private function do_raise_php_limits()
    {
        $php_limits = array(
            'memory_limit' => $this->memory_limit,
            'max_execution_time' => $this->max_execution_time,
            'pcre.backtrack_limit' => $this->pcre_backtrack_limit,
            'pcre.recursion_limit' =>  $this->pcre_recursion_limit
        );

        // If current settings are higher respect them.
        foreach ($php_limits as $name => $suggested) {
            $current = $this->normalize_int(ini_get($name));
            // memory_limit exception: allow -1 for "no memory limit".
            if ($current > -1 && ($suggested == -1 || $current < $suggested)) {
                ini_set($name, $suggested);
            }
        }
    }