Bug#1131473: cinnamon: Threads and Alt-Tab incompatibles

[Fabio Fantoni]

Hi Frederic,

thanks for the report, and sorry for the long delay.

Some background on how Alt-Tab works in Cinnamon, because it explains what

not use the window manager's own MRU (most recently used) list. It takes the
list of windows in stacking order and re-sorts it by each window's

becomes random after a few hours of uptime".


depend on the number of logical CPUs. What changing that BIOS setting does
require is a reboot, and a reboot is what clears the accumulated timestamps.


three things would tell us what is going on:


   BIOS setting? This is the key test to tell a reboot apart from Hyper-
   Threading.

2. The output of:

       grep "comparison timestamp" ~/.xsession-errors


   would confirm that some application is sending bad timestamps.


   outputs:





   The first one is the order Alt-Tab uses, the second one is the window

   diagnosis above is confirmed.


related upstream issues ask for the opposite behaviour, that is, a static

by a stale bot without a resolution). So a precise, reproducible description
from you is what it would take to get this looked at upstream.

Thanks,

[1] https://github.com/linuxmint/cinnamon/issues/8758
[2] https://github.com/linuxmint/cinnamon/issues/9410

could be going on. Unlike most window managers, the Cinnamon app switcher does _NET_WM_USER_TIME property (js/ui/appSwitcher/appSwitcher.js). That property is only partly under the window manager's control: applications set it themselves, and a client sending a bad timestamp can end up with a window that stays pinned at the top of the order for the rest of the session. That would match "the order Hyper-Threading, on the other hand, is unlikely to be the real variable here: the ordering is a plain single-threaded computation in Cinnamon, and it does not Do you still see this, and would you be willing to help debug it? If so, these 1. Does the problem also go away if you just restart the session (log out and    log back in), or restart Cinnamon (Ctrl+Alt+Escape), without touching the    Lines like "last_user_time (...) is greater than comparison timestamp (...)" 3. While the problem is happening, please open Looking Glass (Alt+F2, then type    "lg"), go to the "Evaluator" tab and run these two lines, then send us both        global.get_window_actors().map(a => a.get_meta_window()).map(w => w.get_wm_class() + " | " + w.get_title() + " | " + w.get_user_time() + " | min=" + w.minimized).join("\n")        global.display.get_tab_list(imports.gi.Meta.TabList.NORMAL, global.workspace_manager.get_active_workspace()).map(w => w.get_wm_class() + " | " + w.get_title()).join("\n")    manager's real MRU order. If the second is correct and the first is not, the One more thing worth knowing: there is no upstream report about this. The few Alt-Tab order instead of the most-recently-used one ([1], [2], the latter closed

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