Memoy leak using QtCharts

kshegunov

@kuzulis said in Memoy leak using QtCharts:

I spat on QtCharts and replaced it with Qwt. (Because I haven't time to unterstand why QtCharts does not work as expected.. This was in Qt 5.9, as I remember).

It hasn't improved since then. I did the same as you but picked QCustomPlot instead.

aawawa

@Christian-Ehrlicher : please find a micro project here : link text

@mrjj : if I comment as this :

//SerieToAdd->append(i, sin(static_cast<double>(i) * 3.14*2

I have always the memory leak but it seems to be less important (around 6ko)

mrjj

@aawawa
Ok so it does seems related to the series.
If you want to dig into it, you can very handy browse code here
https://code.woboq.org/qt5/

Super with sample.

aawawa

@mrjj I 'm going to take a look to your link. Is it a database or you want me to send my code there?

mrjj

@aawawa
Hi
Its a code browser. it makes it really easy to see what is being used. all call to functions are links and
its almost as good as the debugger. at least to see what is going on.
I was thinking you would go and look how it deletes the series or something like that.
The sample is for Christian-Ehrlicher as he might make it into a bug report if we can
reproduce it and find no good reason for not release the mem on RemoveAllSeries.

Christian Ehrlicher

I can see some kind of 'leak' but need to do some more investigations.

Christian Ehrlicher

Ok, no leak there. Just a lot of data. You're creating 100000 QLineSeries with 10000 each - this will need some memory and time. I would rather try to add the points to one QLineSeries.

aawawa

@Christian-Ehrlicher thank you... But it is supposed to be deleted 100000 times in my case no when I use RemoveAllSeries no?

aawawa

@Christian-Ehrlicher would rather try to add the points to one QLineSeries this strategy works quiet well.
By changing y program as this for the header :

class MyChartView:public QChartView
{
public:
	MyChartView();
	~MyChartView();
	void Draw(void);

private:	
	QLineSeries *mSeries;
};

and for the .cpp

MyChartView::MyChartView()
{

	mSeries = new QLineSeries;
	chart()->addSeries(mSeries);

}


MyChartView::~MyChartView()
{
}

void MyChartView::Draw(void)
{
	int Length = 1000;
	mSeries->clear();
	for (int i = 0; i < Length; i++)
	{
		mSeries->append(QPoint (i, sin(2 * i*3.141516*0.1)));
	}
	//update();

}

It seems (I have to confirm this point later) to not have anymore memory leak

Christian Ehrlicher

@aawawa said in Memoy leak using QtCharts:

But it is supposed to be deleted 100000 times in my case no when I use RemoveAllSeries no?

You're right. I think I found the culprit:

qlineseries.cpp:112

QLineSeries::QLineSeries(QObject *parent)
    : QXYSeries(*new QLineSeriesPrivate(this), parent)

this is never deleted... :/

JonB

@Christian-Ehrlicher
I think this is the second time I've seen that *new cause this. When will people decide that C++ is getting too clever for its boots? ;-)

SGaist

Hi,

@Christian-Ehrlicher said in Memoy leak using QtCharts:

QLineSeriesPrivate

~~It's QObject based, so when the QXYSeries object is deleted it should also get deleted.~~

It's indeed QObject based but stored in a QScopedPointer so it will automatically get delete on object's destruction.

aawawa

@Christian-Ehrlicher Thank you. It's the first time I see *new in c++ what does it mean?

mrjj

@aawawa
Hi
Its a Dereference
http://www.cplusplus.com/doc/tutorial/pointers/
See section Dereference operator (*)

aawawa

@mrjj yes... I understand... But I don't understand the location of the asterix (*). I am used for example to write

int *a = new int;

what does

*new int

means?

mrjj

@aawawa
Means
value pointed to by ptr
The actual value.

int copy = *SomeIntPtr;
that will copy the value to the copy var.
if you did
int copy = SomeIntPtr;
you get the address of pointer into copy

Christian Ehrlicher

Ok, no memleak at all. You testcase is wrong / inaccurate.
The problem with your testcase is that your eventloop is not (yet) running and that you also call it in an loop without a chance for the eventloop to do it's work. Since the internals of QLineSeries is cleaned up with a deferred delete it is not cleaned up until the eventloop is called (and after app.exec()). That's also the reason I thought the dtor is not called at all.

JosuGZ

@Christian-Ehrlicher said in Memoy leak using QtCharts:

Ok, no memleak at all. You testcase is wrong / inaccurate.
The problem with your testcase is that your eventloop is not (yet) running and that you also call it in an loop without a chance for the eventloop to do it's work. Since the internals of QLineSeries is cleaned up with a deferred delete it is not cleaned up until the eventloop is called (and after app.exec()). That's also the reason I thought the dtor is not called at all.

It seems to me that there are some memory leaks happening here.

This code increases memory usage continuously:

aSeries->remove(aSeries->points().size() - 1);
aSeries->append(timestamp, mean);

Bit this one does not:

aSeries->replace(aSeries->points().size() - 1, timestamp, mean);

I'm using Qt 5.11.2.

JonB

@JosuGZ
In the last post 4 months ago made by @Christian-Ehrlicher, he explained that memory would only be recovered (and hence [hopefully] not permanently grow) when the OP allowed his code to reach the main event loop. I don't know how replace works, but remove surely will do a deferred delete. So in your example you need to be clear/show us how your code hits the event loop each time after do the remove/append?

J.Hilk

hi @JosuGZ and welcome

if you only monitor the memory your OS gives your application, then that is inaccurate.

You have no influence over when the os decides that your freed memory will no longer be reserved for your application.

Therefore
remove -> append is memory is "freed" and a new allocation happens
replace -> new data overwrites old data