Restart a QThread

[jefftee]

Once you fix the shadow variable issue that @anda_skoa pointed out, you'll need to redo your connects after you've created the new workerThread, it is a new instance, etc.

[P51D]

Sorry, my fault. Off course it is not a local member...

For better understanding I have here the code (sry, this should be the first thing when asking for help).

Main window

class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
public slots:
    void update_detection_lb();
    void Streaming();
 
private:
    Ui::MainWindow *ui;
 
    // UHD backround worker thread
    workerThread *backgroundWorker;
};
 
 
 
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    backgroundWorker = NULL;
    backgroundWorker = new workerThread;
    //Setup callback for cleanup when it finishes
    connect(backgroundWorker, SIGNAL(finished()), backgroundWorker, SLOT(deleteLater()));
 
    // Setup signal slot connections
    connect(ui->StartStopStreaming_pb, SIGNAL(clicked()), this, SLOT(Streaming()));
    connect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
 
}
 
 
void MainWindow::Streaming()
{
    if(ui->StartStopStreaming_pb->text() == "Start streaming")
    {
        ui->StartStopStreaming_pb->setText("Stop streaming");
 
        if(backgroundWorker == NULL)
        {
            backgroundWorker = new workerThread;
            connect(backgroundWorker, SIGNAL(finished()), backgroundWorker, SLOT(deleteLater()));
            connect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
        }
        backgroundWorker->start(QThread::HighestPriority);
 
        std::cout << "Start streaming in background thread" << std::endl;
    }
    else{
        ui->StartStopStreaming_pb->setText("Start streaming");
 
        backgroundWorker->requestInterruption();
        if(!backgroundWorker->wait(5000))
        {
            std::cout << boost::format("Thread deadlock detected, bad things may happen!") << std::endl;
            backgroundWorker->quit();
            backgroundWorker->wait();
        }
        std::cout << "Stop streaming and terminate background thread" << std::endl;
        delete backgroundWorker;
    }
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

public slots:
    void update_detection_lb();
    void Streaming();

private:
    Ui::MainWindow *ui;

    // UHD backround worker thread
    workerThread *backgroundWorker;
};




MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    backgroundWorker = NULL;
    backgroundWorker = new workerThread;
    //Setup callback for cleanup when it finishes
    connect(backgroundWorker, SIGNAL(finished()), backgroundWorker, SLOT(deleteLater()));

    // Setup signal slot connections
    connect(ui->StartStopStreaming_pb, SIGNAL(clicked()), this, SLOT(Streaming()));
    connect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));

}


void MainWindow::Streaming()
{
    if(ui->StartStopStreaming_pb->text() == "Start streaming")
    {
        ui->StartStopStreaming_pb->setText("Stop streaming");

        if(backgroundWorker == NULL)
        {
            backgroundWorker = new workerThread;
            connect(backgroundWorker, SIGNAL(finished()), backgroundWorker, SLOT(deleteLater()));
            connect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
        }
        backgroundWorker->start(QThread::HighestPriority);

        std::cout << "Start streaming in background thread" << std::endl;
    }
    else{
        ui->StartStopStreaming_pb->setText("Start streaming");

        backgroundWorker->requestInterruption();
        if(!backgroundWorker->wait(5000))
        {
            std::cout << boost::format("Thread deadlock detected, bad things may happen!") << std::endl;
            backgroundWorker->quit();
            backgroundWorker->wait();
        }
        std::cout << "Stop streaming and terminate background thread" << std::endl;
        delete backgroundWorker;
    }
}

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Worker thread

class workerThread : public QThread
{
    Q_OBJECT
 
public:
    workerThread();
    ~workerThread();
 
protected:
    void run();
 
signals:
    void finished();
    void FrameReady();
 
private:
 
    // UHD member
    uhd::usrp::multi_usrp::sptr usrp;
    uhd::rx_streamer::sptr rx_stream;
};
 
 
workerThread::workerThread()
{
    std::cout << "Thread created" << std::endl;
}
 
workerThread::~workerThread()
{
 
}
 
 
void workerThread::run()
{
    std::cout << "Thread running" << std::endl;
 
    while(!this->isInterruptionRequested())
    {
        // Do streaming stuff
        emit FrameReady();
    }
 
    std::cout << "Thread terminated" << std::endl;
    emit finished();
}

class workerThread : public QThread
{
    Q_OBJECT

public:
    workerThread();
    ~workerThread();

protected:
    void run();

signals:
    void finished();
    void FrameReady();

private:

    // UHD member
    uhd::usrp::multi_usrp::sptr usrp;
    uhd::rx_streamer::sptr rx_stream;
};


workerThread::workerThread()
{
    std::cout << "Thread created" << std::endl;
}

workerThread::~workerThread()
{

}


void workerThread::run()
{
    std::cout << "Thread running" << std::endl;

    while(!this->isInterruptionRequested())
    {
        // Do streaming stuff
        emit FrameReady();
    }

    std::cout << "Thread terminated" << std::endl;
    emit finished();
}

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The Problem is still the same. During the first start/stop all works fine. But when I try to restart the thread, I don't come into the if(backgroundWorker == NULL) and the program hangs at the backgroundWorker->start line.

[jefftee]

Perhaps set background worker to null after you delete it in line 66?

[anda_skoa]

The Problem is still the same. During the first start/stop all works fine. But when I try to restart the thread, I don't come into the if(backgroundWorker == NULL) and the program hangs at the backgroundWorker->start line.

You are artifically creating a different situation for startup vs. runtime by creating and connecting a thread in the constructor.

As far as I can tell the only thing the slot would need to do is to disconnect() from the old thread if it exists and create and start the new thread.
Since the thread is deleted via deleteLater(), you will need a QPointer for "backgroundWorker" so it can track if the object still exists.

void MainWindow::Streaming()
{
    if(ui->StartStopStreaming_pb->text() == "Start streaming")
    {
        ui->StartStopStreaming_pb->setText("Stop streaming");
 
        backgroundWorker = new workerThread;
        connect(backgroundWorker, SIGNAL(finished()), backgroundWorker, SLOT(deleteLater()));
        connect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
        backgroundWorker->start(QThread::HighestPriority);
 
        std::cout << "Start streaming in background thread" << std::endl;
    }
    else{
        ui->StartStopStreaming_pb->setText("Start streaming");
 
        if(backgroundWorker != 0)
        {
              disconnect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
              backgroundWorker->requestInterruption();
        }
    }
}

void MainWindow::Streaming()
{
    if(ui->StartStopStreaming_pb->text() == "Start streaming")
    {
        ui->StartStopStreaming_pb->setText("Stop streaming");

        backgroundWorker = new workerThread;
        connect(backgroundWorker, SIGNAL(finished()), backgroundWorker, SLOT(deleteLater()));
        connect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
        backgroundWorker->start(QThread::HighestPriority);

        std::cout << "Start streaming in background thread" << std::endl;
    }
    else{
        ui->StartStopStreaming_pb->setText("Start streaming");

        if(backgroundWorker != 0)
        {
              disconnect(backgroundWorker, SIGNAL(FrameReady()), this, SLOT(update_detection_lb()));
              backgroundWorker->requestInterruption();
        }
    }
}

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Alternatively you could look into keeping the same thread object and just making it "pause/resume".

Cheer,
_