`worker.unref()` doesn't make Node.js process exit depend on where `worker.on('message')` appears about node HOT 4 CLOSED

Marking this as won't fix. Every time the worker receives an event listener it unrefs the internal handle and rewire it again after listeners are set. It unrefs (at first) for graceful shutdown as documented; that seems to be an intended behavior; consider unref the messagePort as shown in #53036 (comment) if you need the worker.unref to unref even after future listeners.

I'll close this issue, but feel free to re open if needed or something.

from node.

w.unref()
w.on('message', () => {})
// ❗️ stuck

Node.js will call w.[kPublicPort].ref() when listen the message event. So the process will not exit.

But i think there is a bug in the follows code.

w.on('message', () => {})
w.unref()
w.on('message', () => {})

It looks like the process won't exit but it does.

1. call w.on('message', () => {}) Node.js will run the follows code.

// size means the number of message listener, here is 0
if (size === 0) {
      port.ref();
      FunctionPrototypeCall(MessagePortPrototype.start, port);
}

2. then call w.unref() Node.js will run port.ref() but the number of message listener is still 1.
3. so when call w.on('message', () => {}) again, Node.js will run the follows code again.

// size is 1, so do nothing
if (size === 0) {
      port.ref();
      FunctionPrototypeCall(MessagePortPrototype.start, port);
}

finally the port is unref so the process exits.

from node.

Yes, @theanarkh is right; the problem here is that the parentPort still opened and listening for events, the handle will remain open.

By modifying the snippet a bit. The issue is gone without stop listening to parentPort messages.

process.once('beforeExit', () => {
  console.log('beforeExit')
})

const { Worker } = require('worker_threads')

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

// w.on('message', () => {}) // <--- enable this line to let Node.js exit

w.unref()

w.on('message', () => {}) // <--- or comment this line to let Node.js exit

from node.

I found a workaround. A possible fix for this.

from node.