Non blocking delayed debugger for production

delayed_debug.rb

module Developer
  extend self
  delegate :establish_connection, :clear_all_connections!, :to => ActiveRecord::Base

  def delayed_debug(scope)
    detach_process do
      close_io_objects
      establish_connection
      setup_process_name
      notify_developers
      place_debugger_in scope
    end
  end

  private

  def setup_process_name
    $0 = 'delayed_debug'
  end

  def detach_process
    kill_running_debugger
    clear_all_connections!
    Process.detach fork { yield }
    establish_connection
    cleanup_on_exit
  end

  def place_debugger_in(scope)
    code = debugger_code + app_code_from(scope)
    scope.eval code, *file_and_line_after_debugger(scope)
  end

  def debugger_code
    <<-RUBY
      require 'ruby-debug'
      Debugger.wait_connection = true
      Debugger.start_remote
      debugger
    RUBY
  end

  def notify_developers
    HoptoadNotifier.notify \
      :error_class    => 'debugger',
      :error_message  => 'Delayed Debugger was triggerred'
  end

  def cleanup_on_exit
    @at_exit_hook ||= at_exit { kill_running_debugger }
  end

  def app_code_from(scope)
    current_method(scope).source.gsub(/(\A.*debug[^\n\;]*)|(end\Z)/m, '')
  end

  def current_method(scope)
    scope.eval %q{ singleton_class.instance_method __method__ }
  end

  def file_and_line_after_debugger(scope)
    file, line = scope.eval %q{ caller[0].split(':') }
    [file, line.to_i-4]
  end

  def kill_running_debugger
    `pkill -f delayed_debug`
  end

  def close_io_objects
    ObjectSpace.each_object(IO) do |io|
      next if [STDIN, STDOUT, STDERR].include? io
      io.close unless io.closed? rescue nil
    end
  end
end