Problem with QWebView

Fakhri

@JoeCFD Like the following post, I need to run qapplication several times in a plugin and load a url. This code simulates it.

https://forum.qt.io/topic/13855/calling-qapplication-exec-multiple-times-in-loop-is-possible-if-yes-how

jsulm

@Fakhri Remove first app.exec()!

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    QUrl url("https://google.com");
    QWebView view1;
    view1.load(url);
    view1.show();
 
    QWebView view2;
    view2.load(url);
    view2.show();
    return app.exec();    
}

"I need to run qapplication several times in a plugin and load a url" - there is no need to call app.exec() twice to do that! I app.exec() must be called only once.

Fakhri

@jsulm first of all thank you for your reply.

I have a C++ (non QT) application. It can load plugins with specific structure. I developed a plugin with qt for it. In my plugin I have a method that should create a qtapplication and load a url with a QWebview. So please note that this method will be called several times. In the first time the url will be loaded without any problem. But after that, the url will be loaded but some hyperlink (buttons) not act correctly.

In fact, the main that I attached isn't the real code, but it's a scenario that occurred in my application.

This is real scenario:

Start C++(non qt)
Loading the plugins
Calling the method inside the plugin
- qapplication
- qwebview
- load url
- app.exec
- ...
- close
  ....
Calling the method inside the plugin
- qapplication
- qwebview
- load url
- app.exec
- url won't be loaded correctly

jsulm

@Fakhri Well, then you have to exit the event loop before loading second qwebview.
To exit event loop call https://doc.qt.io/qt-5/qcoreapplication.html#exit
And read this: https://doc.qt.io/qt-5/qcoreapplication.html#exit
"After this function has been called, the application leaves the main event loop and returns from the call to exec(). The exec() function returns returnCode. If the event loop is not running, this function does nothing."

Fakhri

@jsulm This is my method in the plugin:

int foo(QUrl url) {

    AuthResult OAuth::authorize(Provider *provider){
        AuthResult result;
        int argc=1;
        char **argv=nullptr;
        QApplication app(argc, argv);
        QCoreApplication::exit();
        QWebView view;
        view.load(url);
        view.show();
        return app.exec();
}

For the first time is ok, but in the second time it has segmentation fault in app.exec(). This is the backtrace with gdb:

