Best Method to Plot Data Coming through a Socket.

[babu198649]

Hi
I want to plot the data which comes through socket continously.So i have created a thread which receives the data from the socket and emits it as shown in the code.

void Thread::run()
{
    QTcpSocket socket;
    qDebug()<<"Connecting to host";
    do
    {//Even if the server is not started keep trying
        socket.connectToHost(QHostAddress::LocalHost,12345);
        if(socket.waitForConnected(-1))
            break;
        qDebug()<<"Unable to connect to host "<<socket.errorString()<<" retrying...";
    }while(true);
 
    qDebug()<<"Connected...";
 
    while(true)
    {
        do
        {
            socket.waitForReadyRead(-1);
        }while(socket.bytesAvailable() < sizeof(short int));
 
        QByteArray byteArray = socket.read(socket.bytesAvailable() - (socket.bytesAvailable()%sizeof(short int)));
        short int si;
        for(int i=0; i<(byteArray.size() / sizeof(short int)); i++)
        {
            si = *((short int *)(byteArray.constData() + i*sizeof(short int)));
            emit send(si);
        }
    }
}

void Thread::run()
{
    QTcpSocket socket;
    qDebug()<<"Connecting to host";
    do
    {//Even if the server is not started keep trying
        socket.connectToHost(QHostAddress::LocalHost,12345);
        if(socket.waitForConnected(-1))
            break;
        qDebug()<<"Unable to connect to host "<<socket.errorString()<<" retrying...";
    }while(true);
    
    qDebug()<<"Connected...";
    
    while(true)
    {
        do
        {
            socket.waitForReadyRead(-1);
        }while(socket.bytesAvailable() < sizeof(short int));

        QByteArray byteArray = socket.read(socket.bytesAvailable() - (socket.bytesAvailable()%sizeof(short int)));
        short int si;
        for(int i=0; i<(byteArray.size() / sizeof(short int)); i++)
        {
            si = *((short int *)(byteArray.constData() + i*sizeof(short int)));
            emit send(si);
        }
    }
}

To copy to clipboard, switch view to plain text mode 

In the gui thread the signal is caught and is plotted as shown in the below code.

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    plot = new QwtPlot();
    // Disable polygon clipping
    QwtPainter::setDeviceClipping(false);
 
    // We don't need the cache here
    plot->canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, false);
    plot->canvas()->setPaintAttribute(QwtPlotCanvas::PaintPacked, false);
    setCentralWidget(plot);
    curve = new QwtPlotCurve();
    curve->attach(plot);
    memset(data,0,sizeof(data));
    for(int i = 0; i< HISTORY;i++)
        timeData[i] = i;
    curve->setRawData(timeData,data,HISTORY);
    plot->setAxisScale(QwtPlot::xBottom, timeData[0],timeData[HISTORY - 1]);
    thread = new Thread;
    connect(thread,SIGNAL(send(short)),this,SLOT(receive(short)));
    thread->start();
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::receive(short si)//This is the slot which receives and updates the plot.
{
        for(int i = 0; i < HISTORY-1; ++i)
             data[i] = data[i+1];
        data[HISTORY - 1] = si;
 
    plot->replot();
    QCoreApplication::processEvents();
}

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    
    plot = new QwtPlot();
    // Disable polygon clipping
    QwtPainter::setDeviceClipping(false);
    
    // We don't need the cache here
    plot->canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, false);
    plot->canvas()->setPaintAttribute(QwtPlotCanvas::PaintPacked, false);
    setCentralWidget(plot);
    curve = new QwtPlotCurve();
    curve->attach(plot);
    memset(data,0,sizeof(data));
    for(int i = 0; i< HISTORY;i++)
        timeData[i] = i;
    curve->setRawData(timeData,data,HISTORY);
    plot->setAxisScale(QwtPlot::xBottom, timeData[0],timeData[HISTORY - 1]);
    thread = new Thread;
    connect(thread,SIGNAL(send(short)),this,SLOT(receive(short)));
    thread->start();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::receive(short si)//This is the slot which receives and updates the plot.
{
        for(int i = 0; i < HISTORY-1; ++i)
             data[i] = data[i+1];
        data[HISTORY - 1] = si;
    
    plot->replot();
    QCoreApplication::processEvents();
}

To copy to clipboard, switch view to plain text mode 

But the above program gets crashed after some time of plotting .What is the bug in above code that causes the crash.

Should i follow the dataplot example in which a timerEvent is used for plotting ,or is there any other method available.

Thanks in advance.