Implements experimental diff with optimized moves calculation to prod…

…uce only minimal required moves
Instagram · Jul 20, 2018 · 6e173c2 · 6e173c2
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 ### Enhancements
 
+- Implemented experimental diff with optimized moves calculation to produce only minimal required moves, enabled by `IGListExperimentOptimizedMoves` option. [Nickolay Tarbayev](https://github.com/tarbayev) [(#1139)](https://github.com/Instagram/IGListKit/pull/1139)
+
 - Add support for UICollectionView's interactive reordering in iOS 9+. Updates include `-[IGListSectionController canMoveItemAtIndex:]` to enable the behavior, `-[IGListSectionController moveObjectFromIndex:toIndex:]` called when items within a section controller were moved through reordering, `-[IGListAdapterDataSource listAdapter:moveObject:from:to]` called when section controllers themselves were reordered (only possible when all section controllers contain exactly 1 object), and `-[IGListUpdatingDelegate moveSectionInCollectionView:fromIndex:toIndex]` to enable custom updaters to conform to the reordering behavior. The update also includes two new examples `ReorderableSectionController` and `ReorderableStackedViewController` to demonstrate how to enable interactive reordering in your client app. [Jared Verdi](https://github.com/jverdi) [(#976)](https://github.com/Instagram/IGListKit/pull/976)
 
 - 5x improvement to diffing performance when result is only inserts or deletes. [Ryan Nystrom](https://github.com/rnystrom) [(tbd)](tbd)

diff --git a/IGListKit.xcodeproj/project.pbxproj b/IGListKit.xcodeproj/project.pbxproj
@@ -7,6 +7,10 @@
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 /* Begin PBXBuildFile section */
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+ 0179E636207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */; };
+ 0179E637207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */; };
+ 01A3FEE120FFB30100E91657 /* GameplayKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 01A3FEE020FFB30000E91657 /* GameplayKit.framework */; };
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@@ -407,6 +411,8 @@
 /* End PBXContainerItemProxy section */
 
 /* Begin PBXFileReference section */
+ 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = IGListDiffExperimentOptimizedMovesTests.m; sourceTree = "<group>"; };
+ 01A3FEE020FFB30000E91657 /* GameplayKit.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = GameplayKit.framework; path = System/Library/Frameworks/GameplayKit.framework; sourceTree = SDKROOT; };
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@@ -661,6 +667,7 @@
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+ 01A3FEE120FFB30100E91657 /* GameplayKit.framework in Frameworks */,
  887D0B401D870D7F009E01F7 /* IGListKit.framework in Frameworks */,
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  );
@@ -846,6 +853,7 @@
  41882EBBC340173A8053E3AF /* Frameworks */ = {
  isa = PBXGroup;
  children = (
+ 01A3FEE020FFB30000E91657 /* GameplayKit.framework */,
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  1AB7195278D0BBB5DA88D36F /* Pods_IGListKitTests.framework */,
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@@ -975,6 +983,7 @@
  294AC6311DDE4C19002FCE5D /* IGListDiffResultTests.m */,
  88144EE61D870EDC007C7F66 /* IGListDiffSwiftTests.swift */,
  88144EE81D870EDC007C7F66 /* IGListDiffTests.m */,
+ 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */,
  88144EE91D870EDC007C7F66 /* IGListDisplayHandlerTests.m */,
  29DA5CA21EA7C72400113926 /* IGListGenericSectionControllerTests.m */,
  88144EEB1D870EDC007C7F66 /* IGListKitTests-Bridging-Header.h */,
@@ -1559,6 +1568,7 @@
  files = (
  298DDA381E3B168E00F76F50 /* IGLayoutTestItem.m in Sources */,
  885FE2361DC51B76009CE2B4 /* IGListStackSectionControllerTests.m in Sources */,
+ 0179E636207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */,
  885FE2311DC51B76009CE2B4 /* IGListDisplayHandlerTests.m in Sources */,
  298DDA3B1E3B16F800F76F50 /* IGLayoutTestDataSource.m in Sources */,
  29C474901DDF460500AE68CE /* IGListSectionMapTests.m in Sources */,
@@ -1681,6 +1691,7 @@
  294AC6321DDE4C19002FCE5D /* IGListDiffResultTests.m in Sources */,
  88144F141D870EDC007C7F66 /* IGListTestOffsettingLayout.m in Sources */,
  8240C7FB1DC2F6CF00B3AAE7 /* IGListTestAdapterStoryboardDataSource.m in Sources */,
+ 0179E635207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */,
  298DDA011E3AE28000F76F50 /* IGTestDiffingObject.m in Sources */,
  88144F131D870EDC007C7F66 /* IGListTestAdapterDataSource.m in Sources */,
  88144F071D870EDC007C7F66 /* IGListAdapterE2ETests.m in Sources */,
@@ -1732,6 +1743,7 @@
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+ 0179E637207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */,
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  88DF89891E010F6500B1B9B4 /* IGListDiffSwiftTests.swift in Sources */,
  882BC1321E0118CB0083B311 /* IGTestObject.m in Sources */,

