QT how to restart a thread?

Question

How to properly restart a QThread? I have been googling this four hours and can't find any concrete answer.

What I have is the basic moveToThread implementation:

VideoHandler::VideoHandler()
{
    VideoBurner *videoBurner = new VideoBurner;
    videoBurner->moveToThread(&videoBurnerThread);

    connect(this, &VideoHandler::signalVideoData, videoBurner, &VideoBurner::setVideoData);
    connect(this, &VideoHandler::signalVideoBurn, videoBurner, &VideoBurner::initVideoBurn);

    // don't really want it since there is only 1 object
    //connect(&videoBurnerThread, &QThread::finished, videoBurner, &QObject::deleteLater);

    connect(videoBurner, &VideoBurner::burnProcess, this, [=](QString step, int percentage){
        emit burningProcess(step, percentage);
    });
}

This is the declaration of my Class:

class VideoHandler : public QObject
{
    Q_OBJECT
    QThread videoBurnerThread;
... 
bunch of defintions
...
}

The VideoBurner class is also a subclass of QObject

class VideoBurner : public QObject
{
    Q_OBJECT
...
bunch of definitions
...
}

For the first run this works perfect, signals and slots all work. The issue happens when I want to "cancel" the thread. For example it is working on some "heavy" calculation that I want to stop from the main thread so I call: videoBurnerThread.quit(); with a cancel function from VideoHandler.

I don't wait() on it as it would block the main thread.

quit() triggers &QThread::finished, but I commented out that connection as it destroys my only object instance.

(also I can't find any example that creates an object and puts it on a thread outside a constructor, if that's even possible? when I tried the app would just close without errors)

I found that the quit() only stops the event loop, not doing anything besides that, which leads to the issue of restarting the tread.

After I want to do the "heavy" stuff again, and I call videoBurnerThread.start(); to start it again, I get results of last performed function from VideoBurner and some signals from it, before it actually starts doing what it should.

Can I somehow stop whatever it was working on and just restart it? I tried sending an "abort" signal from VideoHandler so it doesn't emit signals, but that didn't work.

Do I absolutely need the &QObject::deleteLater so it stops? If so, how to reinitialize VideoBurner correctly inside some function and reconnect it's signal/slot?

Also there is no logic in VideoBurner destructor just a public: virtual ~VideoBurner(){};, could this be an issue?

QT how to restart a thread?

0 Answers