V8 + Sinatra + Fibers + EM

app.rb

require 'sinatra'
require 'fiber'
require 'v8'
require 'rack/fiber_pool'
require 'eventmachine'

class Evaluator
  include EM::Deferrable

  def initialize exp
    @log = ::Logger.new STDOUT
    @exp = exp
  end

  def run
    @log.info ">>> Running"
    ctx = ::V8::Context.new
    val = ctx.eval @exp
    @log.info ">>> VAL: #{val}"
    self.succeed  val
    @log.info ">>> DISPOSING"
    ctx.dispose
  end
end
class App < Sinatra::Base

  use Rack::FiberPool, size: 100
  set :logging, true

  get "/" do

    logger.info "ok"
    ev = Evaluator.new "1+2"

    f  = Fiber.current
    ev.callback do |val|
      logger.info "from callback"
      f.resume val
    end
    EM.next_tick do
      logger.info "scheduling"
      ev.run
    end
    v = Fiber.yield
    logger.info "v: #{v}"
    body  v.to_s

  end
end

config.ru

require './app'

run App

Gemfile

source :rubygems
gem 'therubyracer'
gem 'rack-fiber_pool'
gem 'sinatra'
gem 'thin'