commit af384636e9c86a41f398e9913e6363a7549bdcd6
Author: Nathan Froyd <froydnj@mozilla.com>
Date:   Mon May 4 13:38:41 2015 -0400

    support new-style __atomic_* primitives
    
    Recent versions of GCC/clang feature a new set of compiler intrinsics
    for performing atomic operations, motivated by the operations needed to
    support the C++11 memory model.  These intrinsics are more flexible than
    the old __sync_* intrinstics and offer efficient support for atomic load
    and store operations.

diff --git a/build/aclocal.cairo.m4 b/build/aclocal.cairo.m4
index 2f4873b..44ba5fd 100644
--- a/build/aclocal.cairo.m4
+++ b/build/aclocal.cairo.m4
@@ -168,6 +168,13 @@ int atomic_cmpxchg(int i, int j, int k) { return __sync_val_compare_and_swap (&i
 		  cairo_cv_atomic_primitives="Intel"
 		  )
 
+		AC_TRY_LINK([
+int atomic_add(int i) { return __atomic_fetch_add(&i, 1, __ATOMIC_SEQ_CST); }
+int atomic_cmpxchg(int i, int j, int k) { return __atomic_compare_exchange_n(&i, &j, k, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); }
+], [],
+		   cairo_cv_atomic_primitives="cxx11"
+		   )
+
 		if test "x$cairo_cv_atomic_primitives" = "xnone"; then
 			AC_CHECK_HEADER([atomic_ops.h],
 					cairo_cv_atomic_primitives="libatomic-ops")
@@ -178,6 +185,11 @@ int atomic_cmpxchg(int i, int j, int k) { return __sync_val_compare_and_swap (&i
 					cairo_cv_atomic_primitives="OSAtomic")
 		fi
 	])
+	if test "x$cairo_cv_atomic_primitives" = xcxx11; then
+		AC_DEFINE(HAVE_CXX11_ATOMIC_PRIMITIVES, 1,
+			  [Enable if your compiler supports the GCC __atomic_* atomic primitives])
+	fi
+
 	if test "x$cairo_cv_atomic_primitives" = xIntel; then
 		AC_DEFINE(HAVE_INTEL_ATOMIC_PRIMITIVES, 1,
 			  [Enable if your compiler supports the Intel __sync_* atomic primitives])
diff --git a/src/cairo-atomic-private.h b/src/cairo-atomic-private.h
index 327fed1..11b2887 100644
--- a/src/cairo-atomic-private.h
+++ b/src/cairo-atomic-private.h
@@ -53,6 +53,96 @@
 
 CAIRO_BEGIN_DECLS
 
+/* C++11 atomic primitives were designed to be more flexible than the
+ * __sync_* family of primitives.  Despite the name, they are available
+ * in C as well as C++.  The motivating reason for using them is that
+ * for _cairo_atomic_{int,ptr}_get, the compiler is able to see that
+ * the load is intended to be atomic, as opposed to the __sync_*
+ * version, below, where the load looks like a plain load.  Having
+ * the load appear atomic to the compiler is particular important for
+ * tools like ThreadSanitizer so they don't report false positives on
+ * memory operations that we intend to be atomic.
+ */
+#if HAVE_CXX11_ATOMIC_PRIMITIVES
+
+#define HAS_ATOMIC_OPS 1
+
+typedef int cairo_atomic_int_t;
+
+static cairo_always_inline cairo_atomic_int_t
+_cairo_atomic_int_get (cairo_atomic_int_t *x)
+{
+    return __atomic_load_n(x, __ATOMIC_SEQ_CST);
+}
+
+static cairo_always_inline void *
+_cairo_atomic_ptr_get (void **x)
+{
+    return __atomic_load_n(x, __ATOMIC_SEQ_CST);
+}
+
+# define _cairo_atomic_int_inc(x) ((void) __atomic_fetch_add(x, 1, __ATOMIC_SEQ_CST))
+# define _cairo_atomic_int_dec(x) ((void) __atomic_fetch_sub(x, 1, __ATOMIC_SEQ_CST))
+# define _cairo_atomic_int_dec_and_test(x) (__atomic_fetch_sub(x, 1, __ATOMIC_SEQ_CST) == 1)
+
+#if SIZEOF_VOID_P==SIZEOF_INT
+typedef int cairo_atomic_intptr_t;
+#elif SIZEOF_VOID_P==SIZEOF_LONG
+typedef long cairo_atomic_intptr_t;
+#elif SIZEOF_VOID_P==SIZEOF_LONG_LONG
+typedef long long cairo_atomic_intptr_t;
+#else
+#error No matching integer pointer type
+#endif
+
+static cairo_always_inline cairo_bool_t
+_cairo_atomic_int_cmpxchg_impl(cairo_atomic_int_t *x,
+			       cairo_atomic_int_t oldv,
+			       cairo_atomic_int_t newv)
+{
+    cairo_atomic_int_t expected = oldv;
+    return __atomic_compare_exchange_n(x, &expected, newv, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+}
+
+#define _cairo_atomic_int_cmpxchg(x, oldv, newv) \
+  _cairo_atomic_int_cmpxchg_impl(x, oldv, newv)
+
+static cairo_always_inline cairo_atomic_int_t
+_cairo_atomic_int_cmpxchg_return_old_impl(cairo_atomic_int_t *x,
+					  cairo_atomic_int_t oldv,
+					  cairo_atomic_int_t newv)
+{
+    cairo_atomic_int_t expected = oldv;
+    (void) __atomic_compare_exchange_n(x, &expected, newv, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+    return expected;
+}
+
+#define _cairo_atomic_int_cmpxchg_return_old(x, oldv, newv) \
+  _cairo_atomic_int_cmpxchg_return_old_impl(x, oldv, newv)
+
+static cairo_always_inline cairo_bool_t
+_cairo_atomic_ptr_cmpxchg_impl(void **x, void *oldv, void *newv)
+{
+    void *expected = oldv;
+    return __atomic_compare_exchange_n(x, &expected, newv, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+}
+
+#define _cairo_atomic_ptr_cmpxchg(x, oldv, newv) \
+  _cairo_atomic_ptr_cmpxchg_impl(x, oldv, newv)
+
+static cairo_always_inline void *
+_cairo_atomic_ptr_cmpxchg_return_old_impl(void **x, void *oldv, void *newv)
+{
+    void *expected = oldv;
+    (void) __atomic_compare_exchange_n(x, &expected, newv, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+    return expected;
+}
+
+#define _cairo_atomic_ptr_cmpxchg_return_old(x, oldv, newv) \
+  _cairo_atomic_ptr_cmpxchg_return_old_impl(x, oldv, newv)
+
+#endif
+
 #if HAVE_INTEL_ATOMIC_PRIMITIVES
 
 #define HAS_ATOMIC_OPS 1