problems with Qt::QueuedConnection

Revi

Hi,
I am pretty sure it is an easy error or a general misunderstanding but I don't see it so I am posting here.

I have a MainWindow class which holds a Sync object and a Logger object.

After a action is triggered a function in the mainwindow starts a function from the sync object in another thread. (std::thread).
e.g.: std::thread a(&Sync::startSyncProcess,sync_.get());
The thread is immediately detached.

The sync Objects holds a pointer to a log object which holds pointers to all objects that needs information about the sync process.
The "Logger" is a QObject with a Q_Object macro.
The sync objects calls a Logger::report(int step) function which emits a Logger::report_progress_to_mwnd(step) function.

In the Constructor of the Logger I made a Qt::QueuedConnection between the Logger::report and Logger::reports_progress_to_mwnd function.

Here is the basic code:

class Logger : public QObject
{
	Q_OBJECT
public:
	Logger(QProgressBar * mwpb) : mw_pb_(mwpb)
	{
		QObject::connect(this, SIGNAL(report(int)), this, SLOT(report_progress_to_mwnd(int)), Qt::QueuedConnection);
	}
	void report(int step){ 
		emit(report_progress_to_mwnd(step)); 
	}
	void report_progress_to_mwnd(int steps)
	{
		mw_pb_->setMinimum(0);
		mw_pb_->setMaximum(5);
		mw_pb_->setValue(steps);
	}
};

I thought that the report_progress_to_mwnd(int steps); function would be emited in the Thread of the MainWindow but it is still executed in the thread that I launched from the MainWindow. What do I oversee?

Please do not recommend to change std::thread with QThread I need a solution with std::threads.

Thanks for your help.

Regards,
Revi

Chris Kawa

Hi, welcome to devnet.

That's not how you define signals and slots and emitting a slot makes no sense.

class Logger : public QObject
{
   Q_OBJECT
public:
   Logger(QProgressBar * mwpb) : mw_pb_(mwpb) {
       connect(this, SIGNAL(reported(int)), this, SLOT(report_progress_to_mwnd(int)), Qt::QueuedConnection);
   }
   void report(int step) {
      emit reported(step); //you emit a signal, not a slot
   }

signals:
   void reported(int); //you don't implement signals. they are generated by moc

public slots:
   void report_progress_to_mwnd(int steps) {
      mw_pb_->setMinimum(0);
      mw_pb_->setMaximum(5);
      mw_pb_->setValue(steps);
   }
};

Now calling a report method will emit signal reportedand that in turn will schedule the connected report_progress_to_mwnd slot to execute.

Btw. Please use ``` at the beginning and end of code blocks to enable code highlighter.

Revi

Thank you very much for the clarification that solved my problem.