Description
Open the following page in your favorite COI-enabled dev server. The code works in the main thread, but fails in a worker:
<!doctype html>
<html lang="en">
<head>
<title>Polyscript</title>
<script type="module" src="https://cdn.jsdelivr.net/npm/polyscript"></script>
</head>
<body>
<script>
function aFunc(myArray) {
console.log(myArray[0], myArray[1])
}
</script>
<script type="module">
import { XWorker } from "https://cdn.jsdelivr.net/npm/polyscript";
const w = new XWorker("./workertest.py", { type: "pyodide"});
</script>
</body>
</html>import polyscript
f = polyscript.xworker.window.aFunc
print(f([1,2]))Specifically, there error I see is:
pyodide.ffi.JsException: TypeError: 'set' on proxy: trap returned falsish for property 'length'
This (very similar) code runs fine in Pyodide (0.24.1) in the main thread, or in a <script type="pyodide"> tag in PolyScript:
<script type="pyodide">
import js
f = js.aFunc
print(f([1,2]))
</script>Context
First, you might have noticed that grabbing polyscript.xworker.window is basically what PyScript does in magic_js. This is no accident, I was working on getting matplotlib to work in workers in PyScript, but am attempting to follow the issue upstream.
Second: if the issue I was trying to solve was code I controlled, the problem can be solved by manually converting the Python list [1,2] into a JavaScript array inside worker.py.
import polyscript
from pyodide.ffi import to_js
f = polyscript.xworker.window.aFunc
print(f(to_js([1,2])))HOWEVER the original code is not code I control, it's code within the matplotlib-pyodide backend that gets Matplotlib working in the browser, which passes a list to canvas.setLineDash().
From my understanding, the same code Python code should work in the main thread and in workers, generally, with the exception of some dances around some global objects (document, devicePixelRatio, etc) needing to be brought in via xworker. Those exceptions I could figure out, but this one is stumping me.
Finally, as usual, I can't tell if this is an actual "bug" or just something I don't understand about js Proxies. Apologies in advance if it's the latter.