#0  0x00007fffef90e4d6 in ?? ()
   from /gnu/store/rhwni6dl3qzsp5haq374kqjl2kg3vm9a-qt-5.11.3/lib/qt5/plugins/platforms/../../../libQt5XcbQpa.so.5
#1  0x00007ffff3e851b3 in ?? () from /home/panther/.guix-profile/lib/libQt5Gui.so.5
#2  0x00007ffff3e858f9 in QPainter::drawGlyphRun(QPointF const&, QGlyphRun const&) ()
   from /home/panther/.guix-profile/lib/libQt5Gui.so.5
#3  0x00007ffff62a75e6 in WebCore::drawQtGlyphRun(WebCore::GraphicsContext&, QGlyphRun const&, QPointF const&, double) [clone .constprop.48] () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#4  0x00007ffff62a7e23 in WebCore::FontCascade::drawGlyphs(WebCore::GraphicsContext&, WebCore::Font const&, WebCore::GlyphBuffer const&, int, int, WebCore::FloatPoint const&, WebCore::FontSmoothingMode) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#5  0x00007ffff6179e0b in WebCore::FontCascade::drawGlyphBuffer(WebCore::GraphicsContext&, WebCore::TextRun const&, WebCore::GlyphBuffer const&, WebCore::FloatPoint&) const () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#6  0x00007ffff617a185 in WebCore::FontCascade::drawText(WebCore::GraphicsContext&, WebCore::TextRun const&, WebCore::FloatPoint const&, int, int, WebCore::FontCascade::CustomFontNotReadyAction) const ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#7  0x00007ffff618861e in WebCore::GraphicsContext::drawText(WebCore::FontCascade const&, WebCore::TextRun const&, WebCore::FloatPoint const&, int, int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#8  0x00007ffff5a147ad in WebCore::TextPainter::drawTextOrEmphasisMarks(WebCore::FontCascade const&, WebCore::TextRun const&, WTF::AtomicString const&, int, WebCore::FloatPoint const&, int, int) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#9  0x00007ffff5a149da in WebCore::TextPainter::paintTextWithShadows(WebCore::ShadowData const*, WebCore::FontCascade const&, WebCore::TextRun const&, WebCore::FloatRect const&, WebCore::FloatPoint const&, int, int, WTF::AtomicString const&, int, bool) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#10 0x00007ffff5a14a90 in WebCore::TextPainter::paintTextAndEmphasisMarksIfNeeded(WebCore::TextRun const&, WebCore::FloatRect const&, WebCore::FloatPoint const&, int, int, WebCore::TextPaintStyle const&, WebCore::ShadowData const*) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#11 0x00007ffff5a14fd5 in WebCore::TextPainter::paintText(WebCore::TextRun const&, int, WebCore::FloatRect const&, WebCore::FloatPoint const&, int, int, bool, bool) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#12 0x00007ffff5a9d13a in WebCore::SimpleLineLayout::paintFlow(WebCore::RenderBlockFlow const&, WebCore::SimpleLineLayou--Type <RET> for more, q to quit, c to continue without paging--
t::Layout const&, WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#13 0x00007ffff59bf7a1 in WebCore::RenderBlock::paintContents(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#14 0x00007ffff5ac7d12 in WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#15 0x00007ffff5ae191d in WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#16 0x00007ffff59cc203 in WebCore::RenderElement::paintAsInlineBlock(WebCore::PaintInfo&, WebCore::LayoutPoint const&)
    () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#17 0x00007ffff59f9d14 in WebCore::InlineElementBox::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&, WebCore::LayoutUnit, WebCore::LayoutUnit) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#18 0x00007ffff5ae7935 in WebCore::InlineFlowBox::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&, WebCore::LayoutUnit, WebCore::LayoutUnit) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#19 0x00007ffff5ae7b24 in WebCore::RootInlineBox::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&, WebCore::LayoutUnit, WebCore::LayoutUnit) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#20 0x00007ffff5ac3978 in WebCore::RenderLineBoxList::paint(WebCore::RenderBoxModelObject*, WebCore::PaintInfo&, WebCore::LayoutPoint const&) const () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#21 0x00007ffff59bf7a1 in WebCore::RenderBlock::paintContents(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#22 0x00007ffff5ac7d12 in WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#23 0x00007ffff5ae191d in WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#24 0x00007ffff59c216c in WebCore::RenderBlockFlow::paintFloats(WebCore::PaintInfo&, WebCore::LayoutPoint const&, bool)
    () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#25 0x00007ffff5ac7f55 in WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#26 0x00007ffff5ae191d in WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
--Type <RET> for more, q to quit, c to continue without paging--
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#27 0x00007ffff59cc479 in WebCore::RenderBlock::paintChild(WebCore::RenderBox&, WebCore::PaintInfo&, WebCore::LayoutPoint const&, WebCore::PaintInfo&, bool, WebCore::RenderBlock::PaintBlockType) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#28 0x00007ffff59cc6e6 in WebCore::RenderBlock::paintChildren(WebCore::PaintInfo&, WebCore::LayoutPoint const&, WebCore::PaintInfo&, bool) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#29 0x00007ffff59bf77b in WebCore::RenderBlock::paintContents(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#30 0x00007ffff5ac7d12 in WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#31 0x00007ffff5ae191d in WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#32 0x00007ffff5a34d6d in WebCore::RenderLayer::paintForegroundForFragmentsWithPhase(WebCore::PaintPhase, WTF::Vector<WebCore::LayerFragment, 1ul, WTF::CrashOnOverflow, 16ul> const&, WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int, WebCore::RenderObject*) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#33 0x00007ffff5acbf9c in WebCore::RenderLayer::paintForegroundForFragments(WTF::Vector<WebCore::LayerFragment, 1ul, WTF::CrashOnOverflow, 16ul> const&, WebCore::GraphicsContext&, WebCore::GraphicsContext&, WebCore::LayoutRect const&, bool, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int, WebCore::RenderObject*, bool) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#34 0x00007ffff5ae31cd in WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#35 0x00007ffff5ae4000 in WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#36 0x00007ffff5aea6e5 in WebCore::RenderLayer::paintList(WTF::Vector<WebCore::RenderLayer*, 0ul, WTF::CrashOnOverflow, 16ul>*, WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#37 0x00007ffff5ae2fcf in WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#38 0x00007ffff5ae4000 in WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintin--Type <RET> for more, q to quit, c to continue without paging--
gInfo const&, unsigned int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#39 0x00007ffff5aea6e5 in WebCore::RenderLayer::paintList(WTF::Vector<WebCore::RenderLayer*, 0ul, WTF::CrashOnOverflow, 16ul>*, WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#40 0x00007ffff5ae2fcf in WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#41 0x00007ffff5ae4000 in WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext&, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) () from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#42 0x00007ffff5ae4163 in WebCore::RenderLayer::paint(WebCore::GraphicsContext&, WebCore::LayoutRect const&, WebCore::LayoutSize const&, unsigned int, WebCore::RenderObject*, unsigned int) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#43 0x00007ffff60bf52c in WebCore::FrameView::paintContents(WebCore::GraphicsContext&, WebCore::IntRect const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#44 0x00007ffff50961ef in QWebFrameAdapter::renderRelativeCoords(QPainter*, int, QRegion const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKit.so.5
#45 0x00007ffff7f3fa8e in QWebFrame::render(QPainter*, QFlags<QWebFrame::RenderLayer>, QRegion const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKitWidgets.so.5
#46 0x00007ffff7f3fab1 in QWebFrame::render(QPainter*, QRegion const&) ()
   from /home/panther/.guix-profile/lib/libQt5WebKitWidgets.so.5
#47 0x00007ffff7f4b6fd in QWebView::paintEvent(QPaintEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5WebKitWidgets.so.5
#48 0x00007ffff7a7da88 in QWidget::event(QEvent*) () from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#49 0x00007ffff7f4c81b in QWebView::event(QEvent*) () from /home/panther/.guix-profile/lib/libQt5WebKitWidgets.so.5
#50 0x00007ffff7a4114c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#51 0x00007ffff7a48280 in QApplication::notify(QObject*, QEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#52 0x00007ffff38b22a8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5Core.so.5
--Type <RET> for more, q to quit, c to continue without paging--
#53 0x00007ffff7a7694a in QWidgetPrivate::sendPaintEvent(QRegion const&) ()
   from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#54 0x00007ffff7a77012 in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#55 0x00007ffff7a5033a in ?? () from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#56 0x00007ffff7a5057a in ?? () from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#57 0x00007ffff7a66c0f in QWidgetPrivate::syncBackingStore() () from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#58 0x00007ffff7a7db90 in QWidget::event(QEvent*) () from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#59 0x00007ffff7f4c81b in QWebView::event(QEvent*) () from /home/panther/.guix-profile/lib/libQt5WebKitWidgets.so.5
#60 0x00007ffff7a4114c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#61 0x00007ffff7a48280 in QApplication::notify(QObject*, QEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5Widgets.so.5
#62 0x00007ffff38b22a8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /home/panther/.guix-profile/lib/libQt5Core.so.5
#63 0x00007ffff38b4cdb in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) ()
   from /home/panther/.guix-profile/lib/libQt5Core.so.5
#64 0x00007ffff39063f3 in ?? () from /home/panther/.guix-profile/lib/libQt5Core.so.5
#65 0x00007ffff1f14b57 in g_main_context_dispatch ()
   from /gnu/store/cgy82g6yv8l1chawgch47zh23b0jll3l-glib-2.56.3/lib/libglib-2.0.so.0
#66 0x00007ffff1f14d98 in g_main_context_iterate.isra ()
   from /gnu/store/cgy82g6yv8l1chawgch47zh23b0jll3l-glib-2.56.3/lib/libglib-2.0.so.0
#67 0x00007ffff1f14e3c in g_main_context_iteration ()
   from /gnu/store/cgy82g6yv8l1chawgch47zh23b0jll3l-glib-2.56.3/lib/libglib-2.0.so.0
#68 0x00007ffff3905a5f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /home/panther/.guix-profile/lib/libQt5Core.so.5
#69 0x00007fffef9083c1 in ?? ()
   from /gnu/store/rhwni6dl3qzsp5haq374kqjl2kg3vm9a-qt-5.11.3/lib/qt5/plugins/platforms/../../../libQt5XcbQpa.so.5
#70 0x00007ffff38b0bfa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
#70 0x00007ffff38b0bfa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
--Type <RET> for more, q to quit, c to continue without paging--
   from /home/panther/.guix-profile/lib/libQt5Core.so.5
#71 0x00007ffff38b94f0 in QCoreApplication::exec() () from /home/panther/.guix-profile/lib/libQt5Core.so.5
[...]

