Azure Messaging-ServiceBus Messaging消息队列技术系列6-消息回执

上篇博文中我们介绍了Azure Messaging的重复消息机制、At most once 和At least once.

 Azure Messaging-ServiceBus Messaging消息队列技术系列5-重复消息：at-least-once at-most-once

本文中我们主要研究并介绍Azure Messaging的消息回执机制：实际应用场景：

同步收发场景下，消息生产者和消费者双向应答模式，例如：张三写封信送到邮局中转站，然后李四从中转站获得信，然后在写一份回执信，放到中转站，然后张三去取，当然张三写信的时候就得写明回信地址。还

有，生成订单编号场景，发送一个生成订单编号的消息，消息消费者接收生成订单编号的消息，并通过消息回执返回。

Azure Messaging的消息回执机制主要通过：基于带会话的Queue/Topic、SessionId、ReplyTo属性来实现

在代码实现中，我们需要：

1. 两个工作线程，一个线程用于消息发送和接收回执消息，一个线程用于消息接收和发送消息回执。

2. 一个会话标识：ReceiptSession　　

3. 两个队列Queue：RequestQueue：发送消息、接收消息，ResponseQueue：发送回执消息，接收回执消息。

直接Show Code：

首先，我们在ServiceBusMQManager增加一个线程安全的创建带回话的QueueClient方法：

private static object syncObj = new object();
        /// <summary>
        /// 获取要求会话带Session的QueueClient
        /// </summary>
        /// <param name="queueName">队列名称</param>
        /// <returns>QueueClient</returns>
        public QueueClient GetSessionQueueClient(string queueName)
        {
            var namespaceClient = NamespaceManager.Create();
            if (!namespaceClient.QueueExists(queueName))
            {
                lock (syncObj)
                {
                    if (!namespaceClient.QueueExists(queueName))
                    {
                        var queue = new QueueDescription(queueName) { RequiresSession = true };
                        namespaceClient.CreateQueue(queue);
                    }
                }
            }

            return QueueClient.Create(queueName, ReceiveMode.ReceiveAndDelete);
        }

然后我们定义一些常量：

        private static readonly string ReplyToSessionId = "ReceiptSession";

        const double ResponseMessageTimeout = 20.0;

        private static readonly string requestQueueName = "RequestQueue";

        private static readonly string responseQueueName = "ResponseQueue";

实现发送并接收回执消息的方法：

        /// <summary>
        /// 发送并接收回执消息
        /// </summary>
        /// <param name="bills"></param>
        public static void SendMessage()
        {
            var manager = new ServiceBusUtils();
            var responseClient = manager.GetSessionQueueClient(responseQueueName);
            var requestClient = manager.GetSessionQueueClient(requestQueueName);

            var messsageReceiver = responseClient.AcceptMessageSession(ReplyToSessionId);
            var order = CreateSalesOrder(1);

            //发送消息
            var message = new BrokeredMessage(order);
            message.Properties.Add("Type", order.GetType().ToString());
            message.SessionId = ReplyToSessionId;
            message.MessageId = "OrderMessage001";
            message.ReplyTo = responseQueueName;
            requestClient.Send(message);
            Console.WriteLine("Send message: " + message.MessageId + ", SalesOrder ID: " + order.OrderID);

            //接收消息回执
            var receivedMessage = messsageReceiver.Receive(TimeSpan.FromSeconds(ResponseMessageTimeout * 2));

            var receivedOrder = receivedMessage.GetBody<SalesOrder>();
            Console.WriteLine("Receive receipt message: " + receivedMessage.MessageId + ", SalesOrder ID: " + receivedOrder.OrderID);
            messsageReceiver.Close();
        }

实现接收消息并发送回执方法：

 1         /// <summary>
        /// 接收消息并回执
        /// </summary>
        public static void ReceiveMessage()
        {
            var manager = new ServiceBusUtils();

            var requestClient = manager.GetSessionQueueClient(requestQueueName);
            var session = requestClient.AcceptMessageSession();
            var requestMessage = session.Receive();
           
            if (requestMessage != null)
            {
                var receivedOrder = requestMessage.GetBody<SalesOrder>();
                Console.WriteLine("Receive message: " + requestMessage.MessageId + ", SalesOrder ID: " + receivedOrder.OrderID);

                var responseMessage = new BrokeredMessage(receivedOrder);
                responseMessage.Properties.Add("Type", receivedOrder.GetType().ToString());
                responseMessage.ReplyToSessionId = ReplyToSessionId;
                responseMessage.MessageId = "ResponseOrderMessage001";
                responseMessage.SessionId = requestMessage.SessionId;
               
                //发送回执消息
                var responseClient = manager.GetSessionQueueClient(requestMessage.ReplyTo);
                responseClient.Send(responseMessage);
                Console.WriteLine("Send receipt message: " + responseMessage.MessageId + ", SalesOrder ID: " + receivedOrder.OrderID);               
            }
        }

Main方法中，启动两个工作线程：一个线程用于消息发送和接收回执消息，一个线程用于消息接收和发送消息回执。

因为涉及到Azure Messaging中队列的第一次创建，Azure Messaging是不支持多个请求同时创建同一个队列的，因此，我们两个线程间做一个简单的Task.Delay(3000).Wait();

        static void Main(string[] args)
        {
            var sendTask = Task.Factory.StartNew(() => { SendMessage(); });
            Task.Delay(3000).Wait();
            var receiveTask = Task.Factory.StartNew(() => { ReceiveMessage(); });

            Task.WaitAll(sendTask, receiveTask);

            Console.ReadKey();           
        }

我们看看程序输出：

Azure 服务总线中的队列：

可以看出：Azure Messaging-ServiceBus Messaging 基于带会话的Queue/Topic、SessionId、ReplyTo属性来实现消息回执机制。

周国庆

2017/3/23