QT5's QApplication::setOverrideCursor(Qt::WaitCursor); is blocking the previous operations

Question

In my loadDatabase function, I have clearly set the status to display the message "loading coverage database..." before setOverrideCursor(Qt::WaitCursor), but the status bar is only displaying the message after restoreOverrideCursor() is called. I have tried various ways to display the message before setOverrideCursor(Qt::WaitCursor), but I'm unsure of the reason behind this behavior.

void loadDatabase(const QString &name) {
    //setting statusBar's message
    statusBar()->showMessage("loading coverage database...");

    QApplication::setOverrideCursor(Qt::WaitCursor);
    //loading the database and setting up the GUI are CPU-intensive operations.
    m_logger_widget->clear();
    m_logger_widget->info("opening database %s", name.toStdString().data());
    auto coverage_database = new CoverageDatabase(name, m_logger_widget);
    m_instance_view->setModel(coverage_database->getInstanceModel());
    QApplication::restoreOverrideCursor();
}

I hope to identify the reason why "loading coverage database..." is not displayed and to have it shown before setting the WaitCursor.

Answer 1

Your loadDatabase() function runs in the main GUI thread, it blocks all further GUI updates until it completes.

One possibility is to call the function QCoreApplication::processEvents() after you have set the status message.

https://doc.qt.io/qt-6/qcoreapplication.html#processEvents

However, I would outsource the loading to an asynchronous task/thread. This way you also get the possibility to abort the loading process.