Create transfer-array method and use it

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -332,6 +332,9 @@
 		CC224E962066CA6D00BBA57F /* configuration.json in Resources */ = {isa = PBXBuildFile; fileRef = CC224E952066CA6D00BBA57F /* configuration.json */; };
 		CC2F65EE1E5FFB1600DA57C9 /* ASMutableElementMap.h in Headers */ = {isa = PBXBuildFile; fileRef = CC2F65EC1E5FFB1600DA57C9 /* ASMutableElementMap.h */; };
 		CC2F65EF1E5FFB1600DA57C9 /* ASMutableElementMap.m in Sources */ = {isa = PBXBuildFile; fileRef = CC2F65ED1E5FFB1600DA57C9 /* ASMutableElementMap.m */; };
+		CC35CEC320DD7F600006448D /* ASCollections.h in Headers */ = {isa = PBXBuildFile; fileRef = CC35CEC120DD7F600006448D /* ASCollections.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		CC35CEC420DD7F600006448D /* ASCollections.m in Sources */ = {isa = PBXBuildFile; fileRef = CC35CEC220DD7F600006448D /* ASCollections.m */; };
+		CC35CEC620DD87280006448D /* ASCollectionsTests.m in Sources */ = {isa = PBXBuildFile; fileRef = CC35CEC520DD87280006448D /* ASCollectionsTests.m */; };
 		CC3B20841C3F76D600798563 /* ASPendingStateController.h in Headers */ = {isa = PBXBuildFile; fileRef = CC3B20811C3F76D600798563 /* ASPendingStateController.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		CC3B20861C3F76D600798563 /* ASPendingStateController.mm in Sources */ = {isa = PBXBuildFile; fileRef = CC3B20821C3F76D600798563 /* ASPendingStateController.mm */; };
 		CC3B208A1C3F7A5400798563 /* ASWeakSet.h in Headers */ = {isa = PBXBuildFile; fileRef = CC3B20871C3F7A5400798563 /* ASWeakSet.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -839,6 +842,9 @@
 		CC2E317F1DAC353700EEE891 /* ASCollectionView+Undeprecated.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "ASCollectionView+Undeprecated.h"; sourceTree = "<group>"; };
 		CC2F65EC1E5FFB1600DA57C9 /* ASMutableElementMap.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASMutableElementMap.h; sourceTree = "<group>"; };
 		CC2F65ED1E5FFB1600DA57C9 /* ASMutableElementMap.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASMutableElementMap.m; sourceTree = "<group>"; };
+		CC35CEC120DD7F600006448D /* ASCollections.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ASCollections.h; sourceTree = "<group>"; };
+		CC35CEC220DD7F600006448D /* ASCollections.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = ASCollections.m; sourceTree = "<group>"; };
+		CC35CEC520DD87280006448D /* ASCollectionsTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = ASCollectionsTests.m; sourceTree = "<group>"; };
 		CC3B20811C3F76D600798563 /* ASPendingStateController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASPendingStateController.h; sourceTree = "<group>"; };
 		CC3B20821C3F76D600798563 /* ASPendingStateController.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ASPendingStateController.mm; sourceTree = "<group>"; };
 		CC3B20871C3F7A5400798563 /* ASWeakSet.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASWeakSet.h; sourceTree = "<group>"; };
@@ -1115,6 +1121,8 @@
 		058D09B1195D04C000B7D73C /* Source */ = {
 			isa = PBXGroup;
 			children = (
+				CC35CEC120DD7F600006448D /* ASCollections.h */,
+				CC35CEC220DD7F600006448D /* ASCollections.m */,
 				058D0A42195D058D00B7D73C /* Base */,
 				CCE04B1D1E313E99006AEBBB /* Collection Data Adapter */,
 				DE89C1691DCEB9CC00D49D74 /* Debug */,
@@ -1238,6 +1246,7 @@
 		058D09C5195D04C000B7D73C /* Tests */ = {
 			isa = PBXGroup;
 			children = (
+				CC35CEC520DD87280006448D /* ASCollectionsTests.m */,
 				DBC452DD1C5C6A6A00B16017 /* ArrayDiffingTests.m */,
 				AC026B571BD3F61800BBC17E /* ASAbsoluteLayoutSpecSnapshotTests.m */,
 				696FCB301D6E46050093471E /* ASBackgroundLayoutSpecSnapshotTests.mm */,
@@ -2019,6 +2028,7 @@
 				CCCCCCDB1EC3EF060087FE10 /* ASTextLine.h in Headers */,
 				9C70F20E1CDBE9E5007D6C76 /* NSArray+Diffing.h in Headers */,
 				CCCCCCE71EC3F0FC0087FE10 /* NSAttributedString+ASText.h in Headers */,
+				CC35CEC320DD7F600006448D /* ASCollections.h in Headers */,
 				CC7AF196200D9BD500A21BDE /* ASExperimentalFeatures.h in Headers */,
 				CCCCCCDF1EC3EF060087FE10 /* ASTextRunDelegate.h in Headers */,
 				9C49C3701B853961000B0DD5 /* ASStackLayoutElement.h in Headers */,
@@ -2300,6 +2310,7 @@
 				1A6C00111FAB4EDD00D05926 /* ASCornerLayoutSpecSnapshotTests.mm in Sources */,
 				254C6B541BF8FF2A003EC431 /* ASTextKitTests.mm in Sources */,
 				05EA6FE71AC0966E00E35788 /* ASSnapshotTestCase.m in Sources */,
+				CC35CEC620DD87280006448D /* ASCollectionsTests.m in Sources */,
 				ACF6ED631B178DC700DA7C62 /* ASStackLayoutSpecSnapshotTests.mm in Sources */,
 				E52AC9C01FEA916C00AA4040 /* ASRectMapTests.m in Sources */,
 				CCE4F9BA1F0DBB5000062E4E /* ASLayoutTestNode.mm in Sources */,
@@ -2444,6 +2455,7 @@
 				CCA282B51E9EA7310037E8B7 /* ASTipsController.m in Sources */,
 				B35062271B010EFD0018CF92 /* ASRangeController.mm in Sources */,
 				0442850A1BAA63FE00D16268 /* ASBatchFetching.m in Sources */,
+				CC35CEC420DD7F600006448D /* ASCollections.m in Sources */,
 				68FC85E61CE29B9400EDD713 /* ASNavigationController.m in Sources */,
 				CC4C2A791D88E3BF0039ACAB /* ASTraceEvent.m in Sources */,
 				34EFC76F1B701CF700AD841F /* ASRatioLayoutSpec.mm in Sources */,

