app: set the number of threads on GeglConfig again, it needs testing

- enable the setting code in gimp-gegl.c again
- but set the default to one thread in GimpGeglConfig, with a CPP warning
- rename "processors" to "threads" in the GUI
- add a warning box about unexpected results when increasing #threads

app/config/gimpgeglconfig.c

@@ -139,9 +139,14 @@ gimp_gegl_config_class_init (GimpGeglConfigClass *klass)
 
   num_processors = MIN (num_processors, GIMP_MAX_NUM_THREADS);
 
+#ifdef __GNUC__
+#warning Defaulting # of threads to 1
+#endif
+  num_processors = 1;
+
   GIMP_CONFIG_PROP_UINT (object_class, PROP_NUM_PROCESSORS,
                          "num-processors",
-                         "Number of processors to use",
+                         "Number of threads to use",
                          NUM_PROCESSORS_BLURB,
                          1, GIMP_MAX_NUM_THREADS, num_processors,
                          GIMP_PARAM_STATIC_STRINGS);

app/config/gimprc-blurbs.h

@@ -253,7 +253,7 @@ _("Sets the size of the navigation preview available in the lower right " \
   "corner of the image window.")
 
 #define NUM_PROCESSORS_BLURB \
-_("Sets how many processors GIMP should try to use simultaneously.")
+_("Sets how many threads GIMP should use for operations that support it.")
 
 #define PALETTE_PATH_BLURB \
 "Sets the palette search path."

app/dialogs/preferences-dialog.c

@@ -1080,8 +1080,18 @@ prefs_dialog_new (Gimp       *gimp,
 
 #ifdef ENABLE_MP
   prefs_spin_button_add (object, "num-processors", 1.0, 4.0, 0,
-                         _("Number of _processors to use:"),
+                         _("Number of _threads to use:"),
                          GTK_TABLE (table), 4, size_group);
+
+  vbox2 = g_object_new (GIMP_TYPE_HINT_BOX,
+                        "icon-name", GIMP_ICON_DIALOG_WARNING,
+                        "hint",      _("Threading support is not yet stable.\n"
+                                       "Setting this to greater than one might\n"
+                                       "result in image errors or crashes."),
+                        NULL);
+  gtk_table_attach (GTK_TABLE (table), vbox2, 1, 2, 5, 6,
+                    GTK_FILL | GTK_EXPAND, GTK_FILL, 0, 0);
+  gtk_widget_show (vbox2);
 #endif /* ENABLE_MP */
 
   /*  Hardware Acceleration  */

app/gegl/gimp-gegl.c

@@ -49,15 +49,9 @@ gimp_gegl_init (Gimp *gimp)
 
   config = GIMP_GEGL_CONFIG (gimp->config);
 
-#ifdef __GNUC__
-#warning not setting GeglConfig:threads
-#endif
-
   g_object_set (gegl_config (),
                 "tile-cache-size", (guint64) config->tile_cache_size,
-#if 0
                 "threads",         config->num_processors,
-#endif
                 "use-opencl",      config->use_opencl,
                 NULL);
 
@@ -87,11 +81,9 @@ gimp_gegl_notify_tile_cache_size (GimpGeglConfig *config)
 static void
 gimp_gegl_notify_num_processors (GimpGeglConfig *config)
 {
-#if 0
   g_object_set (gegl_config (),
                 "threads", config->num_processors,
                 NULL);
-#endif
 }
 
 static void