Hanging when using `MessagePort` from ES customization hooks via `--import`

[elliotgoodrich]

Version

v21.1.0

Platform

Microsoft Windows NT 10.0.22631.0 x64

Subsystem

No response

What steps will reproduce the bug?

Running node --import ./bootstrap.mjs ./index.mjs will hang with the following code.

// hooks.mjs
export async function initialize({ port }) {
  port.postMessage('initialize');
}

// bootstrap.mjs
import { register } from 'node:module';
import { MessageChannel } from 'node:worker_threads';

const { port1, port2 } = new MessageChannel();

port1.on('message', (msg) => {
  console.log(`msg = ${msg}`);
});

register('./hooks.mjs', {
  parentURL: import.meta.url,
  data: { port: port2 },
  transferList: [port2],
});

// index.mjs
console.log('Hello World');

How often does it reproduce? Is there a required condition?

Reproducible 100% of the time.

What is the expected behavior? Why is that the expected behavior?

For node to print

$ node --import ./bootstrap.mjs ./index.mjs
msg = initialize
Hello World

and return normally.

What do you see instead?

node hangs, but prints the expected to the console

$ node --import ./bootstrap.mjs ./index.mjs
msg = initialize
Hello World

Additional information

node returns normally and no longer hangs if

1. port.close() is added after port.postMessage('initialize');,
2. or, removing the call to port1.on('message', ...)

This code was taken and simplified from the example in the documentation here https://nodejs.org/api/module.html#initialize.