replace top level mutex with rw lock

src/core/render.rs

@@ -62,6 +62,12 @@ impl<T: Render> Render for Arc<Mutex<T>> {
     }
 }
 
+impl<T: Render + Sync> Render for Arc<RwLock<T>> {
+    fn render (&self, b: &mut Buffer, a: Rect) -> Usually<Rect> {
+        self.read().unwrap().render(b, a)
+    }
+}
+
 impl WidgetRef for &dyn Render {
     fn render_ref (&self, area: Rect, buf: &mut Buffer) {
         Render::render(*self, buf, area).expect("Failed to render device.");