Rails is A Follower

what we can learn from dRuby’s metaprogramming magic.
@ dRubyConf2012

Transcript

1. Rails is A Follower
   what we can learn from dRuby’s metaprogramming magic
   Masatoshi SEKI
   Makoto Inoue
   

   View Slide

2. Makoto Inoue
   Web Developer @ New Bamboo (UK)
   Translator of “The dRuby Book”
   

   View Slide

3. Masatoshi Seki
   Ruby committer
   Author of dRuby/Rinda
   Author of ERB
   Pokemon Master
   The ERB Book
   Embed ruby script in any
   document using ERB
   

   View Slide

4. Seki san @ Work
   Embedded
   RealTime
   Network
   GUI
   

   View Slide

5. Seki san @ RubyKaigi (06 - 11)
   2006 dRuby as a session storage
   2007 Rinda: Distributed TupleSpace
   2008 RIP ERB
   2009 dRuby and BigTable
   2010 dRuby and Object Database
   2011 Drip: A stream based database
   

   View Slide

6. History of dRuby
   1999-3
   ERB
   1999-9
   DRb
   2003
   committer
   2010
   pokemon-master
   2000
   Rinda
   1998
   started ruby
   2006 - 2011
   Ruby Kaigi
   

   View Slide

7. Thank you to Our Sponsors
   Ruby No Kai
   new bamboo
   

   View Slide

8. Thank you to Our Sponsors
   @PUPRL @ayumin
   @arika @mame
   @ vestige_ @track8
   @ nagachika
   "ruby trunk changes"
   @ktou
   Powered by Rabbit
   @tsuboi @ayako119
   @hisashim
   

   View Slide

9. Table Of Contents
   What is dRuby ?
   Before dRuby (BD)
   Designing dRuby
   Q&A
   

   View Slide

10. What is dRuby?
    Distributed Object System
    Can invoke methods in different processes
    Can send objects between processes
    Pure Ruby
    Ruby standard library
    

    View Slide

11. Demo1 Starting up
    

    View Slide

12. Demo2 Which is the server?
    

    View Slide

13. Demo3 Distributed Queue
    

    View Slide

14. dRuby usage: distributed RSpec
    Used at Cookpad
    Ask @mrkn for the detail
    

    View Slide

15. dRuby usage: prototyping
    

    View Slide

16. Before dRuby (BD)
    

    View Slide

17. Old-fashioned programmer (BD8)
    Used to program in old Unix style
    IPC (Inter-Process Communication)
    fork/pipe, SystemV IPC
    

    View Slide

18. Simple world of CGI (BD5)
    request/response, stateless
    Converted my IPC programs to CGI
    

    View Slide

19. Ruby & shttpsrv (BD1)
    1998-9 Met Ruby & shttpsrv
    

    View Slide

20. Ruby & shttpsrv
    Web server written in Ruby
    Before WEBrick
    Small and extensible
    

    View Slide

21. Embedding HTTP into processes
    Embedding web server into small apps are fun
    Application communication via HTTP
    

    View Slide

22. Ruby everywhere
    I used to play with various languages with CGI, but now
    everything is Ruby
    

    View Slide

23. Not so cool because...
    Converting Ruby way into Web way
    HTTP restricts how to exchange objects
    Server - Client relationship
    Functional APIʢRPCʣ
    Cool URL
    No REST at that time
    

    View Slide

24. I just want Ruby to talk each other
    Converting Ruby world to Web world is restricting
    Too much abstraction?
    

    View Slide

25. Back to Ruby
    They are Ruby objects. Let’s call them in Ruby-ish way
    

    View Slide

26. Back to Ruby
    Distributed objects acting like Ruby
    RPC -> RMI
    Extending Ruby’s method invocation to socket programming
    

    View Slide

27. Why metaprogramming?
    Need a perfect proxy acting like Ruby
    Perfect fake that acts like normal Ruby
    

    View Slide

28. Designing dRuby
    method_missing
    Marshal
    ObjectSpace._id2ref & send
    Other Techniques
    

    View Slide

29. method_missing
    Respond to unknown methods
    Used for Proxies to catch method calls
    

    View Slide

30. class DRbObject
    ...
    def method_missing(msg_id, *a)
    succ, result = DRbConn.new(@uri).send_message(self, msg_id, *a)
    raise result if ! succ
    result
    end
    ...
    end
    

    View Slide

31. Marshal
    Serializes objects
    

    View Slide

32. module DRbProtocol
    ...
    def dump(obj, soc)
    begin
    str = Marshal::dump(obj)
    rescue
    ro = DRbObject.new(obj)
    str = Marshal::dump(ro)
    end
    soc.write(str) if soc
    str
    end
    ...
    end
    

