gtype: Use the system allocator on UNIX

Instead of replacing the slice allocator wholesale, we can start phasing
it out by having GTypeInstance use the system allocator on operating
systems where we can assume good performance profiles.

We cannot commit to fully gutting GSlice in the cases where we might
still need it, like the G(S)List allocator and small, similarly-sized
data structures.

The main user of GSlice is still GTypeInstance/GObject, and those have
moved out of the sweet spot of GSlice's performance envelove over the
years, with larger instance sizes and private data.

See: #1079

1 files changed, 16 insertions, 4 deletions

diff --git a/gobject/gtype.c b/gobject/gtype.c
index 40953843d..66db7bc9d 100644
--- a/gobject/gtype.c
+++ b/gobject/gtype.c
@@ -1824,6 +1824,18 @@ type_iface_blow_holder_info_Wm (TypeNode *iface,
     }
 }
 
+/* We use the system allocator on UNIX-y systems, where we know we have
+ * access to a decent allocator. On other systems, we fall back to the
+ * slice allocator, as we know its performance profile
+ */
+#ifdef G_OS_UNIX
+# define instance_alloc(s)  g_malloc0 ((s))
+# define instance_free(s,p) g_free ((p))
+#else
+# define instance_alloc(s)  g_slice_alloc0 ((s))
+# define instance_free(s,p) g_slice_free1 ((s),(p))
+#endif
+
 /**
  * g_type_create_instance: (skip)
  * @type: an instantiatable type to create an instance for
@@ -1900,7 +1912,7 @@ g_type_create_instance (GType type)
       private_size += ALIGN_STRUCT (1);
 
       /* Allocate one extra pointer size... */
-      allocated = g_slice_alloc0 (private_size + ivar_size + sizeof (gpointer));
+      allocated = instance_alloc (private_size + ivar_size + sizeof (gpointer));
       /* ... and point it back to the start of the private data. */
       *(gpointer *) (allocated + private_size + ivar_size) = allocated + ALIGN_STRUCT (1);
 
@@ -1910,7 +1922,7 @@ g_type_create_instance (GType type)
     }
   else
 #endif
-    allocated = g_slice_alloc0 (private_size + ivar_size);
+    allocated = instance_alloc (private_size + ivar_size);
 
   instance = (GTypeInstance *) (allocated + private_size);
 
@@ -2000,14 +2012,14 @@ g_type_free_instance (GTypeInstance *instance)
       /* Clear out the extra pointer... */
       *(gpointer *) (allocated + private_size + ivar_size) = NULL;
       /* ... and ensure we include it in the size we free. */
-      g_slice_free1 (private_size + ivar_size + sizeof (gpointer), allocated);
+      instance_free (private_size + ivar_size + sizeof (gpointer), allocated);
 
       VALGRIND_FREELIKE_BLOCK (allocated + ALIGN_STRUCT (1), 0);
       VALGRIND_FREELIKE_BLOCK (instance, 0);
     }
   else
 #endif
-    g_slice_free1 (private_size + ivar_size, allocated);
+    instance_free (private_size + ivar_size, allocated);
 
 #ifdef	G_ENABLE_DEBUG
   IF_DEBUG (INSTANCE_COUNT)