Address comments

Source/ASDisplayNode+Layout.mm

@@ -912,7 +912,7 @@ - (void)_locked_setCalculatedDisplayNodeLayout:(std::shared_ptr<ASDisplayNodeLay
   ASDisplayNodeAssertTrue(displayNodeLayout->layout.size.height >= 0.0);
 
   // Flatten the layout if it wasn't done before (@see -calculateLayoutThatFits:).
-  if (ASDisplayNode.shouldStoreUnflattenedLayouts) {
+  if ([ASDisplayNode shouldStoreUnflattenedLayouts]) {
     _unflattenedLayout = displayNodeLayout->layout;
     displayNodeLayout->layout = [_unflattenedLayout filteredNodeLayoutTree];
   }

Source/ASDisplayNode.h

@@ -554,14 +554,25 @@ extern NSInteger const ASDefaultDrawingPriority;
 @interface ASDisplayNode (Debugging) <ASDebugNameProvider>
 
 /**
- * Whether ASDisplayNode should store their unflattened layouts. The layout can be accessed via `-unflattenedCalculatedLayout`.
- * Flattened layouts use less memory and are faster to lookup, while unflattened ones are useful for debugging
- * because they reserve original information.
+ * Set to YES to tell all ASDisplayNode instances to store their unflattened layouts.
  *
- * Defaults to NO.
+ * The layout can be accessed via `-unflattenedCalculatedLayout`.
+ *
+ * Flattened layouts use less memory and are faster to lookup. On the other hand, unflattened layouts are useful for debugging
+ * because they preserve original information.
  */
 + (void)setShouldStoreUnflattenedLayouts:(BOOL)shouldStore;
 
+/**
+ * Whether or not ASDisplayNode instances should store their unflattened layouts. 
+ *
+ * The layout can be accessed via `-unflattenedCalculatedLayout`.
+ * 
+ * Flattened layouts use less memory and are faster to lookup. On the other hand, unflattened layouts are useful for debugging
+ * because they preserve original information.
+ *
+ * Defaults to NO.
+ */
 + (BOOL)shouldStoreUnflattenedLayouts;
 
 @property (nonatomic, strong, readonly, nullable) ASLayout *unflattenedCalculatedLayout;

Source/ASDisplayNode.mm

@@ -82,7 +82,7 @@ @implementation ASDisplayNode
 @synthesize threadSafeBounds = _threadSafeBounds;
 
 static BOOL suppressesInvalidCollectionUpdateExceptions = NO;
-static BOOL storesUnflattenedLayouts = NO;
+static std::atomic_bool storesUnflattenedLayouts = ATOMIC_VAR_INIT(NO);
 
 + (BOOL)suppressesInvalidCollectionUpdateExceptions
 {
@@ -1042,7 +1042,7 @@ - (ASLayout *)calculateLayoutThatFits:(ASSizeRange)constrainedSize
 
   // Return the (original) unflattened layout if it needs to be stored. The layout will be flattened later on (@see _locked_setCalculatedDisplayNodeLayout:).
   // Otherwise, flatten it right away.
-  if (! storesUnflattenedLayouts) {
+  if (! [ASDisplayNode shouldStoreUnflattenedLayouts]) {
     layout = [layout filteredNodeLayoutTree];
   }
 
@@ -3296,16 +3296,17 @@ @implementation ASDisplayNode (Debugging)
 
 + (void)setShouldStoreUnflattenedLayouts:(BOOL)shouldStore
 {
-  storesUnflattenedLayouts = shouldStore;
+  storesUnflattenedLayouts.store(shouldStore);
 }
 
 + (BOOL)shouldStoreUnflattenedLayouts
 {
-  return storesUnflattenedLayouts;
+  return storesUnflattenedLayouts.load();
 }
 
 - (ASLayout *)unflattenedCalculatedLayout
 {
+  ASDN::MutexLocker l(__instanceLock__);
   return _unflattenedLayout;
 }
 

Source/Layout/ASLayout.h

@@ -177,11 +177,17 @@ ASDISPLAYNODE_EXTERN_C_END
 @interface ASLayout (Debugging)
 
 /**
- * Set to YES to tell all ASLayout instances to retain their sublayouts. Defaults to NO.
- * Can be overridden at instance level. 
+ * Set to YES to tell all ASLayout instances to retain their sublayout elements. Defaults to NO.
+ * Can be overridden at instance level.
  */
 + (void)setShouldRetainSublayoutLayoutElements:(BOOL)shouldRetain;
 
+/**
+ * Whether or not ASLayout instances should retain their sublayout elements.
+ * Can be overridden at instance level.
+ */
++ (BOOL)shouldRetainSublayoutLayoutElements;
+
 /**
  * Recrusively output the description of the layout tree.
  */

Source/Layout/ASLayout.mm

@@ -76,11 +76,16 @@ @implementation ASLayout
 
 @dynamic frame, type;
 
-static BOOL static_retainsSublayoutLayoutElements = NO;
+static std::atomic_bool static_retainsSublayoutLayoutElements = ATOMIC_VAR_INIT(NO);
 
 + (void)setShouldRetainSublayoutLayoutElements:(BOOL)shouldRetain
 {
-  static_retainsSublayoutLayoutElements = shouldRetain;
+  static_retainsSublayoutLayoutElements.store(shouldRetain);
+}
+
++ (BOOL)shouldRetainSublayoutLayoutElements
+{
+  return static_retainsSublayoutLayoutElements.load();
 }
 
 - (instancetype)initWithLayoutElement:(id<ASLayoutElement>)layoutElement
@@ -125,7 +130,7 @@ - (instancetype)initWithLayoutElement:(id<ASLayoutElement>)layoutElement
     }
 
     _flattened = NO;
-    self.retainSublayoutLayoutElements = static_retainsSublayoutLayoutElements;
+    self.retainSublayoutLayoutElements = [ASLayout shouldRetainSublayoutLayoutElements];
   }
 
   return self;