Hi,
I did a sample test for learning thread.I have the follwoing code but for saome reson the wait or busy dialog does not run properly.I have attached a video where you can see dialog initialize hangs https://youtu.be/mjpnrLUx1VI.Here is the sample code:-

Main Window.cpp
Qt Code: 
  1. MainWindow::MainWindow(QWidget *parent) :
  2.     QMainWindow(parent),
  3.     ui(new Ui::MainWindow),m_count(0)
  4. {
  5.     ui->setupUi(this);
  6.  
  7.     QThread* thread = new QThread;
  8.     Worker* worker = new Worker();
  9.     m_dialog = new WaitOrBusyDialog;         //A custom class to busy dialog
  10.  
  11.     worker->moveToThread(thread);
  12.     connect(worker, SIGNAL(error(QString)), this, SLOT(errorString(QString)),Qt::QueuedConnection);
  13.     connect(thread, SIGNAL(started()), worker, SLOT(process()),Qt::QueuedConnection);
  14.     connect(worker,SIGNAL(showDialog()),this,SLOT(onDi  alog()),Qt::QueuedConnection);
  15.     connect(worker, SIGNAL(finished()), thread, SLOT(quit()),Qt::QueuedConnection);
  16.     connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()),Qt::QueuedConnection);
  17.     connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()),Qt::QueuedConnection);
  18.     thread->start();
  19.  
  20. }
  21.  
  22. MainWindow::~MainWindow()
  23. {
  24.     delete ui;
  25. }
  26.  
  27. void MainWindow::onDialog()
  28. {
  29.     m_dialog->show();
  30. }
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WorkerThread.cpp
Qt Code: 
  1. void Worker::process() {
  2.     qApp->processEvents();
  3.     int i=0;
  4.     emit showDialog();
  5.     while(i<10000)
  6.     {
  7.         qApp->processEvents();
  8.         qDebug("Hello World!");
  9.         i++;
  10.     }
  11.     emit finished();
  12. }
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This is just a sample code to know simultanoeusly backgroud (debug output) and ui foreground process.The problem is why initially dialog hangs.