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Clean up C-function `extern` decorators. [Adlai Holler](https://github.com/Adlai-Holler)
 - Add an experiment to reduce work involved in collection teardown. [Adlai Holler](https://github.com/Adlai-Holler)
 - Optimize layout flattening, particularly reducing retain/release operations. [Adlai Holler](https://github.com/Adlai-Holler)
+- Create a method to transfer strong C-arrays into immutable NSArrays, reducing retain/release traffic. [Adlai Holler](https://github.com/Adlai-Holler)
 
 ## 2.7
 - Fix pager node for interface coalescing. [Max Wang](https://github.com/wsdwsd0829) [#877](https://github.com/TextureGroup/Texture/pull/877)

Source/ASCollectionView.mm

@@ -23,6 +23,7 @@
 #import <AsyncDisplayKit/ASCollectionInternal.h>
 #import <AsyncDisplayKit/ASCollectionLayout.h>
 #import <AsyncDisplayKit/ASCollectionNode+Beta.h>
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/ASCollectionViewLayoutController.h>
 #import <AsyncDisplayKit/ASCollectionViewLayoutFacilitatorProtocol.h>
 #import <AsyncDisplayKit/ASCollectionViewFlowLayoutInspector.h>
@@ -751,19 +752,7 @@ - (NSIndexPath *)convertIndexPathToCollectionNode:(NSIndexPath *)indexPath
 
