Search code examples
c++multithreadingqtassertsignals-slots

What is triggering "ASSERT failure in QCoreApplication::sendEvent" here?

I'm getting this error: ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 0x0x20e51b65eb0. Receiver 'gw2g' (of type 'gw2g') was created in thread 0x0x20e4fd0c930"

DEBUG:

MAIN_thread started: QThread(0x20e4fd0c930)

DUMMY_LOOP started: QThread(0x20e51b65eb0)

What could cause this error?

gw2g.cpp

addExtenders()
{
     //...model gets set etc
     //
     connect(this, SIGNAL(xprep_ready(bool)), ui->connectButton, SLOT(setEnabled(bool)), Qt::AutoConnection);
     connect(ui->listView->selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), this, SLOT(prep_connectx(QItemSelection)), Qt::AutoConnection);
}

While debugging with breakpoints I found out that I get this error after leaving addExtenders()

I also set breakpoints inside destructor of dummyMain_c and gw2g, neither gets destroyed unwantedly. Sometimes dummyMain_c does get destroyed unexpectedly.

(Press Retry to debug the application) QCoreApplication::exec: The event loop is already running

Maybe it has something to do with this event_loop

emit extend_list();
wait_xcon.exec();

It gets quit when clicking one of the buttons in the GUI.

QObject::connect(mwindow.ui->connectButton, &QPushButton::clicked, &dummy_main.wait_xcon, &QEventLoop::quit);

I don't even get to that part though unfortunately.

the threads in the picture are the main (0x0x2059fdfd9b0) and the dummy (0x0x205a1c85ff0)

enter image description here

I also checked if all main window functions run in the main thread - they do. So all GUI stuff happens in the main - I don't know anymore.

Solution

  • I figured it out.

    The error message was very misleading, since the problem was the QEventLoop in dummy.

    When main window(gw2g) QPushButton is clicked it quits this eventloop, so why is the receiver (gw2g)?

    So, I just got rid of

    wait_xcon.exec();

    and replaced it with a simple

    while(!quitloop){}

    clicking the button now sets this bool to true