RPC使用EventMachine＆RabbitMQ
我已经开始尝试使用AMQP gem doc中提供的RabbitMQ RPC示例代码，尝试编写执行同步远程调用的非常简单的代码：
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, channel, 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, channel, 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：我想有一个消息队列总是准备好的（这是通过rabbit方法处理的）。 每当客户想要发送一个请求时，它首先创建一个响应的临时队列以及一个消息ID; 它然后将该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，以便知道何时针对该特定请求的答案准备就绪。 我猜想message_id对于临时队列是多余的（因为队列也应该是唯一的）。
我现在使用这个客户端/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：
Client代码中，如果我想让我的消息真正发布，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，在这里发布发布时，“一切”应该是“准备好”的。 可悲的是，很少有代码可用于在线处理EM / AMQP，所以任何帮助将深表感谢！ 关于这个效率的任何评论也将非常感谢。
挖掘文档，我终于发现，我确实需要once_declared回调来确保客户端开始使用它时队列已准备就绪。
关于连接问题，似乎使用EM::Deferrable引起了一些问题，所以这个（非常不令人满意的）解决方案仅仅是不包括EM::Deferrable 。
require "amqp"
module RPC
module Base
def rabbit(rabbit_callback)
rabbit_loop = Proc.new {
AMQP.start do |connection|
AMQP::Channel.new(connection) do |channel|
channel.queue("rpc.queue", :exclusive => false, :durable => true) do |requests_queue|
requests_queue.once_declared do
rabbit_callback.call(connection, channel, requests_queue)
end
end
end
end
Signal.trap("INT") { AMQP.stop { EM.stop } }
Signal.trap("TERM") { AMQP.stop { EM.stop } }
}
if !EM.reactor_running?
@do_not_stop_reactor = false
EM.run do
rabbit_loop.call
end
else
@do_not_stop_reactor = true
rabbit_loop.call
end
end
end
class Server
include Base
def run
server_loop = Proc.new do |connection, channel, 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
include Base
def sync_push(request)
result = nil
sync_request = Proc.new do |connection, channel, 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
AMQP.stop { EM.stop unless @do_not_stop_reactor }
end
end
response_queue.once_declared 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
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