Wrap SharedLayoutContext::canvas_layers_sender in a Mutex.

components/layout/context.rs

@@ -108,7 +108,7 @@ pub struct SharedLayoutContext {
     pub new_animations_sender: Mutex<Sender<Animation>>,
 
     /// A channel to send canvas renderers to paint task, in order to correctly paint the layers
-    pub canvas_layers_sender: Sender<(LayerId, IpcSender<CanvasMsg>)>,
+    pub canvas_layers_sender: Mutex<Sender<(LayerId, IpcSender<CanvasMsg>)>>,
 
     /// The visible rects for each layer, as reported to us by the compositor.
     pub visible_rects: Arc<HashMap<LayerId, Rect<Au>, DefaultState<FnvHasher>>>,
@@ -123,7 +123,6 @@ pub struct SharedLayoutContext {
 // FIXME(#6569) This implementations is unsound:
 // XXX UNSOUND!!! for image_cache_task
 // XXX UNSOUND!!! for stylist
-// XXX UNSOUND!!! for canvas_layers_sender
 #[allow(unsafe_code)]
 unsafe impl Sync for SharedLayoutContext {}
 

components/layout/display_list_builder.rs

@@ -1150,7 +1150,7 @@ impl FragmentDisplayListBuilding for Fragment {
                             let data = receiver.recv().unwrap();
 
                             // Propagate the layer and the renderer to the paint task.
-                            layout_context.shared.canvas_layers_sender.send(
+                            layout_context.shared.canvas_layers_sender.lock().unwrap().send(
                                 (layer_id, (*ipc_renderer).clone())).unwrap();
 
                             data

components/layout/layout_task.rs

@@ -456,7 +456,7 @@ impl LayoutTask {
             viewport_size: rw_data.viewport_size.clone(),
             screen_size_changed: screen_size_changed,
             font_cache_task: Mutex::new(self.font_cache_task.clone()),
-            canvas_layers_sender: self.canvas_layers_sender.clone(),
+            canvas_layers_sender: Mutex::new(self.canvas_layers_sender.clone()),
             stylist: &*rw_data.stylist,
             url: (*url).clone(),
             visible_rects: rw_data.visible_rects.clone(),