function multiDownload($urlArray) {

    if (empty($urlArray)) return false;

    

    $isStr = false;

    if (is_string($urlArray)) {

        $urlArray = array($urlArray);

        $isStr = true;

    }

    

    self::log(sprintf("%s Multi thread download begin...", __METHOD__));

    

    $mh = curl_multi_init(); //curl_multi_init --  Returns a new cURL multi handle

    $curlArray = array(); 

    foreach ($urlArray as $i => $url) { 

        self::log(sprintf("%s Download url: |%s|...", __METHOD__, $url));

        $curlArray[$i] = curl_init($url); 

        curl_setopt($curlArray[$i], CURLOPT_RETURNTRANSFER, true); //设置为true表示返回抓取的内容，而不是直接输出到浏览器上。TRUE to return the transfer as a string of the return value of curl_exec() instead of outputting it out directly

        curl_setopt($curlArray[$i], CURLOPT_AUTOREFERER, true); //自动设置referer。TRUE to automatically set the Referer: field in requests where it follows a Location: redirect.

        curl_setopt($curlArray[$i], CURLOPT_FOLLOWLOCATION, true); //跟踪url的跳转，比如301, 302等

        curl_setopt($curlArray[$i], CURLOPT_MAXREDIRS, 2); //跟踪最大的跳转次数

        curl_setopt($curlArray[$i], CURLOPT_HEADER, 0); //TRUE to include the header in the output. 

        curl_setopt($curlArray[$i], CURLOPT_ENCODING, ""); //接受的编码类型,The contents of the "Accept-Encoding: " header. This enables decoding of the response. Supported encodings are "identity", "deflate", and "gzip". If an empty string, "", is set, a header containing all supported encoding types is sent. 

        curl_setopt($curlArray[$i], CURLOPT_CONNECTTIMEOUT, 5); //连接超时时间         

        curl_multi_add_handle($mh, $curlArray[$i]); //curl_multi_add_handle --  Add a normal cURL handle to a cURL multi handle 

    }

     

    $running = NULL;

    $count = 0;

    do { 

        //10秒钟没退出，就超时退出

        if ($count++>100) break; 

        usleep(100000); 

        curl_multi_exec($mh, $running); //curl_multi_exec --  Run the sub-connections of the current cURL handle 

    } while($running > 0);

    

    $content = array(); 

    foreach ($urlArray as $i => $url) {

        $content[$url] = curl_multi_getcontent($curlArray[$i]); //curl_multi_getcontent --  Return the content of a cURL handle if CURLOPT_RETURNTRANSFER is set

    } 

    

    //curl_multi_remove_handle --  Remove a multi handle from a set of cURL handles

    foreach ($urlArray as $i => $url){ 

        curl_multi_remove_handle($mh, $curlArray[$i]); 

    }

    

    //curl_multi_close --  Close a set of cURL handles 

    curl_multi_close($mh);

    

    self::log(sprintf("%s Multi thread download end...", __METHOD__));

    

    //如果参数$urlArray是字符串，则将返回值也转换为字符串

    if ($isStr) $content = implode('', $content);

    

    return $content;

}