半模对话框 QProgressDialog
http://doc.qt.io/qt-4.8/qprogressdialog.html
progressdialog 用到了qfuture
http://blog.csdn.net/liang19890820/article/details/51067310
QEventLoop *loop = new QEventLoop;
QTimer::singleShot(3000, loop, SLOT(quit()));
loop->exec();
