Valgrind shows many warnings/errors of simple QML application

Question

I have project written in C++ and QML and tried to investigate memory leaks using Valgrind, but it shows a great number of errors even if the application is the simplest possible like this:

#include <QtGui/QApplication>
#include "qmlapplicationviewer.h"
Q_DECL_EXPORT int main(int argc, char *argv[])
{
    QScopedPointer<QApplication> app(createApplication(argc, argv));
    QScopedPointer<QmlApplicationViewer> viewer(QmlApplicationViewer::create());
    viewer->setOrientation(QmlApplicationViewer::ScreenOrientationAuto);
    viewer->setMainQmlFile(QLatin1String("qml/Interface/main2.qml"));
    viewer->showExpanded();
    return app->exec();
}

QML file is:

import QtQuick 1.0
Rectangle {
    width: 800
    height: 480
    color: "blue"
    MouseArea {
        anchors.fill: parent
        onClicked: Qt.quit()
    }
}

I'm running Valgrind using command:

valgrind -v --leak-check=full --show-reachable=yes --track-origins=yes --log-file=Interface2.valgrind.log ./Interface2

The Valgrind summary says:

==16840== LEAK SUMMARY:
==16840==    definitely lost: 344 bytes in 2 blocks
==16840==    indirectly lost: 20 bytes in 1 blocks
==16840==      possibly lost: 9,935 bytes in 308 blocks
==16840==    still reachable: 133,085 bytes in 2,234 blocks
==16840==         suppressed: 0 bytes in 0 blocks

Below are a few (of about 3000 lines of log) messages obtained from Valgrind:

==16840== Memcheck, a memory error detector
==16840== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==16840== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==16840== Command: ./Interface2
==16840== Parent PID: 13367
==16840== 
--16840-- 
--16840-- Valgrind options:
--16840--    --suppressions=/usr/lib/valgrind/debian-libc6-dbg.supp
--16840--    -v
--16840--    --leak-check=full
--16840--    --show-reachable=yes
--16840--    --track-origins=yes
--16840--    --log-file=Interface2.valgrind.log
--16840-- Contents of /proc/version:
--16840--   Linux version 2.6.32-43-generic (buildd@roseapple) (gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5.1) ) #97-Ubuntu SMP Wed Sep 5 16:43:09 UTC 2012
--16840-- Arch and hwcaps: X86, x86-sse1-sse2
--16840-- Page sizes: currently 4096, max supported 4096
--16840-- Valgrind library directory: /usr/lib/valgrind
--16840-- Reading syms from /lib/ld-2.11.1.so (0x4000000)
--16840-- Reading debug info from /lib/ld-2.11.1.so ..
--16840-- .. CRC mismatch (computed 1f70923a wanted 671e42e8)
--16840-- Reading debug info from /usr/lib/debug/lib/ld-2.11.1.so ..
--16840-- Reading syms from /root/workspace/CC5/AIO_CC5/Tools/Interface/Interface2 (0x8048000)
--16840-- Reading syms from /usr/lib/valgrind/memcheck-x86-linux (0x38000000)
--16840--    object doesn't have a dynamic symbol table
--16840-- Reading suppressions file: /usr/lib/valgrind/debian-libc6-dbg.supp
--16840-- Reading suppressions file: /usr/lib/valgrind/default.supp
--16840-- REDIR: 0x4016100 (index) redirected to 0x3803e9b3 (vgPlain_x86_linux_REDIR_FOR_index)
--16840-- Reading syms from /usr/lib/valgrind/vgpreload_core-x86-linux.so (0x401f000)
--16840-- Reading syms from /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so (0x4022000)
==16840== 148 (128 direct, 20 indirect) bytes in 1 blocks are definitely lost in loss record 133 of 200
==16840==    at 0x4024F20: malloc (vg_replace_malloc.c:236)
==16840==    by 0x60438C1: ??? (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x60443C4: ??? (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x60444D9: ??? (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x6048876: ??? (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x60493C0: ??? (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x61CACFD: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61CBBC0: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61CD412: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61CDCD9: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61C6F02: XML_ParseBuffer (in /lib/libexpat.so.1.5.2)
==16840==    by 0x604724A: FcConfigParseAndLoad (in /usr/lib/libfontconfig.so.1.4.4)


