Improvements to thread safety during closely spaced edit events.

This applies primarily when beginUpdates / endUpdates is not used.
Due to user interaction-driven edits, like reloads or adding content
at the bottom, sometimes this is unavoidable in app design and thus
critical.

I have a diff in flight to make ASDataController / ASRangeController
robust against very aggressive thrash testing, which will be added
both to the unit test suite and this new example project.

AsyncDisplayKitTests/ASTableViewTests.m

@@ -10,6 +10,10 @@
 
 #import "ASTableView.h"
 
+#define NumberOfSections 10
+#define NumberOfRowsPerSection 20
+#define NumberOfReloadIterations 50
+
 @interface ASTestTableView : ASTableView
 @property (atomic, copy) void (^willDeallocBlock)(ASTableView *tableView);
 @end
@@ -52,6 +56,32 @@
 
 @end
 
+@interface ASTableViewFilledDataSource : NSObject <ASTableViewDataSource, ASTableViewDelegate>
+
+@end
+
+@implementation ASTableViewFilledDataSource
+
+- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
+{
+  return NumberOfSections;
+}
+
+- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
+{
+  return NumberOfRowsPerSection;
+}
+
+- (ASCellNode *)tableView:(ASTableView *)tableView nodeForRowAtIndexPath:(NSIndexPath *)indexPath
+{
+  ASTextCellNode *textCellNode = [ASTextCellNode new];
+  textCellNode.text = indexPath.description;
+  
+  return textCellNode;
+}
+
+@end
+
 @interface ASTableViewTests : XCTestCase
 @end
 
@@ -60,27 +90,60 @@
 - (void)DISABLED_testTableViewDoesNotRetainItselfAndDelegate
 {
   ASTestTableView *tableView = [[ASTestTableView alloc] initWithFrame:CGRectZero style:UITableViewStylePlain];
-
+  
   __block BOOL tableViewDidDealloc = NO;
   tableView.willDeallocBlock = ^(ASTableView *v){
     tableViewDidDealloc = YES;
   };
-
+  
   ASTableViewTestDelegate *delegate = [[ASTableViewTestDelegate alloc] init];
-
+  
   __block BOOL delegateDidDealloc = NO;
   delegate.willDeallocBlock = ^(ASTableViewTestDelegate *d){
     delegateDidDealloc = YES;
   };
-
+  
   tableView.asyncDataSource = delegate;
   tableView.asyncDelegate = delegate;
-
+  
   [delegate release];
   XCTAssertTrue(delegateDidDealloc, @"unexpected delegate lifetime:%@", delegate);
-
+  
   XCTAssertNoThrow([tableView release], @"unexpected exception when deallocating table view:%@", tableView);
   XCTAssertTrue(tableViewDidDealloc, @"unexpected table view lifetime:%@", tableView);
 }
 
+- (void)testReloadData
+{
+  // Keep the viewport moderately sized so that new cells are loaded on scrolling
+  ASTableView *tableView = [[ASTableView alloc] initWithFrame:CGRectMake(0, 0, 100, 500)
+                                                        style:UITableViewStylePlain
+                                            asyncDataFetching:YES];
+  
+  ASTableViewFilledDataSource *dataSource = [ASTableViewFilledDataSource new];
+  
+  tableView.asyncDelegate = dataSource;
+  tableView.asyncDataSource = dataSource;
+  
+  [tableView reloadData];
+  
+  [tableView reloadSections:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(1,2)] withRowAnimation:UITableViewRowAnimationNone];
+  
+  // FIXME: Early return because we can't currently pass this test :).  Diff is in progress to resolve.
+  return;
+  
+  for (int i = 0; i < NumberOfReloadIterations; ++i) {
+    NSInteger randA = arc4random_uniform(NumberOfSections - 1);
+    NSInteger randB = arc4random_uniform(NumberOfSections - 1);
+    
+    [tableView reloadSections:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(MIN(randA, randB), MAX(randA, randB) - MIN(randA, randB))] withRowAnimation:UITableViewRowAnimationNone];
+    
+    BOOL animated = (arc4random_uniform(1) == 0 ? YES : NO);
+    
+    [tableView setContentOffset:CGPointMake(0, arc4random_uniform(tableView.contentSize.height - tableView.bounds.size.height)) animated:animated];
+    
+    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.01]];
+  }
+}
+
 @end