I ran into a strange problem with QStyle.

victorman

I am using QT5, but I have occasionally encountered problems during my development.

When I use this method to refresh the widget,

    widget->setProperty("Hovered", "true");
    widget->style()->unpolish(widget);
    widget->style()->polish(widget);

I occasionally see a crash stack like this

int std::__1::__cxx_atomic_fetch_sub<int>(std::__1::__cxx_atomic_base_impl<int>*, int, std::__1::memory_order) (atomic:1072)
std::__1::__atomic_base<int, true>::fetch_sub(int, std::__1::memory_order) (atomic:1725)
std::__1::__atomic_base<int, true>::operator--() (atomic:1760)
bool QAtomicOps<int>::deref<int>(std::__1::atomic<int>&) (qatomic_cxx11.h:289)
QBasicAtomicInteger<int>::deref() (qbasicatomic.h:119)
QSharedDataPointer<QStyleSheetImageData>::~QSharedDataPointer() (qshareddata.h:93)
QSharedDataPointer<QStyleSheetImageData>::~QSharedDataPointer() (qshareddata.h:93)
QRenderRule::~QRenderRule() (qstylesheetstyle.cpp:510)
QRenderRule::~QRenderRule() (qstylesheetstyle.cpp:510)
QHashData::free_helper(void (*)(QHashData::Node*)) (qhash.cpp:572)
QHashData::free_helper(void (*)(QHashData::Node*)) (qhash.cpp:572)
QHash<int, QHash<unsigned long long, QRenderRule>>::freeData(QHashData*) (qhash.h:619)
QHash<int, QHash<unsigned long long, QRenderRule>>::~QHash() (qhash.h:250)
QHash<int, QHash<unsigned long long, QRenderRule>>::~QHash() (qhash.h:250)
QHashNode<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::~QHashNode() (qhash.h:147)
QHashNode<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::~QHashNode() (qhash.h:147)
QHash<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::deleteNode2(QHashData::Node*) (qhash.h:595)
QHash<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::deleteNode(QHashNode<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>*) (qhash.h:585)
QHash<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::remove(QObject const* const&) (qhash.h:824)
QStyleSheetStyle::unpolish(QWidget*) (qstylesheetstyle.cpp:2992)

Does anyone know what caused this?

Christian Ehrlicher

This sounds similar to https://bugreports.qt.io/browse/QTBUG-69204

victorman

@Christian-Ehrlicher Sorry, I forgot to mention my development environment. I am currently using Qt version 5.15.14. The development machine is MacOS m1.

I see this crash you mentioned (https://bugreports.qt.io/browse/QTBUG-69204) was fixed in 5.12.4, 5.14.0 Alpha.
When I was using setStyleSheet directly, I occasionally had updateObjects crash.

setStyleSheet(QString("a{b:c}"));

The crash stack looks like

int std::__1::__cxx_atomic_load<int>(std::__1::__cxx_atomic_base_impl<int> const*, std::__1::memory_order) (atomic:1006)
std::__1::__atomic_base<int, false>::load(std::__1::memory_order) const (atomic:1615)
int QAtomicOps<int>::loadRelaxed<int>(std::__1::atomic<int> const&) (qatomic_cxx11.h:239)
QBasicAtomicInteger<int>::loadRelaxed() const (qbasicatomic.h:107)
QtPrivate::RefCount::deref() (qrefcount.h:66)
QHash<QString, QVariant>::~QHash() (qhash.h:250)
QHash<QString, QVariant>::~QHash() (qhash.h:250)
QRenderRule::~QRenderRule() (qstylesheetstyle.cpp:510)
QRenderRule::~QRenderRule() (qstylesheetstyle.cpp:510)
QHashData::free_helper(void (*)(QHashData::Node*)) (qhash.cpp:572)
QHashData::free_helper(void (*)(QHashData::Node*)) (qhash.cpp:572)
QHash<int, QHash<unsigned long long, QRenderRule>>::freeData(QHashData*) (qhash.h:619)
QHash<int, QHash<unsigned long long, QRenderRule>>::~QHash() (qhash.h:250)
QHash<int, QHash<unsigned long long, QRenderRule>>::~QHash() (qhash.h:250)
QHashNode<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::~QHashNode() (qhash.h:147)
QHashNode<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::~QHashNode() (qhash.h:147)
QHash<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::deleteNode2(QHashData::Node*) (qhash.h:595)
QHash<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::deleteNode(QHashNode<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>*) (qhash.h:585)
QHash<QObject const*, QHash<int, QHash<unsigned long long, QRenderRule>>>::remove(QObject const* const&) (qhash.h:824)
updateObjects(QList<QObject const*> const&) (qstylesheetstyle.cpp:2769)
QStyleSheetStyle::repolish(QWidget*) (qstylesheetstyle.cpp:2969)

So I changed to use QStyleSheetStyle::unpolish, hoping to reduce the occurrence of collapse. But occasionally there is a crash.

Christian Ehrlicher

Please provide a minimal, compilable example of your problem. Check it with a recent Qt6 version and if the issue still exists, create a bug report (or post it here and I'll take a look on it).