[Interest] Annoying Bug - Qt 4.8.1 bug?

[Etienne Sandré-Chardonnal]

Dear all,

I'm tracking a bug since a few days, which happens at the end of file
saving in my app. It saves using a separate thread, while the GUI displays
a modal progress dialog. The app crashes in the QProgressDialog destructor,
and this does not happen all the time. I have double checked that the
destructor is called only once; it's allocated on the heap and I let Qt
destroy it with the flag WA_DeleteOnClose.

I spent a few hours stripping my app to the bare minimum that keeps it
crashing. The good news is that it's possible to reproduce it with a small
project, the bad is the probability for crashing at each click on the
"save" button decreases when the GUI becomes simple (I had to keep a few
widgets and UI to keep it at a detectable level) but everything is made
with .ui's and generated by Qt, so my code is minimal. You may find the
project attached, I'm running Qt 4.8.1 under win7 64 bit, with mingw32 and
mingw64 (both crash). *To trigger the crash, you need to click on "Save"
toolbutton, then press enter. This needs to be repeated several times,
several varying between 2 and 50.*


Here is the only non trivial code that could contain the bug if it's not a
Qt bug. This is a QThread subclass worker doing the file saving (here it
does nothing but this crashes anyway on the QProgressDialog destruction)


BackgroundFileWorker::BackgroundFileWorker(QObject *parent) :

	QThread(parent)

{

}



bool BackgroundFileWorker::startWriting()

{

	if(isRunning())

	{

		return false;

	}


	_progress =  0;


	//Create a timer for polling progress update

	QTimer * progressPollingTimer = new QTimer(this);

	progressPollingTimer->setInterval(200);

	connect(this, SIGNAL(started()), progressPollingTimer, SLOT(start()));

	connect(progressPollingTimer, SIGNAL(timeout()), this, SLOT(updateProgress()));

	connect(this, SIGNAL(finished()), progressPollingTimer, SLOT(stop()));

	connect(this, SIGNAL(finished()), progressPollingTimer, SLOT(deleteLater()));

	connect(this, SIGNAL(finished()), this, SLOT(updateProgress()));



	//Create an application modal progress dialog

	QProgressDialog * progress = new QProgressDialog("Please wait while
writing the file...", "Abort", 0, 100,
dynamic_cast<QWidget*>(parent()));

	progress->setWindowTitle("Saving File");

	connect(this, SIGNAL(progressChanged(int)), progress, SLOT(setValue(int)));

	connect(this, SIGNAL(finished()), progress, SLOT(close()));

	progress->setWindowModality(Qt::WindowModal);

	progress->setAttribute(Qt::WA_DeleteOnClose);

	progress->setMinimumDuration(0);


	emit progressChanged(0);


	start();

	return true;

}


void BackgroundFileWorker::updateProgress()

{

	if(isRunning() )

	{

		_progress+=10;

		emit progressChanged(_progress);

	}

	else if (_progress!=100)

	{

			_progress = 100;

			emit progressChanged(_progress);

	}

}


void BackgroundFileWorker::run()

{

}




Thanks,

Etienne
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