Using EventMachine to make multiple request using same connection?

Question

I have an EventMachine running that is listening for UDP packets. Every time a UDP packet is received, I would like to forward the data to some database using a REST call. I have created an EM::Connection subclass in which the receive_data method forwards the data through a REST call.

Since the frequency of data is quite high, I would like to reuse the connection between requests (using "keep-alive") and if possible also use pipelining. What would be a good way to share the connection between different calls?

Currently my UDPHandler looks something like the following:

module Udp
  module Collector
    class UDPHandler < EM::Connection
      def receive_data(data)
        http = EventMachine::HttpRequest.new('http://databaseurl.com/').post body: data
      end
    end
  end
end

This class is called as follows:

EM.run do
  EM.open_datagram_socket('0.0.0.0', 9000, Udp::Collector::UDPHandler)
end

I thought of making the request object a class variable but I don't think that is a good idea in the context of eventmachines. Or is it?

score 2 · Accepted Answer · answered Mar 28 '14 at 10:44

I believe something like this should work

module Udp
  module Collector
    class UDPHandler < EM::Connection
      def http_connection
        @http_connection ||= EventMachine::HttpRequest.new('http://databaseurl.com/')
      end

      def receive_data(data)
        http = http_connection.post body: data, keepalive: true
      end
    end
  end
end

But you can't execute parallel request in this manner, so you need to use some kind of connection pool.

The most simplest one without queueing and other stuff is:

module Udp
  module Collector
    class UDPHandler < EM::Connection
      def connection_pool
        @connection_pool ||= []
      end

      def get_connection
        conn = connection_pool.shift
        conn ||= EventMachine::HttpRequest.new('http://databaseurl.com/')
        conn
      end

      def receive_data(data)
        conn = get_connection
        request = conn.post body: data, keepalive: true
        request.callback do
          connection_pool << conn
        end
      end
    end
  end
end

Using EventMachine to make multiple request using same connection?

1 Answers1