Looks like the SIGNAL loadFinished(bool) is not emitted anymore with Qt 6.8.1
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In my source it crashes every time under Linux 6.8.1!
Sadly it is large and so you want to have a smaller file of course, but then he bug doesn't occur.
It is like if I use a Qt function like this:
qt_foo(myCode.size());And in this Qt function is source like this: (This is not the real source. Only a bad example):
a[10];
...
for(int i=0; i<x; i++)
sum+=a[i];
}and you tell me: "Ohh... Wait: Your example code is too large. You must do a smaller sample code and prove that it doesn't work. Nobody will check such a large example. Your sample code is only allowed to have a small example that doesn't work."
My source code is sadly large. I can't make my source code smaller. If I make my source code smaller, then it is just higher luck that the bug doesn't occur. -
@Volker75
This forum is a user from, for users of Qt just like yourself. It is not a The Qt Company forum. If you want to report a bug that is done at TQtC https://bugreports.qt.io/. I think you will find they want a small program which reproduces bad behaviour. I don't know that they will look at your larger existing application, but up to you.In my source it crashes every time under Linux 6.8.1!
I agree that is problematic. You might supply them with the stack trace on crash, which you have not shown us.
I pay 50€ to the guy that fix this bug.
LOL :)
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Maybe am am not skilled enough with gdb.
I used gdb and used "r". And tried to get the crash.
Then I get this error:Thread 1 "Test" received signal SIGSEGV, Segmentation fault. Downloading source file /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp QWebEngineView::page (this=0x555556a22710) at /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp:1058 Warnung: 1058 /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp: Datei oder Verzeichnis nicht gefundenIt is translated: File or Folder not found
So similar to the bug that i descriped in the other topic that i linked a few posts ago.Please give me more advice what I can do to locate the bug.
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Sorry, I forgot the bt stuff. I hope anyone understand it:
[Thread 0x7fff7cc006c0 (LWP 13329) exited] Thread 1 "Test" received signal SIGSEGV, Segmentation fault. Downloading source file /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp QWebEngineView::page (this=0x555556a22710) at /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp:1058 Warnung: 1058 /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp: Datei oder Verzeichnis nicht gefunden (gdb) bt #0 QWebEngineView::page (this=0x555556a22710) at /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp:1058 #1 0x00007ffff7f50f26 in QWebEngineView::setHtml (this=<optimized out>, html=<Fehler beim Lesen der Variable: Cannot access memory at address 0x7fffffffc038>, baseUrl=...) at /home/qt/work/qt/qtwebengine/src/webenginewidgets/api/qwebengineview.cpp:1102 #2 0x0000555555ae0436 in operator() (__closure=0x555556a59390) at src/timetableprintform.cpp:58 #3 0x0000555555ae0ced in operator() (__closure=0x7fffffffc120) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:141 #4 0x0000555555ae0d94 in QtPrivate::FunctorCallBase::call_internal<void, QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()> >::call(TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()>&, void**)::<lambda()> >(void **, struct {...} &&) (args=0x7fffffffc258, fn=...) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:65 Backtrace stopped: Cannot access memory at address 0x7fffffffc108 -
Apologies for being a bit abrupt in my last post.
I have posted two pieces of code. The first was a simple one-widget form that looked a bit like the problem statement (and worked when the obvious other elements were added), and the second was a self-contained example that worked without addition. There was no intent that these were to be copied and pasted into anywhere as a solution.
