public function join()
    {
        while (true) {
            $finished = true;
            foreach ($this->processes as $pid => $process) {
                if ($process->isAlive()) {
                    $finished = false;
                    break;
                }
            }

            if ($finished) {
                break;
            }

            unset($finished);
            usleep(10000);
        }
    }