[Pkg-xfce-devel] Bug#884802: Bug#884802: xfce4-panel: Undeletable buttons of nonexistent processes.

Lorenzo Ancora lorenzolucio at live.it
Wed Jan 17 14:28:15 UTC 2018

control: tag - unreproducible

after getting no answers I've studied how to debug XFCE 4.
I'm adding new and more useful debug information to help fixing the
problem and also explain why you can't reproduce it.
Apparently the source of the bug is unallocated memory (a NULL pointer,
0x0..0 in gdb) and there are also signs of an incompatibility with the
signal management of a specific version of GLib 2:
> (xfce4-panel:1964): GLib-GObject-WARNING **:
> /build/glib2.0-B1uXKV/glib2.0-2.50.3/./gobject/gsignal.c:3492: signal
> name 'selection_changed' is invalid for instance '0x55b07a0221c0' of
> type 'GailMenuItem'
> (xfce4-panel:1964): libtasklist-CRITICAL **: tasklist-widget.c:1777
> (xfce_tasklist_window_removed): expression 'n == 5' failed.
> (xfce4-panel:1603): libtasklist-CRITICAL **: tasklist-widget.c:2681
> (xfce_tasklist_button_enter_notify_event): expression
> 'XFCE_IS_TASKLIST (child->tasklist)' failed.
> (xfce4-panel:1603): libtasklist-CRITICAL **: tasklist-widget.c:2805
> (xfce_tasklist_button_enter_notify_event_disconnected): expression
> 'WNCK_IS_WINDOW (child->window)' failed.
> (xfce4-panel:1603): libtasklist-CRITICAL **: tasklist-widget.c:1871
> (xfce_tasklist_update_icon_geometries): expression 'WNCK_IS_WINDOW
> (child->window)' failed.
> (xfce4-panel:1603): libtasklist-CRITICAL **: tasklist-widget.c:2883
> (xfce_tasklist_button_activate): expression 'WNCK_IS_WINDOW
> (child->window)' failed.
> (xfce4-panel:1603): GLib-GObject-WARNING **: instance with invalid
> (NULL) class pointer
> (xfce4-panel:1603): GLib-GObject-CRITICAL **:
> g_signal_handlers_disconnect_matched: assertion 'G_TYPE_CHECK_INSTANCE
> (instance)' failed
In my opinion the bug could be traced to a single value:
'tasklist-widget.c' is trying to access the wrong object of a collection
and this is caused by the incorrect handling of signals in 'gsignal.c',
that can be the root cause of the problem.

I've attached 2 log files, the 1st with PANEL_DEBUG=gdb and the 2nd with
PANEL_DEBUG=tasklist, so you have all debugging information plus the
correct library versions to reproduce it.

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