From 86ecc600856b4199f8a31359140753955f02b5a4 Mon Sep 17 00:00:00 2001
From: Maxime Ollivier <maxo@fb.com>
Date: Fri, 26 Jun 2020 10:03:47 -0700
Subject: [PATCH] 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                             | 2 ++
 Source/IGListDiffKit/IGListExperiments.h | 4 +---
 Source/IGListKit/IGListAdapterUpdater.h  | 6 ++++++
 Source/IGListKit/IGListAdapterUpdater.m  | 4 +++-
 Tests/IGListAdapterE2ETests.m            | 2 --
 5 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 25419320d..869de515d 100644
--- a/CHANGELOG.md
+++ b/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)
diff --git a/Source/IGListDiffKit/IGListExperiments.h b/Source/IGListDiffKit/IGListExperiments.h
index 293e8b22d..1f3c0f2c7 100644
--- a/Source/IGListDiffKit/IGListExperiments.h
+++ b/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,
 };
 
 /**
diff --git a/Source/IGListKit/IGListAdapterUpdater.h b/Source/IGListKit/IGListAdapterUpdater.h
index 71b745071..c7895fa12 100644
--- a/Source/IGListKit/IGListAdapterUpdater.h
+++ b/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.
  */
diff --git a/Source/IGListKit/IGListAdapterUpdater.m b/Source/IGListKit/IGListAdapterUpdater.m
index 721f5a14a..29f333d68 100644
--- a/Source/IGListKit/IGListAdapterUpdater.m
+++ b/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);
diff --git a/Tests/IGListAdapterE2ETests.m b/Tests/IGListAdapterE2ETests.m
index d98a5ae7f..dec957597 100644
--- a/Tests/IGListAdapterE2ETests.m
+++ b/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)];