在PHP中并行多次运行函数

Question

    $users = $db->query('SELECT * FROM users ORDER BY RAND() LIMIT '.$limit)->fetchAll();
    foreach($users as $user){
        $cookie = $_SERVER['DOCUMENT_ROOT'].'/data/'.md5($user['id']);
        echo StartFun($id, $type, $cookie);
    }

I want to run StartFun function multiple times in parallel with different values of $cookie, how can i do this?
Please help me for this, i googles to solved this but didn't got any good results.