rbx_rack_profiler.rb

require 'rack'
require 'rubinius/profiler'

class RbxRackProfiler
  def initialize(app)
    @app = app
  end

  def call(env)
    profiler = Rubinius::Profiler::Instrumenter.new

    profiler.start

    retval = @app.call(env)

    profiler.stop

    puts
    puts "=== #{env['REQUEST_METHOD']} #{env['PATH_INFO'].inspect} ==="
    puts

    profiler.show

    return retval
  end
end

class MyApp
  def call(env)
    return [200, {'Content-Type' => 'text/plain'}, ['Hello world!']]
  end
end

use RbxRackProfiler

run MyApp.new