No, the message is not harmless at all. The object you have created has a null parent and no reference on the thread association and thus its thread() method may return a dangling pointer at any time. It cannot safely use timers nor receive cross-thread calls. It is basically as useless object, and you're asking for undefined behavior to strike. This shouldn't be a warning, but a failure. Qt did you a disservice here by allowing you to continue.
The idiomatic way of doing it is first of all not to derive from QThread. QThread is a thread handle. It wraps a system resource. Put all of your functionality into a regular QObject moved into a QThread. The idiomatic way to endlessly "do stuff" on any thread, including the main thread, is to use a zero-duration timer. Note that zero-duration timers have nothing to do with timing at all. They are essentially event loop handles, calling them a timer is a misnomer.
To wit:
// https://github.com/KubaO/stackoverflown/tree/master/questions/thread-simple-50632807
#include <QtNetwork>
class Thread final : public QThread {
Q_OBJECT
public:
void takeObject(QObject *obj) {
obj->moveToThread(this);
}
~Thread() override {
requestInterruption();
quit();
wait();
}
};
class Class : public QObject {
Q_OBJECT
QBasicTimer m_workTimer;
QNetworkAccessManager m_manager{this};
void doWorkChunk() {
qDebug() << "tick...";
QThread::sleep(1); // emulate a blocking operation
}
protected:
void timerEvent(QTimerEvent *ev) override {
if (ev->timerId() != m_workTimer.timerId())
return;
doWorkChunk();
}
public:
explicit Class(QObject *parent = {}) : QObject(parent) {
m_workTimer.start(0, this);
}
};
int main(int argc, char *argv[]) {
QCoreApplication app(argc, argv);
Class object;
Thread workThread;
workThread.start();
workThread.takeObject(&object);
QTimer::singleShot(3000, &QCoreApplication::quit);
return app.exec();
}
#include "main.moc"
The QBasicTimer::stop: Failed. Possibly trying to stop from a different thread warning is relatively benign and indicates an internal timer handle leak. For a workaround, see this answer.
