Error on QtConcurrent::run

[KroMignon]

@peter-70 Perhaps you have to enable concurrent in your PRO file:

QT += concurrent

[J.Hilk]

@peter-70 is that a valid overload of run ? If I remember correctly the first paramter has to be a member function not an object.

I may be wrong however.

[KroMignon]

@J.Hilk This usage is totally legal.

For example, from Qt documentation => https://doc.qt.io/qt-5/qtconcurrentrun.html

// call 'QList<QByteArray>  QByteArray::split(char sep) const' in a separate thread
QByteArray bytearray = "hello world";
QFuture<QList<QByteArray> > future = QtConcurrent::run(bytearray, &QByteArray::split, ',');
...
QList<QByteArray> result = future.result();

[KroMignon]

@peter-70 What is the type of synchronizer? It should be QFutureSynchronizer<void> to match PositionGroupbox::Select() signature.

[kshegunov]

Does PositionGroupbox derive from QWidget directly or indirectly?

[peter-70]

@KroMignon said in Error on QtConcurrent::run:

QT += concurrent

Good idea, but unfortunately it does not help

[J.Hilk]

@peter-70
if you forgot QT += concurrent inside your *pro file, you have to do a complete rebuild - deleting build folder running qmake - for it to take effect, after adding it!

Did you do that?

[peter-70]

@kshegunov

Yes, PositionGroupbox derive from QWidget directly. But What does it matter?

[peter-70]

@J.Hilk At first, I did not do it. Now I've deleted the output folder and the makefile. Then recreate the makefile and invoke rebuild my project. But that does not help either :-(

[peter-70]

@KroMignon

It should be QFutureSynchronizer<void> to match PositionGroupbox::Select() signature

Yes it is!

Here is the code snippet:

QFutureSynchronizer<void> synchronizer;

    while ((rc = position.Fetch()) && rowIndex < itemsCount)
    {
        auto p = new Position;
        p->Copy(&position);

        auto positionWidget = new PositionGroupbox(p, this);
        p->SetContainer(positionWidget);

        synchronizer.addFuture(QtConcurrent::run(positionWidget, &PositionGroupbox::Select, false));

[KroMignon]

@peter-70 This sound very strange to me.

I have used QtConcurrent::run() and never run in this error.

I think you have include header:

#include <QtConcurrent/QtConcurrent>

Can you show the declaration of PositionGroupbox::Select?

[peter-70]

@KroMignon

Can you show the declaration of PositionGroupbox::Select?

Yes, the include is as you write it here. But the declaration of PositionGroupbox::Select is the right question and solution!!!

100 points for you! ;-)

The declaration is:

void Select(bool isSelected, bool refreshColors = false);

Now I call

synchronizer.addFuture(QtConcurrent::run(positionWidget, &PositionGroupbox::Select, false, false));

and everything is ok!

@all: Thank you very much! Specially for KroMignon :-)

[KroMignon]

@peter-70 your welcome

[kshegunov]

@peter-70 said in Error on QtConcurrent::run:

Yes, PositionGroupbox derive from QWidget directly. But What does it matter?

It matters quite a lot. QWidget is not thread-safe and it's not reentrant. You can't touch anything QWidget-y outside the GUI thread, including creating the actual object. Failing to observe this is a race condition and ultimately a bug. That is to say, you have bigger problems than a syntax error.