private function startProgressBars(BufferedOutputInterface $output)
    {
        // Start and display the progress bars.
        foreach ($this->processes as $processInfo) {
            $processInfo['progressBar']->start();
            $output->write("\n");

            // Set the current index. For simplicity we overwrite the value each time.
            $this->currentIndex = $processInfo['index'];
        }
    }