A way to measure how long it takes Rails to boot

app_boot_benchmark.rb

require 'date'
require 'open3'
require 'timeout'
require 'socket'

class AppBootBenchmark
  RAILS_PORT = 9191

  def initialize(options = {})
    @stream_output = options[:stream_output]
  end

  def call
    # start the clock
    start_time = Time.now.to_f

    # start rails in a forked child process running on port 9191
    input, output, error, thread = Open3.popen3 "rails server thin -p #{RAILS_PORT}"

    if @stream_output
      Thread.new do
        until output.closed?
          buffer = output.readpartial(1024)
          STDOUT.write(buffer)
        end
      end

      Thread.new do
        until error.closed?
          buffer = error.readpartial(1024)
          STDERR.write(buffer)
        end
      end
    end

    # wait until port 9191 is accepting connections
    until booted?
      sleep 0.1
    end

    # stop the clock
    stop_time = Time.now.to_f

    # send the child process a SIGKILL
    Process.kill("TERM", thread.pid)

    puts "%.3fs" % (stop_time - start_time)
  end

  private

  def booted?
    is_port_bound?('127.0.0.1', RAILS_PORT)
  end

  # based on http://stackoverflow.com/a/517638/243215
  def is_port_bound?(ip, port)
    begin
      Timeout::timeout(1) do
        begin
          s = TCPSocket.new(ip, port)
          s.close
          return true
        rescue Errno::ECONNREFUSED, Errno::EHOSTUNREACH
          return false
        end
      end
    rescue Timeout::Error
    end

    return false
  end
end

AppBootBenchmark.new.call