Multi tool use

C++ QThread and connect causing crashes

My QThread counter crashes giving odd results for what the number should be as the Thread counts properly but in the SetLabel function I get a different number to whats in the QThread ands it then crashes after 3 seconds and the label doesnt seem to update.

QThread* CountThread = new QThread;
Counter* Count = new Counter();
Count->moveToThread(CountThread);
connect(CountThread, SIGNAL(started()), Count, SLOT(Process()));
connect(Count, &Counter::SecondsUpdate, this, [=]{ SetLabel(Count->Seconds) ;});
connect(Count, SIGNAL(finished()), CountThread, SLOT(quit()));
CountThread->start();


void Counter::Process()
{
int secs = 0;
while (secs < 1000)
{
qDebug() << "hello" << secs;
secs += 1;
Sleep(1000);
emit SecondsUpdate();
}
emit finished();
}


void BaseWindow::SetLabel(int Seconds)
{
qDebug() << Seconds;
this->Test->setText(QString("Seconds: " + QString::number(Seconds)));
}

class Counter : public QObject
{
Q_OBJECT
public slots:
void Process();

signals:
void finished();
void SecondsUpdate();

public:
int getValue() { return Seconds;}
int Seconds;

};


EDIT: The issue seems to lie in the changing of the label as I commented this->Text->setText out and it didnt crash

Count->Seconds

2 Answers
2

The code shown has two basic problems.

Counter::Seconds

Count

QThread

You could solve both of these by getting rid of the Seconds member and just passing the local counter secs as a parameter to the Counter::SecondsUpdate signal...

Seconds

secs

Counter::SecondsUpdate

class Counter: public QObject
{
Q_OBJECT;
public slots:
void Process();
signals:
void finished();
void SecondsUpdate(int seconds);
public:
};

void Counter::Process ()
{
int secs = 0;
while (secs < 1000)
{
qDebug() << "hello" << secs;
secs += 1;

/*
* Sleep(1000) --> QThread::sleep(1)
*/
QThread::sleep(1);

/*
* Pass secs as a parameter to the SecondsUpdate signal.
*/
emit SecondsUpdate(secs);
}
emit finished();
}


Then, change the relevant connect call from...

connect

connect(Count, &Counter::SecondsUpdate, this, [=]{ SetLabel(Count->Seconds) ;});


to...

connect(Count, &Counter::SecondsUpdate, this, &BaseWindow::SetLabel);


connect(Count, &Counter::SecondsUpdate, this, [=](int seconds) { SetLabel(seconds); });

connect(Count, &Counter::SecondsUpdate, this, &BaseWindow::SetLabel)

Fixed by passing through the label as a pointer and edited it in the function.

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