关于多个进程无法产生随机数问题

     function getNonceStr($length = 32) 
    {
        $chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
        $str ="";
        for ( $i = 0; $i < $length; $i++ )  {  
            $str .= substr($chars, mt_rand(0, strlen($chars)-1), 1);  
        } 
        return $str;
    }

$consumer->onWorkerStart = function($consumer)
{
    \Workerman\Lib\Timer::add(0.5, function() use ($consumer){
        while(1)
        {           
            echo getNonceStr();         
        }               
    });
};