Swift：使用DispatchQueue.global（qos：.userInitiated）.asyncAfter]重复返回的结果

Question

我有以下代码：（内部：ServerApiManager.sharedInstance.fetchMessages是用于调用api的函数。）>

返回的结果是：

====didRequestReloadThread ATC Chat Thread DispatchQueue.global 633 fetchMessages DispatchQueue.global 633 fetchMessages ServerApiManager.sharedInstance.fetchMessage DispatchQueue DispatchQueue messagesCollectionView ServerApiManager.sharedInstance.fetchMessage DispatchQueue DispatchQueue messagesCollectionView ==> Wrong result because of duplicate.

预期结果是：

====didRequestReloadThread ATC Chat Thread DispatchQueue.global 633 fetchMessages ServerApiManager.sharedInstance.fetchMessage DispatchQueue DispatchQueue messagesCollectionView

任何人都可以帮忙吗？

DispatchQueue.global(qos: .userInitiated).asyncAfter(deadline: .now() + 5) {

            print("DispatchQueue.global")
            if(self.messages.count > 0){
                let lastMessage = self.messages[self.messages.count-1]
                print(633)
                ServerApiManager.sharedInstance.fetchMessages(channel: self.channel, minId: lastMessage.id ?? 0, loggedInUser: self.user, onSuccess: { (messages) -> () in
                    self.messages.append(contentsOf: messages)
                    print("ServerApiManager.sharedInstance.fetchMessage")
                    MessageStorage.sharedInstance.messageDic[self.channel.id] = self.messages
                    print("DispatchQueue")
                    DispatchQueue.main.async {
                        print("DispatchQueue messagesCollectionView" )
                        self.messagesCollectionView.reloadData()
                        self.messagesCollectionView.scrollToBottom()
                    }

                }, onFailure: { (msg, logged) -> () in

                });
            }
}

我有以下代码：（内部：ServerApiManager.sharedInstance.fetchMessages是用于调用api的函数）。返回的结果是：==== didRequestReloadThread ATC聊天线程DispatchQueue ....