It seems that in November, Apple updated both the NSManagedObjectContext Class Reference and the Core Data Programming Guide documents to explicitly bless serial GCD Dispatch Queues and NSOperationQueues as acceptable mechanisms for synchronising access to a NSManagedObjectContext. But their advice seems ambiguous and possibly contradictory, and I want to make sure I've understood it properly.
Previously the accepted wisdom seemed to be that a NSManagedObjectContext could only be accessed from the thread that created it, and that using a serial queue for synchronisation was not sufficient; although serial queues only perform one operation at a time, these operations can potentially be scheduled on different threads, and a MOC doesn't like that.
But now, from the programming guide, we have:
You can use threads, serial operation queues, or dispatch queues for concurrency. For the sake of conciseness, this article uses “thread” throughout to refer to any of these.
So far, so good (although their conflation of threads and queues is unhelpful). So I can safely use a single context per (serial) queue, instead of one per operation/block, right? Apple even has a visual depiction of this in the Core Data WWDC sessions.
But... where do you create the context for the queue? In the NSManagedObjectContext documentation, Apple state:
[A context] assumes the default owner is the thread or queue that allocated it—this is determined by the thread t