Segfault in `waybar::modules::sway::Language::set_current_layout`

[Invizory]

I've got the following segfault in Waybar 0.14.0:

Core was generated by `/nix/store/g2r7rc3p1d6m36d5y1ja53rkranfgxwr-waybar-0.14.0/bin/waybar -b bar-0'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f72f8702d18 in g_source_set_name_full (source=0x7f72300061a0, name=0x7f72f93b43f8 "[gtk+] gdk_frame_clock_paint_idle", is_static=0) at ../glib/gmain.c:2202
2202	 if (!source->priv->static_name)
[Current thread is 1 (Thread 0x7f725e7fc6c0 (LWP 35434))]

(gdb) list
2197	 /* setting back to NULL is allowed, just because it's
2198	  * weird if get_name can return NULL but you can't
2199	  * set that.
2200	  */
2201	
2202	 if (!source->priv->static_name)
2203	   g_free (source->name);
2204	
2205	 if (is_static)
2206	   source->name = (char *)name;
(gdb) bt full
#0  0x00007fe245702d18 in g_source_set_name_full (source=0x7fe188006400, name=0x7fe2463b43f8 "[gtk+] gdk_frame_clock_paint_idle", is_static=0) at ../glib/gmain.c:2202
        context = <optimized out>
        _g_boolean_var_89 = <optimized out>
        _g_boolean_var_90 = <optimized out>
        gaig_temp = <optimized out>
#1  0x00007fe245d10de9 in gtk_widget_add_tick_callback (widget=0x55bd49ab9f80 [gtkmm__GtkWindow], callback=callback@entry=0x7fe245afb960 <gtk_css_widget_node_queue_callback>, user_data=user_data@entry=0x55bd49a3f7f0, notify=notify@entry=0x0) at ../gtk/gtkwidget.c:5368
        priv = 0x55bd49ab9e90
        info = <optimized out>
        frame_clock = 0x55bd49d9d060 [GdkFrameClockIdle]
#2  0x00007fe245afb946 in gtk_css_widget_node_queue_validate (node=0x55bd49a3f7f0 [GtkCssWidgetNode]) at ../gtk/gtkcsswidgetnode.c:95
        widget_node = 0x55bd49a3f7f0 [GtkCssWidgetNode]
#3  0x00007fe245ad83cb in gtk_css_node_invalidate_style (cssnode=0x55bd49b58f40 [GtkCssWidgetNode]) at ../gtk/gtkcssnode.c:727
#4  gtk_css_node_invalidate (cssnode=cssnode@entry=0x55bd49b58f40 [GtkCssWidgetNode], change=<optimized out>, change@entry=1) at ../gtk/gtkcssnode.c:1372
#5  0x00007fe245ad8ad5 in gtk_css_node_remove_class (cssnode=0x55bd49b58f40 [GtkCssWidgetNode], style_class=<optimized out>) at ../gtk/gtkcssnode.c:1254
#6  0x000055bd41f1303a in waybar::modules::sway::Language::set_current_layout (this=this@entry=0x55bd49c632a0, current_layout="Russian") at ../src/modules/sway/language.cpp:128
#7  0x000055bd41f160bb in waybar::modules::sway::Language::onEvent (this=0x55bd49c632a0, res=...) at ../src/modules/sway/language.cpp:89
        lock = {_M_device = <optimized out>}
        payload = {static minLargestInt = -9223372036854775808, static maxLargestInt = 9223372036854775807, static maxLargestUInt = 18446744073709551615, static minInt = -2147483648, static maxInt = 2147483647, static maxUInt = 4294967295, static minInt64 = -9223372036854775808, static maxInt64 = 9223372036854775807, static maxUInt64 = 18446744073709551615, static defaultRealPrecision = 17, static maxUInt64AsDouble = 1.8446744073709552e+19, value_ = {int_ = 140606626094832, uint_ = 140606626094832, real_ = 6.9468903531101842e-310, bool_ = 240, string_ = 0x7fe188005ef0 "\205\343\030v\346\177", map_ = 0x7fe188005ef0}, bits_ = {value_type_ = 7, allocated_ = 0}, comments_ = {ptr_ = std::unique_ptr<struct std::array<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, 3>> = {get() = 0x0}}, start_ = 35, limit_ = 295}
#8  0x000055bd41f06bfe in sigc::internal::signal_emit1<void, waybar::modules::sway::Ipc::ipc_response const&, sigc::nil>::emit (impl=0x55bd49b59c10, _A_a1=...) at /nix/store/blx56cg23z09bihhxlv4xsa3zb58irzp-libsigc++-2.12.1-dev/include/sigc++-2.0/sigc++/signal.h:1041
        slot = @0x55bd49b59c50: {<sigc::functor_base> = {<No data fields>}, rep_ = 0x55bd49b59b80, blocked_ = false}
        exec = {sig_ = 0x55bd49b59c10}
        slots = Python Exception <class 'gdb.error'>: value has been optimized out
{slots_ = <optimized out>, placeholder = }
#9  0x000055bd41f06af7 in sigc::signal1<void, waybar::modules::sway::Ipc::ipc_response const&, sigc::nil>::emit (this=0x55bd49c635c8, _A_a1=...) at /nix/store/blx56cg23z09bihhxlv4xsa3zb58irzp-libsigc++-2.12.1-dev/include/sigc++-2.0/sigc++/signal.h:2961
#10 waybar::modules::sway::Ipc::handleEvent (this=0x55bd49c635c8) at ../src/modules/sway/ipc/client.cpp:154
        res = {size = 297, type = 2147483669, payload = "{ \"change\": \"xkb_layout\", \"input\": { \"identifier\": \"0:0:wlr_virtual_keyboard_v1\", \"name\": \"wlr_virtual_keyboard_v1\", \"type\": \"keyboard\", \"repeat_delay\": 600, \"repeat_rate\": 25, \"xkb_layout_names\": [ \""...}
#11 0x000055bd41f150a7 in operator() (__closure=<optimized out>) at ../src/modules/sway/language.cpp:40
#12 std::__invoke_impl<void, waybar::modules::sway::Language::Language(const std::string&, const Json::Value&)::<lambda()>&> (__f=<optimized out>) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/invoke.h:63
#13 std::__invoke_r<void, waybar::modules::sway::Language::Language(const std::string&, const Json::Value&)::<lambda()>&> (__fn=<optimized out>) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/invoke.h:113
#14 std::_Function_handler<void(), waybar::modules::sway::Language::Language(const std::string&, const Json::Value&)::<lambda()> >::_M_invoke(const std::_Any_data &) (__functor=<optimized out>) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/std_function.h:292
#15 0x000055bd41e5ce62 in std::function<void()>::operator() (this=0x55bd49b64720) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/std_function.h:593
#16 waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}::operator()() const (__closure=0x55bd49b64718) at ../include/util/sleeper_thread.hpp:48
#17 std::__invoke_impl<void, waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}>(std::__invoke_other, waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}&&) (__f=...) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/invoke.h:63
#18 std::__invoke<waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}>(waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}&&) (__fn=...) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/invoke.h:98
#19 std::thread::_Invoker<std::tuple<waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}> >::_M_invoke<0ul>(std::_Index_tuple<0ul>) (this=0x55bd49b64718) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/std_thread.h:303
#20 std::thread::_Invoker<std::tuple<waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}> >::operator()() (this=0x55bd49b64718) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/std_thread.h:310
#21 std::thread::_State_impl<std::thread::_Invoker<std::tuple<waybar::util::SleeperThread::operator=(std::function<void ()>)::{lambda()#1}> > >::_M_run() (this=0x55bd49b64710) at /nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/bits/std_thread.h:255
#22 0x00007fe244cf2ce4 in execute_native_thread_routine () at /nix/store/xc0ga87wdclrx54qjaryahkkmkmqi9qz-gcc-15.2.0-lib/lib/libstdc++.so.6
#23 0x00007fe24489be3c in start_thread (arg=<optimized out>) at pthread_create.c:447
        ret = <optimized out>
        pd = <optimized out>
        out = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {140608169572032, 2201921418368590696, 140608169572032, 140721872088400, 2, 140721872088663, 2201921418353910632, 2200436341414765416}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}}
        not_first_call = <optimized out>
#24 0x00007fe2449246cc in __GI___clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78
(gdb) frame 6
#6  0x000055bd41f1303a in waybar::modules::sway::Language::set_current_layout (this=this@entry=0x55bd49c632a0, current_layout="Russian") at ../src/modules/sway/language.cpp:128
128	 label_.get_style_context()->remove_class(layout_.short_name);
(gdb) list
123	 // Call parent update
124	 ALabel::update();
125	}
126	
127	auto Language::set_current_layout(std::string current_layout) -> void {
128	 label_.get_style_context()->remove_class(layout_.short_name);
129	 layout_ = layouts_map_[current_layout];
130	 label_.get_style_context()->add_class(layout_.short_name);
131	}
132	
(gdb) p layout_
$1 = {full_name = "Russian", short_name = "ru", variant = "", short_description = "ru"}

I'm using the default configuration for the sway/language module.

Possibly related to #3702, #4751.

[sliedes]

Looks identical to #4751. And I think the backtrace tells us exactly what is going on (I am seeing the same crash, FWIW).

...
#5  0x00007fe245ad8ad5 in gtk_css_node_remove_class (cssnode=0x55bd49b58f40 [GtkCssWidgetNode], style_class=<optimized out>) at ../gtk/gtkcssnode.c:1254
#6  0x000055bd41f1303a in waybar::modules::sway::Language::set_current_layout (this=this@entry=0x55bd49c632a0, current_layout="Russian") at ../src/modules/sway/language.cpp:128
...
#23 0x00007fe24489be3c in start_thread (arg=<optimized out>) at pthread_create.c:447
#24 0x00007fe2449246cc in __GI___clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78

GTK functions are being called from a thread while the GTK event loop is running on the main thread. Quoting from https://docs.gtk.org/gtk4/section-threading.html:

Most GTK objects are not threadsafe and can only be used from the main thread, since they are all connected by references (all widgets are connected via the widget tree, and they all reference the display object).

IOW, most GTK code, and particularly any GTK code that touches widgets, can only safely be called from the event loop.

[sliedes]

Ipc::handleEvent calls signal_event.emit:

Waybar/src/modules/sway/ipc/client.cpp

Line 154 in 03a77c5

signal_event.emit(res);

signal_event is a sigc::signal instead of a SafeSignal, so the handling functions just get called on the same thread:

Waybar/include/modules/sway/ipc/client.hpp

Line 30 in 03a77c5

sigc::signal<void, const struct ipc_response&> signal_event;

Perhaps this can be fixed simply by switching to SafeSignal here?