✅ Structs/arrays ✅ i31 references ✅ Type hierarchy ✅ Subtyping ✅ Recursive types ✅ Type casts ✅ Locals with non-nullable types ✅ Table initializers *⃣ JS API support 🅾 Bulk array operations 🅾 Misc other missing instructions Plus more testing and optimization! ✅ Done *⃣ Partial 🅾 TODO
- 15. To track our progress: ☂ https://bugs.webkit.org/show_ bug.cgi?id=247394
- 16. ♺ The takeaway
- 17. This is an exciting time for Wasm! ● Other browsers have shipped or will ship Wasm GC soon (the proposal is at phase 4) ● Once JSC also ships, Wasm GC supported in all major browser engines ● Developers can then target Wasm with Java, OCaml, and many more languages to come Future Wasm will likely build further on GC ��
- 18. ♺ Q & A Thanks for listening!