Memory use with repeated creation/destruction of ListView's

SergeQt

Hi, everyone.

Qt 4.7.3, Windows
Qt 4.7.2, Linux fedora

I have a problem with a program we are currently developing here. We repeatedly create and destroy ListView's and it seems that memory is leaking.

Our code is in C++ (with QDeclarativeComponent::create), but one of my co-workers wrote a QML-only version that exhibits the problem in QMLViewer. I attached the two QML files to the present message. Load the memory_leak.qml file in QMLViewer and press Return repeatedly (or hold it down) to create ListView's from TemplateListView.qml.

If you check the memory used by the QMLViewer process, you will see it increase in time. You can add pictures in the model/view to make it more obvious.

What are we doing wrong?

2 Files below:
main.qml
@
import QtQuick 1.0

Item{
id: root

function createList(){
    var qtComponent = Qt.createComponent("TemplateListView.qml");
    var qtObject = qtComponent.createObject(container);
    if (qtObject == null){
        console.log("Error in createList() : qtObject is null !");
        return;
    }
    container.isEmpty = false;
}

width: 500
height: 600
focus: true

Keys.onReturnPressed: if (container.isEmpty) createList()

Text{
    anchors.horizontalCenter: parent.horizontalCenter
    anchors.top: parent.top
    anchors.topMargin: 40
    width: 500
    height: 40
    text: "press Return to create a listview and the listview will auto destructs after 100 ms."
}

Item{
    id: container

    property bool isEmpty: true

    anchors.top: parent.top
    anchors.topMargin: 100
    width: 500
    height: 500
}

ListModel{
    id: myModel

    ListElement{ label: "label1" }
    ListElement{ label: "label2" }
    ListElement{ label: "label3" }
    ListElement{ label: "label4" }
    ListElement{ label: "label5" }
    ListElement{ label: "label6" }
    ListElement{ label: "label7" }
    ListElement{ label: "label8" }
    ListElement{ label: "label9" }
    ListElement{ label: "label10" }
}

}
@

TemplateListView.qml
@
import QtQuick 1.0

ListView{
id: template

anchors.fill: parent
opacity: 1
focus: false
model: myModel
delegate: Component{
    Rectangle{
        width: template.width
        height: 100
        color: "grey"

        Text{ text: label }
    }
}
highlight: Rectangle { color: "black" }

Component.onCompleted: opacity = 0;

Behavior on opacity {
    NumberAnimation {
        duration: 100
        onRunningChanged: if (!running) {template.parent.isEmpty = true;template.destroy();}
    }
}

}
@

--
Serge

Hornsj2

I've had some similar concerns about Loaders. In my code I'm constantly changing screens and using Loaders to create/destroy new/current screens. When I look at my memory manager (top and task manager) all I see is a climbing number. It never seems to go back down.

I think behind the scenes model-based QML elements also load visual elements dynamically.

I use visual leak detector on the Windows side and it reports no leaks. Is the cause a lazy garbage collection algorithm?

nesaver

I've had similar problem about Loader and ListView, when I show and hide Page, contain Loaders with ListView, memory increase incremently, and not go down :(.

Could you help me ?

Many thanks

mbrasser

Hi,

A couple notes:

Because of the way QML works, it is normal to see memory usage increase up to a point. This is due to things like image caches and a garbage collected JS environment. There is a gc() function you can call from QML to manually trigger a garbage collection, if you'd like to see if it helps.
From memory there were a number of memory leaks fixed post 4.7.3, such as http://qt.gitorious.org/qt/qt/commit/3750d24175904916fe5ab8b1a76db956b1904e72 and http://qt.gitorious.org/qt/qt/commit/340c22999d9f9678c9035c1dc372423e970b8ca7. I'm not sure if these make any difference in your particular cases, but if you are able you could also try the 4.8 beta and see if things are improved there.

Regards,
Michael

Choudhary Ramesh

Still facing this same problem in qt 6.2 . when i push and remove page in stack view ,program memory kept rising and never go down even after manually call to gc();
The page contain toolbar,image ,rectangle and buttons and doesn't contain any custom qml type .

JoeCFD

@Hornsj2 you may need to make a debug build of Qt in order to see the leaks of Qt code. Often people install Qt release build and will not be able to see the leaks of Qt.