Azure服务总线-使用OnMessage（）方法接收消息

Question

根据MS文档，从订阅接收消息并不困难。但是，如果我希望我的应用程序在每次发布新消息时都接收一条消息--一个恒定的轮询。因此，使用了SubscriptionClient类的OnMessage（）方法。

MS文档说：“...当调用OnMessage时，客户端启动一个内部消息泵，该消息泵不断轮询队列或订阅。该消息泵由发出Receive（）调用的无限循环组成。如果调用超时，它发出下一个Receive（）调用。...”

但是当应用程序运行时，调用moment OnMessage（）方法只接收最新消息。当发布新消息时，持续轮询似乎不起作用。在尝试了许多不同的方法之后，唯一的方法是使用无限循环将代码放入一个单独的任务中，使应用程序在收到新消息时做出反应。在这么多层面上，这似乎是完全错误的！（请参阅下面的代码）。

有没有人可以帮助我修正我的代码或者发布一个工作样例来完成相同的功能而不需要循环？谢谢你！

 public void ReceiveMessageFromSubscription(string topicName, string subscriptionFilter)
        {
            var newMessage = new MessageQueue();
            int i = 0;

            Task listener = Task.Factory.StartNew(() =>
            {
                while (true)
                {
                    SubscriptionClient Client = SubscriptionClient.CreateFromConnectionString(connectionString, topicName, subscriptionFilter);

                    Dictionary<string, string> retrievedMessage = new Dictionary<string, string>();

                    OnMessageOptions options = new OnMessageOptions();
                                     options.AutoComplete = false;
                                     options.AutoRenewTimeout = TimeSpan.FromMinutes(1);

                    Client.OnMessage((message) =>
                    {
                        try
                        {
                            retrievedMessage.Add("messageGuid", message.Properties["MessageGuid"].ToString());
                            retrievedMessage.Add("instanceId", message.Properties["InstanceId"].ToString());
                            retrievedMessage.Add("pId", message.Properties["ProcessId"].ToString());
                            retrievedMessage.Add("processKey", message.Properties["ProcessKey"].ToString());
                            retrievedMessage.Add("message", message.Properties["Message"].ToString());

                            newMessage.AnnounceNewMessage(retrievedMessage); // event ->

                            message.Complete(); // Remove message from subscription.
                        }
                        catch (Exception ex)
                        {
                            string exmes = ex.Message;
                            message.Abandon();
                        }

                    }, options);

                    retrievedMessage.Clear();

                    i++;

                    Thread.Sleep(3000);
                }

            });
        }

Answer 1

你的代码有几个问题需要解决-

• 它会失败，我假设您的应用程序会退出--或者至少正在侦听消息的线程会终止。
• 您的while循环会不断重复代码以挂起消息处理程序，您只需要执行一次操作。
• 您需要一种方法来保持调用堆栈活动，并防止应用程序垃圾收集您的对象。

下面的内容将会看到你走向成功的道路。祝你好运.

 ManualResetEvent CompletedResetEvent = new ManualResetEvent(false);
    SubscriptionClient Client;

    public void ReceiveMessagesFromSubscription(string topicName, string subscriptionFilter, string connectionString)
    {
        Task listener = Task.Factory.StartNew(() =>
        {
            // You only need to set up the below once. 
            Client = SubscriptionClient.CreateFromConnectionString(connectionString, topicName, subscriptionFilter);

            OnMessageOptions options = new OnMessageOptions();
            options.AutoComplete = false;
            options.AutoRenewTimeout = TimeSpan.FromMinutes(1);
            options.ExceptionReceived += LogErrors;

            Client.OnMessage((message) =>
            {
                try
                {
                    Trace.WriteLine("Got the message with ID {0}", message.MessageId);
                    message.Complete(); // Remove message from subscription.
                }
                catch (Exception ex)
                {
                    Trace.WriteLine("Exception occurred receiving a message: {0}" + ex.ToString());
                    message.Abandon(); // Failed. Leave the message for retry or max deliveries is exceeded and it dead letters.
                }

            }, options);

            CompletedResetEvent.WaitOne();
        });
    }

    /// <summary>
    /// Added in rudimentary exception handling .
    /// </summary>
    /// <param name="sender">The sender.</param>
    /// <param name="ex">The <see cref="ExceptionReceivedEventArgs"/> instance containing the event data.</param>
    private void LogErrors(object sender, ExceptionReceivedEventArgs ex)
    {
        Trace.WriteLine("Exception occurred in OnMessage: {0}" + ex.ToString());
    }

    /// <summary>
    /// Call this to stop the messages arriving from subscription.
    /// </summary>
    public void StopMessagesFromSubscription()
    {
        Client.Close(); // Close the message pump down gracefully
        CompletedResetEvent.Set(); // Let the execution of the listener complete and terminate gracefully 
    }

var messages = await queueClient.ReceiveBatchAsync(10, TimeSpan.FromSeconds(30),
                                                       cancellationToken);