Remove protecting mutex in darktable.gui

1. There is no reason for the protecting mutex as all gui data changing happens in main thread.
2. We don't need to set darktable.gui to NULL as all pointers were set to NULL at the very start.

Author: jenshannoschwalm

src/common/darktable.c

@@ -1892,11 +1892,9 @@ int dt_init(int argc,
         && !(dbfilename_from_command && !strcmp(dbfilename_from_command, ":memory:"));
 
   }
-  else
-    darktable.gui = NULL;
 
   dt_splash_screen_set_progress(_("loading image formats"));
-
+ 
   darktable.imageio = (dt_imageio_t *)calloc(1, sizeof(dt_imageio_t));
   dt_imageio_init(darktable.imageio);
 

src/gui/gtk.c

@@ -205,10 +205,7 @@ static void _toggle_tooltip_visibility(dt_action_t *action)
 static inline void _update_focus_peaking_button()
 {
   // read focus peaking global state and update toggle button accordingly
-  dt_pthread_mutex_lock(&darktable.gui->mutex);
   const gboolean state = darktable.gui->show_focus_peaking;
-  dt_pthread_mutex_unlock(&darktable.gui->mutex);
-
   gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(darktable.gui->focus_peaking_button),
                                state);
 }
@@ -217,17 +214,12 @@ static void _focuspeaking_switch_button_callback(GtkWidget *button,
                                                  gpointer user_data)
 {
   // button method
-  dt_pthread_mutex_lock(&darktable.gui->mutex);
   const gboolean state_memory = darktable.gui->show_focus_peaking;
-  dt_pthread_mutex_unlock(&darktable.gui->mutex);
-
   const gboolean state_new = gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(button));
 
   if(state_memory == state_new) return; // nothing to change, bypass
 
-  dt_pthread_mutex_lock(&darktable.gui->mutex);
   darktable.gui->show_focus_peaking = state_new;
-  dt_pthread_mutex_unlock(&darktable.gui->mutex);
 
   gtk_widget_queue_draw(button);
 
@@ -810,8 +802,6 @@ gboolean _valid_window_placement(const gint saved_x,
 
 int dt_gui_gtk_load_config()
 {
-  dt_pthread_mutex_lock(&darktable.gui->mutex);
-
   GtkWidget *widget = dt_ui_main_window(darktable.gui->ui);
   const int width = dt_conf_get_int("ui_last/window_w");
   const int height = dt_conf_get_int("ui_last/window_h");
@@ -842,15 +832,11 @@ int dt_gui_gtk_load_config()
   else
     darktable.gui->show_focus_peaking = FALSE;
 
-  dt_pthread_mutex_unlock(&darktable.gui->mutex);
-
   return 0;
 }
 
 int dt_gui_gtk_write_config()
 {
-  dt_pthread_mutex_lock(&darktable.gui->mutex);
-
   GtkWidget *widget = dt_ui_main_window(darktable.gui->ui);
   gint x, y, width, height;
   // Use gtk_window_get_size() instead of gtk_widget_get_allocation() to get
@@ -871,8 +857,6 @@ int dt_gui_gtk_write_config()
                     & GDK_WINDOW_STATE_FULLSCREEN));
   dt_conf_set_bool("ui/show_focus_peaking", darktable.gui->show_focus_peaking);
 
-  dt_pthread_mutex_unlock(&darktable.gui->mutex);
-
   return 0;
 }
 
@@ -1318,8 +1302,6 @@ int dt_gui_theme_init(dt_gui_gtk_t *gui)
 
 int dt_gui_gtk_init(dt_gui_gtk_t *gui)
 {
-  dt_pthread_mutex_init(&gui->mutex, NULL);
-
   // force gtk3 to use normal scroll bars instead of the popup
   // thing. they get in the way of controls the alternative would be
   // to gtk_scrolled_window_set_overlay_scrolling(..., FALSE); every

src/gui/gtk.h

@@ -146,8 +146,6 @@ typedef struct dt_gui_gtk_t
   guint sidebar_scroll_mask;
 
   cairo_filter_t filter_image;    // filtering used to scale images to screen
-
-  dt_pthread_mutex_t mutex;
 } dt_gui_gtk_t;
 
 typedef struct _gui_collapsible_section_t