Merge pull request #1283 from Adlai-Holler/AHPendingStateLocking

[ASPendingStateController] Relinquish Lock Before Applying Pending States

AsyncDisplayKit/Private/ASPendingStateController.mm

@@ -58,22 +58,18 @@
   [self scheduleFlushIfNeeded];
 }
 
-/**
- * NOTE: There is a small re-entrancy hazard here.
- * If the user gives us a subclass of UIView/CALayer that
- * adds side-effects to property sets, and one side effect
- * waits on a background thread that sets a view/layer property
- * on a loaded node, then we've got a deadlock.
- */
 - (void)flush
 {
   ASDisplayNodeAssertMainThread();
-  ASDN::MutexLocker l(_lock);
-  for (ASDisplayNode *node in _dirtyNodes) {
+  _lock.lock();
+    ASWeakSet *dirtyNodes = _dirtyNodes;
+    _dirtyNodes = [[ASWeakSet alloc] init];
+    _flags.pendingFlush = NO;
+  _lock.unlock();
+
+  for (ASDisplayNode *node in dirtyNodes) {
     [node applyPendingViewState];
   }
-  [_dirtyNodes removeAllObjects];
-  _flags.pendingFlush = NO;
 }