public function capturePage($id = null, $ttl = null, $exit = true)
    {
        if ($id === null) {
            $id = md5(serialize($_SERVER['REQUEST_URI']) . serialize($_REQUEST));
        }

        if ($this->start($id)) {
            if ($exit) {
                exit;
            }
            return true;
        }
        $self = $this;
        register_shutdown_function(function() use ($self, $ttl) { $self->end($ttl); });
        return false;
    }