Memory leaks in Qt app

[Cobra91151]

Hi! I have checked my app with Visual Leak Detector and it has found more than 2000 memory leaks.

Visual Leak Detector detected 2106 memory leaks (237576 bytes).
Largest number used: 238113 bytes.
Total allocations: 241457 bytes.

How to fix these issues?

[A Former User]

Hi! Are these leaks in your code or in code from the Qt framework?

[Cobra91151]

@Wieland

Some in my code and some in qt:
VLD output:

Qt5Cored.dll!QPauseAnimation::duration() + 0x44B42D bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x456349 bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x44CC79 bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x505C71 bytes
qwindowsd.dll!qt_plugin_instance() + 0xD7661 bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x503988 bytes
USER32.dll!CallWindowProcW() + 0x4F4 bytes
USER32.dll!DispatchMessageW() + 0x1BC bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x504392 bytes
qwindowsd.dll!qt_plugin_instance() + 0xD7621 bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x44607F bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x4462C5 bytes
Qt5Cored.dll!QPauseAnimation::duration() + 0x449196 bytes
Qt5Guid.dll!QOpenGLFunctions_1_1::glVertex2iv() + 0x99E9D bytes

[A Former User]

I'd say fix your bugs first and then look for known issues / report issues at https://bugreports.qt.io.

[Cobra91151]

@Wieland

Ok. But how to fix this:

c:\..\..\qt projects\test\main.cpp (16): Test.exe!main() + 0x6 bytes

On 16 line is return app.exec(); function?

[A Former User]

You need to check the body of your main() function for heap allocations / non-deleted objects. If you like, post it here, so we can try to find the problem together.

[Cobra91151]

@Wieland

ManageStartup *appWindow = new ManageStartup();
appWindow->setParent(nullptr);
return app.exec();

ManageStartup - QObject class, in this class I check some data before displaying the main GUI window.

Also I have noticed that Qt 5.7.1 in debug mode when debugging app takes more memory than in release. In Qt 5.7.0 memory management was the same in debug and release modes.

[A Former User]

And that's a bug. You allocate appWindow on the heap. As it is a QObject, you could do the following:

appWindow->setParent(&app);

In this case, once app gets destroyed (when control leaves main), app would automatically delete its child `` appWindow```.

But right now, appWindow has no QObject-parent, so you have to delete it by yourself.

Or just make it a stack object:

ManageStartup appWindow;

[Cobra91151]

@Wieland

Thanks. I have changed code to:

ManageStartup appWindow;
appWindow.setParent(&app);
return app.exec();

and check for memory leaks again, but the leak is still in main.cpp (16): Test.exe!main() + 0x6 bytes, return app.exec();

Main.cpp:

#include <QApplication>
#include <vld.h>
#include "managestartup.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QThread::currentThread()->setPriority(QThread::HighestPriority);
    QSharedMemory sharedMemory(APP_NAME);
    app.setApplicationVersion(APP_VERSION);

    if (sharedMemory.create(1) && sharedMemory.error() != QSharedMemory::AlreadyExists) {
        ManageStartup appWindow;
        appWindow.setParent(&app);
        return app.exec();
    } else {
       int userRespond = QMessageBox::warning(nullptr, QObject::tr("Test"), QObject::tr("Another instance?"), QMessageBox::Yes | QMessageBox::No);

       if (userRespond == QMessageBox::Yes) {
           ManageStartup appWindow;
           appWindow.setParent(&app);
           return app.exec();
       }
    }    
}

[A Former User]

That looks good to me so far. Now follow the call stack in the VLD log. I guess the next leak is in ManageStartup.

[Cobra91151]

@Wieland

Ok. I will check it. Thanks.

[Cobra91151]

@Wieland

Hi! I have fixed some memory leaks by changing objects from heap memory allocation to stack but some leaks still exists.

c:..\qt projects\test\test.cpp (2885): Test.exe!Test::event()

bool Test::event(QEvent *event)
{
    if (event->type() == QEvent::WindowStateChange) {
        appSettings.beginGroup("AppSettings");

        if (this->isMinimized() && appSettings.allKeys().contains("minimizeToTray") && appSettings.value("minimizeToTray") == true) {
            setNotifyIcon();
            showNotification();
            this->hide();
        }

        appSettings.endGroup();
    }

    return QWidget::event(event);
}

On line 2885 is } so I think something with return QWidget::event(event)? Thanks in advance.

[A Former User]

The reported potential leak regarding event is a false positive, just ignore it. VLD simply isn't smart enough to understand what's going on.

See also QCoreApplication Class:

the post event queue will take ownership of the event and delete it once it has been posted

[Cobra91151]

@Wieland

Ok. Thanks.

[Cobra91151]

My app gets WMI data and displays it as QTreeWidgetItem, but it consumes to much RAM memory when changing languages.

void MyApp::appOSThread()
{
   try {
        osWorker = new Worker();
        osThread = new QThread(osWorker);
        osWorker->moveToThread(osThread);
        connect(osThread, &QThread::started, osWorker, &Worker::appOSWMIData);
        connect(osWorker, &Worker::appOSData, this, &MyApp::osWMIData);
        connect(osWorker, &Worker::hardwareDataNotAvailable, this, &MyApp::osWMIDataNotAvailable);
        connect(osWorker, &Worker::errorNotSupportedOS, this, &MyApp::appNotSupportedOS);
        connect(osWorker, &Worker::finished, osThread, &QThread::quit, Qt::DirectConnection);
        connect(osThread, &QThread::destroyed, osThread, &QThread::deleteLater);
        osThread->start();
        logData(QObject::tr("Application: gets OS information"));
    } catch (...) {
        QMessageBox::critical(this, QObject::tr("Error"), QObject::tr("An error has occurred with detecting OS!"));
    }
}

void MyApp::osWMIData(QStringList property, QStringList data)
{
    int countOSProperties = property.count();
    QString osProperty;
    QString osData;

    for (int i = 0; i < countOSProperties; i++) {
        osProperty = property.at(i);
        osData = data.at(i);
        osItem = new QTreeWidgetItem(osView); //osView - QTreeWidget
        osItem->setText(0, osProperty);
        osItem->setText(1, osData);
    }
}

void MyApp::appLocalization()
{
    osView->clear();
    appOSThread();
}

For example when app is started takes 30 MB when change language then it takes 3 - 5 MB RAM and when changing again it takes again 5 - 10 MB of RAM.

Any ideas?