php不重复唯一值怎么实现

<?php

class RequestID{ // class start
 
    
    public static function generateV7(){
        // 使用session_create_id()方法创建前缀
        $prefix = session_create_id(date('YmdHis'));
        // 使用uniqid()方法创建唯一id
        $request_id = strtoupper(md5(uniqid($prefix, true)));
        // 格式化请求id
        return self::fORMat($request_id);
    }
 
    public static function generate(){
        // 创建前缀
        $prefix = self::create_guid(date('YmdHis'));
        // 使用uniqid()方法创建唯一id
        $request_id = strtoupper(md5(uniqid($prefix, true)));
        // 格式化请求id
        return self::format($request_id);
    }
 
    public static function create_guid($namespace = '') {  
        static $guid = '';
        $uid = uniqid("", true);
        $data = $namespace;
        $data .= $_SERVER['REQUEST_TIME'];
        $data .= $_SERVER['Http_USER_AGENT'];
        $data .= isset($_SERVER['LOCAL_ADDR'])?$_SERVER['LOCAL_ADDR']:$_SERVER['SERVER_ADDR'];
        $data .= isset($_SERVER['LOCAL_PORT'])?$_SERVER['LOCAL_PORT']:$_SERVER['SERVER_PORT'];
        $data .= $_SERVER['REMOTE_ADDR'];
        $data .= $_SERVER['REMOTE_PORT'];
        $hash = strtoupper(hash('ripemd128', $uid . $guid . md5($data)));
        $guid = '{' . 
          substr($hash, 0, 8) .
          '-' .
          substr($hash, 8, 4) .
          '-' .
          substr($hash, 12, 4) .
          '-' .
          substr($hash, 16, 4) .
          '-' .
          substr($hash, 20, 12) .
          '}';
        return $guid;
    }
 
    
    private static function format($request_id, $format='8,4,4,4,12'){
        $tmp = array();
        $offset = 0;
        $cut = explode(',', $format);
        // 根据设定格式化
        if($cut){
            foreach($cut as $v){
                $tmp[] = substr($request_id, $offset, $v);
                $offset += $v;
            }
        }
        // 加入剩余部分
        if($offset<strlen($request_id)){
            $tmp[] = substr($request_id, $offset);
        }
        return implode('-', $tmp);
    }
} // class end
 
// 生成10个请求id
for($i=0; $i<10; $i++){
 echo RequestID::generate().PHP_EOL.'<br>';
}