    View Slide

33. Marshal
    File, Thread, Proc raise exceptions
    If you can not serialize, then serialize its proxy
    Send Object references
    

    View Slide

34. module DRbProtocol
    ...
    def dump(obj, soc)
    begin
    str = Marshal::dump(obj)
    rescue
    ro = DRbObject.new(obj)
    str = Marshal::dump(ro)
    end
    soc.write(str) if soc
    str
    end
    ...
    end
    

    View Slide

35. ObjectSpace._id2ref & send
    Find a object using object id
    The server finds the object and dispatches the method to it
    

    View Slide

36. class DRbServer
    ...
    ! ro, msg, argv = recv_request(s)
    ! if ro and ro.ref
    ! obj = ObjectSpace._id2ref(ro.ref)
    ! else
    ! obj = DRb.front
    ! end
    ! result = obj.__send__(msg.intern, *argv)
    ! succ = true
    ...
    end
    

    View Slide

37. class DRbServer
    ...
    ! ro, msg, argv = recv_request(s)
    ! if ro and ro.ref
    ! obj = ObjectSpace._id2ref(ro.ref)
    ! else
    ! obj = DRb.front
    ! end
    ! result = obj.__send__(msg.intern, *argv)
    ! succ = true
    ...
    end
    

    View Slide

38. Other techniques
    How do you recover unknown objects?
    Multithreading
    Handling method call with block
    

    View Slide

39. Demo4 DRbUnknown
    

    View Slide

40. What has just happened?
    Who did replace Foo with DRbUnknown?
    

    View Slide

41. class DRbMessage
    ...
    def load(soc)
    ...
    begin
    ...
    Marshal.load(str)
    rescue NameError, ArgumentError
    DRbUnknown.new($!, str)
    ensure
    ...
    end
    ...
    end
    end
    

    View Slide

42. class DRbUnknown
    def initialize(err, buf)
    case err.to_s
    when /uninitialized constant (\S+)/
    @name = $1
    when /undefined class\/module (\S+)/
    @name = $1
    else
    @name = nil
    end
    @buf = buf
    end
    

    View Slide

43. class DRbUnknown
    ...
    def _dump(lv)
    @buf
    end
    ...
    end
    

    View Slide

44. What has just happened?
    How does DRbUnkown#reload work?
    

    View Slide

45. class DRbUnknown
    ...
    def self._load(s)
    begin
    Marshal::load(s)
    rescue NameError, ArgumentError
    DRbUnknown.new($!, s)
    end
    end
    def reload
    self.class._load(@buf)
    end
    end
    

    View Slide

46. Multithreading
    Ruby socket programming patterns from shttpsrv
    

    View Slide

47. Thread.start(@soc.accept) do |s|
    begin
    ro, msg, arg = recv_request(s)
    ...
    send_response(s, succ, result)
    ensure
    s.close
    end
    end
    

    View Slide

48. Handling method call with block
    kvs.each do |k,v|
    p v
    end
    

    View Slide

49. ro, msg, argv, block = recv_request(s)
    obj = ro_to_obj(ro)
    if block
    result = obj.__send__(msg.intern, *argv) do |*x|
    block.call(*x)
    end
    else
    result = obj.__send__(msg.intern, *argv)
    end
    

    View Slide

50. break?
    kvs.each do |k,v|
    break if k == "foo"
    p v
    end
    LocalJumpError: break from proc-closure
    ! from (druby://eleven.local:61018) .....
    ! from (druby://eleven.local:61018) .....
    ! from (druby://eleven.local:61018) .....
    

    View Slide

51. def perform_with_block
    @obj.__send__(@msg_id, *@argv) do |*x|
    jump_error = nil
    begin
    block_value = block_yield(x)
    rescue LocalJumpError
    jump_error = $!
    end
    if jump_error
    case jump_error.reason
    when :break
    break(jump_error.exit_value)
    else
    raise jump_error
    end
    end
    block_value
    end
    endɹ
    

    View Slide

52. Did you get it?
    

    View Slide

53. Summary
    IPC -> http RPC -> dRuby
    dRuby metaprogramming techniques
    It’s your turn now.
    

    View Slide

54. My thoughts on Metaprogramming
    Isn’t metaprogramming too magical?
    Magic should not look like magic.
    Your magic is complete if no one notices it
    

    View Slide

55. You have everything you need
    Now it’s your turn
    

    View Slide