Can't pass a signal with QSharedPointer (or std::shared_ptr<>) between threads

[michalos]

Hi
I'm trying to catch a signal emitted with a shared pointer, but the signal is not being caught in a class that is in a different thread.
When I try to catch an empty signal, everything works fine.

My code :

//creating the QShared ptr
//   std::shared_ptr<Message> msgShared (new Message());

    QSharedPointer<Message> message(new Message());

// emiting : (works)
            emit parsingTextMessageFinished(message);

//different class:

 void PBXReader::initHandlers(){
 smsHandler = new SMSTagHandler(req_ans_mangr, this);

  connect(smsHandler,&SMSTagHandler::parsingTextMessageFinished,this,&PBXReader::gotParsingTextMessageFromSMSHandler);

}

void PBXReader::gotParsingTextMessageFromSMSHandler(QSharedPointer<Message> msg)
{
    emit parsingTextMessageFinShared(msg);
    emit parsingTextMessageFin();

}

and in the main thread:

public slots:
    void gotParsingTextMessage(QSharedPointer<Message>);
    void gotParsingTextMesg();

    connect(pbxReader,&PBXReader::parsingTextMessageFin,this,&MessengerCTI::gotParsingTextMesg);
    connect(pbxReader,&PBXReader::parsingTextMessageFinShared,this,&MessengerCTI::gotParsingTextMessage);

Does anyone got any idea why?

[mrjj]

@michalos

Hi normally
Signals between threads is Qt::QueuedConnection
and you must use type that is known how to queue.

I wonder if QSharedPointer<Message>
is seens as new type.

You dont get any warnings ?

[michalos]

@mrjj
Thank You for Your answer.
I was wondering the same thing.
I don't get any info, that I should register a metatype (qRegisterMetaType).
I do not get any warnings nor debug info.
When I use a C style pointer (as below) everything works fine.

    Message *message = new Message(this);

[mrjj]

@michalos
Yes it was the qRegisterMetaType i was thinking of.
But it seems you are fully aware of this and would see any warning so its not htat.

Next question is.

Does it go out of scope? ( for some reason)

[michalos]

@mrjj
That is a good question.
I do not know if it's out of scope.

If I create it like that:

QSharedPointer<Message> message(new Message());

or

std::shared_ptr<Message> msgShared (new Message());

will it go out of scope?
Isn't it created on the heap?

[mrjj]

I'm not sure. ( its with new so ..)

Is Message your own class?

I wonder if you can put aDebug() or breakpoint in the destructor and see if it dies when copied..

Also make sure you have Qt::QueuedConnection on your connects

[michalos]

I've changed the connection to Qt::QueuedConnection and it worked :)

I thought that this is done automatically when connecting between threads, but in this case it didn't.

Thank You for Your help :)

[mrjj]

@michalos
Oh. super.
I do wonder how it could work with no QueuedConnection and
no QSharedPointer but I guess its just random :)

[michalos]

I make most of my signal and slot connections without specifying that it's a QueuedConnection (actually all exept this one) and everything works fine.

[mrjj]

@michalos

Well, seems its all explained here
http://doc.qt.io/qt-5/threads-qobject.html
I guess that Auto Connection does guess. :)