public function append()
    {
        if (!$this->hasMultiHandle()) {
            $this->setMultiHandle(curl_multi_init());
        }

        // init
        $this
            ->initOption()
            ->buildBody();

        $curl = curl_init();
        curl_setopt_array($curl, $this->getOptions());
        curl_multi_add_handle($this->getMultiHandle(), $curl);

        $this->curls[] = $curl;
    }