Exception with PFUbiquityPeer involved when adding a persistent store with Core Data & iCloud

Question

When I add a persistent store with NSPersistentStoreUbiquitousContentNameKey and NSPersistentStoreUbiquitousContentURLKey my application crashes every second time with an exception. This happens during the call to addPersistentStoreWithType:configuration:URL:options:error:

The stack trace looks like this:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException',
  reason: 'An NSManagedObject of class 'PFUbiquityPeer' must have a valid
  NSEntityDescription.'
*** First throw call stack:
(
     0   CoreFoundation   0x00007fff8b35ffc6 __exceptionPreprocess + 198
     1   libobjc.A.dylib  0x00007fff83368d5e objc_exception_throw + 43
     2   CoreData         0x00007fff82c28c06 -[NSManagedObject initWithEntity:insertIntoManagedObjectContext:] + 182
     3   CoreData         0x00007fff82d4d3dc +[PFUbiquityPeer(UbiquityMethods) peerForPeerID:inManagedObjectContext:createIfMissing:] + 364
     4   CoreData         0x00007fff82d4f809 -[PFUbiquityPeerRange(UbiquityMethods) loadFromStoreMetadataDictionary:] + 105
     5   CoreData         0x00007fff82d80372 -[PFUbiquityStoreMetadataMedic recoverPeerRangesWithError:] + 418
     6   CoreData         0x00007fff82d80ab5 -[PFUbiquityStoreMetadataMedic recoverMetadataWithError:] + 1749
     7   CoreData         0x00007fff82d831dc -[PFUbiquitySetupAssistant performPostStoreSetupWithStore:error:] + 732
     8   CoreData         0x00007fff82c04001 -[NSPersistentStoreCoordinator addPersistentStoreWithType:configuration:URL:options:error:] + 3537
     9   MyApp            0x000000010323de60 -[AppDelegate persistentStoreCoordinator] + 4224
     10  MyApp            0x000000010323e43f -[AppDelegate managedObjectContext] + 95
     11  Foundation       0x00007fff863b5384 _NSGetUsingKeyValueGetter + 62
     12  Foundation       0x00007fff863b5339 -[NSObject(NSKeyValueCoding) valueForKey:] + 392
     13  Foundation       0x00007fff863d4dc6 -[NSObject(NSKeyValueCoding) valueForKeyPath:] + 348
     14  AppKit           0x00007fff87fb1ae2 -[NSBinder _valueForKeyPath:ofObject:mode:raisesForNotApplicableKeys:] + 654
     15  AppKit           0x00007fff87fb17cc -[NSBinder valueForBinding:resolveMarkersToPlaceholders:] + 171
     16  AppKit           0x00007fff87fb143a -[NSObjectParameterBinder _updateObject:observedController:observedKeyPath:context:] + 1181
     17  AppKit           0x00007fff87fa3777 -[NSObject(NSKeyValueBindingCreation) bind:toObject:withKeyPath:options:] + 591
     18  AppKit           0x00007fff87f9ca89 -[NSIBObjectData nibInstantiateWithOwner:topLevelObjects:] + 1079
     19  AppKit           0x00007fff87f9309f loadNib + 322
     20  AppKit           0x00007fff87f9259c +[NSBundle(NSNibLoading) _loadNibFile:nameTable:withZone:ownerBundle:] + 217
     21  AppKit           0x00007fff87f924b7 +[NSBundle(NSNibLoading) loadNibFile:externalNameTable:withZone:] + 141
     22  AppKit           0x00007fff87f923fa +[NSBundle(NSNibLoading) loadNibNamed:owner:] + 364
     23  AppKit           0x00007fff882059b3 NSApplicationMain + 398
     24  MyApp            0x0000000103239522 main + 34
     25  MyApp            0x00000001032394f4 start + 52
     26  ???              0x0000000000000003 0x0 + 3
)
terminate called throwing an exception(lldb)

When I don’t add the NSPersistentStoreUbiquitousContentNameKey and NSPersistentStoreUbiquitousContentURLKey options to the store everything works without problems. I get this exception only on every second application launch. For testing purposes (and because I thought that the issue could have something to do with concurrency), I removed all Core Data access and bindings from the main NIB file and tried to access the Core Data stack programmatically inside the applicationDidFinishLaunching: method. In the first test I did this directly, the second time I performed the selector (managedObjectContext) after a delay of 10 seconds. Both tests resulted in the same exception on every second application launch.

