How to send message to multiple threads from another one?

Question

I have a worker which creates MessageChannel and sends one of ports to main thread

// worker1.js
const { parentPort, MessageChannel } = require('worker_threads');

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

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

parentPort.postMessage(port2, [port2]);

Second type of worker just receive MessagePort and send data into port

// sub_worker.js
const { parentPort, MessageChannel } = require('worker_threads');

parentPort.on('message',  (port) => {
  port.postMessage('some data')
});

Main thread code

// main thread
const { Worker } = require('worker_threads');

const mw = new Worker('worker1.js');
mw.on('message', (port) => {
  for (let i = 0; i < 5; i++) {
    const w = new Worker('sub_worker.js');
    w.postMessage(port, [port]);
  }
})

The problem is error when I send one channel to multiple workers.

Error text: DataCloneError: MessagePort in transfer list is already detached

Answer 1

If anybody else is coming across this problem: it's not possible to do it the way you are trying. A channel is a one to one link between threads. So you've got two choices:

1. Set up multiple channels, one per worker, and the main thread needs to post a message to each work individually
2. Use a Broadcast channel. This is currently experimental.