qFatal calling QCoreApplication::processEvents

I reduced the following example to the absolute minimum. So the nested QTimer::singleShot is indeed necessary. The actual code where I engaged this bug is much more complicated, with lock_guard's and Q_ASSERT and multiple threads.

Here I enqueue one lambda to the event loop which does nothing more than placing a function call to f on the event loop and calling f directly after that.

I expect the event loop to handle one event after the other. So function f should be called once and after it returns to the event loop it should get called a second time.

What I do not expect is, that the function f gets entered twice before returning once.

But this is what actually happens. The call to qFatal seems to process events.

// console output of example program, if you ignore the fatal dialogs

1 - enter f
2 - inside f
1 - enter f
2 - inside f
3 - leave f
3 - leave f

I noticed this bug in another project, when I got an assertion and the dialog popped up and I pressed ignore, because the assertion failure was not critical to me, but the unexpected event processing crashed my program.

It is possible, that this problem is Windows specific. But I don't expect QT functions to process events in general. If I want to do that, I would call QCoreApplication :: processEvents directly.

#include <QCoreApplication>
#include <QTimer>

void f()
{
    qInfo("1 - enter f");
    qFatal("2 - inside f");
    qInfo("3 - leave f");
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QTimer::singleShot(0, [] {
        QTimer::singleShot(0, f);

        f();
    });

    return a.exec();
}