Camera class in QThread

[Creatorczyk]

Hi,

I woluld like to implement the Camera class in a separate thread to be able to independently retrieve data from a device and process it in the run() method. Unfortunately, when calling the run() method, the code gets stuck in a loop and won't come out. As a result, I cannot stop the camera with the stop() method. How could I fix that?

camera.h:

class Camera : public QThread
{
    Q_OBJECT
public:
    Camera();
    ~Camera() {}

    void run();
    void stop() { camera_running = false; }

private:
    rs2::config cfg;
    rs2::pipeline pipe;
    rs2::frameset frames;
    bool camera_running;

signals:
    void FrameReady(rs2::depth_frame frame);
};

camera.cpp:

Camera::Camera()
{
    camera_running = true;
  
    cfg.enable_stream(RS2_STREAM_DEPTH,
                      CAMERA::RESOLUTION::DEPTH_WIDTH,
                      CAMERA::RESOLUTION::DEPTH_HIGHT,
                      RS2_FORMAT_Z16,
                      CAMERA::FPS);

    pipe.start(cfg);
}
void Camera::run()
{
    while(!this->isInterruptionRequested())
    {
        try{
            frames = pipe.wait_for_frames();
            rs2::depth_frame depth = frames.get_depth_frame();
           emit FrameReady(depth);
        }
        catch(const rs2::error& e)
        {
            std::cout << "ERROR: " << e.get_failed_function() << "(" <<e.get_failed_args() <<")    "<<e.what()<<std::endl;
        }
    }
}

main.cpp:

QThread cameraThread;
    Camera *camera = new Camera();
    QObject::connect(camera, &Camera::FrameReady, mqttClient, &MqttClient::sendFrame);
    camera->moveToThread(&cameraThread);
    camera->run();
    qDebug()<<"Started";  //Will not be done
    camera->stop(); //Will not be done
    qDebug()<<"Stopped"; //Will not be done

[stryga42]

I think the problem is that you call run directly from your GUI thread - this is a simple (blocking) call, not the start of a new thread. You should call start() on your camera object, I guess.
Edit: Your have two QThread objects - cameraThread and camera (which is derived from QThread) why? You mix the two options to use QThread (moving a worker object to QThread or reimplementing QThread::run(). )

[Creatorczyk]

@stryga42 If I change the inheritance from QThread to QObject, nothing will change

[Christian Ehrlicher]

@Creatorczyk Since you don't start the thread anywhere nothing happens.

[Creatorczyk]

@Christian-Ehrlicher I change code in main.cpp to:

QThread cameraThread;
    Camera *camera = new Camera();
    QObject::connect(camera, &Camera::FrameReady, mqttClient, &MqttClient::sendFrame);
    camera->moveToThread(&cameraThread);
    cameraThread.start();
    camera->run();
    qDebug()<<"Started";   //Will not be done
    camera->stop();   //Will not be done
    qDebug()<<"Stopped";   //Will not be done

Unfortunately nothing happened. Futher code does not execute

[Christian Ehrlicher]

@Creatorczyk Again: you don't start your thread anywhere, you just call a function named run() in your Camera object - nothing more.

[Creatorczyk]

@Christian-Ehrlicher calling "cameraThread.start();" will not start thread?

[Christian Ehrlicher]

@Creatorczyk It will, but then you call a blocking function in your main thread.

[stryga42]

@Creatorczyk

cameraThread.start();

is the right thing to do. Yes, this starts a new thread "within" the object cameraThread. This call to start() does not block. Check it it out by inserting a qDebug() output right after the call.
But then you call (unnecessarily) Camera::run(), which will block. Use signals to "trigger" your camera object. Again, I think you mix up the two ways to use QThread: Usually you EITHER use the "moveToTrhread-style" OR the "reimplement QThread::run-style", but not both at the same time. If you want your code in Camera::run() to be executed without signaling, you have to call start() on your (then QThread derived) Camera object. Som thing like

camera->start();

should do the job. cameraThread is then not required at all.

[jsulm]

@Creatorczyk said in Camera class in QThread:

calling "cameraThread.start();" will not start thread?

Did you read https://doc.qt.io/qt-5/qthread.html#start ?
start() calls run() - you do not have to call run() by yourself and you should NOT!

[Creatorczyk]

@stryga42 @Christian-Ehrlicher @jsulm Thanks, I fixed it!