QThread crashes on exit

[mhoover]

QThread attempts to lock something when it exits using a QMutexLocker class.

void QThread::exit(int returnCode)
{
    Q_D(QThread);
    QMutexLocker locker(&d->mutex);   // <------ Crashes here! d == 0x0
    d->data->quitNow = true;
    for (int i = 0; i < d->data->eventLoops.size(); ++i) {
        QEventLoop *eventLoop = d->data->eventLoops.at(i);
        eventLoop->exit(returnCode);
    }
}

void QThread::exit(int returnCode)
{
    Q_D(QThread);
    QMutexLocker locker(&d->mutex);   // <------ Crashes here! d == 0x0
    d->data->quitNow = true;
    for (int i = 0; i < d->data->eventLoops.size(); ++i) {
        QEventLoop *eventLoop = d->data->eventLoops.at(i);
        eventLoop->exit(returnCode);
    }
}

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Just trying to declare the QMutexLocker causes a crash.

This looks like a Qt bug, but I'm not sure.

Any ideas? It looks like "d" might not have been allocated.

[nish]

now see... thousands of ppl use QThread everyday.. if it was so easy to crash it than it would have been found and fixed there and then... so the problem is in your case..
whenever your proggi crashes in Qt code, then make a minimal compilable example that would reproduce the bug and submit it to trolltech... it would also be helpful to answer you if you submit it here ...

[lyuts]

Is there core dump?

[wysota]

Aren't you calling exit() on an uninitialized QThread pointer by any chance?

[mhoover]

There is no core dump. How do you enable that again? I'm using RedHat if that matters.

In this case the threads are declared as member variables on the stack, so the threads can't be uninitialized pointers. I suppose there could be other uninitialized pointers ...

I realize there are a lot of people who use QThreads all the time, but I don't think a large portion of the herd is running in my direction (lots of threads containing networking classes). The other thing is I wonder how a private Qt-class variable is not initialized ...

[wysota]

In this case the threads are declared as member variables on the stack, so the threads can't be uninitialized pointers.

Sure they can.

The other thing is I wonder how a private Qt-class variable is not initialized ...

Probably because it was deleted or has not been initialized yet. Or... you have stack corruption.

[mhoover]

Thanks again, everyone for your help.

This solved the problem:

UDPThread::~UDPThread()
{
    exit();
    while( this->isRunning() == true ) {
 
    }
 
}

UDPThread::~UDPThread()
{
    exit();
    while( this->isRunning() == true ) {

    }

}

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My assumption was exit() didn't return until the thread was finished running, but it keeps going.

It looks like exit() stops the event loop and then stops the run() a bit later.

[spirit]

try to use "native" methods of QThread

UDPThread::~UDPThread()
{
	if (isRunning()) {
		quit();
		wait();
	}
}

UDPThread::~UDPThread()
{
	if (isRunning()) {
		quit();
		wait();
	}
}

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[mhoover]

Oh, right.

I was trying to use the intellisense thing to quickly see what methods were available.

I will change it.