Question about Qt::QueuedConnection

AccWhid

I'm curious about the behavior of signals when connected to slots via Qt::QueuedConnection, specifically what if you call to emit the same signal from two different threads.

i.e.:

class A : public QObject
{
    Q_OBJECT
public:

    A()
    {
        auto worker = new B();
        auto thread = new QThread();
        worker.moveToThread(thread);

        connect(this, &A::fireTestSignal, worker, &B::testSlot);

    }

    void fireTestSignal()
    {
        emit fireTestSignal();
    }

signals:

    void testSignal();

};

class B : public QObject
{
    Q_OBJECT

public:

    B()
    {

    }

public slots:

    void testSlot()
    {
        qInfo() << "Test";
    };
};

int main()
{
    
    //Assume QCoreApplication created here

    const auto testClass = std::make_shared<A>();

    QtConcurrent::run(QThreadPool(), [testClass]()
    {
        testClass->fireTestSignal();
    });

    testClass->fireTestSignal();


    return 0;
}

Does firing the same signal from two threads cause issues if the connection is a Queued Connection type? Is calling the signal itself thread safe?

Thanks!

dheerendra

No
Yes