 - (NSArray<NSIndexPath *> *)convertIndexPathsToCollectionNode:(NSArray<NSIndexPath *> *)indexPaths
 {
-  if (indexPaths == nil) {
-    return nil;
-  }
-
-  NSMutableArray<NSIndexPath *> *indexPathsArray = [NSMutableArray arrayWithCapacity:indexPaths.count];
-
-  for (NSIndexPath *indexPathInView in indexPaths) {
-    NSIndexPath *indexPath = [self convertIndexPathToCollectionNode:indexPathInView];
-    if (indexPath != nil) {
-      [indexPathsArray addObject:indexPath];
-    }
-  }
-  return indexPathsArray;
+  return ASArrayByFlatMapping(indexPaths, NSIndexPath *viewIndexPath, [self convertIndexPathToCollectionNode:viewIndexPath]);
 }
 
 - (ASCellNode *)supplementaryNodeForElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath
@@ -2225,13 +2214,7 @@ - (void)nodesDidRelayout:(NSArray<ASCellNode *> *)nodes
     return;
   }
 
-  NSMutableArray<NSIndexPath *> *uikitIndexPaths = [NSMutableArray arrayWithCapacity:nodes.count];
-  for (ASCellNode *node in nodes) {
-    NSIndexPath *uikitIndexPath = [self indexPathForNode:node];
-    if (uikitIndexPath != nil) {
-      [uikitIndexPaths addObject:uikitIndexPath];
-    }
-  }
+  auto uikitIndexPaths = ASArrayByFlatMapping(nodes, ASCellNode *node, [self indexPathForNode:node]);
 
   [_layoutFacilitator collectionViewWillEditCellsAtIndexPaths:uikitIndexPaths batched:NO];
 

Source/ASCollections.h

@@ -0,0 +1,42 @@
+//
+//  ASCollections.h
+//  Texture
+//
+//  Copyright (c) 2018-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface NSArray<__covariant ObjectType> (ASCollections)
+
+/**
+ * Create an immutable NSArray from a C-array of strong pointers.
+ *
+ * Note: The memory for the array you pass in will be zero'd (to prevent ARC from releasing
+ * the references when the array goes out of scope.)
+ *
+ * Can be combined with vector like:
+ * vector<NSString *> vec;
+ * vec.push_back(@"foo");
+ * vec.push_back(@"bar");
+ * NSArray *arr = [NSArray arrayTransferring:vec.data() count:vec.size()]
+ * ** vec is now { nil, nil } **
+ *
+ * Unfortunately making a convenience method to do this is currently impossible because
+ * vector<NSString *> can't be converted to vector<id> by the compiler (silly).
+ *
+ * See the private __CFArrayCreateTransfer function.
+ */
++ (NSArray<ObjectType> *)arrayByTransferring:(ObjectType _Nonnull __strong * _Nonnull)pointers
+                                       count:(NSUInteger)count NS_RETURNS_RETAINED;
+
+@end
+
+NS_ASSUME_NONNULL_END

Source/ASCollections.m

@@ -0,0 +1,65 @@
+//
+//  ASCollections.m
+//  Texture
+//
+//  Copyright (c) 2018-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+
+#import "ASCollections.h"
+
+/**
+ * A private allocator that signals to our retain callback to skip the retain.
+ * It behaves the same as the default allocator, but acts as a signal that we
+ * are creating a transfer array so we should skip the retain.
+ */
+static CFAllocatorRef gTransferAllocator;
+
+static const void *ASTransferRetain(CFAllocatorRef allocator, const void *val) {
+  if (allocator == gTransferAllocator) {
+    // Transfer allocator. Ignore retain and pass through.
+    return val;
+  } else {
+    // Other allocator. Retain like normal.
+    // This happens when they make a mutable copy.
+    return (&kCFTypeArrayCallBacks)->retain(allocator, val);
+  }
+}
+
+@implementation NSArray (ASCollections)
+
++ (NSArray *)arrayByTransferring:(__strong id *)pointers count:(NSUInteger)count NS_RETURNS_RETAINED
+{
+  // Custom callbacks that point to our ASTransferRetain callback.
+  static CFArrayCallBacks callbacks;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    callbacks = kCFTypeArrayCallBacks;
+    callbacks.retain = ASTransferRetain;
+    CFAllocatorContext ctx;
+    CFAllocatorGetContext(NULL, &ctx);
+    gTransferAllocator = CFAllocatorCreate(NULL, &ctx);
+  });
+
+  // NSZeroArray fast path.
+  if (count == 0) {
+    return @[]; // Does not actually call +array when optimized.
+  }
+
+  // NSSingleObjectArray fast path. Retain/release here is worth it.
+  if (count == 1) {
+    NSArray *result = [[NSArray alloc] initWithObjects:pointers count:1];
+    pointers[0] = nil;
+    return result;
+  }
+
+  NSArray *result = (__bridge_transfer NSArray *)CFArrayCreate(gTransferAllocator, (void *)pointers, count, &callbacks);
+  memset(pointers, 0, count * sizeof(id));
+  return result;
+}
+
+@end