diff --git a/Source/Common/IGListDiff.mm b/Source/Common/IGListDiff.mm
@@ -94,6 +94,105 @@ static void addIndexToCollection(BOOL useIndexPaths, __unsafe_unretained id coll
  return paths;
 }
 
+// Calculates indexes which require no explicit moves based on a longest increasing indexes set using O(n log n) complexity algorithm
+static NSIndexSet *autoMovedIndexes(const vector<IGListRecord> &newResultsArray, NSIndexSet *untouchedIndexes)
+{
+ NSUInteger count = newResultsArray.size();
+ vector<NSUInteger> prevIndexes(count);
+ vector<NSUInteger> indexes(count + 1);
+
+ NSUInteger length = 0;
+ for (NSUInteger i = 0; i < count; i++) {
+ // Binary search for the largest positive j ≤ length
+ // such that X[M[j]] < X[i]
+ NSUInteger lo = 1;
+ NSUInteger hi = length;
+ NSInteger currentIndex = newResultsArray[i].index;
+
+ NSUInteger nextUntouched = [untouchedIndexes indexGreaterThanIndex:i];
+
+ if (nextUntouched != NSNotFound && currentIndex > nextUntouched) {
+ continue;
+ }
+
+ NSUInteger prevUntouched = [untouchedIndexes indexLessThanIndex:i];
+
+ if (prevUntouched != NSNotFound && currentIndex < prevUntouched) {
+ continue;
+ }
+
+ while (lo <= hi) {
+ auto mid = lo + (hi - lo) / 2;
+ NSInteger prevIndex = newResultsArray[indexes[mid]].index;
+ if (prevIndex < currentIndex && (prevUntouched == NSNotFound || prevIndex > prevUntouched)) {
+ lo = mid + 1;
+ } else {
+ hi = mid - 1;
+ }
+ }
+
+ // After searching, lo is 1 greater than the
+ // length of the longest prefix of X[i]
+ auto newLength = lo;
+
+ // The predecessor of X[i] is the last index of
+ // the subsequence of length newLength-1
+ prevIndexes[i] = indexes[newLength - 1];
+ indexes[newLength] = i;
+
+ if (newLength > length) {
+ // If we found a subsequence longer than any we've
+ // found yet, update L
+ length = newLength;
+ }
+ }
+
+ // Reconstruct the longest increasing indexes
+ NSMutableIndexSet *result = [NSMutableIndexSet new];
+ auto k = indexes[length];
+ for (NSUInteger i = 0; i < length; i++) {
+ NSUInteger index = newResultsArray[k].index;
+
+ // Ignore inserted entries
+ if (index != NSNotFound) {
+ [result addIndex:index];
+ }
+ k = prevIndexes[k];
+ }
+ return result;
+}
+
+class IGListMoveChecker {
+public:
+ virtual bool isMove(const NSInteger oldIndex,
+ const NSInteger newIndex,
+ const NSInteger insertOffset,
+ const NSInteger deleteOffset) {
+
+ return (oldIndex - deleteOffset + insertOffset) != newIndex;
+ }
+
+ virtual ~IGListMoveChecker() {}
+};
+
+class IGListOptimalMoveChecker : public IGListMoveChecker
+{
+ NSIndexSet *_autoMovedIndexes;
+
+public:
+ IGListOptimalMoveChecker(const vector<IGListRecord> &newResultsArray, NSIndexSet *untouchedIndexes)
+ : _autoMovedIndexes(autoMovedIndexes(newResultsArray, untouchedIndexes))
+ {}
+
+ virtual bool isMove(const NSInteger oldIndex,
+ const NSInteger newIndex,
+ const NSInteger insertOffset,
+ const NSInteger deleteOffset) {
+
+ return (oldIndex != newIndex) && ![_autoMovedIndexes containsIndex:oldIndex];
+ }
+};
+
 static id IGListDiffing(BOOL returnIndexPaths,
  NSInteger fromSection,
  NSInteger toSection,
@@ -245,9 +344,11 @@ static id IGListDiffing(BOOL returnIndexPaths,
  }
 
