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c++qtqthreadqtimer

QTimer not firing in a thread

I have an Qt5 c++ app with 2 threads, thread A is started when the main program starts up. The start method of thread A runs successfully.

So far so good. Next, in the main program I send a signal to Thread A to start a QTimer, which it does - but that timer never expires!

Thread B handles tcp connections. When I initiate a telnet connection to my app, thread B fires up and suddenly I see my Qtimer from thread A expiring at normal intervals.

Why is the QTimer from thread A not expiring until thread B starts?

I suspect my threads are getting messed up. note the last section of code below products this:

thread of this:  QThread(0x200fe00)  
thread of timer:  QThread(0x1fff470)

Which suggest my worker object (this), is in a different thread from my timer object. This timer thread address is actually the MAIN thread. Why? I'm confused.

Suggestions?

In my main app I create and start my thread like this:

QThread * MyControllerThread = new QThread(this);

if (MyControllerThread) {

    TheController *worker = new TheController(MyControllerThread);

    if (worker) {
        connect(MyControllerThread, SIGNAL(started()), worker, SLOT(start()));
        connect(MyControllerThread, SIGNAL(finished()), worker, SLOT(deleteLater()));
        connect(MyControllerThread, SIGNAL(finished()), MyControllerThread, SLOT(deleteLater()));
        worker->moveToThread(MyControllerThread);  
        MyControllerThread->start();  
    }

and in my main app I emit a signal to the new thread:

    emit sig_startlocalpeer(Types::EActionLocalServiceStart);  // Move the local peer to standby mode to start remote tests

which runs a slot in my thread (TheController object):

connect(&m_remotetestintervaltimer,SIGNAL(timeout()),this,SLOT(expiredRemoteTestIntervalTimer()));
m_remotetestintervaltimer.setTimerType(Qt::VeryCoarseTimer);
m_remotetestintervaltimer.start(REMOTETEST_TIMER_INTERVAL);  // Wait between ticks
qDebug() << "thread of this: " << this->thread();
qDebug() << "thread of timer: " << m_remotetestintervaltimer.thread();
Solution

  • The best answer seems to be a combination of RobbieE and Kuba:

    You have to explicitly set the parent of the member variable in constructor. The parent-child feature is a Qt thing that exists among classes derived from QObject, it is not a feature of C++.

    I never knew this - I assumed that when an object was created, its members variables automatically had their parent set to the object. Good to know!!