Cannot create children for a parent that is in a different thread

pingal

I've creating an object (which inherits from QObject) in my main and passing this object to another thread i.e.

main.cpp

QGuiApplication app(argc, argv);
ClientListWrapper clients;
 if (!clients.initialize())
        return -1;
args2thread->Pointer2clients = &clients;     // Passing this object to thread 
std::thread Listening_thread(thread_function, args2thread);  // Creating a thread

Now in my thread function I'm modifying client object i.e.

myThread.cpp

//Receive data from client here
.
args2thread->clients->addClient(data);  // Store the received data
.

Why QT complains about it ? And how do i solve this

mrjj

Hi
Well you create ClientListWrapper clients; in the Main thread and simply
assigning its adress to a variable won't move it.

Have you considered using QThread and
https://doc.qt.io/qt-5/qobject.html#moveToThread

pingal

I'm actually passing the address of clients variable to my thread. In that thread, I'm putting some data using that address. This approach works well in C++ but QT has some problem with this approach. It maybe because ClientListWrapper inherets from QObject (?)

mrjj

@pingal
Hi
I would guess on that too even I have not mixed std::thread with QObjects before.
The Qt way would be to emit the data from Listening_thread via a custom signal and
have ClientListWrapper clients connect to that.

Christian Ehrlicher

You create a QObject derived class (and pass a parent) in the secondary thread which is not allowed. All objects of an object tree must live in the same thread. So you have two options - either move the whole object tree to the other thread or don't put the newly created QObject in the object tree from the main thread.

pingal

I've now used QThread instead of std::thread and used signal/slots to transfer data from my Listening_thread to main thread. problem solved.

Thanks for the helpful replies.