How to log file descriptor count in a rails or rack application

config.ru

require_relative 'config/environment'

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

  def call(env)
    if 1000==rand(1001)
      unclosed_files = 0
      ObjectSpace.each_object(IO) do |f|
        begin
          unclosed_files +=1 unless f.closed?
        rescue IOError
          puts "encountered IOError when checking if a file was closed"
        end
      end
      puts "file descriptors - unclosed ruby files: #{unclosed_files}"
      puts "file descriptors - linux: #{`cat /proc/sys/fs/file-nr`.strip}"
    end

    @app.call(env)
  end
end

use FileDescriptorLogger
run Rails.application