nicklockwood/NSOperationStack — pull request #2 by blader (2012-12-05 02:46:41+00:00)
Title: Fixes a crasher (seen in production) under heavy loads

NSOperationQueue's operations method actually returns a copy of the current state of the queue, so it is possible (and has been observed to happen) for the queue to change between the if statement and the objectAtIndex call, which results in a crash.