Improve Our Handling of Subnodes (#223)

* Improve the subnodes/fast enumeration situation

* Increment changlag

* Assert our subnodes match

CHANGELOG.md

@@ -7,3 +7,4 @@
 - [Yoga Beta] Improvements to the experimental support for Yoga layout [Scott Goodson](appleguy)
 - Update the rasterization API and un-deprecate it. [Adlai Holler](https://github.com/Adlai-Holler)[#82](https://github.com/TextureGroup/Texture/pull/49)
 - Simplified & optimized hashing code. [Adlai Holler](https://github.com/Adlai-Holler) [#86](https://github.com/TextureGroup/Texture/pull/86)
+- Improve the performance & safety of ASDisplayNode subnodes. [Adlai Holler](https://github.com/Adlai-Holler) [#223](https://github.com/TextureGroup/Texture/pull/223)

Source/ASDisplayNode.h

@@ -121,7 +121,7 @@ extern NSInteger const ASDefaultDrawingPriority;
  *
  */
 
-@interface ASDisplayNode : NSObject <ASLayoutElement, ASLayoutElementStylability, NSFastEnumeration>
+@interface ASDisplayNode : NSObject <ASLayoutElement, ASLayoutElementStylability>
 
 /** @name Initializing a node object */
 

Source/ASDisplayNode.mm

@@ -430,8 +430,6 @@ - (void)dealloc
     [self _scheduleIvarsForMainDeallocation];
   }
 
-  _subnodes = nil;
-
 #if YOGA
   if (_yogaNode != NULL) {
     YGNodeFree(_yogaNode);
@@ -1411,17 +1409,15 @@ - (void)_layoutSublayouts
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
 
   ASLayout *layout;
-  NSArray<ASDisplayNode *> *subnodes;
   {
     ASDN::MutexLocker l(__instanceLock__);
-    if (_calculatedDisplayNodeLayout->isDirty() || _subnodes.count == 0) {
+    if (_calculatedDisplayNodeLayout->isDirty()) {
       return;
     }
     layout = _calculatedDisplayNodeLayout->layout;
-    subnodes = [_subnodes copy];
   }
 
-  for (ASDisplayNode *node in subnodes) {
+  for (ASDisplayNode *node in self.subnodes) {
     CGRect frame = [layout frameForElement:node];
     if (CGRectIsNull(frame)) {
       // There is no frame for this node in our layout.
@@ -2675,7 +2671,12 @@ - (void)_setSupernode:(ASDisplayNode *)newSupernode
 - (NSArray *)subnodes
 {
   ASDN::MutexLocker l(__instanceLock__);
-  return ([_subnodes copy] ?: @[]);
+  if (_cachedSubnodes == nil) {
+    _cachedSubnodes = [_subnodes copy];
+  } else {
+    ASDisplayNodeAssert(ASObjectIsEqual(_cachedSubnodes, _subnodes), @"Expected _subnodes and _cachedSubnodes to have the same contents.");
+  }
+  return _cachedSubnodes ?: @[];
 }
 
 /*
@@ -2736,6 +2737,7 @@ - (void)_insertSubnode:(ASDisplayNode *)subnode atSubnodeIndex:(NSInteger)subnod
       _subnodes = [[NSMutableArray alloc] init];
     }
     [_subnodes insertObject:subnode atIndex:subnodeIndex];
+    _cachedSubnodes = nil;
   __instanceLock__.unlock();
 
   // This call will apply our .hierarchyState to the new subnode.
@@ -3071,6 +3073,7 @@ - (void)_removeSubnode:(ASDisplayNode *)subnode
 
   __instanceLock__.lock();
     [_subnodes removeObjectIdenticalTo:subnode];
+    _cachedSubnodes = nil;
   __instanceLock__.unlock();
 
   [subnode _setSupernode:nil];
@@ -4060,13 +4063,6 @@ - (CGRect)_frameInWindow
   }
 }
 
-#pragma mark - NSFastEnumeration
-
-- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id __unsafe_unretained _Nullable [_Nonnull])buffer count:(NSUInteger)len
-{
-  return [self.subnodes countByEnumeratingWithState:state objects:buffer count:len];
-}
-
 #pragma mark - ASPrimitiveTraitCollection
 
 - (ASPrimitiveTraitCollection)primitiveTraitCollection

Source/Private/ASDisplayNodeInternal.h

@@ -127,6 +127,9 @@ FOUNDATION_EXPORT NSString * const ASRenderingEngineDidDisplayNodesScheduledBefo
   ASDisplayNode * __weak _supernode;
   NSMutableArray<ASDisplayNode *> *_subnodes;
 
+  // Set this to nil whenever you modify _subnodes
+  NSArray<ASDisplayNode *> *_cachedSubnodes;
+
   ASLayoutElementStyle *_style;
   ASPrimitiveTraitCollection _primitiveTraitCollection;