Running a WASI program as a web worker with stdio as messages?

[coolreader18]

At first, it seems like it'd be natural to map WASI processes and stdio to the browser with wasmer/wasi and workers and postMessage passing, but I can't seem to get it to work in practice due to the need for fd_read to be synchronous, and the fact web workers can't block (e.g. with while (true) {}) while waiting for a message to be sent, since control can't be yielded to the event loop. Does anybody have any ideas for implementing something like this, or is this basically impossible? (without widespread SharedArrayBuffer support)

[caspervonb]

Continuations, which aren't a thing right now but I think @rossberg is working on a proposal for stack switching as I remember a talk about it but can't find the link video right now.

Until then, you can use a transform like @kripken's asyncify to wind/unwind and rewind the stack.

[kripken]

Asyncify is definitely meant for this, as @caspervonb said. It's designed to run on any wasm file. You would need support on the JS side too, though (not sure if wasmer-js that was mentioned has that; in emscripten there is a PR).

[coolreader18]

Great, thank you! I'll look into asyncify; it seems like I would need to fork wasmer-js/wasi.

[caspervonb]

Stumbled across the talk I was referring to earlier: Evolving WASM into a proper misnomer, stack switching is at around 55 minutes in.

[sunfishcode]

The question here seems answered; please reopen or file new issues if there's any followup!