What's the correct way to share memory between my AssemblyScript module and my JS?

Question

I'm following this code here, trying to share memory between my AssemblyScript code and my JS:

  let aryPtr = instance.exports.allocateF32Array(3);
  let ary = new Float32Array(instance.exports.memory.buffer, aryPtr, 3);

  ary[0] = 1.0;
  ary[1] = 2.0;
  instance.exports.addArray(aryPtr);

And my index.ts:

export function allocateF32Array(length: i32): Float32Array {
  return new Float32Array(length);
}

export function addArray(data: Float32Array): i32 {
  data[2] = data[0] + data[1];
  return data.length;
}

But this results in RuntimeError: memory access out of bounds in addArray. Have I misunderstood how this is supposed to work?

Answer 1

I recommend to use the official loader for such purposes.

On the JavaScript side: (node.js for example)

const fs = require("fs");
const loader = require("@assemblyscript/loader");
const module = loader.instantiateSync(
  fs.readFileSync("optimized.wasm"),
  {}
);
var ptrArr = module.__retain(module.__allocArray(module.FLOAT32ARRAY, [1, 2, 0]));
console.log('length:', module.addArray(ptrArr));

const arr = module.__getFloat32Array(ptrArr);
console.log('result:', arr[2]);

// free array
module.__release(ptrArr);

On the AssemblyScript side:

export const FLOAT32ARRAY = idof<Float32Array>();

export function addArray(data: Float32Array): i32 {
  data[2] = data[0] + data[1];
  return data.length;
}