Let it crash

Transcript

1. Let It Crash An introduction to Erlang/OTP supervisors Tuesday, February

   28, 12

2. When it comes to error-handling I have shown how to

   “abstract out” the errors, and argued that the program should be divided into “pure” code and code which “fixes the errors.” – Joe Armstrong Tuesday, February 28, 12

3. process("1 + 1") # 2 process("foo") # "" process("1") #

   "" process(1) # "" Tuesday, February 28, 12

4. def process(message): result = "" if isinstance(message, str): split_message =

   message.split() if len(split_message) == 3: a, operator, b = split_message if a.isdigit() and b.isdigit(): result = int(a) + int(b) return result Tuesday, February 28, 12

5. def process(message): result = "" if isinstance(message, str): split_message =

   message.split() if len(split_message) == 3: a, operator, b = split_message if a.isdigit() and b.isdigit(): result = int(a) + int(b) return result Tuesday, February 28, 12

6. process(Message) -> [A, _, B] = string:tokens(Message, " "), list_to_integer(A)

   + list_to_integer(B). Tuesday, February 28, 12

7. Processes Tuesday, February 28, 12

8. Isolated Tuesday, February 28, 12

9. Isolated Tuesday, February 28, 12

10. Can Communicate A B Mailbox A Mailbox B Tuesday, February

    28, 12

11. Can Communicate A B Mailbox A Mailbox B Tuesday, February

    28, 12

12. Can Communicate A B Mailbox A Mailbox B Tuesday, February

    28, 12

13. Can Communicate A B Mailbox A Mailbox B Tuesday, February

    28, 12

14. Distributable Machine A Tuesday, February 28, 12

15. Distributable Machine A Machine B Machine C Tuesday, February 28,

    12

16. Process Links Tuesday, February 28, 12

17. B C D A Tuesday, February 28, 12

18. B C D A Tuesday, February 28, 12

19. B C D A Tuesday, February 28, 12

20. B C D A Tuesday, February 28, 12

21. B D A Tuesday, February 28, 12

22. B D Tuesday, February 28, 12

23. Errors Tuesday, February 28, 12

24. % all functions will return a value or % generate

    an exception Tuesday, February 28, 12

25. % all functions will return a value or % generate

    an exception % you can cause exceptions manually: exit(Pid, Reason). Tuesday, February 28, 12

26. % all functions will return a value or % generate

    an exception % you can cause exceptions manually: exit(Pid, Reason). % or they will be raised for you: add(A,B) -> A + B. add(foo, 2). % {'EXIT',{badarith,[{intro,add,2}, ... Tuesday, February 28, 12

27. % if a process exits all linked processes % will

    receive an exit signal and exit Tuesday, February 28, 12

28. % if a process exits all linked processes % will

    receive an exit signal and exit % if the exit message is the atom ‘normal’ % the linked processes will not exit exit(normal). Tuesday, February 28, 12

29. % if a process exits all linked processes % will

    receive an exit signal and exit % if the exit message is the atom ‘normal’ % the linked processes will not exit exit(normal). % we can stop linked processes from exiting % by setting the trap_exit process flag process_flag(trap_exit, true). Tuesday, February 28, 12

30. % if a process exits all linked processes % will

    receive an exit signal and exit % if the exit message is the atom ‘normal’ % the linked processes will not exit exit(normal). % we can stop linked processes from exiting % by setting the trap_exit process flag process_flag(trap_exit, true). % we can override trap_exit by setting the % exit message to the atom ‘kill’ exit(kill). Tuesday, February 28, 12

31. OTP Tuesday, February 28, 12

32. • open telephone platform • libraries • behaviors Tuesday, February

    28, 12

33. Supervisors Tuesday, February 28, 12

34. • monitor child processes • handle restarts on errors •

    trap_exit Tuesday, February 28, 12

35. Child Specs Tuesday, February 28, 12

36. { Id, StartFunc, Restart, Shutdown, Type, Modules } Tuesday, February

    28, 12

37. { Id, % atom identifying the process StartFunc, Restart, Shutdown,

    Type, Modules } Tuesday, February 28, 12

38. { Id, % atom identifying the process StartFunc, % {Module,

    Function, Args} Restart, Shutdown, Type, Modules } Tuesday, February 28, 12

39. { Id, % atom identifying the process StartFunc, % {Module,

    Function, Args} Restart, % atom ‘permanent’, ‘temporary’ or ‘transient’ Shutdown, Type, Modules } Tuesday, February 28, 12

