Let it crash

Learn about the "Let it crash" philosophy popularized by Erlang and an introduction to OTP supervisors.

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