多线程上的核心数据操作导致插入但不获取

我使用CoreData来插入数据和获取数据,因为我有很多数据,所以为了线程安全,我在多个线程上使用core数据。

问题是我可以在CoreData中插入数据,但从CoreData中提取数据时,结果为零, 当我关闭应用程序并从数据库中获取数据时,就会发生这种情况 .这和 NSMangedObjectContext 但我想不出来。

以下是我的代码片段:

class CoreDataManager {

    static let sharedManager = CoreDataManager()
    private init() {}

    lazy var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "My_Contacts")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()

    func saveContext() {
        let context = CoreDataManager.sharedManager.persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }

    func insertContact(id:Int, firstName : String,lastName : String,emaild : String,isFavorite : Bool,phoneNum : String,profilePic : String,sync : Bool) -> Contact? {
        let managedContext = CoreDataManager.sharedManager.persistentContainer.viewContext
        let privateManagedObjectContext: NSManagedObjectContext = {
            //NSPrivateQueueConcurrencyType
            let moc = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
            moc.parent = managedContext
            return moc
        }()


        let entity = NSEntityDescription.entity(forEntityName: "Contact",
                                                in: privateManagedObjectContext)!
        let contact = NSManagedObject(entity: entity,
                                     insertInto: privateManagedObjectContext)
        contact.setValue(firstName, forKey: "first_name")
        contact.setValue(lastName, forKey: "last_name")
        contact.setValue(emaild, forKey: "email")
        contact.setValue(isFavorite, forKey: "favorite")
        contact.setValue(phoneNum, forKey: "phone_number")
        contact.setValue(profilePic, forKey: "profile_pic")
        contact.setValue(sync, forKey: "syncStatus")
        contact.setValue(id, forKey: "contactId")

        do {
            try privateManagedObjectContext.save()
            return contact as? Contact
        } catch let error as NSError {
            print("Could not save. \(error), \(error.userInfo)")
            return nil
        }
    }


    func fetchAllContacts() -> [Contact]?{

        let managedContext = CoreDataManager.sharedManager.persistentContainer.viewContext
        let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Contact")

        do {
            let people = try managedContext.fetch(fetchRequest)
            return people as? [Contact]
        } catch let error as NSError {
            print("Could not fetch. \(error), \(error.userInfo)")
            return nil
        }
    }
}