StackView is cause of Memory leak?

ynatynat

I'm creating an app using Stackview.
When I monitored the memory usage of the app while switching pages, I found that the memory usage gradually increased.
So, when I created a simple Staciview test program and verified it, I found that the memory usage gradually increased and was not released.

I suspect a memory leak. Is there any solution?
I uses Qt 6.5.2.

test method on test program:
main page->click button and move to page1->click button and move to page2->back button (pop)->back button (pop)-> main page

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>


int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(u"qrc:/main.qml"_qs);
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
        &app, [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

main.qml

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtQuick.Layouts 1.15
ApplicationWindow {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")


Timer{
    interval: 100; running: false; repeat: true
    onTriggered: {

    }
}
StackView {
    id: stackView
    width:parent.width*0.98
    height:parent.height*0.98
    anchors.centerIn: parent

    focus: true
    initialItem:buttons
    onCurrentItemChanged: {
        console.log("stack depth=",stackView.depth)
    }

}

ListModel{
    id:menuItems
    ListElement{
        _txt:qsTr("1")
        _url: "Page1.qml"
        _accent:false
        _name:"page1"
        _type:"btn"
    }
    ListElement {
        _txt:qsTr("2")
        _url:"Page2.qml"
        _accent:false
        _name:"page2"
        _type:"btn"
    }
}
Component{
    id:buttons

    GridView{
        id:grid
        cellWidth:parent.width/3
        cellHeight:parent.height/3

        model:menuItems
        delegate:
            Button{
                text:_txt
                //checkable: name==="conveyormode"?true:false
                onClicked:{


                        stackView.push(Qt.resolvedUrl(_url),StackView.Immediate)

                }

            }

    }

}
}

Page1.qml

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtQuick.Layouts 1.15
Page {
Rectangle{
    width:100;height:100

    Button{
        id:bk
        text:"(1) back"
        onClicked:stackView.pop(StackView.Immediate);
    }
    Button{
        text:"to 2"
        onClicked:stackView.push(Qt.resolvedUrl("Page2.qml"),StackView.Immediate)
        anchors.left: bk.right
    }
}
}

Page2.qml

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtQuick.Layouts 1.15
Page {
Rectangle{
    width:100;height:100

    Button{
        text:"(2) back"
        onClicked:stackView.pop(StackView.Immediate);
    }
}
}

ynatynat

I have been tested well my app which modified including gc() excluding Glow{}& Qt5Compat.GraphicalEffects.
As a result, it didn't consume much memory.

[Conclusion]
StackView is not a cause of memory leak.

--in my app:
Glow{} (Qt5Compat.GraphicalEffects) was the cause of memory leak. So I removed them.
Periodically running gc() is effective to reduce memory consumption if user operate continuously.

jsulm

@ynatynat As I wrote here https://forum.qt.io/topic/152053/best-practices-of-handling-multiple-forms?_=1699862117332 I doubt there is a memory leak.

ynatynat

@jsulm
Thank you for replaying.
You means it's not a memory leak, but memory is increasing due to natural memory management by the OS (not freeing it for reuse), right?
I'm creating an app that will be used in a factory, and I don't have many chances to shut down the app, so I would like to reduce memory consumption as much as possible. How can I achieve this?

jsulm

@ynatynat You would need to reserve and release more memory many times to see whether there is really a memory leak. Releasing one window and seeing that the memory is still not released does not automatically mean that there is a memory leak.

JonB

@ynatynat
You do not necessarily have to shut down the app to get the memory back. Once memory is allocated by a process it is "unlikely" to be returned to the OS until the process ends. However, the hope is that the process will re-use that memory after being freed when the process comes to allocate fresh memory.

The true test is more like: keep allocating and freeing memory (allowing it to be properly freed by Qt), see whether total memory allocated to the process "settles down" over time rather than keeping growing indefintely.

ynatynat

@jsulm
@JonB
Thank you for replying.

I tested the app.
test operation: main-move to page1(push(page1))- move to page2(push(page2))-pop()-pop()-main

[Result]
Just open:53.6MB
after 1st operation: 55.7MB
after 20th operation:55.9MB
wait one minute and restart operation.
after 40th opereation 55.9MB
after 60th operation 56.2MB

It seems to keep growing.

JonB

@ynatynat
Run it 100 times.
OIC, you seem to have run it several times, I think. In any case if you are commenting on a difference between 53/55/56MB this is so small it may not be significant.

You might also use a tool like valgrind to examine memory allocation. Whether that tool, or another, has issues (e.g. "false positives") with QML code I do not know.

From time to time people post asking/reporting something similar. It is unlikely there are any "leaks" in Qt code, and the behaviour is what it is.

ynatynat

@JonB
Thank you for advice.

I understood that a change of about a few MB is not a critical memory leak.
As a result of investigating on my app, rather than test app, I also found that when I press a button that uses Glow{} (Qt5Compat.GraphicalEffects), memory consumption increases continuously. I think it seems a critical leak.

I also found it is better to use gc() if there is a possibility of continuous operation. document

That's why, I expect that my program will improve by excluding Glow{}, Qt5Compat.GraphicalEffects and add periodically running gc().

Although I have only been able to do a few tests so far, it appears that memory consumption tends to be less likely to increase when these are included.

ynatynat

I have been tested well my app which modified including gc() excluding Glow{}& Qt5Compat.GraphicalEffects.
As a result, it didn't consume much memory.

[Conclusion]
StackView is not a cause of memory leak.

--in my app:
Glow{} (Qt5Compat.GraphicalEffects) was the cause of memory leak. So I removed them.
Periodically running gc() is effective to reduce memory consumption if user operate continuously.