Based on the backtrace I would start with the assumption that, at line 58 of your code, the
viewpointer is invalid (probably not null) at the time the slot/lambda executes. This could be because it is not initialised yet, the referenced object has been deleted, you have two variables calledviewwith one (invalid) masking the other (valid) etc. -
Thank you very much for your answer!
hmm.. Since I also used your code in my project and your name of the view was different, it should not be a shadowing problem.In fact in my source I have a lot of similar names in different dialogs. In the main dialog and also in a sub dialog:
mainwindow.h class MainWindow : public QMainWindow { … QWebEngineView *viewPreview; … } mainwindow.cpp void MainWindow::printTimetable() { TimetablePrintForm dialog(this); if (dialog.exec()) { } ... }This mainwindow executes the timetableprintform:
timetableprintform.h class TimetablePrintForm: public Qdialog{ { … QWebEngineView *viewPreview; … }I renamed QWebEngineView *viewPreview; in the timetableprintform to an other name. The bug is still present. So it is not a shadowing problem of the view. :-(
But while coding it, it reminds me on an 12 years old TODO. Maybe that is producing the shadowing problem? I sadly don't know if my comment it true and how to fix it:
main.cpp ... QApplication* app=NULL; QTranslator TTranslator; ... int main(int argc, char *argv[]){ ... QApplication app(argc, argv); //TODO: QApplication shadows the global Qapplication? app.setApplicationName(NAME); app.setApplicationVersion(VERSION); ... if(TSettings->language==""){ selectLanguage(NULL); } setLanguage(app, NULL); ... if(TSettings->languageRTL) app.setLayoutDirection(Qt::RightToLeft); ... MainWindow mainWin(check); mainWin.show(); return app.exec(); }Any advice? Thank you very much.
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@Volker75 said in Looks like the SIGNAL loadFinished(bool) is not emitted anymore with Qt 6.8.1:
QApplication app(argc, argv);
This is correct. QApplication instance is usually created in main() - there should not be any global instances of that class.
Did you address what @ChrisW67 wrote: "at line 58 of your code, the view pointer is invalid"? -
Thank you. I think I addressed that, since like I already wrote "I renamed QWebEngineView *viewPreview; in the timetableprintform to an other name. The bug is still present.". So the pointer got a new unique name. So there shouldn't be a shadowing.
Maybe I misunderstand you. Is there an other way to do? What should can I do? Just check if the pointer is !=NULL (But even if it is NULL, what should I do in that case?)? -
I coded now this:
if(viewPreview2==NULL){ qDebug("NULL"); } else { qDebug("Not NULL"); } viewPreview2->setHtml(updateHTMLprintString(true));The last line is the problem.
Debug tells me "Not NULL" in the terminal.
Is there any thing else that I could check to locate the bug more detailed? -
Here are some things to try in your code:
TimetablePrintForm::TimetablePrintForm(QWidget *parent): QDialog(parent){ QVBoxLayout *layout = new QVBoxLayout(this); QWebEngineView *view = new QWebEngineView(this); qDebug() << "As constructed" << view; connect(view, &QWebEngineView::loadFinished, this, &TimetablePrintForm::loadFinished); layout->addWidget(view); QTimer::singleShot(0, [=](){ qDebug() << "In lambda 1" << view; view->setHtml("<html><head><title>Initial page</title></head><body><p>Initial content</p></body></html>"); } ); QTimer::singleShot(3000, [=](){ qDebug() << "In lambda 2" << view; view->setHtml("<html><head><title>Three seconds page</title></head><body><p>New content</p></body></html>"); } );Do the three qDebugs print the same value?
What is the value ofviewin the slotTimetablePrintForm::loadFinished?Replace QWebEngineView with a basic instrumented subclass (something like):
class MyWebEngineView: public QWebEngineView { Q_OBJECT public: explicit MyWebEngineView(QWidget *parent = nullptr) : QWebEngineView(parent) { qDebug() << "Constructing MyWebEngineView" << this; } ~MyWebEngineView() { qDebug() << "Destructing MyWebEngineView" << this; } };Do you see constructions/destructions you were not expecting?
Matching pairs?When it crashes in your debugger, what is the complete backtrace?
