Dynamic created objects are not released within QML's Column!

jackmack

Hi all,

I'm using Qt 5.9.7 on Windows. And I tested it with Qt 5.12.2: same issue!

During runtime I want to fill a Column with dynamic created items.
This is done with setting the parent of the created item to Column.

I hold the items in an JS array to have access later e.g. setting values, texts.
But when I want to clear (make empty) the Column it seems the memory is not given free.

Now the situation is that the Column is very often filled and cleared during runtime which later leads to an application crash because "out of memory".

I have verfied this by observing memory with task manager.

Is that bug or is my code wrong?
Using a repeater is not parctical because the dynamic created items are very complex and would blast implementing them by a delegate.

Here is a short example to test it, press key "1" to add item, "2" for delete all, "T" to start filling/deleting automatically to see better changes in task manager:

import QtQuick 2.4

Rectangle {
    width: 480
    height: 320
    color: "gray"
    clip: true

    property var items: []

    // adds an item to column
    //
    function addItem() {
        var item = component.createObject(column)
        items.push(item)
        text.text = "Count of items: " + items.length
    }

    // deletes all items of column
    //
    function deleteAllItems() {
        for (var i = 0; i < items.length; i++) {
            items[i].parent = null
            items[i].destroy()
            items[i] = null
        }

        items.length = 0
        text.text = "Count of items: " + items.length
    }

    Column {
        id: column
        spacing: 1
    }

    // shows only the number of columns items
    //
    Text {
        id: text
        anchors.left: column.right
    }

    // used for fast insert of items to column
    //
    Timer {
        id: timer
        interval: 100
        repeat: true

        onTriggered: {
            // more than 50 items ? then we delete all!
            //
            if (items.length > 50) {
                deleteAllItems()
            }
            else {
                addItem()
            }
        }
    }

    // some key for testing
    //
    focus: true
    Keys.onPressed: {
        if (event.key === Qt.Key_1) {
            addItem()
        }
        else if (event.key === Qt.Key_2) {
            deleteAllItems()
        }
        else if (event.key === Qt.Key_T) {
            if (timer.running)
                timer.stop()
            else
                timer.start()
        }

        event.accepted = true
    }

    // columns item
    //
    Component {
        id: component

        Rectangle {
            id: rect
            width: 120
            height: 50
            color: "red"

            // need some space. better to see in taskmanager!
            //
            property string text1: "kjdkfdjkjfksdfsdkfsdkfdsjf"
            property string text2: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
            property string text3: "bbbbbbbbbbbbbbbb"
            property string text4: "llllllllllllllllllllllllllllllllllllllllllll"

            Text { text: "index " + rect.Positioner.index }
        }
    }
}

THX

fcarney

Cannot reproduce:

import QtQuick 2.4
import QtQuick.Window 2.2

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    property var items: []

    // adds an item to column
    //
    function addItem() {
        var item = component.createObject(column)
        items.push(item)
        text.text = "Count of items: " + items.length
    }

    // deletes all items of column
    //
    function deleteAllItems() {
        for (var i = 0; i < items.length; i++) {
            items[i].parent = null
            items[i].destroy()
            items[i] = null
        }

        items.length = 0
        text.text = "Count of items: " + items.length
    }

    //import QtQuick 2.4

    Rectangle {
        width: 480
        height: 320
        color: "gray"
        clip: true





        Column {
            id: column
            spacing: 1
        }

        // shows only the number of columns items
        //
        Text {
            id: text
            anchors.left: column.right
        }

        // used for fast insert of items to column
        //
        Timer {
            id: timer
            interval: 1 // 100
            repeat: true

            onTriggered: {
                // more than 50 items ? then we delete all!
                //
                if (items.length > 1000) {//50) {
                    deleteAllItems()
                }
                else {
                    addItem()
                }
            }
        }

        // some key for testing
        //
        focus: true
        Keys.onPressed: {
            if (event.key === Qt.Key_1) {
                addItem()
            }
            else if (event.key === Qt.Key_2) {
                deleteAllItems()
            }
            else if (event.key === Qt.Key_T) {
                if (timer.running)
                    timer.stop()
                else
                    timer.start()
            }

            event.accepted = true
        }

        // columns item
        //
        Component {
            id: component

            Rectangle {
                id: rect
                width: 120
                height: 50
                color: "red"

                // need some space. better to see in taskmanager!
                //
                property string text1: "kjdkfdjkjfksdfsdkfsdkfdsjf"
                property string text2: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
                property string text3: "bbbbbbbbbbbbbbbb"
                property string text4: "llllllllllllllllllllllllllllllllllllllllllll"

                Text { text: "index " + rect.Positioner.index }
            }
        }
    }
}

main.c:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

I do not get runaway memory allocation occuring. It actually seems very low memory allocation.
I am running:
Ubuntu Linux 18.04
Qt 5.12.2
Mingw 7.3 64 bit
Monitored memory with top command

jackmack

Hhhm...

the code was only a simple snipped. The original code where the issue occurs is more complex, import scripts, uses inheritance, access C++ objects.

The posted example was very small and tight.

Now I have prepared a better example, consists of serveral files (qml, js). It's similar to original code structure. When I start this example at beginning the memory usage rises fast and much space. After short while its rises slower and less space... but rises continually.

I have tested it with Qt's qmlscene.exe.

Note:
I have tested also on Win10, with Qt 5.4.1, no memory issue!
Strange