QThread - QThread::wait() does not terminate

strenkwalder

I have a fairly simple QThread class that causes me quite some headaches. I assume it is something super obvious that I'm just missing.
I'm using Qt 5.8 on Ubuntu with normal gcc toolchain.

I have a simple OpenCV video feed capturing QThread:

class VideoCaptureThread : public QThread
{
    bool terminating;
    int id;
    VideoBuffer *buffer;

public:
    VideoCaptureThread(int camID = 0, VideoBuffer *b = 0);
    virtual ~VideoCaptureThread();

    // QThread interface
protected:
    void run() override;

public slots:
    void stopCapuring();
    void setID(int);
    void setBuffer(VideoBuffer *);
};

with:

VideoCaptureThread::VideoCaptureThread(int camID, VideoBuffer *b) :
    terminating(false),
    id(camID),
    buffer(b)
{}

VideoCaptureThread::~VideoCaptureThread(){
    cv::destroyWindow("CaptureThread Test");
    terminating = true;

    this->quit(); //I tried exit(0) or terminate() as well
    this->wait(); //Wait always blocks
}

void VideoCaptureThread::run(){

    //This all works fine
    cv::VideoCapture video(id);
    cv::Mat frame;

    while(!terminating && video.isOpened() && buffer != 0){

        video >> frame;

        cv::imshow("CaptureThread Test",frame);

        buffer->addFrame(frame);
        qDebug() << buffer->size();

        QCoreApplication::processEvents();
    }
}

void VideoCaptureThread::stopCapuring(){ terminating = true; }
void VideoCaptureThread::setID(int i){ id = i; }
void VideoCaptureThread::setBuffer(VideoBuffer *b){ buffer = b; }

I call this by:

    VideoCaptureThread *capThread = new VideoCaptureThread( 0, &vBuffer);
    connect(this,SIGNAL(stopCapturing()), capThread, SLOT(deleteLater()));

    //alternatively I tried -> (but this caused SigSeg .. in my main() -> a.exec() <--- QApplication
    //connect(this,SIGNAL(stopCapturing()), capThread, SLOT(stopCaputing()));
    //connect(capThread,SIGNAL(finished()),capThread,SLOT(deleteLater()));
    
    capThread->start(QThread::HighestPriority);

When I use all this, my application gets stuck at ~VideoCaptureThread (this.wait()).
This is such a simple thread. But I still can't see the problem.

I would appreciate your help.

SGaist

Hi,

Quit will only work if run start's the thread event loop which is not your case.

You are using a loop so you have to exit that loop for your thread to end which you do in the second line of your destructor.

Gojir4

This post is deleted!

VRonin

Please see this thread from that point onward. You fell in the same misconceptions about QThread as that user. In your case you even have things like void VideoCaptureThread::setBuffer(VideoBuffer *b){ buffer = b; } as public which is a ticking time bomb.

P.S.
cv::imshow creates a window if I'm not mistaken and it should not be done in a secondary thread (on Windows your app would crash straight away)