Proposal: loader instantiation fix/improvement

[sijakret]

Hi Everyone,

When instantiating any real-world module (>4KB) using the loader the following error comes up (at the very least in chrome):

RangeError: WebAssembly.Instance is disallowed on the main thread, if the buffer size is larger than 4KB. Use WebAssembly.instantiate.

This is the code segment that causes the issue (lib/loader/index.js):

/** Instantiates an AssemblyScript module using the specified imports. */
function instantiate(module, imports) {
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    new WebAssembly.Instance(module, imports)
  );
}

If i monkey patch it like below it becomes usable (albeit async)

/** Instantiates an AssemblyScript module using the specified imports. */
async function instantiate(module, imports) {
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    await WebAssembly.instantiate(module, imports)
  );
}

I would assume that this issue will be faced by others..

I see two easy ways to fix it:

1. my patch above
2. export postInstantiate(..) and preInstantiate(..) hooks so users can build costum instantiation flows.

What do you guys think?

[sijakret]

Has no one else encountered this?

[dcodeIO]

Iirc the expectation there was that one would use instantiateStreaming in such a context, but that might not cover every use case. If so, I suggest adding a separate instantiateAsync using your patch.

[sijakret]

I encountered the issue in the context I mentioned above. The reason I suggested option 2 is because it is extremely uninvasive = low risk. Since the instantiate method itself is so high level and simple in flow, just exporting pre.. and post.., would allow for a custom flow there and might be the easiest fix.

[dcodeIO]

Sure, I don't see any issues with exporting these.

[MaxGraey]

Should be fixed in #916