nodejs/test/parallel/test-worker-ref.js

'use strict';
const common = require('../common');
const { Worker } = require('worker_threads');

// Test that calling worker.unref() leads to 'beforeExit' being emitted, and
// that we can resurrect the worker using worker.ref() from there.

const w = new Worker(`
const { parentPort } = require('worker_threads');
parentPort.once('message', (msg) => {
  parentPort.postMessage(msg);
});
`, { eval: true });

process.once('beforeExit', common.mustCall(() => {
  console.log('beforeExit');
  w.ref();
  w.postMessage({ hello: 'world' });
}));

w.once('message', common.mustCall((msg) => {
  console.log('message', msg);
}));

w.on('exit', common.mustCall(() => {
  console.log('exit');
}));

w.unref();