C++ application does not kill all processes on exit

Question

This is my main.cpp which starts the mainwindow:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    TabWindow w;
    w.show();
    return a.exec();
}

Even with the a.connect(...) I do not understand why myApplication.exe still runs after I close the mainwindow. Any suggestions on how I can fully end all processes after the quit button is clicked?

EDIT: The Qt Documentation says this: We recommend that you connect clean-up code to the aboutToQuit() signal, instead of putting it in your application's main() function. This is because, on some platforms, the QApplication::exec() call may not return.

@ratchetfreak Yes I do. Now that you mentioned, I am using `QtConcurrent`to start a worker thread and this error occurs when I close the application BEFORE the worker thread finishes. — BurninatorDor, Oct 03 '14 at 16:04
@ratchetfreak Is there a way to delete all threads before exiting the application? — BurninatorDor, Oct 03 '14 at 16:17

score 2 · Answer 1 · answered Oct 03 '14 at 15:15

There's nothing wrong with your code. And your connect doesn't do anything.

Unless you call QGuiApplication::setQuitOnLastWindowClosed(true) somewhere, application should exit when the last window is closed. Probably you block event loop somewhere in your window code.

score 1 · Accepted Answer · answered Oct 03 '14 at 19:48

Thanks to the comment posted by @ratchetfreak in my question, I figured out where the problem was.

In my MainWindow, I started a worker thread which was not terminated and thus still persisted as a process after the application was closed. In order to fix this, I registered the close event and kept track of the existence of the thread - i.e. basically, ignored the closeEvent until the thread was deleted as well.

void MainWindow::closeEvent(QCloseEvent *event)
{
    if (workerThreadExists) {
        // Gracefully exiting all tasks inside the worker thread
        while (workerThreadExists){
            event->ignore();
        }
        event->accept();

    }
}

...and for me workerThreadExists is just a BOOLEAN that is set to true once the thread is created and then it is set to false when the thread is deleted. Hope this helps!

Dmitry Sazonov · Answer 3 · 2014-10-03T15:17:32.347

0

You should have something like this:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    TabWindow w;
    w.show();
    return a.exec();
}

// Do quit in your TabWindow:
TabWindow::TabWindow()
  : public QWidget(NULL)
{
  connect( ui->myQuitButton, SIGNAL( clicked() ), qApp, SLOT( quit() ) );
}

edited Oct 03 '14 at 15:17

answered Oct 03 '14 at 15:10

Dmitry Sazonov

8,801
1
35
61

I see your point. But then what can I do to actually kill all processes on exit? – BurninatorDor Oct 03 '14 at 15:12
1

There's no any infinite loop, because `aboutToQuit` signal can be emitted only once. Calling QApplication::quit() multiple times does not lead to multiple `aboutToQuit` signals. – Oleg Shparber Oct 03 '14 at 15:20
1

@DmitrySazonov that wasnt me man. I fixed it with an upvote. Appreciate your help! – BurninatorDor Oct 03 '14 at 15:23

score -5 · Answer 4 · answered Oct 03 '14 at 15:06

-5

just replace

return a.exec();

with

return 0;

That should end all processes which is associated with that program.

answered Oct 03 '14 at 15:06

DarkEvE

171
12

2

`a.exec()` runs Qt event loop, without it application would be mostly unusable. – Oleg Shparber Oct 03 '14 at 15:10

C++ application does not kill all processes on exit

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