Class: RJR::Nodes::AMQP

Inherits:
RJR::Node show all
Defined in:
lib/rjr/nodes/amqp.rb

Overview

AMQP node definition, implements the RJR::Node interface to listen for and invoke json-rpc requests over the Advanced Message Queuing Protocol.

Clients should specify the amqp broker to connect to when initializing a node and specify the remote queue when invoking requests.

Examples:

Listening for json-rpc requests over amqp

# initialize node,
server = RJR::Nodes::AMQP.new :node_id => 'server', :broker => 'localhost'

# register rjr dispatchers (see RJR::Dispatcher)
server.dispatcher.handle('hello') do |name|
  "Hello #{name}!"
end

# listen, and block
server.listen
server.join

Invoking json-rpc requests over amqp

client = RJR::Nodes::AMQP.new :node_id => 'client', :broker => 'localhost'
puts client.invoke('server-queue', 'hello', 'mo') # the queue name is set to "#{node_id}-queue"

Constant Summary collapse

RJR_NODE_TYPE = 
:amqp
PERSISTENT_NODE = 
true

Instance Attribute Summary

Attributes inherited from RJR::Node

#dispatcher, #message_headers, #node_id

Instance Method Summary collapse

Methods inherited from RJR::Node

#clear_event_handlers, em, #halt, #join, #node_type, #on, #persistent?, persistent?, tp

Constructor Details

#initialize(args = {}) ⇒ AMQP

AMQPNode initializer

Parameters:

  • args (Hash) (defaults to: {}) —

    the options to create the amqp node with

Options Hash (args):

  • :broker (String) —

    the amqp message broker which to connect to



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# File 'lib/rjr/nodes/amqp.rb', line 117

def initialize(args = {})
   super(args)
   @broker        = args[:broker]
   @amqp_lock     = Mutex.new
end

Instance Method Details

#invoke(routing_key, rpc_method, *args) ⇒ Object

Instructs node to send rpc request, and wait for and return response.

Implementation of RJR::Node#invoke

Do not invoke directly from em event loop or callback as will block the message subscription used to receive responses

Parameters:

  • routing_key (String) —

    destination queue to send request to

  • rpc_method (String) —

    json-rpc method to invoke on destination

  • args (Array) —

    array of arguments to convert to json and invoke remote method wtih

Returns:

  • (Object) —

    the json result retrieved from destination converted to a ruby object

Raises:

  • (Exception) —

    if the destination raises an exception, it will be converted to json and re-raised here



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# File 'lib/rjr/nodes/amqp.rb', line 168

def invoke(routing_key, rpc_method, *args)
  message = RequestMessage.new :method => rpc_method,
                               :args   => args,
                               :headers => @message_headers
  @@em.schedule do
    init_node {
      subscribe # begin listening for result
      send_msg(message.to_s, :routing_key => routing_key, :reply_to => @queue_name)
    }
  end

  # TODO optional timeout for response
  result = wait_for_result(message)

  if result.size > 2
    raise Exception, result[2]
  end
  return result[1]
end

#listen ⇒ Object

Instruct Node to start listening for and dispatching rpc requests.

Implementation of RJR::Node#listen



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# File 'lib/rjr/nodes/amqp.rb', line 147

def listen
  @@em.schedule do
    init_node {
      subscribe # start receiving messages
    }
  end
  self
end

#notify(routing_key, rpc_method, *args) ⇒ Object

Instructs node to send rpc notification (immadiately returns / no response is generated)

Implementation of RJR::Node#notify

Parameters:

  • routing_key (String) —

    destination queue to send request to

  • rpc_method (String) —

    json-rpc method to invoke on destination

  • args (Array) —

    array of arguments to convert to json and invoke remote method wtih



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# File 'lib/rjr/nodes/amqp.rb', line 199

def notify(routing_key, rpc_method, *args)
  # will block until message is published
  published_l = Mutex.new
  published_c = ConditionVariable.new

  invoked = false
  message = NotificationMessage.new :method => rpc_method,
                                    :args   => args,
                                    :headers => @message_headers
  @@em.schedule do
    init_node {
      send_msg(message.to_s, :routing_key => routing_key, :reply_to => @queue_name){
        published_l.synchronize { invoked = true ; published_c.signal }
      }
    }
  end
  published_l.synchronize { published_c.wait published_l unless invoked }
  nil
end

#send_msg(msg, metadata, &on_publish) ⇒ Object

Publish a message using the amqp exchange

Implementation of RJR::Node#send_msg



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# File 'lib/rjr/nodes/amqp.rb', line 130

def send_msg(msg, metadata, &on_publish)
  @amqp_lock.synchronize {
    #raise RJR::Errors::ConnectionError.new("client unreachable") if @disconnected
    routing_key = metadata[:routing_key]
    reply_to    = metadata[:reply_to]
    @exchange.publish msg,
                      :routing_key => routing_key,
                      :reply_to => reply_to do |*cargs|
      on_publish.call unless on_publish.nil?
    end
  }
  nil
end

#to_s ⇒ Object 



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# File 'lib/rjr/nodes/amqp.rb', line 123

def to_s
  "RJR::Nodes::AMQP<#{@node_id},#{@broker},#{@queue_name}>"
end