Merge pull request #145 from alexdowad/volatile_semantics_for_atomic_get_set

Volatile semantics for atomic get set

Author: jdantonio

ext/concurrent_ruby_ext/atomic_reference.c

@@ -27,18 +27,31 @@ VALUE ir_initialize(int argc, VALUE* argv, VALUE self) {
 }
 
 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);
 }
 
 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;
 }
 
 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/concurrent_ruby_ext/extconf.rb

@@ -43,12 +43,11 @@ def compiler_is_gcc
       end
     end
 
-    try_run(<<CODE,$CFLAGS) && ($defs << '-DHAVE_GCC_CAS')
-int main() {
-  int i = 1;
-  __sync_bool_compare_and_swap(&i, 1, 4);
-  return (i != 4);
-}
+    try_run(<<CODE,$CFLAGS) && ($defs << '-DHAVE_GCC_SYNC')
+      int main() {
+        __sync_synchronize();
+        return 0;
+      }
 CODE
 
     create_makefile(EXTENSION_NAME)