Benchmark optimization on Rack::Builder

benchmark.rb

require 'rack'
require 'benchmark'

class OptimizedRackBuilder < Rack::Builder
  def call(env)
    @to_app ||= to_app
    @to_app.call(env)
  end
end

def stub_middleware
  Class.new do
    def initialize(app)
      @app = app
    end

    def call(env) 
      @app.call(env)
      [200, {}, ['xxx']]
    end
  end
end

def stub_app
  Proc.new do |env|
    [200, {}, ['hello']]
  end
end

def define_routes(klass)
  klass.new do
    map '/foo' do
      use stub_middleware
      run stub_app
    end

    map '/bar' do
      use stub_middleware
      run stub_app
    end

    map '/baz' do
      use stub_middleware
      run stub_app
    end
  end
end

original_app = define_routes(Rack::Builder)
optimized_app = define_routes(OptimizedRackBuilder)

env = {
  "REQUEST_METHOD" => "GET",
  "REQUEST_PATH"   => '/bar',
  "PATH_INFO"      => '/bar',
  "SCRIPT_NAME"    => '',
  "SERVER_NAME"    => 'localhost',
  "SERVER_PORT"    => '80',
  "REQUEST_URI"    => 'http://localhost/bar',
  "HTTP_HOST"      => 'localhost'
}

n = 50_000
Benchmark.bm do |x|
  x.report('original') { n.times do; original_app.call(env); end }
  x.report('optimized') { n.times do; optimized_app.call(env); end }
end

# Results on my machine:
#            user       system     total    real
# original   5.930000   0.040000   5.970000 (  5.986689)
# optimized  0.390000   0.000000   0.390000 (  0.390511)