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();

echo uniqid(), PHP_EOL;echo uniqid(), PHP_EOL;

568c83e69c671568c83e69c671

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;

201601063753201601063753

$Idwork = new Idwork(1);echo $Idwork->nextId(), PHP_EOL;echo $Idwork->nextId(), PHP_EOL;$test = new Idwork(1);echo $test->nextId(), PHP_EOL;echo $test->nextId(), PHP_EOL;

$mch = curl_multi_init();for($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;

568c83e69c671568c83e69c671

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;

201601063753201601063753

$Idwork = new Idwork(1);echo $Idwork->nextId(), PHP_EOL;echo $Idwork->nextId(), PHP_EOL;$test = new Idwork(1);echo $test->nextId(), PHP_EOL;echo $test->nextId(), PHP_EOL;

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;