QTextCursor causes segmentation fault

bs55

Hello everyone,

I am developping a motion capture secquence recording program and I am trying to log the color messages in a QTextEdit (black = normal, orange = warning, red = critical).
Unfortunatly the QTextCursor sometimes causes sefmentation fault.

Here is my code:

void MainWindow::logWarning(QString qs_Entry) {
    qWarning() << qs_Entry;

    try {
        QTextCursor qtc(qte_Log->textCursor());

        QTextCharFormat qtcf;
        qtcf.setForeground(QBrush(QColor("Orange")));
        qtc.setCharFormat(qtcf);

        qtc.insertText(qs_Entry + "\n");
    } catch (...) {
        qInfo() << "An unexpected error occured when logging a warning!";
    }
}

The try catch does not seems to catch the error.

Did I do something wrong?
If not, is there another way to display color messages in the QTextEdit without causing segmentation faults?

Note: I don't know if it's relevant but my program is heavily multithreaded.

SGaist

Hi,

Might be a silly question but are you sure that qte_Log is a valid pointer ?

Otherwise, what does the stack trace tell you ?

bs55

@bs55 said in QTextCursor causes segmentation fault:

qte_Log

Yes, this pointer is valid.

I forgot to specify that the code works but sometimes causes segmentation fault.

Here is the debuger stack trace:
1 ?? 0x7ffff3df5aac
2 ?? 0x7ffff3dea28e
3 ?? 0x7ffff3dea2e5
4 QTextEngine::itemize() const 0x7ffff3dee69c
5 QTextEngine::lineNumberForTextPosition(int) 0x7ffff3df0bed
6 QTextLayout::lineForTextPosition(int) const 0x7ffff3df785c
7 QTextCursorPrivate::setX() 0x7ffff3e47c4e
8 QTextCursor::insertText(QString const&, QTextCharFormat const&) 0x7ffff3e49775
9 QTextCursor::insertText(QString const&) 0x7ffff3e4a704
10 MainWindow::log mainwindow.cpp 843 0x416edb
11 MainWindow::captureProgressHandler mainwindow.cpp 600 0x414309
12 QtPrivate::FunctorCall<QtPrivate::IndexesList<0, 1>, QtPrivate::List<int, double>, void, void (MainWindow:: *)(int, double)>::call qobjectdefs_impl.h 136 0x425cf0
13 QtPrivate::FunctionPointer<void (MainWindow:: *)(int, double)>::call<QtPrivate::List<int, double>, void> qobjectdefs_impl.h 169 0x4251bf
14 QtPrivate::QSlotObject<void (MainWindow:: *)(int, double), QtPrivate::List<int, double>, void>::impl qobject_impl.h 120 0x4243c6
15 QMetaObject::activate(QObject *, int, int, void * *) 0x7ffff3756b96
16 CaptureThread::signalCaptureProgress moc_capturethread.cpp 158 0x42d414
17 CaptureThread::run capturethread.cpp 98 0x427dc8
18 ?? 0x7ffff355d70a
19 start_thread pthread_create.c 333 0x7ffff1b926ba
20 clone clone.S 109 0x7ffff2c5841d
... <More>

JonB

@bs55

The try catch does not seems to catch the error.

Just to be clear, try ... catch will only catch genuine, recoverable "errors". Once you have something like a Seg Fault, nothing will catch that.

jsulm

@bs55 To add to @JonB : Qt itself does not use (throw) exceptions.

VRonin

@bs55 said in QTextCursor causes segmentation fault:

Note: I don't know if it's relevant but my program is heavily multithreaded.

Is MainWindow::logWarning called directly from a secondary thread?

JonB

@jsulm said in QTextCursor causes segmentation fault:

@bs55 To add to @JonB : Qt itself does not use (throw) exceptions.

OK. But if the underlying OS/windowing system does throw exceptions, would Qt catch them guaranteed or would they pass through to the calling code?

SGaist

Qt by default is build without exception support disabled.

For the rest see the Exception Safety chapter in Qt's documentation.

bs55

@VRonin No the threads emit signals connected to a slot that uses the logWarning function.

jsulm

@bs55 Did you use QueuedConnection in connect?

VRonin

@bs55 said in QTextCursor causes segmentation fault:

No the threads emit signals connected to a slot that uses the logWarning function

Looks like they are connected with Qt::DirectConnection though which is equal to calling the slot from another thread

11 MainWindow::captureProgressHandler mainwindow.cpp 600 0x414309
[...]
16 CaptureThread::signalCaptureProgress moc_capturethread.cpp 158 0x42d414
17 CaptureThread::run capturethread.cpp 98 0x427dc8