Merge pull request #4 from alexdowad/volatile_semantics_for_get_set

Volatile semantics for #get, #set, and #swap

Author: jdantonio

ext/atomic_reference.c

@@ -37,18 +37,31 @@ static VALUE ir_initialize(int argc, VALUE* argv, VALUE self) {
 }
 
 static VALUE ir_get(VALUE self) {
+#if HAVE_GCC_SYNC
+    __sync_synchronize();
+#elif defined _MSC_VER
+    MemoryBarrier();
+#elif __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1050
+    OSMemoryBarrier();
+#endif
     return (VALUE) DATA_PTR(self);
 }
 
 static VALUE ir_set(VALUE self, VALUE new_value) {
     DATA_PTR(self) = (void *) new_value;
+#if HAVE_GCC_SYNC
+    __sync_synchronize();
+#elif defined _MSC_VER
+    MemoryBarrier();
+#elif __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1050
+    OSMemoryBarrier();
+#endif
     return new_value;
 }
 
 static VALUE ir_get_and_set(VALUE self, VALUE new_value) {
-    VALUE old_value;
-    old_value = (VALUE) DATA_PTR(self);
-    DATA_PTR(self) = (void *) new_value;
+    VALUE old_value = ir_get(self);
+    ir_set(self, new_value);
     return old_value;
 }
 

ext/extconf.rb

@@ -37,11 +37,10 @@ def compiler_is_gcc
   end
 end
 
-try_run(<<CODE,$CFLAGS) && ($defs << '-DHAVE_GCC_CAS')
+try_run(<<CODE,$CFLAGS) && ($defs << '-DHAVE_GCC_SYNC')
 int main() {
-  int i = 1;
-  __sync_bool_compare_and_swap(&i, 1, 4);
-  return (i != 4);
+  __sync_synchronize();
+  return 0;
 }
 CODE