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Thank you very much! I am using Qt 6.8.1:
Terminal:15 As constructed QWebEngineView(0x5beb9e2e2120) In lambda 1 QWebEngineView(0x5beb9e2e2120) 15 Speicherzugriffsfehler (Speicherabzug geschrieben)"Speicherzugriffsfehler" = segmentation fault
"15" that is a debug information from my mainwindow.cpp file; not from the timetableprintform.cpp file.Debuginfod has been enabled. To make this setting permanent, add 'set debuginfod enabled on' to .gdbinit. Downloading separate debug info for system-supplied DSO at 0x7ffff7fc3000 Downloading separate debug info for /home/volker/Dokumente/TMP-to-publish/TiTiTo/libSimpleMail2Qt6.so.0 Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6PrintSupport.so.6 Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Widgets.so.6 Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Gui.so.6 Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Sql.so.6 Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Network.so.6 Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". 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separate debug info for /lib/x86_64-linux-gnu/libdrm_nouveau.so.2 Downloading separate debug info for /lib/x86_64-linux-gnu/libdrm_intel.so.1 Downloading separate debug info for /lib/x86_64-linux-gnu/libedit.so.2 Downloading separate debug info for /lib/x86_64-linux-gnu/libtinfo.so.6 Warnung: could not find '.gnu_debugaltlink' file for /lib/x86_64-linux-gnu/libtinfo.so.6 Downloading separate debug info for /lib/x86_64-linux-gnu/libtinfo.so.6 Downloading separate debug info for /lib/x86_64-linux-gnu/libxml2.so.2 [New Thread 0x7fffddc006c0 (LWP 19383)] [New Thread 0x7fffdd2006c0 (LWP 19384)] [New Thread 0x7fffce8006c0 (LWP 19385)] [New Thread 0x7fffcde006c0 (LWP 19386)] [New Thread 0x7fffcd4006c0 (LWP 19387)] [New Thread 0x7fffcca006c0 (LWP 19388)] [New Thread 0x7fffc7e006c0 (LWP 19389)] [New Thread 0x7fffc74006c0 (LWP 19390)] [New Thread 0x7fffc6a006c0 (LWP 19391)] Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/iconengines/libqsvgicon.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/iconengines/../../lib/libQt6Svg.so.6 [New Thread 0x7fffc60006c0 (LWP 19392)] [New Thread 0x7fffc56006c0 (LWP 19393)] /home/volker/Dokumente/TMP-to-publish/TiTiTo/TiTiTo Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/sqldrivers/libqsqlite.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/imageformats/libqgif.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/imageformats/libqjpeg.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/imageformats/libqico.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/imageformats/libqsvg.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/tls/libqcertonlybackend.so Downloading separate debug info for /home/volker/Qt6.8/6.8.1/gcc_64/plugins/tls/libqopensslbackend.so [New Thread 0x7fffbbe006c0 (LWP 19397)] [New Thread 0x7fffbb4006c0 (LWP 19398)] [New Thread 0x7fffbaa006c0 (LWP 19399)] [Thread 0x7fffbaa006c0 (LWP 19399) exited] [Thread 0x7fffbb4006c0 (LWP 19398) exited] [Thread 0x7fffbbe006c0 (LWP 19397) exited] [New Thread 0x7fffbbe006c0 (LWP 19400)] [New Thread 0x7fffbb4006c0 (LWP 19401)] [New Thread 0x7fffbaa006c0 (LWP 19402)] [Thread 0x7fffbaa006c0 (LWP 19402) exited] [Thread 0x7fffbb4006c0 (LWP 19401) exited] [Thread 0x7fffbbe006c0 (LWP 19400) exited] [New Thread 0x7fffbbe006c0 (LWP 19403)] [Detaching after fork from child process 19404] [Detaching after fork from child process 19405] [Detaching after fork from child process 19406] [New Thread 0x7fffbb4006c0 (LWP 19407)] [New Thread 0x7fffbaa006c0 (LWP 19408)] [New Thread 0x7fffb8a006c0 (LWP 19409)] [New Thread 0x7fffafe006c0 (LWP 19410)] [New Thread 0x7fffaf4006c0 (LWP 19411)] [New Thread 0x7fffaea006c0 (LWP 19412)] [New Thread 0x7fffae0006c0 (LWP 19413)] [New Thread 0x7fffad6006c0 (LWP 19414)] [New Thread 0x7fffa3e006c0 (LWP 19423)] [New Thread 0x7fffacc006c0 (LWP 19422)] [New Thread 0x7fffa34006c0 (LWP 19424)] [New Thread 0x7fffa2a006c0 (LWP 19425)] [New Thread 0x7fffa20006c0 (LWP 19426)] [New Thread 0x7fffa0c006c0 (LWP 19428)] [New Thread 0x7fffa16006c0 (LWP 19427)] [New Thread 0x7fff97e006c0 (LWP 19429)] [New Thread 0x7fff974006c0 (LWP 19430)] [New Thread 0x7fff96a006c0 (LWP 19431)] [New Thread 0x7fff960006c0 (LWP 19432)] [New Thread 0x7fff956006c0 (LWP 19433)] [New Thread 0x7fff94c006c0 (LWP 19434)] [New Thread 0x7fff8be006c0 (LWP 19435)] [Thread 0x7fff8be006c0 (LWP 19435) exited] [Thread 0x7fff94c006c0 (LWP 19434) exited] [Thread 0x7fff956006c0 (LWP 19433) exited] [New Thread 0x7fff956006c0 (LWP 19436)] [New Thread 0x7fff94c006c0 (LWP 19437)] [New Thread 0x7fff8be006c0 (LWP 19438)] [Thread 0x7fff8be006c0 (LWP 19438) exited] [Thread 0x7fff94c006c0 (LWP 19437) exited] [Thread 0x7fff956006c0 (LWP 19436) exited] [New Thread 0x7fff956006c0 (LWP 19439)] [New Thread 0x7fff94c006c0 (LWP 19440)] [New Thread 0x7fff8be006c0 (LWP 19441)] 15 [New Thread 0x7fff8b4006c0 (LWP 19454)] [New Thread 0x7fff8aa006c0 (LWP 19455)] [New Thread 0x7fff8a0006c0 (LWP 19456)] [New Thread 0x7fff890006c0 (LWP 19457)] [New Thread 0x7fff7fe006c0 (LWP 19458)] [New Thread 0x7fff7f4006c0 (LWP 19459)] [New Thread 0x7fff7ea006c0 (LWP 19460)] As constructed QWebEngineView(0x5555569866f0) In lambda 1 QWebEngineView(0x5555569866f0) [New Thread 0x7fff7e0006c0 (LWP 19466)] [New Thread 0x7fff7d6006c0 (LWP 19467)] [New Thread 0x7fff7cc006c0 (LWP 19469)] [New Thread 0x7fff73e006c0 (LWP 19470)] [New Thread 0x7fff734006c0 (LWP 19471)] [Thread 0x7fff734006c0 (LWP 19471) exited] [Thread 0x7fff73e006c0 (LWP 19470) exited] [Thread 0x7fff7cc006c0 (LWP 19469) exited] [New Thread 0x7fff7cc006c0 (LWP 19472)] [New Thread 0x7fff73e006c0 (LWP 19473)] [New Thread 0x7fff734006c0 (LWP 19474)] [New Thread 0x7fff72a006c0 (LWP 19480)] [New Thread 0x7fff720006c0 (LWP 19481)] [New Thread 0x7fff716006c0 (LWP 19482)] [Thread 0x7fff716006c0 (LWP 19482) exited] [Thread 0x7fff720006c0 (LWP 19481) exited] [Thread 0x7fff72a006c0 (LWP 19480) exited] 15 [Thread 0x7fff734006c0 (LWP 19474) exited] [Thread 0x7fff73e006c0 (LWP 19473) exited] [Thread 0x7fff7cc006c0 (LWP 19472) exited] Thread 1 "Test" received signal SIGSEGV, Segmentation fault. 0x0000555556c0ace0 in ?? () (gdb) bt #0 0x0000555556c0ace0 in ?? () #1 0x00007ffff77da635 in operator<<(QDebug, QWidget const*) () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Widgets.so.6 #2 0x0000555555ae065f in operator() (__closure=0x555556ab0a20) at src/timetableprintform.cpp:52 #3 0x0000555555ae10a7 in operator() (__closure=0x7fffffffc120) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:141 #4 0x0000555555ae114e in QtPrivate::FunctorCallBase::call_internal<void, QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()> >::call(TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()>&, void**)::<lambda()> >(void **, struct {...} &&) (args=0x7fffffffc258, fn=...) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:65 #5 0x0000555555ae10ec in QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()> >::call(struct {...