[Interest] invalidated copies of QString in QCommonStyle::cachedOption

[Mojmír Svoboda]

Hello,

i have a crash in QCommonStyle::subElementRect

     case SE_ItemViewItemDecoration:
     case SE_ItemViewItemText:
     case SE_ItemViewItemFocusRect:
         if (const QStyleOptionViewItem *vopt = ...) {
             if (!d->isViewItemCached(*vopt)) {
                 d->viewItemLayout(...);
                 if (d->cachedOption) {
 >>>>                delete d->cachedOption;
                     d->cachedOption = 0;
                 }
                 d->cachedOption = new QStyleOptionViewItem(*vopt);
             }

with callstack:
   QArrayData::deallocate
   QTypedArrayData<unsigned short>::deallocate(QArrayData * data)
   QString::~QString() Line 1070
   QStyleOptionViewItem::~QStyleOptionViewItem()
   QStyleOptionViewItem::`scalar deleting destructor'(unsigned int)
 > QCommonStyle::subElementRect(QStyle::SubElement sr, const 
QStyleOption * opt, const QWidget * widget) Line 2993
   QWindowsStyle::subElementRect
   QWindowsVistaStyle::subElementRect
   QCommonStyle::drawControl
   QWindowsStyle::drawControl
   QWindowsVistaStyle::drawControl
   QStyledItemDelegate::paint
   QTableViewPrivate::drawCell
   QTableView::paintEvent
   ...


How this occurs:
i have QTableView with custom model that uses memmapped file filled with 
lots of QStringData. These QStringData are set using the technique 
presented in http://woboq.com/blog/qstringliteral.html for example.

The problem is when the storage goes away (widget is closed), because 
there may be copies of those strings, and indeed they are.

One of the copies is in QCommonStylePrivate::cachedOption::text field. I
suspect these style classes use some form of sharing, so when i close 
the widget, the copy of qstring will survive the storage, and then when 
new qtableview opens, it tries to reuse the style and on the first use 
it destroys the old content of .text field and crash follows.

Now what do i do? Try to force somehow the style class to drop the 
d->cachedOption?
Any ideas, please?

Best regards,
Mojmir