Discrepancy in Bun vs Node parentPort.on in async context

[rockisch]

What version of Bun is running?

1.1.36

What platform is your computer?

Darwin 22.4.0 arm64 arm

What steps can reproduce the bug?

Create 2 files in the same folder:

a.js

import { Worker } from "node:worker_threads";

const worker = new Worker("./src/b.js", {});
worker.postMessage("");

b.js

import { parentPort } from "node:worker_threads";

parentPort.on("message", () => {
  console.log("received message");
});

while (true) {
  // some sync code...
  await new Promise((r) => setImmediate(r));
}

Run:

bun a.js

What is the expected behavior?

I expect to see the line in the callback being printed. Here's what happens when running this program through Node:

$ node src/a.js
received message

What do you see instead?

The program never prints anything, supposedly because the callback is never called in the first place.

Additional information

If you move the hot loop inside a function, and call it without awaiting it on the top-level code, it seems like the issue 'gets fixed', which leads me to believe Bun is probably treating top-level async/await differently.

As in:

async function a() {
  while (true) {
    // some sync code...
    await new Promise((r) => setImmediate(r));
  }
}
a();