[dilyevsky]

I wish they added some way of exporting wasm funcs as well so that they could be called from host. Tinygo wasm target supports both "exports" and "imports". The other thing that is worse compared to tinygo is the generated binary size seems to be about 10x larger. From my brief look at the transpiled .wat printout a lot of included funcs aren't being called anywhere...

[jbrandhorst]

Exports are something we'd like to work on but it turns out it's pretty complicated to reconcile the Go runtime with the WebAssembly environment, especially when there's only a single thread. We'll get to exports as soon as we can but it may require Wasm threads to be stable first.

[dilyevsky]

Just curious what state is it (thread support) in now? I saw wasmtime already supporting some pthread style threads so assumed proposal has already been accepted but it’s super hard to actually figure out what state anything is in with wasm…

[pryz]

The answer is: it's complicated. Which is most of the time the answer in the WASI world.

For this case it's complicated because some runtime supports https://github.com/WebAssembly/threads which mostly contains things like the spec for atomic but not the actual "threads" specs and then some runtimes (i.e wasmtime) also supports https://github.com/WebAssembly/wasi-threads which is one version of the threads. But a new proposal came into play https://github.com/abrown/thread-spawn so ... it's complicated.

[dilyevsky]

Yes, "it's complicated" is very diplomatic way of putting it after like 5+ years...

[fathyb]

Don't know about the server side, but I've been using threads on the browser for ~2 months, I didn't hit any bug specific to it yet. I use it both with Rust (wasmbindgen with async/await) and C (Emscripten with pthread support). HTTPS with some headers is required for `SharedArrayBuffer`.

I still build a single-threaded binary for Firefox, and fallback to it if `SharedArrayBuffer` is `undefined` or if the `WebAssembly.Memory` constructor fails (some iOS devices might throw when `shared` is `true` due to a bug).

[beanjuiceII]

I would like to second that last statement. If anyone knows a good place to keep up with it all I'd appreciate it

[cplli]

Threads are Phase 3

https://github.com/WebAssembly/proposals

You can also check out:

https://webassembly.org/roadmap/

And for Go, the proposal project on Github has many interesting conversations from the devs.

And as a reminder to anyone interested in using Go WASM, it’s experimental and does not come with the same compatibility promise as Go itself:

https://github.com/golang/go/wiki/WebAssembly

[dilyevsky]

Yes it's been in phase 3 for what like 2-3 years at this point (judging by when it landed in browsers)? No eta and no next steps. The tp says they are waiting until "it's stable" so I'm assuming phase 4. It qualifies browser support and "at least one toolchain" criteria[0] (zig) and seems like all the other conditions too except maybe "CG consensus" whatever that means, so for all I know it could take anywhere between tomorrow and in a few years from now...

[0] https://github.com/WebAssembly/meetings/blob/main/process/ph...

[rockwotj]

FWIW we simulate exports by instead having `main` call an imported function that blocks until it's ready to return with the needed data.

So instead of:

`host -> call foo on guest -> return to host`

`host -> call guest main -> call foo on host -> host returns when ready -> guest calls foo when done`

FWIW the scheduler (so goroutines) don't work in go if you're not calling from an main, so anytime you call a custom export then try to use a goroutine you'll get panics.

10x size is about the blowup we see as well. It's also likely to be slower (some of the Tinygo authors said ~20% slowdown compared to tinygo) probably due to the simpler/smaller runtime and LLVM being better at optimizing.

[Seb-C]

The only time I tried wasm in Go, the wasm compiled by the native Go was so slow that the equivalent Javascript was faster. Tinygo produced decent performance however.

[jsd1982]

The go-compiled wasm is also extremely slow compared to tinygo's wasm. Doing simple things like `fmt.Printf()` degraded performance significantly.

[alecthomas]

I wonder if fmt.Printf() in particular is slow due to the CGo transition? Assuming there even is a CGo transition when compiled to WASM...

[jbrandhorst]

There's no CGO involved when compiling to Wasm. The sometimes slow performance is due to the hoops the compiled code has to jump through to support the Go runtime and goroutine preemption on a single thread.

[alecthomas]

I understand there's no CGo specifically, but I'm wondering if the Go runtime when running under WASM still has to manage switching out the goroutine stacks for "WASM stacks" when it's calling out through the WASM VM.

Edit edit: from this comment it sounds like it is, as you say, just the general overhead of managing goroutine stacks. I wonder if TinyGo is more performant.

[1] https://news.ycombinator.com/item?id=37501552

[Patrickmi]

Tinygo runtime don’t have g or m threads that’s why it’s Cgo is zero cost

[viccuad]

I'm also waiting for that :) See https://github.com/golang/go/issues/42372

[dilyevsky]

Yeah there is an escape hatch via js package but it’s annoying