ruby – 使用EventMachine和RabbitMQ的RPC

require "amqp"

module RPC
  class Base
    include EM::Deferrable

    def rabbit(rabbit_callback)
      rabbit_loop = Proc.new {
        AMQP.connect do |connection|
          AMQP::Channel.new(connection) do |channel|
            channel.queue("rpc.queue",:exclusive => false,:durable => true) do |requests_queue|
              self.callback(&rabbit_callback)
              self.succeed(connection,channel,requests_queue)
            end # requests_queue
          end # AMQP.channel
        end # AMQP.connect

        Signal.trap("INT")  { connection.close { EM.stop } }
        Signal.trap("TERM") { connection.close { EM.stop } }
      }

      if !EM.reactor_running?
        EM.run do
          rabbit_loop.call
        end
      else
        rabbit_loop.call
      end
    end
  end

  class Server < Base

    def run
      server_loop = Proc.new do |connection,requests_queue|
        consumer = AMQP::Consumer.new(channel,requests_queue).consume
        consumer.on_delivery do |metadata,payload|
          puts "[requests] Got a request #{metadata.message_id}. Sending a reply to #{metadata.reply_to}..."
          channel.default_exchange.publish(Time.now.to_s,:routing_key    => metadata.reply_to,:correlation_id => metadata.message_id,:mandatory      => true)
          metadata.ack
        end
      end
      rabbit(server_loop)
    end

  end

  class Client < Base

    def sync_push(request)
      result = nil
      sync_request = Proc.new do |connection,requests_queue|
        message_id = Kernel.rand(10101010).to_s

        response_queue = channel.queue("",:exclusive => true,:auto_delete => true)
        response_queue.subscribe do |headers,payload|
          if headers.correlation_id == message_id
            result = payload
            connection.close { EM.stop }
          end
        end

        EM.add_timer(0.1) do 
          puts "[request] Sending a request...#{request} with id #{message_id}"
          channel.default_exchange.publish(request,:routing_key => requests_queue.name,:reply_to    => response_queue.name,:message_id  => message_id)
        end
      end

      rabbit(sync_request)
      result
    end
  end
end

这个想法很简单：我想让一个消息队列始终准备好(这是由rabbit方法处理的).每当客户端想要发送请求时,它首先创建响应的临时队列以及消息ID;然后,它将请求发布到主消息队列,并等待临时队列中具有相同消息ID的响应,以便知道该特定请求的答案何时准备就绪.我想,message_id在某种程度上与临时队列是多余的(因为队列也应该是唯一的).

我现在使用此客户端/服务器代码运行虚拟脚本

# server session
>> server = RPC::Server.new
=> #<RPC::Server:0x007faaa23bb5b0>
>> server.run
Updating client properties
[requests] Got a request 3315740. Sending a reply to amq.gen-QCv8nP2dI5Qd6bg2Q1Xhk0...

和

# client session
>> client = RPC::Client.new
=> #<RPC::Client:0x007ffb6be6aed8>
>> client.sync_push "test 1"
Updating client properties
[request] Sending a request...test 1 with id 3315740
=> "2012-11-02 21:58:45 +0100"
>> client.sync_push "test 2"
AMQ::Client::ConnectionClosedError: Trying to send frame through a closed connection. Frame is #<AMQ::Protocol::MethodFrame:0x007ffb6b9c83d0 @payload="x002x00nx00x00x00fx00x00x00x00",@channel=1>

有两点我真的不明白：

>与EventMachine相关：在客户端代码中,如果我希望我的消息实际发布,为什么我必须调用EM.add_timer？为什么使用EM.next_tick不起作用？我的理解是,在这里调用发布时,“一切”应该是“准备好”.
>与AMQP相关：为什么我的客户端因第二次请求的关闭连接而崩溃？每次推送新请求时都应创建一个全新的EM / AMQP循环.

遗憾的是,很少有在线处理EM / AMQP的代码,所以任何帮助都将深表感谢！
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