==16840== 216 bytes in 1 blocks are definitely lost in loss record 137 of 200
==16840==    at 0x4024F20: malloc (vg_replace_malloc.c:236)
==16840==    by 0x60CE9D2: _XimOpenIM (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60CE817: _XimRegisterIMInstantiateCallback (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60B1D77: XRegisterIMInstantiateCallback (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x4BF6A51: ??? (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x4BF4500: QInputContextFactory::create(QString const&, QObject*) (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x4551C2C: QApplication::inputContext() const (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x459DEA6: QWidgetPrivate::inputContext() const (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x45A9E03: QWidget::setAttribute(Qt::WidgetAttribute, bool) (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x4C65E0B: QGraphicsViewPrivate::updateInputMethodSensitivity() (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x4C7185E: QGraphicsView::setScene(QGraphicsScene*) (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x40A5A06: ??? (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtDeclarative.so.4.7.4)


==16840== 256 bytes in 1 blocks are still reachable in loss record 143 of 200
==16840==    at 0x4025016: realloc (vg_replace_malloc.c:525)
==16840==    by 0x602ED60: FcBlanksAdd (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x60495CB: ??? (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x61CACFD: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61CBBC0: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61CD412: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61CDCD9: ??? (in /lib/libexpat.so.1.5.2)
==16840==    by 0x61C6F02: XML_ParseBuffer (in /lib/libexpat.so.1.5.2)
==16840==    by 0x604724A: FcConfigParseAndLoad (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x603D091: FcInitLoadConfig (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x603D19B: FcInitLoadConfigAndFonts (in /usr/lib/libfontconfig.so.1.4.4)
==16840==    by 0x603D29C: FcInit (in /usr/lib/libfontconfig.so.1.4.4)




==16840== 360 bytes in 3 blocks are possibly lost in loss record 144 of 200
==16840==    at 0x4024106: memalign (vg_replace_malloc.c:581)
==16840==    by 0x4024163: posix_memalign (vg_replace_malloc.c:709)
==16840==    by 0x5E9C9C1: slab_allocator_alloc_chunk (gslice.c:1148)
==16840==    by 0x5E9D222: g_slice_alloc (gslice.c:678)
==16840==    by 0x5E9E881: g_slist_prepend (gslist.c:273)
==16840==    by 0x5EA1A94: g_strsplit (gstrfuncs.c:2431)
==16840==    by 0x5EB5731: g_get_language_names (gutils.c:3169)
==16840==    by 0x5EA9B49: g_thread_init_glib (gthread.c:940)
==16840==    by 0x5E3F69D: g_thread_init (gthread-impl.c:360)
==16840==    by 0x50FC7D9: QEventDispatcherGlibPrivate::QEventDispatcherGlibPrivate(_GMainContext*) (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4.7.4)
==16840==    by 0x460CB4C: ??? (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x460CC32: ??? (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)


==16840== 16,352 bytes in 2 blocks are still reachable in loss record 199 of 200
==16840==    at 0x4024F20: malloc (vg_replace_malloc.c:236)
==16840==    by 0x6098833: ??? (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x6098CA6: _XrmInternalStringToQuark (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x609F4C5: XStringToKeysym (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60D2849: _XimParseStringFile (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60D0466: _XimLocalOpenIM (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60CEB3C: _XimOpenIM (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60CE817: _XimRegisterIMInstantiateCallback (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x60B1D77: XRegisterIMInstantiateCallback (in /usr/lib/libX11.so.6.3.0)
==16840==    by 0x4BF6A51: ??? (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x4BF4500: QInputContextFactory::create(QString const&, QObject*) (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)
==16840==    by 0x4551C2C: QApplication::inputContext() const (in /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4.7.4)

The question is: what I need to do to get rid of memory leaks errors from application. Is this a matter of buggy libraries? I've installed it using installer from Qt official site.

Thanks.

Answer 1

It appears to be a matter of buggy libraries, yes. If you think you can track it down to leakiness in Qt, I would definitely report it as a bug with them: http://qt-project.org/wiki/ReportingBugsInQt

That said, I think your use of QScopedPointer is quite curious. Why not simply allocate your application on the stack? Like this:

QApplication app(argc, argv);

I would say the same for your QmlApplicationViewer pointer, but I cannot see what QmlApplicationViewer::create() does :)

Anyway, I don't think it likely that will the solve the leaks for you...