# Core Wasm Proposals and Wasmtime Nick Fitzgerald and Luke Wagner 2024-01-31 <!-- Put the link to this slide here so people can follow --> slides: https://hackmd.io/p/yL4xCgBBT1KcblBKHG1P_A --- # GC https://github.com/WebAssembly/gc Adds user-defined, garbage-collected types to Wasm --- ## GC: Status in Wasmtime ### done: * [x] `wasmparser` * [x] `wat/wast` * [x] `wasm-encoder` * [x] `wasm-smith` --- ## GC: Status in Wasmtime impl owner: fitzgen ### todo: * [ ] "null" GC in wasmtime * [ ] spec tests passing in wasmtime * [ ] embedder API changes * [ ] `wasmtime_runtime::GcInterface` * [ ] the real GC * [ ] component model canonical ABI GC variant? --- # Exception Handling https://github.com/WebAssembly/exception-handling Adds throw/catch-style unwinding to Wasm --- ## Exception Handling: Status in Wasmtime ### done: * [x] `wasmparser` * [x] `wat/wast` * [x] `wasm-smith` * [x] `wasm-encoder` --- ## Exception Handling: Status in Wasmtime impl owner: needed! ### todo: * [ ] bjorn3 has WIP support in Cranelift, maybe? * Unclear if upstreamable * [ ] Design and implement unwinding in Wasmtime and Cranelift * RFC? --- ## Exception Handling Impl Options * Zero-overhead, unwind info tables approach * Swift-style calling convention approach --- # Shared Everything Threads https://github.com/WebAssembly/shared-everything-threads Adds fine-grained sharing of Wasm state (functions, tables, globals, GC objects, etc...) No core `thread.spawn` instruction. `thread.spawn` component model builtin. --- ## Shared-Everything Threads in Wasmtime Challenges: * `vmctx` representation for thread vs instance * is there even a difference? * embedder API * how to represent a thread? * `wasmtime::SharedFunc` and `wasmtime::Func`? * or is `wasmtime::Func` sendable to new stores/instances/what-have-you that represent a thread? * testing? tsan in ci? --- # Stack Switching https://github.com/WebAssembly/stack-switching/ * Add fibers to core wasm (stacks, not threads) * Status * One concrete proposal: * ["algebraic effects"](https://wasmfx.dev) aka "WasmFX" * Implemented in a Wasmtime fork * One less-concrete alternative: * ["bag of stacks"](https://gist.github.com/fgmccabe/afe8bdfdf2ffdc94d69252683f376d15) * More work needed --- ## Stack Switching: in parallel * Adding fibers outside core wasm: * Browser: [JavaScript Promise Integration](https://github.com/WebAssembly/js-promise-integration/blob/main/proposals/js-promise-integration/Overview.md) * Component Model: Preview 3 / native async * Not *dependent* on core stack-switching * But watching to make sure it integrates * Entails much of the "hard work" for runtimes * Useful first steps toward stack-switching --- # Thanks!