请教一个生成唯一id的算法是否存在重复？

class Idwork{    const debug = 1;    static $workerId;    static $twepoch = 1361775855078;    static $sequence = 0;    const workerIdBits = 4;    static $maxWorkerId = 15;    const sequenceBits = 10;    static $workerIdShift = 10;    static $timestampLeftShift = 14;    static $sequenceMask = 1023;    private static $lastTimestamp = -1;    public function __construct($workId)    {        if ($workId > self::$maxWorkerId || $workId < 0) {            throw new Exception('worker Id can\'t be greater than 15 or less than 0');        }        self::$workerId = $workId;    }    public function timeGen()    {        //获得当前时间戳        $time = explode(' ', microtime());        $time2 = substr($time[0], 2, 3);        $timestramp = $time[1] . $time2;        return $time[1] . $time2;    }    public function tilNextMillis($lastTimestamp)    {        $timestamp = $this->timeGen();        while ($timestamp <= $lastTimestamp) {            $timestamp = $this->timeGen();        }        return $timestamp;    }    public function nextId()    {        $timestamp = $this->timeGen();//1452043798718        if (self::$lastTimestamp == $timestamp) {            self::$sequence = self::$sequence + 1 & self::$sequenceMask;            if (self::$sequence == 0) {                $timestamp = $this->tilNextMillis(self::$lastTimestamp);            }        } else {            self::$sequence = 0;        }        if ($timestamp < self::$lastTimestamp) {            throw new Excwption('Clock moved backwards.  Refusing to generate id for ' . (self::$lastTimestamp - $timestamp) . ' milliseconds');        }        self::$lastTimestamp = $timestamp;        $nextId = sprintf('%.0f', $timestamp) - sprintf('%.0f', self::$twepoch) | self::$workerId << self::$workerIdShift | self::$sequence;        return $nextId;    }}$Idwork = new Idwork(1);$a = $Idwork->nextId();

function get_order_sn(){    mt_srand((double) microtime() * 1000000);    return date('Ymd') . str_pad(mt_rand(1, 99999), 4, '0', STR_PAD_LEFT);}echo get_order_sn();

$mch = curl_multi_init();for($i=0; $i<4; $i++) {  $ch = curl_init('http://localhost/Idwork.php');  curl_multi_add_handle($mch, $ch);}$running = NULL;do {    usleep ( 10000 );    curl_multi_exec ( $mch, $running );} while ( $running > 0 );

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echo uniqid(), PHP_EOL;echo uniqid(), PHP_EOL;function get_order_sn(){    mt_srand((double) microtime() * 1000000);      return date('Ymd') . str_pad(mt_rand(1, 99999), 4, '0', STR_PAD_LEFT);}echo get_order_sn(), PHP_EOL;echo get_order_sn(), PHP_EOL;