How to properly delete threads& objects in them ?

Dariusz

Hey

I'd like to delete a bunch of threads & every object that is used by these threads... what is the proper approach to perform that action ?

class myObj : public QObject {
Q_OBJECT
public:
    myObj(QObject *p = nullptr) : QObject(p) {

    }
    ~myObj() {
        qDebug() << "My obj is dyin!" << this;
    }

};

class myThread : public QThread {
Q_OBJECT
public:
    myThread() {

    }
    ~myThread() {
        qDebug() << "My thread dying " << this;
    }
};
int main(int argc, char *argv[]) {
    auto app = QApplication(argc, argv);

    QWidget w;

    w.show();


    auto t = new myThread();
    auto ob = new myObj(&w);
    auto otherOb = new QTcpSocket(ob);
    qDebug() << "Made thread : " << t;
    qDebug() << "Made object : " << ob << ob->parent() << ob->thread();
    ob->setParent(nullptr);
    ob->moveToThread(t);
    QMetaObject::invokeMethod(ob, [&, thread = t, object = ob]() { object->setParent(thread); }, Qt::QueuedConnection);
    ob->setParent(t);
    qDebug() << "Made object : " << ob << ob->parent() << ob->thread();
    t->start();
    t->terminate();
    t->deleteLater();
    app.processEvents();
    uint time = 0;
    while (time < 100) {
        time++;
        QThread::msleep(10);
        app.processEvents();
    }
    qDebug() << "Thread : " << t;
    qDebug() << "ob  : " << ob->thread();
    ob->moveToThread(app.thread());
    ob->deleteLater();
    qDebug() << "ob2 : " << ob->thread();
    app.exec();

    return 1;

}

I'm getting stuck/lost. Say if I delete the thread, then calling ob->deleteLater() will be useless as there won't be any event loop able to handle the request? Since the thread will be gone... any ideas?

mrjj

Hi
One way is to use the signal from the thread
connect(Thread, &QThread::finished, worker, &WorkerObject::deleteLater);

Do notice that using terminate is not recommended
https://doc.qt.io/qt-5/qthread.html#terminate
Its sort of "violent" :)

Normally you do
Thread->quit();
Thread->wait();

Dariusz

@mrjj Ahh I mess up with that termination, I mixed it up with the other one in my head and never checked 2x docs... yeah quit() works as I expected and object now dies properly. Thanks!

So in general, moving object to another thread does not set the thread as it parent does it.

Christian Ehrlicher

@Dariusz said in How to properly delete threads& objects in them ?:

So in general, moving object to another thread does not set the thread as it parent does it.

No because the function is called moveToThread and not moveToThreadAndDoOtherStuffLikeSettingaParent