thread safe core data the easy way

gistfile1.m

//in background operation
backgroundMOC = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[backgroundMOC setParentContext:appDelegate.managedObjectContext];

//in app delegate
if (coordinator != nil) {
  _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
  [_managedObjectContext setPersistentStoreCoordinator:coordinator];
}