public function index()
    {
        $t1   = microtime(true);
        $data = $this->testRange(10000);
        foreach ($data as $file) {
            fputs($file, "Hello World!");
            fclose($file);
        }
        $t2   = microtime(true);
        $tips = "運行時長：" . round(($t2 - $t1), 3) . 's';
        var_dump($tips);
    }

    protected function testRange($len)
    {
        $public = public_path() . "";
        for ($i = 1; $i <= $len; $i++) {
            yield fopen($public . "test_" . $i . ".txt", "w");
        }
    }