Dnsruby can use either its inbuilt (pure Ruby) event loop, or
EventMachine (a native extension to Ruby which must be installed
on the local platform).

Configuring Dnsruby to use EventMachine

I left a couple of switches in Dnsruby::Resolver :

Dnsruby::Resolver.use_eventmachine(on=true)

Dnsruby::Resolver.start_eventmachine_loop(on=true)

The first of these tells Dnsruby to use EventMachine, rather
than its own event loop.

The second tells Dnsruby whether to start the EventMachine loop
or not.

If standard Dnsruby client code is used, then Dnsruby needs to
call EventMachine::run{} in order to start the EventMachine loop.
However, if more than one EventMachine loop is started in a Ruby
process, then the process terminates.

So, if client code is written in an EventMachine style, contained
in an EventMachine::run{} call, then it will need to tell Dnsruby
NOT to start the EventMachine loop (on pain of sudden death!).

Example code

Here is an example of using the code in an EventMachine style :

require 'Dnsruby'
require 'eventmachine'
res = Dnsruby::Resolver.new
Dnsruby::Resolver.use_eventmachine
Dnsruby::Resolver.start_eventmachine_loop(false)
EventMachine::run {
  df = res.send_async(Dnsruby::Message.new("example.com"))
  df.callback {|msg|
     puts "Response : #{msg}"
     EM.stop}
  df.errback {|msg, err|
     puts "Response : #{msg}"
     puts "Error: #{err}"
     EM.stop}
}

And an example in a normal Dnsruby style :

require 'Dnsruby'
res = Dnsruby::Resolver.new
Dnsruby::Resolver.use_eventmachine
Dnsruby::Resolver.start_eventmachine_loop(true) # default
q = Queue.new
id = res.send_async(Dnsruby::Message.new("example.com"),q)
id, response, error = q.pop