"-com.apple.CoreData.ConcurrencyDebug 1" crashes iOS app according to its name on iOS 14

• Enter an app name which is starting with "Music" or "Musik". For example "MusicTest".

• Place "-com.apple.CoreData.ConcurrencyDebug 1" in the scheme run arguments.

• Add a new entity to the data model named "TestEnt"

• Add the following code to the end of the AppDelegate.m file.

Code Block 
- (void)test {
  // ---
  // Set run argument in the scheme as follow:
  // -com.apple.CoreData.ConcurrencyDebug 1
  // ---
  NSLog(@"TEST");
  dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    [managedObjectContext performBlockAndWait:^{
      NSError *error = nil;
      NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"TestEnt"];
      NSArray *result = [managedObjectContext executeFetchRequest:request error:&error];
      NSLog(@"result=%@", result);
    }];
  });
}
- (NSManagedObjectContext *)managedObjectContext {
   
  // The old-fashion way to create a managed object conttext
   
  NSString *documentsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
  NSString *storeFilePath = [[documentsDir stringByAppendingPathComponent:@"MusicTest"] stringByAppendingPathExtension:@"sqlite"];
  NSURL *storeURL = [NSURL fileURLWithPath:storeFilePath];
   
   
  NSURL *objectModelURL = [[NSBundle mainBundle] URLForResource:@"MusicTest"
                          withExtension:@"momd"];
  NSManagedObjectModel *objectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:objectModelURL];
   
  NSPersistentStoreCoordinator *coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:objectModel];
   
  NSDictionary *options = @{NSMigratePersistentStoresAutomaticallyOption: @YES,
               NSInferMappingModelAutomaticallyOption: @YES};
  NSError *error = nil;
  [coordinator addPersistentStoreWithType:NSSQLiteStoreType
               configuration:nil
                    URL:storeURL
                  options:options
                   error:&error];
   
  NSManagedObjectContext *managedObjectContext = nil;
  if (coordinator != nil) {
    managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    managedObjectContext.persistentStoreCoordinator = coordinator;
    managedObjectContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy;
  }
   
  return managedObjectContext;
} 

• Modify code on ViewController.m as follow:

Code Block 
- (void)viewDidLoad {
  [super viewDidLoad];
   
  [(AppDelegate *)UIApplication.sharedApplication.delegate test];
}

• Run project and view crash coming.

Code Block 
Multithreading_Violation_AllThatIsLeftToUsIsHonor

• Select MusicTest project on the project navigator.

• Rename "MusicTest" appearing under "TARGETS" on the main window to "MyMusicTest"

• Run project again

• No crash this time.