QFile writing more than 32mb at once crashes under windows 32bit

GGAllin

Hello everyone!
I have updated my appqt from 5.6 to 5.12.

Before the migration this method works fine

bool writeFile(QFile& file, QByteArray data)
{
   int bufferSize  = 30 * 1024 * 1024; 
    auto bufferSegment = data.left(bufferSize);
    while (!bufferSegment.isEmpty()) {
        qApp->processEvents();
        file.write(bufferSegment);
        data.remove(0, bufferSegment.size());
        bufferSegment = data.left(bufferSize);
    }
    return true;
}


 const QString absPath = baseDir.absoluteFilePath(fi.filePath);
        QFileInfo temp_fi(absPath);
        QDir().mkpath(temp_fi.dir().absolutePath());
        writeFile(absPath, fileData(fi.filePath));

QByteArray fileData(const &QString fileName)const {
      // other code here
 }

After the update, my application are crashing again.

Any ideas?
Thanks in advanced and sorry for my bad english
GG.

mrjj

HI
What lines does it crash in ?
Code looks ok.

Kent-Dorfman

@GGAllin said in QFile writing more than 32mb at once crashes under windows 32bit:

bool writeFile(QFile& file, QByteArray data)

Are you sure that you want to pass that by value?

mrjj

@Kent-Dorfman
Its implicitly shared so not that expensive but good eye :)
https://doc.qt.io/qt-5/implicit-sharing.html

Kent-Dorfman

@mrjj

but what might data.remove() do to it then? Also, what about the size of the object if it is passed on the stack? I envision bad thing happening when you pass huge arrays on the window stack.

mrjj

@Kent-Dorfman
You are right, it should produce a copy since its modified.

JonB

@Kent-Dorfman

but what might data.remove() do to it then?

Correct. But then passing the QByteArray in by reference, the usual thing to do, is going to alter it in the caller, which we can't have. So really the approach taken for buffering needs to be rethought. QIODevice::write(const char *data, qint64 maxSize) looks like the better overload to utilize.

None of which addresses @GGAllin's issue. AS @mrjj asked, where exactly does it crash? If you reduce the buffer size does it make any difference?

kshegunov

@GGAllin said in QFile writing more than 32mb at once crashes under windows 32bit:

After the update, my application are crashing again.

Please provide a stack trace.