QtConcurrent::run for loading HTML page crashes app

[MH24]

Hello,

I have been trying for several days to speed up the load process of an HTML file from disk. using Qt6.5.1 on Ubuntu 22.04LTS and Qt Creator 10.0.2.

In mainwindow.h I define:

QWebEnginePage *page = new QWebEnginePage(); //as a public object

private:
void workerFunction();

In constructor of mainwindow.cpp this is the relevant code:

ui->setupUi(this);
QFuture<void> t1 = QtConcurrent::run([this](){

qDebug()<<"In thread";
workerFunction();
});
connect(page,SIGNAL(loadFinished(bool)),this,SLOT(readPage(bool))); //couldn't get QWebEnginePage::loadFinished(bool) to work //so using the ancient SIGNAL/SLOT

And the workerFunction() is defined:

void MainWindow::workerFunction(){
page->load(QUrl("qrc:/html_page.html"));

}

readPage(bool) is a slot where html is parsed and ui is set so I keep this away from the separate thread.

The app however crashes. I have tried many variants of QConcurrent::run, but they always gave errors. This doesn't give errors but it crashes.
I tried QFuture<void> t1 = QtConcurrent::run(workerFunction); with extern added before void in definition of function as per official documentation. It said Reference to non-static member function must be called..., so I ditched it and tried:

QThreadPool pool;
QFuture<void> t1 = QtConcurrent::run(&pool, workerFunction);

which is also from official docs and got same error as above. I tried creating a worker class as per this answer but it also crashed. I used t1.waitForFinished() but it also gives same error.
If I just have a qDebug() in lambda function it runs fine. As soon as I add page->load... it crashes.

How do I use concurrency and threads to speed up my page load (if not parsing) from disk?

[Christian Ehrlicher]

You must not access gui elements from outside the main (gui) thread and there is no need since QWebEnginePage::load() is asynchronous (like all such functions).

[MH24]

@Christian-Ehrlicher Okay thank you. But how do I speed the loading up? File is just 50KB. I load it, parse the HTML and display on listWidget on UI. On 16GB RAM ubuntu it loads well (could be better), but on Windows 11 with 8GB RAM, it takes a few seconds.

[Christian Ehrlicher]

@MH24 I don't know but a thread will (when it would work) also not speed it up.