The (slightly shortened for this example) managedObjectContext method looks like this:

- (NSManagedObjectContext *)managedObjectContext
{
  if (managedObjectContext_)
  {
    return managedObjectContext_;
  }

  NSPersistentStoreCoordinator *coordinator = self.persistentStoreCoordinator;
  if (!coordinator)
  {
    return nil;
  }

  NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] 
    initWithConcurrencyType:NSMainQueueConcurrencyType];
  [moc performBlockAndWait:
   ^{
    moc.mergePolicy = [[NSMergePolicy alloc] 
      initWithMergeType:NSMergeByPropertyObjectTrumpMergePolicyType];
    [moc setPersistentStoreCoordinator:coordinator];

    [[NSNotificationCenter defaultCenter] addObserver:self
      selector:@selector(mergeChangesFrom_iCloud:) 
      name:NSPersistentStoreDidImportUbiquitousContentChangesNotification 
      object:coordinator];
  }];
  managedObjectContext_ = moc;

  return managedObjectContext_;
}

The relevant part of persistentStoreCoordinator is:

  NSMutableDictionary *storeOptions = [NSMutableDictionary dictionary];
  [storeOptions setObject:[NSNumber numberWithBool:YES] 
    forKey:NSMigratePersistentStoresAutomaticallyOption];
  [storeOptions setObject:[NSNumber numberWithBool:YES] 
    forKey:NSInferMappingModelAutomaticallyOption];

  NSURL *url = [NSURL fileURLWithPath:[applicationSupportDirectory 
    stringByAppendingPathComponent:kJCMyAppDatabaseFilename]];
  NSURL *ubiquityURL = [[NSFileManager defaultManager] 
    URLForUbiquityContainerIdentifier:nil];
  if (ubiquityURL)
  {
    JCDLog(@"User has iCloud enabled.");
    [storeOptions setObject:@"com.juicycocktail.myapp" 
      forKey:NSPersistentStoreUbiquitousContentNameKey];
    [storeOptions setObject:[NSURL fileURLWithPath:[[ubiquityURL path] 
      stringByAppendingPathComponent:kJCMyAppDatabaseFilename]] 
      forKey:NSPersistentStoreUbiquitousContentURLKey];       
  }

  persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] 
    initWithManagedObjectModel:mom];
  NSPersistentStoreCoordinator *psc = persistentStoreCoordinator_;

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
  (dispatch_block_t)^{
    [psc lock];
    if (![psc addPersistentStoreWithType:kJCMyAppStoreType
      configuration:nil URL:url options:storeOptions error:&error])
    {
      dispatch_async(dispatch_get_main_queue(),
      ^{
        [[NSApplication sharedApplication] presentError:error];
        persistentStoreCoordinator_ = nil;

        return;
      });
    }    
    [psc unlock];

    dispatch_async(dispatch_get_main_queue(),
    ^{
      JCDLog(@"asynchronously added persistent store!");
      [[NSNotificationCenter defaultCenter]
        postNotificationName:@"RefetchAllDatabaseData"
        object:self userInfo:nil];
    });
  });

  return persistentStoreCoordinator_;

I guess that the PFUbiquityPeer class could’ve something to do with Core Data’s transaction logs that are kept in iCloud’s mobile documents folder, but I still can’t find the real cause for this issue. Any help how to track the root of this exception is highly appreciated as I’m already getting nuts. Especially a workaround or even a solution would be very helpful for me. I’m also glad if someone has a hint how to at least track down this exception.

Note: I also filed a bug in case this is an API bug (rdar://10892613).

Answer 1

Rebooting OS X solved the issue. This reminds me of an IT Crowd running gag.