40. { Id, % atom identifying the process StartFunc, % {Module,

    Function, Args} Restart, % atom ‘permanent’, ‘transient’ or ‘temporary’ Shutdown, % atom ‘brutal_kill’, ‘infinity’ or an integer Type, Modules } Tuesday, February 28, 12

41. { Id, % atom identifying the process StartFunc, % {Module,

    Function, Args} Restart, % atom ‘permanent’, ‘transient’ or ‘temporary’ Shutdown, % atom ‘brutal_kill’, ‘infinity’ or an integer Type, % atom ‘worker’ or ‘supervisor’ Modules } Tuesday, February 28, 12

42. { Id, % atom identifying the process StartFunc, % {Module,

    Function, Args} Restart, % atom ‘permanent’, ‘transient’ or ‘temporary’ Shutdown, % atom ‘brutal_kill’, ‘infinity’ or an integer Type, % atom ‘worker’ or ‘supervisor’ Modules % list of used modules } Tuesday, February 28, 12

43. { Id, % atom identifying the process StartFunc, % {Module,

    Function, Args} Restart, % atom ‘permanent’, ‘transient’ or ‘temporary’ Shutdown, % atom ‘brutal_kill’, ‘infinity’ or an integer Type, % atom ‘worker’ or ‘supervisor’ Modules % list of used modules } Tuesday, February 28, 12

44. { simple_server, {simple_server, start_link, []}, permanent, 5000, worker, [...] }

    Tuesday, February 28, 12

45. Restart Strategies Tuesday, February 28, 12

46. one_f0r_one supervisor worker Tuesday, February 28, 12

47. supervisor worker one_f0r_one Tuesday, February 28, 12

48. supervisor one_f0r_one Tuesday, February 28, 12

49. supervisor new worker one_f0r_one Tuesday, February 28, 12

50. one_for_all supervisor worker worker worker Tuesday, February 28, 12

51. one_for_all supervisor worker worker worker Tuesday, February 28, 12

52. one_for_all supervisor worker worker Tuesday, February 28, 12

53. one_for_all supervisor new worker new worker new worker Tuesday, February

    28, 12

54. rest_for_one supervisor 1 2 3 Tuesday, February 28, 12

55. rest_for_one supervisor 1 3 2 Tuesday, February 28, 12

56. rest_for_one supervisor 1 3 3 2 Tuesday, February 28, 12

57. rest_for_one supervisor 2 3 1 Tuesday, February 28, 12

58. simple_one_for_one supervisor Tuesday, February 28, 12

59. simple_one_for_one supervisor 1 Tuesday, February 28, 12

60. simple_one_for_one supervisor 1 2 Tuesday, February 28, 12

61. simple_one_for_one supervisor 1 2 n Tuesday, February 28, 12

62. Full Example Tuesday, February 28, 12

63. {ok, { {one_for_one, 10, 60}, [{ simple_server, {simple_server, start_link, []},

    permanent, 5000, worker, [...] }] }} Tuesday, February 28, 12

64. {ok, { {one_for_one, 10, 60}, [{ simple_server, {simple_server, start_link, []},

    permanent, 5000, worker, [...] }] }} Tuesday, February 28, 12

65. {ok, { {one_for_one, 10, 60}, [{ simple_server, {simple_server, start_link, []},

    permanent, 5000, worker, [...] }] }} Tuesday, February 28, 12

66. {ok, { {RestartStrategy, MaxRestart, MaxTime}, [{ simple_server, {simple_server, start_link, []},

    permanent, 5000, worker, [...] }] }} Tuesday, February 28, 12

67. {ok, { {one_for_one, 10, 60}, [{ simple_server, {simple_server, start_link, []},

    permanent, 5000, worker, [...] }] }} Tuesday, February 28, 12

68. {ok, { {RestartStrategy, MaxRestart, MaxTime}, ChildSpecs }} Tuesday, February 28,

    12

69. Example Tuesday, February 28, 12

70. • Erlang and OTP in Action http://www.manning.com/logan/ • Learn you

    some Erlang for Great Good http://learnyousomeerlang.com/ • erldocs http://erldocs.com/ Tuesday, February 28, 12

71. joinbraintree.com Tuesday, February 28, 12

72. Thanks! @benemills / github.com/benmills Tuesday, February 28, 12