gobject: drop OPTIONAL_BIT_LOCK_TOGGLE_REFS lock

It was replaced by the GData lock and g_datalist_id_update_atomic().

Note that we introduced object_bit_lock() to replace global mutexes.
Now, object_bit_lock() is also replaced, by using the GData lock via
g_datalist_id_update_atomic().

This means, all mutex-like locks on the GObject now go through the GData
lock on the GObject's qdata.

For the moment, the object_bit_lock() API is still here and unused. It
will be dropped in a separate commit.

gobject/gobject.c

@@ -124,7 +124,7 @@ enum {
  * parallel as possible. The alternative would be to add individual locking
  * integers to GObjectPrivate. But increasing memory usage for more parallelism
  * (per-object!) is not worth it. */
-#define OPTIONAL_BIT_LOCK_TOGGLE_REFS 1
+#define OPTIONAL_BIT_LOCK_UNUSED 1
 
 #if SIZEOF_INT == 4 && GLIB_SIZEOF_VOID_P >= 8
 #define HAVE_OPTIONAL_FLAGS_IN_GOBJECT 1
@@ -624,7 +624,7 @@ weak_ref_data_has (GObject *object, WeakRefData *wrdata, WeakRefData **out_new_w
 static G_THREAD_LOCAL guint _object_bit_is_locked;
 #endif
 
-static void
+G_GNUC_UNUSED static void
 object_bit_lock (GObject *object, guint lock_bit)
 {
 #if defined(G_ENABLE_DEBUG) && defined(G_THREAD_LOCAL)
@@ -639,7 +639,7 @@ object_bit_lock (GObject *object, guint lock_bit)
   g_bit_lock ((gint *) object_get_optional_flags_p (object), _OPTIONAL_BIT_LOCK);
 }
 
-static void
+G_GNUC_UNUSED static void
 object_bit_unlock (GObject *object, guint lock_bit)
 {
 #if defined(G_ENABLE_DEBUG) && defined(G_THREAD_LOCAL)
@@ -4351,8 +4351,6 @@ toggle_refs_check_and_ref_or_deref (GObject *object,
   *toggle_notify = NULL;
   *toggle_data = NULL;
 
-  object_bit_lock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
-
   /* This is called from g_object_ref()/g_object_unref() and a hot path.
    *
    * We hack the GData open and take the g_datalist_lock() outside. Then we
@@ -4386,14 +4384,12 @@ toggle_refs_check_and_ref_or_deref (GObject *object,
   if (G_UNLIKELY (!success))
     {
       g_datalist_unlock (&object->qdata);
-      object_bit_unlock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
       return FALSE;
     }
 
   if (G_LIKELY (!OBJECT_HAS_TOGGLE_REF (object)))
     {
       g_datalist_unlock (&object->qdata);
-      object_bit_unlock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
       return TRUE;
     }
 
@@ -4406,7 +4402,6 @@ toggle_refs_check_and_ref_or_deref (GObject *object,
                                      toggle_refs_check_and_ref_cb,
                                      (gpointer[2]){ toggle_notify, toggle_data });
 
-  object_bit_unlock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
   return TRUE;
 }
 
@@ -4499,8 +4494,6 @@ g_object_add_toggle_ref (GObject       *object,
 
   g_object_ref (object);
 
-  object_bit_lock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
-
   _g_datalist_id_update_atomic (&object->qdata,
                                 quark_toggle_refs,
                                 toggle_refs_ref_cb,
@@ -4511,8 +4504,6 @@ g_object_add_toggle_ref (GObject       *object,
                                         .data = data,
                                     },
                                 }));
-
-  object_bit_unlock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
 }
 
 static gpointer
@@ -4585,8 +4576,6 @@ g_object_remove_toggle_ref (GObject       *object,
   g_return_if_fail (G_IS_OBJECT (object));
   g_return_if_fail (notify != NULL);
 
-  object_bit_lock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
-
   result = _g_datalist_id_update_atomic (&object->qdata,
                                          quark_toggle_refs,
                                          toggle_refs_unref_cb,
@@ -4598,8 +4587,6 @@ g_object_remove_toggle_ref (GObject       *object,
                                              },
                                          }));
 
-  object_bit_unlock (object, OPTIONAL_BIT_LOCK_TOGGLE_REFS);
-
   found_one = GPOINTER_TO_INT (result);
 
   if (!found_one)