Regression in Frameworks - DBus Hangs

[Michael Pyne]

On Mon, Nov 12, 2018 at 10:52:17PM +1300, Ben Cooksley wrote:
> In this instance I hoped someone would know of a behaviour change they
> introduced around D-Bus or application shutdown stuff, particularly
> given the time window i'd provided.
> 
> >
> > I imagine the majority of people on this list is in the same situation. I don't know what can be realistically expected.
> > It's quite a jump to go from that to saying people don't check emails.
> >
> > David
> 
> Based on this i've run some additional diagnostics on a CI worker this
> evening, and based on my reading of the test code it would appear that
> the culprit is Konsole no longer exiting when it's last window is
> closed. Konsole's code didn't change at all between the test working
> and it breaking, which indicates this is a Frameworks regression.
> 
> The test does this:
> 
>     QDBusInterface iface(_interfaceName,
>                          QStringLiteral("/konsole/MainWindow_1"),
>                          QStringLiteral("org.qtproject.Qt.QWidget"));
>     QVERIFY2(iface.isValid(), "Unable to get a dbus interface to Konsole!");
> 
>     QDBusReply<void> instanceReply = iface.call(QStringLiteral("close"));
> 
> Which indeed results in the Window closing, at least as far as D-Bus
> is concerned:
> 
> jenkins at 0f9cdb19eeb8:/home/jenkins/konsole> qdbus org.kde.konsole-3065
> /
> /KBookmarkManager
> /KBookmarkManager/konsole
> /MainApplication
> /org
> /org/kde
> /org/kde/konsole
> 
> I also confirmed this by taking a screenshot of the Xvfb instance
> being used by this session, which showed nothing but black -
> confirming the window was indeed closed.
> 
> Instructing Konsole to close by running "qdbus org.kde.konsole-3065
> /MainApplication quit" caused the test to finish (as expected).
> 
> Thoughts anyone?

There is a Qt property on QApplication which is devoted to precisely
this feature. The property, "quitOnLastWindowClosed" will cause the
application to automatically quit if the last window has been closed.

It dates back to Qt 4 and a cursory search of qtbase, KF5 and
kde/workspace for any commits that may have changed the default for this
property [1] don't show any recent changes (disabling it when it was
previously enabled by default or vice versa).

Manually enabling the property in konsole might be enough to make the
test pass. That wouldn't explain what the "regression" was but it seems
strictly more correct either way.

If it's a recent change then it may be related to distro
changes to Qt, something to do with Plasma integration (which is why I
searched in kde/workspace), or some other aspect of the way KF5-based
applications configure themselves by default based on the settings of
the desktop they are being run within.

The only reference of any sort that I see in either KF5 or kde/workspace
for "quitOnLastWindowClosed" is in kxmlgui (for KMainWindow). There
aren't many recent commits so anyone who can reproduce the hang should
have a quick job verifying if reverting some of those would help or not.

[1] Using git -P log --since="8 weeks ago" -G quitOnLastWindow --oneline
for each git repository

Regards,
 - Michael Pyne