QProgressDialog::setValue Crash

[joeQ]

In MainWindow, I have the below code snippet.

void MainWindow::Function_1()
{
    /** some code here */

    int threadNum = 1000;///< just code snippet
    if(0 == _progressDlg){
        ///< _progressDlg MainWindow class data member.
        _progressDlg = new QProgressDialog(this);
        _progressDlg->setLabelText("Label text");
        _progressDlg->setRange(0,threadNum);
    }

    for(int i=0; i < subNum; i++){
        EngineTask* task = new EngineTask(...);///< 
        connect(task,&EngineTask::SigEngineTaskFinished,
                this,&MainWindow::StEngineTaskFinished);
        _threadPool->start(task);
    }
}

I want to use the QProgressDialog to indicate the progress had done of my tasks.

EngineTask class

/** some include */

class EngineTask : public QObject, public QRunnable
{
    Q_OBJECT
public:
    EngineTask(...);
    ~EngineTask();

    void run() override; ///< will emit SigEngineTaskFinished(...), in run function

signals:
    void SigEngineTaskFinished(...);

private:
    /** some class members */
};

MainWindow::StEngineTaskFinished

In the slot, I update the value of QProgressDialog, But, some time, it can crashed at here.

void MainWindow::StEngineTaskFinished(...)
{
    /** some code here */

    if(0 != _progressDlg){
        int val = _progressDlg->value();
        val++;
        _progressDlg->setValue(); ///< ??? some time crash at here.
    }
}

I see the Qt help manual.

Warning: If the progress dialog is modal (see QProgressDialog::QProgressDialog()), setValue() calls QApplication::processEvents(), so take care that this does not cause undesirable re-entrancy in your code. For example, don't use a QProgressDialog inside a paintEvent()!

I don't clear it well now.

1. How to work it out?
2. what's best way?

[SGaist]

Hi,

Any chance you forgot to initialise _progressDlg to 0 in your constructor ? Or you should rather use nullptr.

[joeQ]

@SGaist

I didn't forgot to initialise my class members.

[SGaist]

What does the stack trace tell you about the crash ?

[joeQ]

@joeQ

At the moment i do not know waht causes this crash.

I tried many ways to work it out. not, i find one way.

I test this way, not has the crash.

my way

In my mainwindow.h,

    /** MainWindow class data members */
    int              _progressVal   = 0;
    QTimer*          _progressTimer = 0;
    ProgressDialog*  _progressDlg   = 0;

    QThreadPool*     _threadPool    = 0;

In MainWindow construct function

    /** some code */

    _progressTimer = new QTimer(this);
    _progressTimer->setInterval(1000);
    connect(_progressTimer,&QTimer::timeout,
            this,&MainWindow::StProgressTimerOut);

    /** some code */

About the StProgressTimerOut

void MainWindow::StProgressTimerOut()
{
    if(0 == _progressDlg){
        _progressTimer->stop();
        return;
    }

    _progressDlg->setValue(_progressVal); ///< In here to update progressbar value
    if(_threadPool->activeThreadCount() == 0){
        _progressTimer->stop();
        _progressDlg->deleteLater();
        _progressDlg = 0;
        /** ... */
    }
}

So, When begin to start thread

    /** ... */
    int subNum = 100;
    for(int i=0; i < subNum; i++){
        task = new EngineTask(...);
        connect(task,&EngineTask::SigEngineTaskFinished,
                this,&MainWindow::StEngineTaskFinished,Qt::QueuedConnection);
        _threadPool->start(task);
    }

    if(0 == _progressDlg){
        _progressDlg = new ProgressDialog(tr("Label text"),subNum,this);
        _progressTimer->start(500);
        _progressVal = 0;
    }

In, the Slot function

    /**...*/
    _progressVal++;///< Not in slot to update progressbar value, update it in timer out slot function.
    /**...*/

[SGaist]

Why don't you create your dialog directly since you'll obviously use it ?
That would avoid all these existence checks all over the place.

Otherwise, it would also make more sense to create it before you generate your subNum tasks.

[joeQ]

@SGaist yes, i will modify my code after. thank you very much.