adds FML_GUARDED_BY

Author: gaaclarke

fml/concurrent_message_loop.h

@@ -73,9 +73,9 @@ class ConcurrentTaskRunner : public BasicTaskRunner {
  private:
   friend ConcurrentMessageLoop;
 
-  // Raw pointer that is cleared out in ~ConcurrentMessageLoop.
-  ConcurrentMessageLoop* weak_loop_;
   std::mutex weak_loop_mutex_;
+  // Raw pointer that is cleared out in ~ConcurrentMessageLoop.
+  ConcurrentMessageLoop* weak_loop_ FML_GUARDED_BY(weak_loop_mutex_);
 
   FML_DISALLOW_COPY_AND_ASSIGN(ConcurrentTaskRunner);
 };

fml/macros.h

@@ -38,4 +38,12 @@
   TypeName() = delete;                               \
   FML_DISALLOW_COPY_ASSIGN_AND_MOVE(TypeName)
 
+#if defined(__clang__)
+#define FML_THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
+#else
+#define FML_THREAD_ANNOTATION_ATTRIBUTE__(x)  // no-op
+#endif
+
+#define FML_GUARDED_BY(x) FML_THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
+
 #endif  // FLUTTER_FML_MACROS_H_