Buffer Overrun using Qt Threads and Signals

Question

I have to downgrade a project from QT5 to QT4 and get a weird buffer overrun error when doing so. Here's my code:

I create a QThread like so:

thread = new QThread;
reader = new Reader();

reader->setParams(samplingRate);
reader->moveToThread(thread);
connect(thread, SIGNAL(started()), reader, SLOT(read()));
connect(reader, SIGNAL(finished()), thread, SLOT(quit()));
connect(thread, SIGNAL(finished()), this, SLOT(threadFinished()));
connect(reader, SIGNAL(finished()), reader, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(reader, SIGNAL(errorMsg(QString)), this, SLOT(threadErrorMsg(QString)));
thread->start();

In my thread I have the following code:

try {
     while(condition) {
         ...something
     }
} catch(Exception e) {
     emit errorMsg("Error");
}
emit finished();

And the Slots in my main thread look like this:

void MainWindow::threadFinished() {
    reader = NULL;
    delete thread;
    thread = NULL;
}

void MainWindow::threadErrorMsg(QString message) {
    QMessageBox::critical(this, "Error", ("Error: " + message).toStdString().c_str(), QMessageBox::Ok);
}

All of this worked well in QT5. The error message box was displayed correctly and the thread was destroyed. In QT4 (4.8.1) however I get a buffer overrun error when an error occurs and errorMsg() is emitted. The buffer overrun does not occur if I don't emit the errorMsg("Error") and destroy the thread only by calling finished(). Any ideas on what's wrong here?

Update: If i don't access the QString in threadErrorMsgit does work. Like so:

void MainWindow::threadErrorMsg(QString message) {
    QMessageBox::critical(this, "Error", "Error", QMessageBox::Ok);
}

What am I doing wrong?

Answer 1

void MainWindow::threadFinished() {
    reader = NULL;
    delete thread;
    thread = NULL;
}

Deleting the thread directly in the slot is not advised. You should use the deleteLater function.

thread->deleteLater();

However, you've already setup the thread to be deleted in the connection

connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));

So you're now trying to delete it twice!

As for the buffer-overrun, I suspect something has corrupted memory before the error has occurred.