protected function setState(int $state) : bool
    {
        $this->workerState = $state;

        // report idle state to server:
        $this->replySocket->send(json_encode([
            'request' => 'change_state',
            'worker_id' => $this->workerId,
            'state' => $this->workerState
        ]));
        $response = $this->replySocket->recv();
        return ($response === 'ok');
    }