C # queue study notes: RabbitMQ priority queue

    I. Introduction

    In specific business, you may encounter some messages to be processed in advance. For example, the messages of ordinary customers are processed in the order of first-in first-out, and the messages of Vip customers are processed in advance. In RabbitMQ, the message priority is implemented by setting the x-max-priority attribute of the queue when the queue is declared, and then setting the message priority when publishing the message.

    Notes on RabbitMQ priority queue:

    1) Priority queues are only supported after RabbitMQ3.5.

    2) The priority queue will take effect only when there are insufficient consumers and can't consume in time.

    3) The priority ranges from 0 to 9. The larger the value, the higher the priority.

    Second, the example

    2.1. Sending end (production end)

    Create a new console project Send and add a class RabbitMQConfig.

    class RabbitMQConfig
    {
        public static string Host { get; set; }

        public static string VirtualHost { get; set; }

        public static string UserName { get; set; }

        public static string Password { get; set; }

        public static int Port { get; set; }

        static RabbitMQConfig()
        {
            Host = "192.168.2.242";
            VirtualHost = "/";
            UserName = "hello";
            Password = "world";
            Port = 5672;
        }
    }

RabbitMQConfig.cs

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("按任意键开始生产。");
            Console.ReadLine();
            PriorityMessagePublish();
            Console.ReadLine();
        }

        private static void PriorityMessagePublish()
        {
            const string MessagePrefix = "message_";
            const int PublishMessageCount = 6;
            byte messagePriority = 0;

            var factory = new ConnectionFactory()
            {
                HostName = RabbitMQConfig.Host,
                Port = RabbitMQConfig.Port,
                VirtualHost = RabbitMQConfig.VirtualHost,
                UserName = RabbitMQConfig.UserName,
                Password = RabbitMQConfig.Password,
                Protocol = Protocols.DefaultProtocol
            };

            using (var connection =factory.CreateConnection ()) 
            { 
                using ( var channel = connection.CreateModel ()) 
                { 
                    // Set the queue priority, the value range is 0 ~ 255. 
                    Dictionary < string , object > dict = new Dictionary < string , object > 
                    { 
                        { " x-max-priority " , 255 } 
                    }; 

                    // Declare queue 
                    channel.QueueDeclare (queue: " priority ", durable: true, exclusive: false, autoDelete: false, arguments: dict);


                    //向该消息队列发送消息message
                    Random random = new Random();
                    for (int i = 0; i < PublishMessageCount; i++)
                    {
                        var properties = channel.CreateBasicProperties();
                        messagePriority = (byte)random.Next(0, 9);
                        properties.Priority = messagePriority;//Set the message priority, ranging from 0 to 9. 
                        var message = MessagePrefix + i.ToString ();
                         var body = Encoding.UTF8.GetBytes (message); 
                        channel.BasicPublish (exchange: "" , routingKey: " priority " , basicProperties: properties, body: body); 
                        Console.WriteLine ($ " {DateTime.Now.ToString ()} Send {message}, Priority {messagePriority} " ); 
                    } 
                } 
            } 
        } 
    }

Program.cs

    2.2. Receiver (consumer)

    Create a new console project Receive, hold down the Alt key, and drag the RabbitMQConfig class on the sender a shortcut to the Receive project.

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("按任意键开始消费。");
            Console.ReadLine();
            PriorityMessageSubscribe();
        }

        public static void PriorityMessageSubscribe()
        {
            var factory = new ConnectionFactory()
            {
                HostName = RabbitMQConfig.Host,
                UserName = RabbitMQConfig.UserName,
                Password = RabbitMQConfig.Password
            };

            using (var connection = factory.CreateConnection())
            {
                using (var channel = connection.CreateModel())
                {
                    channel.BasicQos(prefetchSize: 0, prefetchCount: 1, global: false);
                    var consumer = new EventingBasicConsumer(channel);
                    consumer.Received += async (model, ea) =>
                    {
                        await Task.Run(() =>
                        {
                            var message = Encoding.UTF8.GetString(ea.Body);
                            Thread.Sleep(1000 * 2);
                            channel.BasicAck(deliveryTag: ea.DeliveryTag, multiple: false);//手动消息确认
                            Console.WriteLine($"{DateTime.Now.ToString()} Received {message}");
                        });
                    };
                    channel.BasicConsume(queue: "priority", noAck: false, consumer: consumer);// The message response needs to be enabled, otherwise the priority is invalid. 
                    Console.ReadKey (); 
                } 
            } 
        } 
    }

Program.cs

    2.3. Operation result

    From the consumption situation, it can be seen that message_2 and message_3 have the highest priority of 7, so they will be consumed at the earliest, and message_5 has a priority of 0, so it will be consumed last.