code: func unregisterCallback(cbArg *callbackArg) {
  	callbacksLock.Lock()
  	defer callbacksLock.Unlock()
  	if _, ok := callbacks[cbArg.id]; !ok {
  		panic(fmt.Sprintf("Callback ID %d not registered", cbArg.id))
  	}
  	delete(callbacks, cbArg.id)
  }
docs: // unregisterCallback unregisters a callback.