} &, void **) (f=..., arg=0x7fffffffc258) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:140 #6 0x0000555555ae1011 in QtPrivate::FunctorCallable<TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()> >::call<QtPrivate::List<>, void>(struct {...} &, void *, void **) (f=..., arg=0x7fffffffc258) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:362 #7 0x0000555555ae0f90 in QtPrivate::QCallableObject<TimetablePrintForm::TimetablePrintForm(QWidget*)::<lambda()>, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void **, bool *) (which=1, this_=0x555556ab0a10, r=0x555556ab0230, a=0x7fffffffc258, ret=0x0) at ../../../Qt6.8/6.8.1/gcc_64/include/QtCore/qobjectdefs_impl.h:572 #8 0x00007ffff5fde038 in ?? () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 #9 0x00007ffff5feb33e in ?? () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 #10 0x00007ffff5fd1e75 in QObject::event(QEvent*) () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 #11 0x00007ffff77903f6 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Widgets.so.6 #12 0x00007ffff5f7bcaa in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 #13 0x00007ffff6129b4a in QTimerInfoList::activateTimers() () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 #14 0x00007ffff625570c in ?? () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Core.so.6 #15 0x00007fffe95145b5 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0timetableprintform.cpp:52 is:
qDebug() << "In lambda 2" << view;I am not sure where I must do "Replace QWebEngineView with a basic instrumented subclass". That is a bit over my skill level. I will try it and report in a few minutes.
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ahh.. Sorry. Now I understand why your code in my project do the semention fault.
TimetablePrintForm::~TimetablePrintForm() { qDebug("~TimetablePrintForm"); }give me:
15 As constructed QWebEngineView(0x5977e8b2e040) In lambda 1 QWebEngineView(0x5977e8b2e040) 15 ~TimetablePrintForm Speicherzugriffsfehler (Speicherabzug geschrieben)I am so sorry for that :-(
I sadly still don't get why my source doesn't work, because with my source I don't close the dialog. It closes only if I press a "close" button. So my code still doesn't emit the loadFinished signal with Qt 6.8.1; but with 6.7.2. -
@ChrisW67 said in Looks like the SIGNAL loadFinished(bool) is not emitted anymore with Qt 6.8.1:
~MyWebEngineView() { qDebug() << "Destructing MyWebEngineView" << this; }I don't mean to detract from the diagnosis attempt, but I think it is actually causing its own problem/seg fault?
If you scroll through to the last backtrace we have been given in https://forum.qt.io/post/818795 we come across:
Thread 1 "Test" received signal SIGSEGV, Segmentation fault. 0x0000555556c0ace0 in ?? () (gdb) bt #0 0x0000555556c0ace0 in ?? () #1 0x00007ffff77da635 in operator<<(QDebug, QWidget const*) () from /home/volker/Qt6.8/6.8.1/gcc_64/lib/libQt6Widgets.so.6 #2 0x0000555555ae065f in operator() (__closure=0x555556ab0a20) at src/timetableprintform.cpp:52This looks to me like the
thisin the destructor codeqDebug() << "Destructing MyWebEngineView" << this;is aQWidget const*and it is actually dying/segging on trying to fetch whatever fromthisis wanted forqDebug()? So although you can accessthisin a destructor I wonder what state theQWidgetis in forqDebug()at this point?@Volker75
You might want to change that line to justqDebug() << "Destructing MyWebEngineView";(so nothis) and see if that changes the backtrace to where whatever you real problem is.