  // track offsets from deleted items to calculate where items have moved
- vector<NSInteger> deleteOffsets(oldCount), insertOffsets(newCount);
+ vector<NSInteger> deleteOffsets(oldCount);
  NSInteger runningOffset = 0;
 
+ auto untouchedIndexes = [NSMutableIndexSet new];
+
  // iterate old array records checking for deletes
  // incremement offset for each delete
  for (NSInteger i = 0; i < oldCount; i++) {
@@ -257,33 +358,42 @@ static id IGListDiffing(BOOL returnIndexPaths,
  if (record.index == NSNotFound) {
  addIndexToCollection(returnIndexPaths, mDeletes, fromSection, i);
  runningOffset++;
+ } else if (record.index == i) {
+ [untouchedIndexes addIndex:record.index];
  }
 
  addIndexToMap(returnIndexPaths, fromSection, i, oldArray[i], oldMap);
  }
 
- // reset and track offsets from inserted items to calculate where items have moved
- runningOffset = 0;
+
+ aligned_union<0, IGListMoveChecker, IGListOptimalMoveChecker>::type moveCheckerBuf;
+
+ IGListMoveChecker *moveChecker = IGListExperimentEnabled(experiments, IGListExperimentOptimizedMoves)
+ ? new (&moveCheckerBuf) IGListOptimalMoveChecker(newResultsArray, untouchedIndexes)
+ : new (&moveCheckerBuf) IGListMoveChecker();
+
+ // offset incremented for each insert
+ NSInteger insertOffset = 0;
 
  for (NSInteger i = 0; i < newCount; i++) {
- insertOffsets[i] = runningOffset;
  const IGListRecord record = newResultsArray[i];
  const NSInteger oldIndex = record.index;
  // add to inserts if the opposing index is NSNotFound
  if (record.index == NSNotFound) {
  addIndexToCollection(returnIndexPaths, mInserts, toSection, i);
- runningOffset++;
+ insertOffset++;
  } else {
  // note that an entry can be updated /and/ moved
  if (record.entry->updated) {
  addIndexToCollection(returnIndexPaths, mUpdates, fromSection, oldIndex);
  }
 
  // calculate the offset and determine if there was a move
- // if the indexes match, ignore the index
- const NSInteger insertOffset = insertOffsets[i];
  const NSInteger deleteOffset = deleteOffsets[oldIndex];
- if ((oldIndex - deleteOffset + insertOffset) != i) {
+
+ if (moveChecker->isMove(oldIndex, i, insertOffset, deleteOffset)) {
+
+ // add move from old index to new index
  id move;
  if (returnIndexPaths) {
  NSIndexPath *from = [NSIndexPath indexPathForItem:oldIndex inSection:fromSection];
@@ -299,6 +409,8 @@ static id IGListDiffing(BOOL returnIndexPaths,
  addIndexToMap(returnIndexPaths, toSection, i, newArray[i], newMap);
  }
 
+ moveChecker->~IGListMoveChecker();
+
  NSCAssert((oldCount + [mInserts count] - [mDeletes count]) == newCount,
  @"Sanity check failed applying %li inserts and %lu deletes to old count %lu equaling new count %li",
  (long)oldCount, (unsigned long)[mInserts count], (unsigned long)[mDeletes count], (long)newCount);

diff --git a/Source/Common/IGListExperiments.h b/Source/Common/IGListExperiments.h
@@ -26,6 +26,8 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
  IGListExperimentFasterVisibleSectionController = 1 << 4,
  /// Test deduping item-level updates.
  IGListExperimentDedupeItemUpdates = 1 << 5,
+ /// Test optimized moves to minimal required number
+ IGListExperimentOptimizedMoves = 1 << 6,
 };
 
 /**