从主线程

Question

我使用DispatchQueue.main.async在主线程上调用Realm，它会抛出错误：

Terminating app due to uncaught exception 'RLMException', reason: 
'Realm accessed from incorrect thread.'

以下是代码：

func add(word: String, toList list: WordList, completion: @escaping ((_ success: Bool) -> (Void))) {

    let listId = list.timestamp

    DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async {

        guard let json = TranslationManager.shared.translateFrom(list.from, to: list.to, text: word, autocorrect: true) else {
            DispatchQueue.main.async {
                completion(false)
            }

            return
        }

        DispatchQueue.main.async {

            let newWord = Word()
            newWord.text = word
            newWord.timestamp = Int(Date().timeIntervalSince1970 * 1000)
            newWord.json = json.rawString(String.Encoding.utf8, options: JSONSerialization.WritingOptions()) ?? "{}"
            newWord.translated = json[NativeJsonIndexes.translated].stringValue

            let realm = try! Realm()
            let currentRealmList = realm.objects(WordList.self).filter({
                record in
                return listId == record.timestamp
            }).first

            try! realm.write {
                realm.add(newWord)
                currentRealmList?.words.append(newWord)
            }

        }
    }

}

我不明白为什么它可能会错误地工作，因为所有Realm交互都发生在主线程中，并且唯一的外部对象是使用ThreadSafeReference类传递的