ship IGListExperimentArrayAndSetOptimization

Summary: This experiment shows a slight decrease in frame-drops on features that have more expensive hashing, so lets ship!

Reviewed By: lorixx

Differential Revision: D25884785

fbshipit-source-id: a5e33abe6f129166ab9b75de80636db801599b74

CHANGELOG.md

@@ -26,6 +26,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Improved performance by using `reloadData` when there are too many diffing updates. Shipped with experiment `IGListExperimentReloadDataFallback` from Ryan Nystrom. [Maxime Ollivier](https://github.com/maxolls) (tbd)
 
+- Small performance improvement by replacing `NSSet` with `NSArray` during the data update to avoid unnecessary hashing, especially when dealing with lots of large objects with non trivial hashes. [Maxime Ollivier](https://github.com/maxolls) (tbd)
+
 ### Fixes
 
 - `IGListCollectionViewLayout` should get the section/index counts via `UICollectionView` to stay in sync, instead of the `dataSource` [Maxime Ollivier](https://github.com/maxolls) (tbd)

Source/IGListDiffKit/IGListExperiments.h

@@ -20,14 +20,12 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
     IGListExperimentBackgroundDiffing = 1 << 2,
     /// Test invalidating layout when cell reloads/updates in IGListBindingSectionController.
     IGListExperimentInvalidateLayoutForUpdates = 1 << 3,
-    /// Test array and set optimization on update
-    IGListExperimentArrayAndSetOptimization = 1 << 4,
     /// Test validating the collectionView count just before performBatchUpdate. `IGListExperimentalAdapterUpdater` only.
-    IGListExperimentSectionCountValidation = 1 << 5,
+    IGListExperimentSectionCountValidation = 1 << 4,
     /// Test skipping performBatchUpdate if we don't have any updates. `IGListExperimentalAdapterUpdater` only.
-    IGListExperimentSkipPerformUpdateIfPossible = 1 << 6,
+    IGListExperimentSkipPerformUpdateIfPossible = 1 << 5,
     /// Test skipping creating {view : section controller} map, which has inconsistency issue.
-    IGListExperimentSkipViewSectionControllerMap = 1 << 7
+    IGListExperimentSkipViewSectionControllerMap = 1 << 6
 };
 
 /**

Source/IGListKit/IGListAdapter.m

@@ -15,7 +15,6 @@
 #import "IGListDebugger.h"
 #import "IGListSectionControllerInternal.h"
 #import "IGListTransitionData.h"
-#import "IGListUpdatedObjectContainer.h"
 #import "IGListUpdatingDelegateExperimental.h"
 #import "UICollectionViewLayout+InteractiveReordering.h"
 #import "UIScrollView+IGListKit.h"
@@ -710,17 +709,8 @@ - (IGListTransitionData *)_generateTransitionDataWithObjects:(NSArray *)objects
     }
 #endif
 
-    NSMutableArray<IGListSectionController *> *sectionControllers;
-    NSMutableArray *validObjects;
-
-    if (IGListExperimentEnabled(_experiments, IGListExperimentArrayAndSetOptimization)) {
-        // Experiment: Pass the capacity count, so that arrays don't have to re-size.
-        sectionControllers = [[NSMutableArray alloc] initWithCapacity:objects.count];
-        validObjects = [[NSMutableArray alloc] initWithCapacity:objects.count];
-    } else {
-        sectionControllers = [NSMutableArray new];
-        validObjects = [NSMutableArray new];
-    }
+    NSMutableArray<IGListSectionController *> *sectionControllers = [[NSMutableArray alloc] initWithCapacity:objects.count];
+    NSMutableArray *validObjects = [[NSMutableArray alloc] initWithCapacity:objects.count];
 
     // push the view controller and collection context into a local thread container so they are available on init
     // for IGListSectionController subclasses after calling [super init]
@@ -776,14 +766,8 @@ - (void)_updateWithData:(IGListTransitionData *)data {
 
     IGListSectionMap *map = self.sectionMap;
 
-    id<IGListUpdatedObjectContainer> updatedObjects;
-    if (IGListExperimentEnabled(_experiments, IGListExperimentArrayAndSetOptimization)) {
-        // Experiment: Avoid using a set, so that we don't need to deal with hashes and equality. The updater
-        // should have dealt with duplicates already.
-        updatedObjects = [NSMutableArray new];
-    } else {
-        updatedObjects = [NSMutableSet new];
-    }
+    // Note: We use an array, instead of a set, because the updater should have dealt with duplicates already.
+    NSMutableArray *updatedObjects = [NSMutableArray new];
 
     for (id object in data.toObjects) {
         // check if the item has changed instances or is new