Is AFNetworking with CoreData thread-safe?

Question

I am running into intermittent, hard-to-reproduce errors on my iPhone app, so I am checking my assumptions around concurrency.

Running AFNetworking v0.10.x, I have the following network call:

[self postPath:@"/myEndPoint"
    parameters:params
       success:^(AFHTTPRequestOperation *request, id response)
          {
              AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
              // do stuff with object context here
              [appDelegate.objectContext save];
          }     
]       
AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
// do other stuff with object context
[appDelegate.objectContext save];      

In my AppDelegate:

-(NSManagedObjectContext*) objectContext
{
    if(nil == _objectContext)
    {
        ... set up sqlite persistent store coordinator and object model ...

        _objectContext = [[NSManagedObjectContext alloc] init];
        [_objectContext setPersistentStoreCoordinator:persistentStoreCoordinator];
        [_objectContext setMergePolicy:NSOverwriteMergePolicy];
    }
    return _objectContext;
}

Is it possible, in this scenario, to end up with concurrency problems? Or, in other words, is AFNetworking's API thread-safe? I thought the NSOverwriteMergePolicy would cover me for conflicts, but crashing persists (albeit intermittently).

Answer 1

AFNetworking's callbacks are executed on the main thread. As a result, they are 'thread-safe', because there is only one thread that is interacting with CoreData. If you only have a single managed object things will be straightforward.

From Apple:

Tasks added to this queue are performed serially on the main thread itself. Therefore, you can use this queue as a synchronization point for work being done in other parts of your application.

There are still lots of considerations when using multi-threaded CoreData and multiple managed object contexts, and for those I refer you to rsswtmr's excellent answer, which doesn't correctly answer my question, but provides links to lots of good information.