Open Radar

 
# Summary
Using NSAttributedString creating with HTML data (using NSHTMLTextDocumentType) is a lengthy operation, but internally makes the main runloop run in a common mode, which leads to other methods, delegates and notifications being delivered while parsing. 

This in turn leads to serious, hard-to-debug crashes.

# Steps to Reproduce:
See minimal UITableViewController demo at https://gist.github.com/n-b/8397563

Basically, it's a UITableViewController that parses and sets attributed text to each of its cell in -cellForRowAtIndexPath.
 
# Expected Results:
HTML parsing should completely block the thread, or at least run in a specific mode.

For example, in -scrollViewDidScroll, one can expect that -visibleCells and -indexPathsForVisibleRows return coherent results. This is no longer the case, because -scrollViewDidScroll is called while parsing HTML, inside -cellForRowAtIndexPath.

# Actual Results:
During HTML parsing, the rest of the app continues to run as if nothing, but the cell is not returned yet.

# Version:
7.0, 7.1b3