Window in focus is blacked after fast switching of windows.

[xambroz]

What's wrong?
If you switch the windows fast couple of times in a row, then the window in focus goes black.
Windows still do display correctly in the "Cover Flow" or the "Activities" view, but once you click on some window and the window is put on focus, then the window shows black. Once you restart gnome-shell with ctrl-f2 + r then everything returns to normal.

What have you tried?
I have tried to:

1. uninstall extension, disable all other extensions including this one, restart gnome-shell.
2. switch windows fast with alt-tab to check that the issue is not there without this extension
3. install and enable this extension fresh from https://extensions.gnome.org/extension/97/coverflow-alt-tab/
4. switch windows fast with alt-tab to check that the issue is there

Automatically detected errors:

GNOME Shell Extensions did not detect any errors with this extension.

Gnome shell javascript console displays these errors during installation:
JS ERROR: !!! WARNING: 'anonymous function does not always return a value'
JS ERROR: !!! WARNING: file '/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@palatis.blogspot.com/switcher.js' line 98 exception 0 number 157

Gnome shell javascript console displays this error when the issue occures as result of fast switching of windows:
Window manager warning: Log level 8: g_source_remove: assertion `tag > 0' failed
JS ERROR: !!! Exception was: TypeError: this._windows is null
JS ERROR: !!! message = '"this._windows is null"'
JS ERROR: !!! fileName = '"/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@palatis.blogspot.com/switcher.js"'
JS ERROR: !!! lineNumber = '171'
JS ERROR: !!! stack = '"()@/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@palatis.blogspot.com/switcher.js:171
()@/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@palatis.blogspot.com/switcher.js:159
"'

Version information:

Shell version: 3.6.2
Extension version: 15 

[xambroz]

Just realized the version in git is not exactly the same as on https://extensions.gnome.org/extension/97/coverflow-alt-tab/
I have tried with the version from git, but the results are the same.

This is the error when installing (or restarting gnome-shell):
JS ERROR: !!! WARNING: 'anonymous function does not always return a value'
JS ERROR: !!! WARNING: file '/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@dmo60.de/switcher.js' line 98 exception 0 number 157

This is the error when the issue occures:
Window manager warning: Log level 8: g_source_remove: assertion `tag > 0' failed
JS ERROR: !!! Exception was: TypeError: this._windows is null
JS ERROR: !!! message = '"this._windows is null"'
JS ERROR: !!! fileName = '"/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@dmo60.de/switcher.js"'
JS ERROR: !!! lineNumber = '171'
JS ERROR: !!! stack = '"()@/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@dmo60.de/switcher.js:171
()@/home/mambroz/.local/share/gnome-shell/extensions/CoverflowAltTab@dmo60.de/switcher.js:159
"'

Sometimes this happens just after 2 alt-tab switches, and sometimes it takes 100 switches.

Best regards
Michal Ambroz

[dmo60]

Thank you for the report! I can reproduce some similar behavior. Randomly when Alt-Tabbing fast, my windows disappear and there's just the desktop dimmed down. Is that what you mean?
I hope I can find a fix soon.

[sgon00]

I have the exact same problem. When the window is chosen, the whole screen become black (or gray?). I have to restart gnome-shell to workaournd it. This happens to me 2 or more times per day. I am using the version in extensions.gnome.org.

PS: It's not related to this problem, but I see the following printout whenever I use "alt+tab":

JS LOG: The property transistion doesn't seem to be a normal object property of [0x26da4d0 ShellGenericContainer:last-child first-child insensitive "panel"] or a registered special property
Window manager warning: Log level 8: g_source_remove: assertion tag > 0' failed Window manager warning: Log level 8: g_source_remove: assertiontag > 0' failed
....

Can you please disable these warning messages somehow?

Regards,
Thank you very much.

[dmo60]

Can you test the newest version from git and check if these issues still exist?

[sgon00]

I tried the git version. So far so good. If I meet the issue again, I will let you know. Btw, the failure messages still exist in the git version whenever using Alt+Tab. Is that possible to prevent it? Thanks a lot.

[dmo60]

The warnings should be gone with the latest version.