QApplication::clipboard()->setMimeData causing the QT application to crash

[PradeepJoy]

Is there an issue with QApplication::clipboard()->setMimeData being used in very quick succession? Observed that the application crashes when the QApplication::clipboard()->setMimeData is made use of to update the clipboard very frequently( for eg: 10 cut operations per second)?

Is there a way that can be suggested to give a throttling effect to the very frequent user operations? (Like restricting the Clipboard update to occur, say once in 500 ms rather at the user defined pace)

[Christian Ehrlicher]

Please show the backtrace. Maybe QApplication::clipboard() returns a nullptr?

[raven-worx]

@PradeepJoy
show the code where you create and insert the QMimeData object into the clipboard.
Note that the clipboard takes ownership of the mimedata object and thus shouldn't have a parent nor destroyed prematurely.

[PradeepJoy]

@Christian-Ehrlicher , @raven-worx
We are using qt version 4.7.3 (if this helps)

Code Pointer

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QMimeData *mimeData = new QMimeData;
QString strToCopy = defToDrag.isEmpty() ? textToDrag : (defToDrag + "{}" + textToDrag);
mimeData->setText(strToCopy);
QApplication::clipboard()->setMimeData(mimeData, QClipboard::Selection);
QApplication::clipboard()->setMimeData(mimeData, QClipboard::Clipboard);

We are not destroying mimeData anywhere..

We are able consistently replicate the crash. Attaching couple of stack traces we observed,
Stack Trace 1

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#0 0x00002aaaab1a1b0e in ?? () from /libQtGui.so.4
#1 0x00002aaaab213304 in QClipboard::event(QEvent*) () from /libQtGui.so.4
#2 0x00002aaaab18b6af in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /libQtGui.so.4
#3 0x00002aaaab190e30 in QApplication::notify(QObject*, QEvent*) () from /libQtGui.so.4
#4 0x00002aaaaac64364 in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /libQtCore.so.4
#5 0x00002aaaab20ac3b in QApplication::x11ProcessEvent(_XEvent*) () from /libQtGui.so.4
#6 0x00002aaaab233622 in ?? () from /libQtGui.so.4
#7 0x0000003cf6640555 in g_main_context_dispatch () from /lib64/libglib-2.0.so.0
#8 0x0000003cf6644d08 in ?? () from /lib64/libglib-2.0.so.0
#9 0x0000003cf6644ec2 in g_main_context_iteration () from /lib64/libglib-2.0.so.0
#10 0x00002aaaaac8fd15 in QEventDispatcherGlib::processEvents(QFlagsQEventLoop::ProcessEventsFlag) () from /libQtCore.so.4
#11 0x00002aaaab23316f in ?? () from /libQtGui.so.4
#12 0x00002aaaaac63715 in QEventLoop::processEvents(QFlagsQEventLoop::ProcessEventsFlag) () from /libQtCore.so.4
#13 0x00002aaaaac6397d in QEventLoop::exec(QFlagsQEventLoop::ProcessEventsFlag) () from /libQtCore.so.4
#14 0x00002aaaaac65176 in QCoreApplication::exec() () from /libQtCore.so.4

Stack Trace 2

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#0 0x00002aaaab211319 in QClipboard::setMimeData(QMimeData*, QClipboard::Mode) () from ../libQtGui.so.4
#1 0x00000000008b1013 in MyClass::slotCut (this=0x18860d0, Cut=true, includeValues=false) at MyClass.C:2511

Thank you for the support..

[jsulm]

@PradeepJoy said in QApplication::clipboard()->setMimeData causing the QT application to crash:

QApplication::clipboard()

So, did you check whether it returns nullptr as @Christian-Ehrlicher suggested?

[PradeepJoy]

@jsulm QApplication::clipboard() was not returning a null pointer.

[RogueWarrior]

See this forum post.
https://forum.qt.io/topic/50701/solved-apparently-qmimedata-is-responsible-for-it-s-own-delete-after-having-been-used-to-set-the-clipboard/6