Source/ASExperimentalFeatures.m

@@ -12,6 +12,8 @@
 
 #import <AsyncDisplayKit/ASExperimentalFeatures.h>
 
+#import <AsyncDisplayKit/ASCollections.h>
+
 NSArray<NSString *> *ASExperimentalFeaturesGetNames(ASExperimentalFeatures flags)
 {
   NSArray *allNames = ASCreateOnce((@[@"exp_graphics_contexts",

Source/ASTableView.mm

@@ -24,6 +24,7 @@
 #import <AsyncDisplayKit/ASBatchFetching.h>
 #import <AsyncDisplayKit/ASCellNode+Internal.h>
 #import <AsyncDisplayKit/ASCollectionElement.h>
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/ASConfigurationInternal.h>
 #import <AsyncDisplayKit/ASDelegateProxy.h>
 #import <AsyncDisplayKit/ASDisplayNodeExtras.h>

Source/AsyncDisplayKit.h

@@ -96,6 +96,7 @@
 #import <AsyncDisplayKit/_ASAsyncTransaction.h>
 #import <AsyncDisplayKit/_ASAsyncTransactionGroup.h>
 #import <AsyncDisplayKit/_ASAsyncTransactionContainer.h>
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/_ASDisplayLayer.h>
 #import <AsyncDisplayKit/_ASDisplayView.h>
 #import <AsyncDisplayKit/ASDisplayNode+Beta.h>

Source/Base/ASBaseDefines.h

@@ -214,13 +214,18 @@
 /**
  * Create a new array by mapping `collection` over `work`, ignoring nil.
  */
-#define ASArrayByFlatMapping(collection, decl, work) ({ \
-  NSMutableArray *a = [[NSMutableArray alloc] init]; \
-  for (decl in collection) {\
-    id result = work; \
-    if (result != nil) { \
-      [a addObject:result]; \
+#define ASArrayByFlatMapping(collectionArg, decl, work) ({ \
+  id __collection = collectionArg; \
+  NSArray *__result; \
+  if (__collection) { \
+    id __buf[[__collection count]]; \
+    NSUInteger __i = 0; \
+    for (decl in __collection) {\
+      if ((__buf[__i] = work)) { \
+        __i++; \
+      } \
     } \
+    __result = [NSArray arrayByTransferring:__buf count:__i]; \
   } \
-  a; \
+  __result; \
 })

Source/Details/ASCollectionFlowLayoutDelegate.m

@@ -22,6 +22,7 @@
 #import <AsyncDisplayKit/ASCollectionElement.h>
 #import <AsyncDisplayKit/ASCollectionLayoutContext.h>
 #import <AsyncDisplayKit/ASCollectionLayoutDefines.h>
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/ASElementMap.h>
 #import <AsyncDisplayKit/ASLayout.h>
 #import <AsyncDisplayKit/ASStackLayoutSpec.h>

