[glib] gatomic: use GCC C11-style atomics, if available

[Ryan Lortie <desrt src gnome org>]

commit db0e43d25a5316f3a6f2f31712a0b8359e247a20
Author: Ryan Lortie <desrt desrt ca>
Date:   Tue May 27 15:28:08 2014 +0200

    gatomic: use GCC C11-style atomics, if available
    
    GCC does not yet support ISO C11 atomic operations, but it has
    compatible versions available as an extension.  Use these for load and
    store if they are available in order to avoid emitting a hard fence
    instruction (since in many cases, we do not need it -- on x86, for
    example).
    
    For now we use the fully seqentially-consistent memory model, since
    these APIs are documented rather explicitly: "This call acts as a full
    compiler and hardware memory barrier".
    
    In the future we can consider introducing new APIs for the more relaxed
    memory models, if they are available (or fall back to stricter ones
    otherwise).
    
    https://bugzilla.gnome.org/show_bug.cgi?id=730807

 glib/gatomic.h |   77 ++++++++++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 64 insertions(+), 13 deletions(-)
---
diff --git a/glib/gatomic.h b/glib/gatomic.h
index 3793374..1c0096a 100644
--- a/glib/gatomic.h
+++ b/glib/gatomic.h
@@ -84,6 +84,54 @@ G_END_DECLS
 
 #if defined(G_ATOMIC_LOCK_FREE) && defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
 
+/* We prefer the new C11-style atomic extension of GCC if available */
+#if defined(__ATOMIC_SEQ_CST)
+
+#define g_atomic_int_get(atomic) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gint));                     \
+    (void) (0 ? *(atomic) ^ *(atomic) : 0);                                  \
+    (gint) __atomic_load_4 ((atomic), __ATOMIC_SEQ_CST);                     \
+  }))
+#define g_atomic_int_set(atomic, newval) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gint));                     \
+    (void) (0 ? *(atomic) ^ (newval) : 0);                                   \
+    __atomic_store_4 ((atomic), (newval), __ATOMIC_SEQ_CST);                 \
+  }))
+
+#if GLIB_SIZEOF_VOID_P == 8
+
+#define g_atomic_pointer_get(atomic) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
+    (gpointer) __atomic_load_8 ((atomic), __ATOMIC_SEQ_CST);                 \
+  }))
+#define g_atomic_pointer_set(atomic, newval) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
+    (void) (0 ? (gpointer) *(atomic) : 0);                                   \
+    __atomic_store_8 ((atomic), (gsize) (newval), __ATOMIC_SEQ_CST);         \
+  }))
+
+#else /* GLIB_SIZEOF_VOID_P == 8 */
+
+#define g_atomic_pointer_get(atomic) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
+    (gpointer) __atomic_load_4 ((atomic), __ATOMIC_SEQ_CST);                 \
+  }))
+#define g_atomic_pointer_set(atomic, newval) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
+    (void) (0 ? (gpointer) *(atomic) : 0);                                   \
+    __atomic_store_4 ((atomic), (gsize) (newval), __ATOMIC_SEQ_CST);         \
+  }))
+
+#endif /* GLIB_SIZEOF_VOID_P == 8 */
+
+#else /* defined(__ATOMIC_SEQ_CST) */
+
 #define g_atomic_int_get(atomic) \
   (G_GNUC_EXTENSION ({                                                       \
     G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gint));                     \
@@ -98,6 +146,22 @@ G_END_DECLS
     *(atomic) = (newval);                                                    \
     __sync_synchronize ();                                                   \
   }))
+#define g_atomic_pointer_get(atomic) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
+    __sync_synchronize ();                                                   \
+    (gpointer) *(atomic);                                                    \
+  }))
+#define g_atomic_pointer_set(atomic, newval) \
+  (G_GNUC_EXTENSION ({                                                       \
+    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
+    (void) (0 ? (gpointer) *(atomic) : 0);                                   \
+    *(atomic) = (__typeof__ (*(atomic))) (gsize) (newval);                   \
+    __sync_synchronize ();                                                   \
+  }))
+
+#endif /* !defined(__ATOMIC_SEQ_CST) */
+
 #define g_atomic_int_inc(atomic) \
   (G_GNUC_EXTENSION ({                                                       \
     G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gint));                     \
@@ -141,19 +205,6 @@ G_END_DECLS
     (guint) __sync_fetch_and_xor ((atomic), (val));                          \
   }))
 
-#define g_atomic_pointer_get(atomic) \
-  (G_GNUC_EXTENSION ({                                                       \
-    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
-    __sync_synchronize ();                                                   \
-    (gpointer) *(atomic);                                                    \
-  }))
-#define g_atomic_pointer_set(atomic, newval) \
-  (G_GNUC_EXTENSION ({                                                       \
-    G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
-    (void) (0 ? (gpointer) *(atomic) : 0);                                   \
-    *(atomic) = (__typeof__ (*(atomic))) (gsize) (newval);                   \
-    __sync_synchronize ();                                                   \
-  }))
 #define g_atomic_pointer_compare_and_exchange(atomic, oldval, newval) \
   (G_GNUC_EXTENSION ({                                                       \
     G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \