Qt Signal from QRunnable not received/not connecting - qt

Question

I'm writing a Qt Application in C++. I have a QRunnable running in a QThreadPool, and it sends a signal to the main thread. The problem is, the connection doesn't work: the signal is never received by the main thread, even though I've verified that the code doing the emit is indeed called. Here is my code:
My QRunnable class:
class OfflineAnalysisThread : public QObject, public QRunnable
{
Q_OBJECT
public:
void run();
void sendMessage(QString &qmsg)
{
emit threadMessageCallback(qmsg);
}
signals:
void threadMessageCallback(QString &string);
};
And the calling class (main thread):
class OfflineAnalysisMain : public QObject
{
Q_OBJECT
public:
(...)
public slots:
void threadMsg(QString &string);
};
The code that instantiates the new QRunnables and starts them:
void OfflineAnalysisMain::myFunction()
{
OfflineAnalysisThread *newTask = new OfflineAnalysisThread();
QObject::connect(newTask, SIGNAL(threadMessageCallback(QString &)), this, SLOT(threadMsg(QString &)));
QThreadPool::globalInstance()->start(newTask);
}
So, from my QRunnable's run function, I call sendMessage and then I do QApplication::exec(). I have a breakpoint on the threadMsg slot implementation in OfflineAnalysisMain.cpp, and that function is never called.
What am I doing wrong?
UPDATE:
Definition of my OfflineAnalysisThread::run() function:
void OfflineAnalysisThread::run()
{
std::string myMsg("This is my message");
sendMessage(myMsg);
QApplication::exec();
}
I have also tried without the QApplication::exec();, without success.

Answer 1

Remove the call to QApplication::exec() from within run(). This is ideally called from within your main function.
In order to get your code to work, I had to write the following main function:
#include <QApplication>
#include <QMetaType>
#include <offlineanalysismain.h>
int main(int argc, char* argv[])
{
QApplication app(argc, argv);
qRegisterMetaType<QString>("QString&");
OfflineAnalysisMain* main = new OfflineAnalysisMain;
main->myFunction();
return app.exec();
}
Note the call to qRegisterMetaType, which allows Qt to pass a QString through a signal-slot connection that cross thread boundaries.