Function setupPortReferencing

lib/internal/worker/io.js:211–247

(port, eventEmitter, eventName)

});

function setupPortReferencing(port, eventEmitter, eventName) {
  // Keep track of whether there are any workerMessage listeners:
  // If there are some, ref() the channel so it keeps the event loop alive.
  // If there are none or all are removed, unref() the channel so the worker
  // can shutdown gracefully.
  port.unref();
  eventEmitter.on('newListener', function(name) {
    if (name === eventName) newListener(eventEmitter.listenerCount(name));
  });
  eventEmitter.on('removeListener', function(name) {
    if (name === eventName) removeListener(eventEmitter.listenerCount(name));
  });
  const origNewListener = eventEmitter[kNewListener];
  setOwnProperty(eventEmitter, kNewListener, function(size, type, ...args) {
    if (type === eventName) newListener(size - 1);
    return ReflectApply(origNewListener, this, arguments);
  });
  const origRemoveListener = eventEmitter[kRemoveListener];
  setOwnProperty(eventEmitter, kRemoveListener, function(size, type, ...args) {
    if (type === eventName) removeListener(size);
    return ReflectApply(origRemoveListener, this, arguments);
  });

  function newListener(size) {
    if (size === 0) {
      port.ref();
      FunctionPrototypeCall(MessagePortPrototype.start, port);
    }
  }

  function removeListener(size) {
    if (size === 0) {
      stopMessagePort(port);
      port.unref();
    }
  }
}


class ReadableWorkerStdio extends Readable {