/**
* 初始化 CURL
*
*/
public static function init()
{
if (!is_resource(self::$ch)) {
self::$ch = curl_init();
curl_setopt(self::$ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt(self::$ch, CURLOPT_CONNECTTIMEOUT, self::$timeout);
curl_setopt(self::$ch, CURLOPT_HEADER, false);
curl_setopt(self::$ch, CURLOPT_USERAGENT, "phpspider-requests/" . self::VERSION);
curl_setopt(self::$ch, CURLOPT_TIMEOUT, self::$timeout + 5);
// 在多线程处理场景下使用超时选项时，会忽略signals对应的处理函数，但是无耐的是还有小概率的crash情况发生
curl_setopt(self::$ch, CURLOPT_NOSIGNAL, true);
}
return self::$ch;
}