Merge pull request #303 from facebook/enable_async_data_fetching

Move ASTableView & ASCollectionView data fetching to background thread

AsyncDisplayKit/ASTableView.h

@@ -35,6 +35,19 @@
  */
 @property (nonatomic, assign) ASRangeTuningParameters rangeTuningParameters;
 
+/**
+ * initializer.
+ * 
+ * @discussion If asyncDataFetching is enabled, the `ASTableView` will fetch data through `tableView:numberOfRowsInSection:` and
+ * `tableView:nodeForRowAtIndexPath:` in async mode from background thread. Otherwise, the methods will be invoked synchronically 
+ * from calling thread.
+ * Enabling asyncDataFetching could avoid blocking main thread for `ASCellNode` allocation, which is frequently reported issue for 
+ * large scale data. On another hand, the application code need take the responsibility to avoid data inconsistence. Specifically, 
+ * we will lock the data source through `tableViewLockDataSource`, and unlock it by `tableViewUnlockDataSource` after the data fetching. 
+ * The application should not update the data source while the data source is locked, to keep data consistence.
+ */
+- (instancetype)initWithFrame:(CGRect)frame style:(UITableViewStyle)style asyncDataFetching:(BOOL)asyncDataFetchingEnabled;
+
 /**
  * Reload everything from scratch, destroying the working range and all cached nodes.
  *
@@ -110,6 +123,24 @@
  */
 - (ASCellNode *)tableView:(ASTableView *)tableView nodeForRowAtIndexPath:(NSIndexPath *)indexPath;
 
+/**
+ * Indicator to lock the data source for data fetching in asyn mode.
+ * We should not update the data source until the data source has been unlocked. Otherwise, it will incur data inconsistence or exception
+ * due to the data access in async mode.
+ *
+ * @param tableView The sender.
+ */
+- (void)tableViewLockDataSource:(ASTableView *)tableView;
+
+/**
+ * Indicator to unlock the data source for data fetching in asyn mode.
+ * We should not update the data source until the data source has been unlocked. Otherwise, it will incur data inconsistence or exception
+ * due to the data access in async mode.
+ *
+ * @param tableView The sender.
+ */
+- (void)tableViewUnlockDataSource:(ASTableView *)tableView;
+
 @end