proposal: wasm: Thread support

[mcjcloud]

Problem

Most browsers (Chrome, FF, Safari, etc.) are shipping with thread support in Wasm. See https://webassembly.org/roadmap.

Based on discussions in #28360 and #28631, this proposal aims to create progress on Wasm thread support in Go. While standardization of threads is still in Phase 2 (with a vote to move to Phase 3 happening later this month), experimental thread support will improve performance for many Go Wasm applications. Wasm is a great tool for performing computationally intensive tasks, but without thread support, it is often more performant to use JavaScript alone.

Proposal

Until standardized, thread support should exist behind the GOWASM environment variable (e.g. GOWASM=threads).

A program using go routines can be compiled using the following:

GOOS=js GOARCH=wasm GOWASM=threads go build -o out.wasm

[seankhliao]

How is this issue different from #28631?

[mcjcloud]

How is this issue different from #28631?

#28631 was not marked as a proposal, I figured filing specifically as a proposal may encourage more progress.

[seankhliao]

A proposal isn't a way to get someone else to do the work, only to accept and approve of work that other people may do.

Duplicate of #28631