emit singnals from another thread

[danics]

Hi everybody!

I want to know if I emit a signal from another thread which event loop is responsible for emitting the signal. in other words, this signal emitted from which thread?

for example mysignal in below code

class O2;
 
class O1 : public QObject
{
Q_OBJECT
public:
O1(QObject *parent = 0): olocal(new O2(this)), QObject(parent) 
{
     m_thread = new QThread;
     olocal->moveToThread(m_thread);
     connect(m_thread, SIGNAL(started()), olocal, SLOT(start()));
     connect(olocal, SIGNAL(finished()), m_thread, SLOT(quit()));
 
....
}
 
~O1() {
   olocal->finish();
   m_thread->wait();
  delete olocal;
  delete m_thread;
}
 
signals:
   void mysignal();
};
 
class O2 : public QObject
{
Q_OBJECT
public:
O2(O1 *parent) : q_ptr(parent) {}
 
signals:
   void finished();
 
public slots:
    void start() { b_start = true; QTimer::singleShot(0, this, SLOT(run())); }
    void finish() { b_finish = true; }
 
    void run() {
        if(b_finished) {
             emit finished();
             return;
         }
 
        // do some staff
        if( /* something */)
             emit q_ptr->mysignal();
 
        if(b_start)
             QTimer::singleShot(0, this, run());
    }
};

class O2;

class O1 : public QObject
{
Q_OBJECT
public:
O1(QObject *parent = 0): olocal(new O2(this)), QObject(parent) 
{
     m_thread = new QThread;
     olocal->moveToThread(m_thread);
     connect(m_thread, SIGNAL(started()), olocal, SLOT(start()));
     connect(olocal, SIGNAL(finished()), m_thread, SLOT(quit()));

....
}

~O1() {
   olocal->finish();
   m_thread->wait();
  delete olocal;
  delete m_thread;
}

signals:
   void mysignal();
};

class O2 : public QObject
{
Q_OBJECT
public:
O2(O1 *parent) : q_ptr(parent) {}

signals:
   void finished();

public slots:
    void start() { b_start = true; QTimer::singleShot(0, this, SLOT(run())); }
    void finish() { b_finish = true; }

    void run() {
        if(b_finished) {
             emit finished();
             return;
         }

        // do some staff
        if( /* something */)
             emit q_ptr->mysignal();

        if(b_start)
             QTimer::singleShot(0, this, run());
    }
};

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thanks in advance

[jefftee]

The signal would be emitted from the thread that is executing your code that does the emit. Your connect statements above will used queued connections when the sender/receiver are in different threads. You can force the connection type, but I would recommend that you use the default queued connection type unless you have very specific requirements.

[anda_skoa]

Just to clarify: there is no event loop involved with emitting
However, with a QueuedConnection the slot it called by the event loop of the thread "owning" the receiver object.

The same is true for an AutoConnection when the thread executing the emit is a different one than the "receiver" thread, as jefftee said.

Cheers,
_