clean up IGListExperimentReloadDataFallback

Summary: This experiment shipped so we can remove it. We still need a way to disable it with `allowsReloadingOnTooManyUpdates` in case we don't want to resign the first responder on large updates.

Reviewed By: Haud

Differential Revision: D22219238

fbshipit-source-id: 98e78f3ed040809db6c4b4c8da8fd0e976aca0a2

CHANGELOG.md

@@ -14,6 +14,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 -  Improved performance by deferring requesting objects from the `IGListAdapterDataSource` until just before diffing is executed. If n updates are coalesced into one, this results in just a single request for objects from the data source. Shipped with experiment `IGListExperimentDeferredToObjectCreation` from Ryan Nystrom.  [Maxime Ollivier](https://github.com/maxolls) (tbd)
 
+- 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) 
+
 ### 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

@@ -18,10 +18,8 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
     IGListExperimentNone = 1 << 1,
     /// Test updater diffing performed on a background queue.
     IGListExperimentBackgroundDiffing = 1 << 2,
-    /// Test fallback to reloadData when "too many" update operations.
-    IGListExperimentReloadDataFallback = 1 << 3,
     /// Test invalidating layout when cell reloads/updates in IGListBindingSectionController.
-    IGListExperimentInvalidateLayoutForUpdates = 1 << 4,
+    IGListExperimentInvalidateLayoutForUpdates = 1 << 3,
 };
 
 /**

Source/IGListKit/IGListAdapterUpdater.h

@@ -68,6 +68,12 @@ NS_SWIFT_NAME(ListAdapterUpdater)
  */
 @property (nonatomic, assign) BOOL allowsBackgroundReloading;
 
+/**
+ If there's more than 100 diff updates, fallback to using `reloadData` to avoid stalling the main thread.
+ Default is YES.
+ */
+@property (nonatomic, assign) BOOL allowsReloadingOnTooManyUpdates;
+
 /**
  A bitmask of experiments to conduct on the updater.
  */

Source/IGListKit/IGListAdapterUpdater.m

@@ -28,6 +28,7 @@ - (instancetype)init {
         _completionBlocks = [NSMutableArray new];
         _batchUpdates = [IGListBatchUpdates new];
         _allowsBackgroundReloading = YES;
+        _allowsReloadingOnTooManyUpdates = YES;
     }
     return self;
 }
@@ -110,6 +111,7 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
     NSMutableArray *completionBlocks = [self.completionBlocks mutableCopy];
     void (^objectTransitionBlock)(NSArray *) = [self.objectTransitionBlock copy];
     const BOOL animated = self.queuedUpdateIsAnimated;
+    const BOOL allowsReloadingOnTooManyUpdates = self.allowsReloadingOnTooManyUpdates;
     IGListBatchUpdates *batchUpdates = self.batchUpdates;
 
     // clean up all state so that new updates can be coalesced while the current update is in flight
@@ -284,7 +286,7 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
             if (collectionView.dataSource == nil) {
                 // If the data source is nil, we should not call any collection view update.
                 fallbackWithoutUpdates();
-            } else if (result.changeCount > 100 && IGListExperimentEnabled(experiments, IGListExperimentReloadDataFallback)) {
+            } else if (result.changeCount > 100 && allowsReloadingOnTooManyUpdates) {
                 reloadDataFallback();
             } else {
                 performUpdate(result);

Tests/IGListAdapterE2ETests.m

@@ -1533,8 +1533,6 @@ - (void)test_whenMassiveUpdate_thatUpdateApplied {
     // init empty
     [self setupWithObjects:@[]];
 
-    ((IGListAdapterUpdater *)self.updater).experiments = IGListExperimentReloadDataFallback;
-
     NSMutableArray *objects = [NSMutableArray new];
     for (NSInteger i = 0; i < 3000; i++) {
         [objects addObject:genTestObject(@(i + 1), @4)];