@jsulm @JoeCFD What's your idea?

jsulm

@Fakhri said in Problem with QWebView:

QCoreApplication::exit();

Why do you call it here?

int argc=1;
char **argv=nullptr;

This is wrong as setting argc to one means that argv contains one element, but it does not in your case as you set the pointer to nullptr.

Thing is that you need to call app.exit() at some point. What is the trigger to close first window? Do you show one window after another and not at the same time? Try to use ONE QApplication instance instead of creating one each time.

Fakhri

@jsulm said in Problem with QWebView:

This is wrong as setting argc to one means that argv contains one element, but it does not in your case as you set the pointer to nullptr.

Yes, you're right. This is a minor bug that isn't my main problem for now. ;)

What is the trigger to close first window?

The user will close the first window.

Do you show one window after another and not at the same time?

At the same time? not. After closing the first window, I can call the method inside the plugin and finally open another window.

Try to use ONE QApplication instance instead of creating one each time.

Since I'm developing a plugin for another application I can't protect this for creating one instance of QApplication.

JonB

@Fakhri
I don't know if it's relevant, but:

        QApplication app(argc, argv);
        QCoreApplication::exit();
        return app.exec();

What is that QCoreApplication::exit() doing/intending to do in that place?

Fakhri

@JonB said in Problem with QWebView:

What is that QCoreApplication::exit() doing/intending to do in that place?

@JonB I should create qapplication several times so I think I should quit from event loop of previous qapplication with it. Please see this post: https://forum.qt.io/post/560665

JonB

@Fakhri
But what happens when it's called first time and there is no "previous" application to close? How do you know whether it affects the QApplication you have just created? Have you tried temporarily commenting it just to see if there is any effect on your crash?

I admit I know nothing about plugins. But this whole multi-application-exit-exec stuff looks pretty hairy to me....

Fakhri

@JonB said in Problem with QWebView:

But what happens when it's called first time and there is no "previous" application to close?

Nothing. Based on the reference: https://doc.qt.io/qt-5/qcoreapplication.html#exit