Rabbitmq 官方给的NET consumer示例代码如下，但使用过程，会遇到connection断开的问题，一旦断开，这个代码就会报错，如果你的消费者端是这样的代码的话，就会导致消费者挂掉。
using System;
using RabbitMQ.Client;
using RabbitMQ.Client.Events;
using System.Text; class ReceiveLogs
{
public static void Main()
{
var factory = new ConnectionFactory() { HostName = "localhost" };
using (var connection = factory.CreateConnection())
{
using (var channel = connection.CreateModel())
{
channel.ExchangeDeclare("logs", "fanout"); var queueName = channel.QueueDeclare().QueueName; channel.QueueBind(queueName, "logs", "");
var consumer = new QueueingBasicConsumer(channel);
channel.BasicConsume(queueName, true, consumer); Console.WriteLine(" [*] Waiting for logs." +
"To exit press CTRL+C");
while (true)
{
var ea = (BasicDeliverEventArgs)consumer.Queue.Dequeue(); var body = ea.Body;
var message = Encoding.UTF8.GetString(body);
Console.WriteLine(" [x] {0}", message);
}
}
}
}
}
那么如何会异常恢复呢？
之前我的操作方式是，建立一个ConnectionPool,在出现异常后，重建channel,也就是说，整个的异常恢复过程是自己处理的。最近研究因为研究Orleans，担心RabbitMQ的NET client使用Task时，会遇到Orleans的坑，所以顺手研究了下RabbitMQ NET Client的源码，研究发现一种自动的错误恢复机制 AutomaticRecoveryEnabled = true 使用方式如下
using System;
using RabbitMQ.Client;
using RabbitMQ.Client.Events;
using System.Text; class ReceiveLogs
{
public static void Main()
{
var factory = new ConnectionFactory() { HostName = "localhost", AutomaticRecoveryEnabled = true };
using (var connection = factory.CreateConnection())
{
using (var channel = connection.CreateModel())
{
channel.ExchangeDeclare("logs", "fanout"); var queueName = channel.QueueDeclare().QueueName; channel.QueueBind(queueName, "logs", "");
var consumer = new QueueingBasicConsumer(channel);
channel.BasicConsume(queueName, true, consumer); Console.WriteLine(" [*] Waiting for logs." +
"To exit press CTRL+C");
while (true)
{
var ea = (BasicDeliverEventArgs)consumer.Queue.Dequeue(); var body = ea.Body;
var message = Encoding.UTF8.GetString(body);
Console.WriteLine(" [x] {0}", message);
}
}
}
}
}
具体的恢复机制如下
1.在AutoRecoveringConnection初始化时，在链接关闭事件委托上增加断开处理
public void init()
{
m_delegate = new Connection(m_factory, false, m_factory.CreateFrameHandler()); AutorecoveringConnection self = this;
EventHandler<ShutdownEventArgs> recoveryListener = (_, args) =>
{
lock (recoveryLockTarget)
{
if (ShouldTriggerConnectionRecovery(args))
{
try
{
self.BeginAutomaticRecovery();
}
catch (Exception e)
{
// TODO: logging
Console.WriteLine("BeginAutomaticRecovery() failed: {0}", e);
}
}
}
};
lock (m_eventLock)
{
ConnectionShutdown += recoveryListener;
if (!m_recordedShutdownEventHandlers.Contains(recoveryListener))
{
m_recordedShutdownEventHandlers.Add(recoveryListener);
}
}
}
观察调用的方式BeginAutomaticRecovery，可以看到这个方法内部调用了PerformAutomaticRecovery方法。我们直接看这个方法的内容，其中第一个调用的是方法RecoverConnectionDelegate
protected void PerformAutomaticRecovery()
{
lock (recoveryLockTarget)
{
RecoverConnectionDelegate();
RecoverConnectionShutdownHandlers();
RecoverConnectionBlockedHandlers();
RecoverConnectionUnblockedHandlers(); RecoverModels();
if (m_factory.TopologyRecoveryEnabled)
{
RecoverEntities();
RecoverConsumers();
} RunRecoveryEventHandlers();
}
}
这个方法中调用的是
protected void RecoverConnectionDelegate()
{
bool recovering = true;
while (recovering)
{
try
{
m_delegate = new Connection(m_factory, false, m_factory.CreateFrameHandler());
recovering = false;
}
catch (Exception)
{
// TODO: exponential back-off
Thread.Sleep(m_factory.NetworkRecoveryInterval);
// TODO: provide a way to handle these exceptions
}
}
}
可以看出，它是执行了死循环，直到连接重新打开，当然，如果遇到异常，它会调用Thread.Sleep来等待一下，然后再次执行连接恢复。