1. ElixirPeeking into Elixir’s
Processes, OTP & Supervisors
21st March 2014
/benjamintanweihao /bentanweihao
benjamintanweihao@gmail.com

2. What will we learn today?
Elixir & Erlang
In less than 5 minutes

3. Elixir & Erlang
In less than 5 minutes
Processes 101
The Basic Concurrency
Primitive
What will we learn today?

4. Elixir & Erlang
In less than 5 minutes
OTP
Framework and much more
Processes 101
The Basic Concurrency
Primitive
What will we learn today?

5. Elixir & Erlang
In less than 5 minutes
OTP
Framework and much more
Supervisors
Fault Tolerance & Recovery
Processes 101
The Basic Concurrency
Primitive
What will we learn today?

6. Ohai, Elixir!

7. Elixir & ErlangIn less than 5 minutes

8. Ohai, Erlang!
Erlang is a general-purpose concurrent,
garbage-collected programming language and
runtime system. The sequential subset of
Erlang is a functional language, with eager
evaluation, single assignment, and dynamic
typing. It was designed by Ericsson to support
distributed, fault-tolerant, soft-real-time, non-
stop applications. It supports hot swapping, so
that code can be changed without stopping a
system.

9. Ohai, Erlang!
Erlang is a general-purpose concurrent,
garbage-collected programming language and
runtime system. The sequential subset of
Erlang is a functional language, with eager
evaluation, single assignment, and dynamic
typing. It was designed by Ericsson to support
distributed, fault-tolerant, soft-real-time, non-
stop applications. It supports hot swapping, so
that code can be changed without stopping a
system.

10. • Free lunch is over
Why Elixir ?

11. Why Elixir ?
• Free lunch is over
• Hyper-threading & Multicore
• Faster software means using all
cores!
• But … Concurrency -> Coordination
• Functional makes this easier

12. Design Goals of Elixir
1.Productivity
2.Extensibility
3.Compatibility

13. Productivity
Complete Elixir Application

14. Productivity
Includes Supervisor Chain

15. Productivity
Testing built-in

16. Extensibility
Macros & Meta-programming
Implementing unless using if

17. Extensibility
Macros & Meta-programming
Implementing unless using if

18. Compatibility
Elixir can call Erlang code,
without any conversion
cost at all.

19. Compatibility
Elixir can use Erlang libraries!

20. The Actor Concurrency Model
• Actor = Process

21. The Actor Concurrency Model
• Actor = Process
• A process performs a specific task
when it receives a message

22. The Actor Concurrency Model
• Actor = Process
• A process performs a specific task
when it receives a message
• In turn, the process can reply to the
sender

23. The Actor Concurrency Model
• Actor = Process
• A process performs a specific task
when it receives a message
• In turn, the process can reply to the
sender
• All messages go to a processes’
mailbox – Q of unprocessed messages
sent from other processes that are not
yet consumed

24. The Actor Concurrency Model
• Actor = Process
• A process performs a specific task
when it receives a message
• In turn, the process can reply to the
sender
• All messages go to a processes’
mailbox – Q of unprocessed messages
sent from other processes that are not
yet consumed Shared-nothing Async Message-passing

25. Processes 101The Basic Concurrency Primitive

26. Creating Processes & Sending Messages in Elixir
Creating a Process

27. Creating Processes & Sending Messages in Elixir
Module, Function, Arguments

28. Creating Processes & Sending Messages in Elixir
Process id

29. Creating Processes & Sending Messages in Elixir
Sending a Message to w1

30. Creating Processes & Sending Messages in Elixir
Process waits for a message …

31. Creating Processes & Sending Messages in Elixir
Pattern matches!

32. Creating Processes & Sending Messages in Elixir
Result is sent back to the
calling process (self)

33. Creating Processes & Sending Messages in Elixir
Returns immediately

34. Creating Processes & Sending Messages in Elixir
Get result from self

35. Creating Processes & Sending Messages in Elixir Demo

36. OTPFramework and much more

37. What is OTP?
• Comes with Elixir/Erlang
• Framework to build
applications that are fault-
tolerant, scalable,
distributed
• Databases + Profilers +
Debuggers

38. OTP Behaviours
• GenServer
• Supervisor
• Application

39. An Example GenServer
Implement the GenServer
Behaviour

40. An Example GenServer
Implement GenServer Callbacks

41. An Example GenServer
Callbacks are NOT called explicitly

42. An Example GenServer
OTP calls the callbacks.

43. An Example GenServer
Synchronous Call:
Caller waits for reply

44. An Example GenServer
Asynchronous Call:
Caller doesn’t wait
for reply

45. An Example GenServer Demo

46. SupervisorsFault Tolerance & Recovery

47. Supervisors for Fault Tolerance and Recovery
one_for_one restart strategy

48. Supervisors for Fault Tolerance and Recovery
rest_for_all restart strategy

49. Supervisors for Fault Tolerance and Recovery
rest_for_one restart strategy

50. An Example Supervisor
Implement the Supervisor
Behaviour

51. An Example Supervisor
Declaring the Supervision
tree. Both Supervisors and
Workers (e.g. GenServers)
can be supervised.

52. An Example Supervisor

53. An Example Supervisor
Declare the restart strategy

54. Supervisor Demo
Supervisor A
Supervisor B Supervisor C
Supervisor D
Server
D
Server
B
Worker 1Worker 1Worker

55. Supervisor Demo
Supervisor A
Supervisor B Supervisor C
Supervisor D
Server
D
Server
B
Worker 1Worker 1Worker
one_for_one

56. Supervisor Demo
Supervisor A
Supervisor B Supervisor C
Supervisor D
Server
D
Server
B
Worker 1Worker 1Worker
one_for_all

57. Supervisor Demo
Supervisor A
Supervisor B Supervisor C
Supervisor D
Server
D
Server
B
Worker 1Worker 1Worker
simple_one_for_one

58. Supervisor Demo
Supervisor A
Supervisor B Supervisor C
Supervisor D
Server
D
Server
B
Worker 1Worker 1Worker
one_for_one

59. Supervisor Demo
Supervisor A
Supervisor B Supervisor C
Supervisor D
Server
D
Server
B
Worker 1Worker 1Worker
one_for_one
simple_one_for_one
one_for_all
one_for_one

60. Elixir & Erlang
In less than 5 minutes
OTP
Framework and much more
Supervisors
Fault Tolerance & Recovery
Processes 101
The Basic Concurrency
Primitive

61. Resources

62. Work in Progress!
!
Sign up at:
http://www.exotpbook.com
Me.

63. Stickers!**Very Limited Quantity

64. Thanks!
/benjamintanweihao /bentanweihao
benjamintanweihao@gmail.com