Add -waitUntilAllUpdatesAreCommitted to ASTableView and ASCollectionView

The API allows consumer of ASTableView or ASCollectionCiew to block execution of the main thread until all section and row updates are committed.

AsyncDisplayKit/ASCollectionView.h

@@ -165,6 +165,11 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)reloadDataImmediately;
 
+/**
+ *  Blocks execution of the main thread until all section and row updates are committed. This method must be called from the main thread.
+ */
+- (void)waitUntilAllUpdatesAreCommitted;
+
 /**
  * Registers the given kind of supplementary node for use in creating node-backed supplementary views.
  *

AsyncDisplayKit/ASCollectionView.mm

@@ -268,6 +268,12 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   [super reloadData];
 }
 
+- (void)waitUntilAllUpdatesAreCommitted
+{
+  ASDisplayNodeAssertMainThread();
+  [_dataController waitUntilAllUpdatesAreCommitted];
+}
+
 - (void)setDataSource:(id<UICollectionViewDataSource>)dataSource
 {
   // UIKit can internally generate a call to this method upon changing the asyncDataSource; only assert for non-nil.

AsyncDisplayKit/ASTableView.h

@@ -163,6 +163,11 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)endUpdatesAnimated:(BOOL)animated completion:(void (^ _Nullable)(BOOL completed))completion;
 
+/**
+ *  Blocks execution of the main thread until all section and row updates are committed. This method must be called from the main thread.
+ */
+- (void)waitUntilAllUpdatesAreCommitted;
+
 /**
  * Inserts one or more sections, with an option to animate the insertion.
  *

AsyncDisplayKit/ASTableView.mm

@@ -394,6 +394,12 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
   [_dataController endUpdatesAnimated:animated completion:completion];
 }
 
+- (void)waitUntilAllUpdatesAreCommitted
+{
+  ASDisplayNodeAssertMainThread();
+  [_dataController waitUntilAllUpdatesAreCommitted];
+}
+
 - (void)layoutSubviews
 {
   if (_nodesConstrainedWidth != self.bounds.size.width) {

AsyncDisplayKit/Details/ASDataController.h

@@ -181,6 +181,8 @@ FOUNDATION_EXPORT NSString * const ASDataControllerRowNodeKind;
 
 - (void)reloadDataImmediatelyWithAnimationOptions:(ASDataControllerAnimationOptions)animationOptions;
 
+- (void)waitUntilAllUpdatesAreCommitted;
+
 /** @name Data Querying */
 
 - (NSUInteger)numberOfSections;

AsyncDisplayKit/Details/ASDataController.mm

@@ -462,6 +462,23 @@ static void *kASSizingQueueContext = &kASSizingQueueContext;
   }];
 }
 
+- (void)waitUntilAllUpdatesAreCommitted
+{
+  ASDisplayNodeAssertMainThread();
+  ASDisplayNodeAssert(_batchUpdateCounter == 0, @"Should not be called between beginUpdate or endUpdate");
+  
+  // This should never be called in a batch update, return immediately therefore
+  if (_batchUpdateCounter > 0) { return; }
+  
+  [_editingTransactionQueue waitUntilAllOperationsAreFinished];
+  
+  // Schedule block in main serial queue to wait until all operations are finished that are
+  // where scheduled while waiting for the _editingTransactionQueue to finish
+  [_mainSerialQueue performBlockOnMainThread:^{
+    ASDisplayNodeAssert(_editingTransactionQueue.operationCount == 0, @"No operation should be in the _editingTransactionQueue anymore");
+  }];
+}
+
 #pragma mark - Data Source Access (Calling _dataSource)
 
 /**