RabbitMQ 持久队列不起作用（RPC-Server、RPC-Client）

Question

我想知道为什么我的 RabbitMQ RPC-Client 总是在重启后处理死消息。 _channel.QueueDeclare(queue, false, false, false, null); 应该禁用缓冲区。如果我在 RPC-Client 中重载QueueDeclare，我将无法连接到服务器。这里有什么问题吗？知道如何解决这个问题吗？

---

RPC-服务器

new Thread(() =>
{
    var factory = new ConnectionFactory { HostName = _hostname };
    if (_port > 0)
        factory.Port = _port;
    _connection = factory.CreateConnection();
    _channel = _connection.CreateModel();

    _channel.QueueDeclare(queue, false, false, false, null);
    _channel.BasicQos(0, 1, false);
    var consumer = new QueueingBasicConsumer(_channel);
    _channel.BasicConsume(queue, false, consumer);
    IsRunning = true;
    while (IsRunning)
    {
        BasicDeliverEventArgs ea;
        try {
            ea = consumer.Queue.Dequeue();
        }
        catch (Exception ex) {
            IsRunning = false;
        }
        var body = ea.Body;
        var props = ea.BasicProperties;
        var replyProps = _channel.CreateBasicProperties();
        replyProps.CorrelationId = props.CorrelationId;

        var xmlRequest = Encoding.UTF8.GetString(body);

        var messageRequest = XmlSerializer.DeserializeObject(xmlRequest, typeof(Message)) as Message;
        var messageResponse = handler(messageRequest);

        _channel.BasicPublish("", props.ReplyTo, replyProps,
                                messageResponse);
        _channel.BasicAck(ea.DeliveryTag, false);
    }
}).Start();

---

RPC 客户端

public void Start()
{
    if (IsRunning)
        return;
    var factory = new ConnectionFactory { 
        HostName = _hostname,
        Endpoint = _port <= 0 ? new AmqpTcpEndpoint(_endpoint) 
                              : new AmqpTcpEndpoint(_endpoint, _port)
    };
    _connection = factory.CreateConnection();
    _channel = _connection.CreateModel();
    _replyQueueName = _channel.QueueDeclare(); // Do not connect any more
    _consumer = new QueueingBasicConsumer(_channel);
    _channel.BasicConsume(_replyQueueName, true, _consumer);
    IsRunning = true;
}

public Message Call(Message message)
{
    if (!IsRunning)
        throw new Exception("Connection is not open.");
    var corrId = Guid.NewGuid().ToString().Replace("-", "");
    var props = _channel.CreateBasicProperties();
    props.ReplyTo = _replyQueueName;
    props.CorrelationId = corrId;

    if (!String.IsNullOrEmpty(_application))
        props.AppId = _application;

    message.InitializeProperties(_hostname, _nodeId, _uniqueId, props);

    var messageBytes = Encoding.UTF8.GetBytes(XmlSerializer.ConvertToString(message));
    _channel.BasicPublish("", _queue, props, messageBytes);

    try 
    {
        while (IsRunning)
        {
            var ea = _consumer.Queue.Dequeue();
            if (ea.BasicProperties.CorrelationId == corrId)
            {
                var xmlResponse = Encoding.UTF8.GetString(ea.Body);
                try
                {
                    return XmlSerializer.DeserializeObject(xmlResponse, typeof(Message)) as Message;
                }
                catch(Exception ex)
                {
                    IsRunning = false;
                    return null;
                }
            }
        }
    }
    catch (EndOfStreamException ex)
    {
        IsRunning = false;
        return null;
    }
    return null;
}

Answer 1

尝试在您的 RPC 客户端代码中将 DeliveryMode 属性设置为非持久性 (1)，如下所示：

public Message Call(Message message)
{
   ...
   var props = _channel.CreateBasicProperties();
   props.DeliveryMode = 1; //you might want to do this in your RPC-Server as well
   ...
}

AMQP Model Explained 包含非常有用的资源，例如解释如何处理最终进入死信队列的消息。

文档中关于队列持久性的另一个有用说明：

持久队列被持久化到磁盘上，因此在代理重启后仍然存在。 不持久的队列称为瞬态队列。并非所有场景 并且用例要求队列是持久的。

队列的持久性不会使消息路由到该队列 队列持久。如果经纪人被撤下然后又重新上线， 持久队列将在代理启动期间重新声明，但是，仅 持久性消息将被恢复。

请注意，它谈论的是代理重启，而不是发布者或消费者重启。