Add atomically reference counted memory

Similar to g_ref_*, we have g_atomic_ref_*, which will ensure that all
reference counting operations are performed atomically.

Not every data structure needs atomic reference counting; for instance,
most of the GTK+ data structures operate under the assumption that only
one thread can access windowing system data. Since atomic operations are
not cheap, forcing them on every data structure can negatively affect
performance.

The underlying reference counting mechanism for g_atomic_ref_* is the
same as for g_ref_*, but instead of adding a "make this atomic" boolean
flag to the g_ref_* API we prefer being explicit, and add the "atomic"
qualifier directly into the API, to avoid misunderstandings.

glib/grefcount.c

@@ -326,3 +326,60 @@ g_ref_release (gpointer ref)
   if (g_ref_counter_release (&real_ref->ref_count))
     g_ref_free (ref);
 }
+
+gpointer
+g_atomic_ref_alloc (gsize          size,
+                    GDestroyNotify notify)
+{
+  g_return_val_if_fail (size > 0, NULL);
+
+  return g_ref_alloc_internal (size, FALSE, TRUE, notify);
+}
+
+gpointer
+g_atomic_ref_alloc0 (gsize          size,
+                     GDestroyNotify notify)
+{
+  g_return_val_if_fail (size > 0, NULL);
+
+  return g_ref_alloc_internal (size, TRUE, TRUE, notify);
+}
+
+gpointer
+g_atomic_ref_dup (gconstpointer  data,
+                  gsize          size,
+                  GDestroyNotify notify)
+{
+  gpointer res;
+
+  g_return_val_if_fail (size > 0, NULL);
+
+  res = g_ref_alloc_internal (size, FALSE, TRUE, notify);
+
+  memcpy (res, data, size);
+
+  return res;
+}
+
+gpointer
+g_atomic_ref_acquire (gpointer ref)
+{
+  GRef *real_ref = G_REF (ref);
+
+  g_return_val_if_fail (ref != NULL, NULL);
+
+  g_ref_counter_acquire (&real_ref->ref_count);
+
+  return ref;
+}
+
+void
+g_atomic_ref_release (gpointer ref)
+{
+  GRef *real_ref = G_REF (ref);
+
+  g_return_if_fail (ref != NULL);
+
+  if (g_ref_counter_release (&real_ref->ref_count))
+    g_ref_free (ref);
+}

glib/grefcount.h

@@ -59,6 +59,27 @@ gpointer        g_ref_acquire                   (gpointer       ref);
 GLIB_AVAILABLE_IN_2_52
 void            g_ref_release                   (gpointer       ref);
 
+#define g_atomic_ref_new(Type,Notify) \
+  (Type *) g_atomic_ref_alloc (sizeof (Type), Notify)
+
+#define g_atomic_ref_new0(Type,Notify) \
+  (Type *) g_atomic_ref_alloc0 (sizeof (Type), Notify)
+
+GLIB_AVAILABLE_IN_2_52
+gpointer        g_atomic_ref_alloc              (gsize          size,
+                                                 GDestroyNotify notify);
+GLIB_AVAILABLE_IN_2_52
+gpointer        g_atomic_ref_alloc0             (gsize          size,
+                                                 GDestroyNotify notify);
+GLIB_AVAILABLE_IN_2_52
+gpointer        g_atomic_ref_dup                (gconstpointer  data,
+                                                 gsize          size,
+                                                 GDestroyNotify notify);
+GLIB_AVAILABLE_IN_2_52
+gpointer        g_atomic_ref_acquire            (gpointer       ref);
+GLIB_AVAILABLE_IN_2_52
+void            g_atomic_ref_release            (gpointer       ref);
+
 G_END_DECLS
 
 #endif /* __G_REF_COUNT_H__ */