// 结束一个下载任务,归还并发数
        public void FinishDownloadTask(DownloadInfo info)
        {
            info.isFinished = true;

            if (info.onComplete != null)
            {
                info.onComplete(info);
            }

            m_DownloadingTasks.Remove(info.fileName);
            --downloadThreads;
        }