Source/Details/ASCollectionGalleryLayoutDelegate.mm

@@ -17,6 +17,7 @@
 #import <AsyncDisplayKit/ASAssert.h>
 #import <AsyncDisplayKit/ASCellNode.h>
 #import <AsyncDisplayKit/ASCollectionElement.h>
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/ASCollectionLayoutContext.h>
 #import <AsyncDisplayKit/ASCollectionLayoutDefines.h>
 #import <AsyncDisplayKit/ASCollectionLayoutState.h>
@@ -102,9 +103,9 @@ + (ASCollectionLayoutState *)calculateLayoutWithContext:(ASCollectionLayoutConte
     return [[ASCollectionLayoutState alloc] initWithContext:context];
   }
 
-  NSMutableArray<_ASGalleryLayoutItem *> *children = ASArrayByFlatMapping(elements.itemElements,
-                                                                          ASCollectionElement *element,
-                                                                          [[_ASGalleryLayoutItem alloc] initWithItemSize:itemSize collectionElement:element]);
+  NSArray<_ASGalleryLayoutItem *> *children = ASArrayByFlatMapping(elements.itemElements,
+                                                                   ASCollectionElement *element,
+                                                                   [[_ASGalleryLayoutItem alloc] initWithItemSize:itemSize collectionElement:element]);
   if (children.count == 0) {
     return [[ASCollectionLayoutState alloc] initWithContext:context];
   }

Source/Layout/ASLayout.mm

@@ -19,6 +19,7 @@
 
 #import <queue>
 
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/ASDimension.h>
 #import <AsyncDisplayKit/ASLayoutSpecUtilities.h>
 #import <AsyncDisplayKit/ASLayoutSpec+Subclasses.h>
@@ -236,7 +237,7 @@ - (ASLayout *)filteredNodeLayoutTree NS_RETURNS_RETAINED
     queue.push_back({sublayout, sublayout.position});
   }
 
-  auto flattenedSublayouts = [[NSMutableArray<ASLayout *> alloc] init];
+  std::vector<ASLayout *> flattenedSublayouts;
 
   while (!queue.empty()) {
     const Context context = std::move(queue.front());
@@ -254,9 +255,9 @@ - (ASLayout *)filteredNodeLayoutTree NS_RETURNS_RETAINED
                                                       size:layout.size
                                                   position:absolutePosition
                                                 sublayouts:@[]];
-        [flattenedSublayouts addObject:newLayout];
+        flattenedSublayouts.push_back(newLayout);
       } else {
-        [flattenedSublayouts addObject:layout];
+        flattenedSublayouts.push_back(layout);
       }
     } else if (sublayoutsCount > 0) {
       // Fast-reverse-enumerate the sublayouts array by copying it into a C-array and push_front'ing each into the queue.
@@ -268,7 +269,10 @@ - (ASLayout *)filteredNodeLayoutTree NS_RETURNS_RETAINED
     }
   }
 
-  ASLayout *layout = [ASLayout layoutWithLayoutElement:_layoutElement size:_size sublayouts:flattenedSublayouts];
+  NSArray *array = [NSArray arrayByTransferring:flattenedSublayouts.data() count:flattenedSublayouts.size()];
+  // flattenedSublayouts is now all nils.
+
+  ASLayout *layout = [ASLayout layoutWithLayoutElement:_layoutElement size:_size sublayouts:array];
   // All flattened layouts must have this flag enabled
   // to ensure sublayout elements are retained until the layouts are applied.
   layout.retainSublayoutLayoutElements = YES;

Source/Layout/ASLayoutSpec.mm

@@ -20,6 +20,7 @@
 
 #import <AsyncDisplayKit/ASLayoutSpec+Subclasses.h>
 
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/ASLayoutElementStylePrivate.h>
 #import <AsyncDisplayKit/ASTraitCollection.h>
 #import <AsyncDisplayKit/ASEqualityHelpers.h>

Source/Private/_ASHierarchyChangeSet.mm

@@ -17,6 +17,7 @@
 
 #import <AsyncDisplayKit/_ASHierarchyChangeSet.h>
 #import <AsyncDisplayKit/ASInternalHelpers.h>
+#import <AsyncDisplayKit/ASCollections.h>
 #import <AsyncDisplayKit/NSIndexSet+ASHelpers.h>
 #import <AsyncDisplayKit/ASAssert.h>
 #import <AsyncDisplayKit/ASDisplayNode+Beta.h>