[ASTextNode] Fix an race condition on ASTextKitAttributes

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## master
 * Add your own contributions to the next release on the line below this with your name.
+- [ASTextNode] Fix an race condition on ASTextKitAttributes [Heberti Almeida](http://github.com/hebertialmeida) [#819]
 - [ASDisplayNode] Add unit tests for layout z-order changes (with an open issue to fix).
 - [ASDisplayNode] Consolidate main thread initialization and allow apps to invoke it manually instead of +load.
 - [ASRunloopQueue] Introduce new runloop queue(ASCATransactionQueue) to coalesce Interface state update calls for view controller transitions.

Source/ASTextNode.mm

@@ -116,10 +116,23 @@ - (BOOL)isEqual:(ASTextNodeRendererKey *)object
   key.attributes = attributes;
   key.constrainedSize = constrainedSize;
 
-  ASTextKitRenderer *renderer = [cache objectForKey:key];
+  static dispatch_queue_t rendererQueue;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    rendererQueue = dispatch_queue_create("org.AsyncDisplayKit.ASTextNode.renderer", DISPATCH_QUEUE_CONCURRENT);
+    dispatch_set_target_queue(rendererQueue, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));
+  });
+
+  __block ASTextKitRenderer *renderer;
+  dispatch_sync(rendererQueue, ^{
+    renderer = [cache objectForKey:key];
+  });
+
   if (renderer == nil) {
     renderer = [[ASTextKitRenderer alloc] initWithTextKitAttributes:attributes constrainedSize:constrainedSize];
-    [cache setObject:renderer forKey:key];
+    dispatch_barrier_async(rendererQueue, ^{
+      [cache setObject:renderer forKey:key];
+    });
   }
 
   return renderer;