Node.js worker_threads with MessageChannel clogging up

main.js

const { MessageChannel, Worker } = require('worker_threads');

const worker = new Worker('./worker.js');
const benchmarkChannel = new MessageChannel();
worker.postMessage({ port: benchmarkChannel.port2 }, [ benchmarkChannel.port2 ]);

(function run() {
  for (let i = 0; i < 1000000; i += 1) {
    benchmarkChannel.port1.postMessage('hello world');
  }
  setImmediate(run);
})();

worker.js

const { parentPort } = require('worker_threads');

const ports = [];
let messageCount = 0;
parentPort.on('message', function({ port }) {
  ports.push(port);
  port.on('message', function() {
    messageCount += 1;
  });
});

setInterval(() => console.log('total messages: %d', messageCount), 1000);