Comment # 27 on bug 964548 from Lorenzo Desole

I don't know if this can be of some use nor do I know if it is a peculiarity of
my setup.

I assumed that switching the monitor off is what causes kscreenlocker () to
exit. That is incorrect. When the monitor is switched off, the screen  is not
removed.  It is also worth noting that kscreenlocker (still without patch)
works perfectly fine if it is executed when the monitor is off. It's when I
switch it back on that the screen is removed and, after a split second, a new
one is added. This causes all sorts of troubles to kscreenlocker.

I have modified UnlockApp::desktopResized() to printout the number of screen
available and launched kscreenlocker in a loop:

$ while : ; do echo -e "\n\n\n*** starting at $(date)***"; echo "Monitor is
$(cat /sys/class/drm/card0-DP-2/status)" ; greeter/kscreenlocker_greet
--testing ; done

As soon as the login screen was shown, I switched off the monitor and waited
for about a minute. This is the output I got:

*** starting at sab 13 feb 2016, 22.58.35, CET***
Monitor is connected
UnlockApp::desktopResized() - Screen count: 1
Locked at 1455400716
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/InfoPane.qml:52:22:
Unable to assign [undefined] to int
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserPasswordPrompt.qml:25:
ReferenceError: userModel is not defined
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/user-identity
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/system-log-out
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/system-switch-user
org.kde.keyboardLayout: Layouts list changed:  ("it")
UnlockApp::desktopResized() - Screen count: 0



*** starting at sab 13 feb 2016, 22.59.32, CET***
Monitor is disconnected
UnlockApp::desktopResized() - Screen count: 1
Locked at 1455400772
QXcbConnection: XCB error: 148 (Unknown), sequence: 170, resource id: 0, major
code: 140 (Unknown), minor code: 20
UnlockApp::desktopResized() - Screen count: 2
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/InfoPane.qml:52:22:
Unable to assign [undefined] to int
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserPasswordPrompt.qml:25:
ReferenceError: userModel is not defined
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/user-identity
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/system-log-out
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/system-switch-user
org.kde.keyboardLayout: Layouts list changed:  ("it")
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/InfoPane.qml:52:22:
Unable to assign [undefined] to int
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserPasswordPrompt.qml:25:
ReferenceError: userModel is not defined
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/user-identity
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/system-log-out
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/UserDelegate.qml:82:9:
QML Image: Cannot open:
file:///usr/share/plasma/look-and-feel/org.openSUSE.desktop/contents/components/system-switch-user
org.kde.keyboardLayout: Layouts list changed:  ("it")

My deductions are:

1) kscreenlocker exited as soon I switched the monitor back on, not when I had
previously switched it off.
2) the while/do loop immediately launched a new instance of kscreenlocker, but
the monitor was still being reported off by Xrandr; UnlockApp::desktopResized()
reports one screen though
3) there's a strange QXcbConnection: XCB error
4) A new (the real one) screen is added and UnlockApp::desktopResized() reports
TWO screens, the fake/virtual/whatever one is not removed).
5) At that point kscreenlocker showed *two* password windows

If I add a "sleep 1" into the middle of the loop, the "QXcbConnection: XCB
error doesn't happen", only one screen is reported by
UnlockApp::desktopResized() and only one password window is shown.