slot/signal in QtConcurrent

lindaah

hi I have 2threads that I would like to activate them at the same time but after some try I had this problem :

Object: Cannot create children for a parent that is in a different thread.
(Parent is QTextDocument(0xaa695e78), parent's thread is QThread(0xba7c18), current thread is QThread(0xbbde50)
2021-07-07 10:32:49 sigHandler: Unhandled signal 11, terminating

code :

 void Lid::on_Lid_clicked()
{
QFuture<void> fut1 = QtConcurrent::run(IMU, this->Folder, this->ui->label_IMU, this->ui->IMU );
QFuture<void> fut = QtConcurrent::run(graphique, this->folder ,this->ui->IMU ,this->ui->Cameratoggle);
}

after a search on the internet I found that it is necessary to use the signal and slot I tested this code :

 void Lid::on_Lid_clicked()
{
QFutureWatcher<void>Watcher1;
Watcher1.setFuture(QtConcurrent::run(IMU, this->Folder, this->ui->label_IMU, this->ui->IMU );

 QFutureWatcher<void>Watcher;
         Watcher.setFuture(QtConcurrent::run(graphique, this->folder ,this->ui->IMU ,this->ui->Cameratoggle));

         connect (&Watcher1,SIGNAL(reset()),&Watcher,SLOT(reset()));
}

but still the same problem could you help me

VRonin

@lindaah said in slot/signal in QtConcurrent:

this->ui->label_IMU, this->ui->IMU

I don't know what your function does but, given the arguments, I have to warn you you can't edit elements of the UI from a secondary thread

Pl45m4

@lindaah said in slot/signal in QtConcurrent:

Object: Cannot create children for a parent that is in a different thread.
(Parent is QTextDocument(0xaa695e78), parent's thread is QThread(0xba7c18), current thread is QThread(0xbbde50)

This is the issue here. You cannot set a parent which lives in another thread.

What does your functions graphique and IMU do? Is it neccessary for them to access ui elements? Because you shouldnt do that (ui->IMU)

lindaah

@Pl45m4 @VRonin so how can we access the ui element, because it s neccessary for me

KroMignon

@lindaah said in slot/signal in QtConcurrent:

so how can we access the ui element, because it s neccessary for me

You can only update ui element in main thread.
And you should only access them in main thread.

cf. https://doc.qt.io/qt-5/thread-basics.html#gui-thread-and-worker-thread

Pl45m4

@lindaah

Only from your gui thread. You can send a signal to your gui therad and change it there.

lindaah

@Pl45m4 how ? can you give me an exemple please?
@KroMignon
but why did they walk for 13 times then please ?
in fact after the 13th time I had this error

KroMignon

@lindaah said in slot/signal in QtConcurrent:

but why did they walk for 13 times then please ?

Because you was 13 times lucky...

lindaah

@KroMignon how can i correct it please

KroMignon

@lindaah said in slot/signal in QtConcurrent:

how can i correct it please

It is simple, do use QObject based items in their thread ;-)

How exactly depends on what you are doing!
There is no magic method.

lindaah

@KroMignon but I would need in a thread to activate another button
that's why I did
this->ui->Cameratoggle

KroMignon

@lindaah said in slot/signal in QtConcurrent:

but I would need in a thread to activate another button

Then you have to do it in button thread.

There are many way to do it, for example:

emit a signal which is connected to this slot.
use QTimer::singleShot()
use QMetaObject::invokeMethod()

lindaah

@KroMignon ok thanks :)

lindaah

@KroMignon I can't do it can you please give me an example

KroMignon

@lindaah said in slot/signal in QtConcurrent:

I can't do it can you please give me an example

What did you try?
Show me the code you are trying and I can give you advice.

lindaah

@KroMignon I have this qchart
and I would like to visualize it in a label and save it as a png
code :
void graphique(QString folder, QLabel *labelgraphe)
{
.
.
.
.
.
QChart *chart = new QChart(); // Pointer sur charte
chart->legend()->hide();
chart->addSeries(series);
chart->createDefaultAxes();
chart->axes(Qt::Vertical).first()->setRange(-3, 3);
chart->axes(Qt::Horizontal).first()->setRange(-10, 10);

                           chart->setBackgroundBrush(QBrush(Qt::black));
                           QChartView *chartView = new QChartView(chart); 
                           chartView->setRenderHint(QPainter::Antialiasing); 
                           QMainWindow window; 
                           window.setCentralWidget(chartView); 
                           window.resize(500, 500); 
                           QString fileim = QDateTime::currentDateTime().toString(QString("'%1/graphe_'yyyy_MM_dd'_'hh_mm_ss'.png").arg(dossier));
                           QPixmap p = chartView->grab();
                           labelgraphe->setPixmap(p);
                          p.save(fileim);

}

void Lid::on_Lid_clicked()
{
QFuture<void> fut1 = QtConcurrent::run(IMU, this->Folder);
QFuture<void> fut = QtConcurrent::run(graphique, this->folder ,this->ui->labelgraphe);
}

SGaist

Hi,

As already stated by my fellows, you can't manipulate GUI elements from other threads than the main thread and it's exactly what you do in your "graphique" function.

lindaah

@SGaist yes I know but how can I correct it?
@KroMignon can you help me please

jsulm

@lindaah said in slot/signal in QtConcurrent:

but how can I correct it?

You already was told to emit a signal in your thread. Then you connect that signal to a slot in GUI thread where you update your UI...

lindaah

@jsulm but i haven't found how i can work with it
can you help me please