将对象的亲和力从QThread更改为GUI主线程

Question

I have a Qt GUI application which contains some classes and a main. For one of the computationally heavy writing operation i created aa QThread as a class member. Something like this:

//class members
std::unique_ptr<QThread> m_savingThread;
std::unique_ptr<DiffClass> m_controller;

connect(this, &SomeClass::saveAll, m_controller.get(), &DiffClass::saveToAll, Qt::QueuedConnection);    
connect(m_controller.get(), &DiffClass::done, m_savingThread.get(), &QThread::quit);

void SomeClass::saveToFile()
{
    //Saving thread
    qDebug() << "From main thread:" << QThread::currentThreadId();

    m_controller->moveToThread(m_savingThread.get());
    m_savingThread->start();

    qRegisterMetaType<std::string>("std::string");
    emit saveAll(someString);
 }

The above code works fine. But i need the m_controller object back to the main GUI thread once the saving operation is finished. I could find something similar here . Briefly, it states that since QThread can only "push" the object into a thread, i need to push it again into the main thread from the current worker thread.

void DiffClass::saveToAll(someString)
{
    qDebug() << "From worker thread:" << QThread::currentThreadId();
    /*saving operation*/
    moveToThread(QApplication::instance()->thread()); //Error QCoreApplication has no member thread()
    emit done();
}

Is there a way to change the affinity of the object back to the main thread?

EDIT 1: My connect to saveToAll is a QueuedConnection.

Answer 1

First and foremost, why would you want to switch thread affinity back and forth? There doesn't seem to be a practical side to this.

Other than that, it should be possible to change it to another threat, the condition is that the object has no parent and the moveToThread() is invoked from the current affinity thread.

You can use QMetaObject::invokeMethod() with Qt::QueuedConnection specified from any thread to schedule a slot execution from the current affinity thread, which will change affinity from the right thread to whatever thread you pass as a parameter.

But seeing how you try to change it from inside the class, that should work as expected, as long as saveToAll() is invoked via the signal/slot mechanism (rather than directly from just about any thread).

//Error QCoreApplication has no member thread()

It most certainly does according to the documentation.