1. Scala Actors from an Erlang
perspective

2. Who am I
• Reidar Sollid (Reidar is an ancient Viking name, and
means warrior and protector of the home)
• I am now a Consutlant at Bouvet
• My background is from R&D and Telecom transport
networks from Nera Networks( now Ceragon) and
Ericsson.

3. Motivation
• Most Scala devs comes from Java
• Hacking Scala with a Java mindset limits your
use of Scala
• Erlang is a pure actor base language
• Getting the mindset from Erlang into Scala
broadens the horizon
• Java + Erlang = Scala

4. The concept of forever
• This is a loaner from Joe Armstrong, he is a lot
funnier than I am but I guess you get the point

• I hope he don’t mind

6. 10 x the size of the

7. The fly

8. Nine nines 99.999999999
• Standard for Telecom equipment is five nines 99.999 (5.2
minutes downtime/year)
• The Ericsson AXD301 has 2 million lines of Erlang code
and nine nines

9. Shared memory

10. Concurrency and shared memory

11. Erlang
• The world is concurrent
• Things in the world don't share data
• Things communicate with messages
• Things fail
– Joe Armstrong

12. What is Erlang
• Created and maintained by Ericsson (now open source)
• Functional, single assignment, strict evaluation, dynamic
typing
• Actor model, concurrent oriented, fault tolerant, soft-real-
time
• Light weight processes that communicate using message
passing (an Erlang process is more light weight than a
Java thread)
• Erlang started life as a modified prolog
• Erlang shell, escript and compiled *.beam bytecode

13. Variables and pattern matching
• Variables starts with capital letter or
underscore
• Variables are immutable, Erlang does not have
mutable variables
• They are variables because they can be
assigned or not assigned
• Erlang variables are the same as val variables
in Scala

14. Erlang variable demo

15. Scala variable demo

16. Atoms and tuples
• An atom is a global constant starting with lower case
• Scala has an equivalent called Symbol
• A tuple is an ordered set of elements
• Erlang doesn’t have classes so we use tuples (see also
records)

17. The spawn keyword
• spawn(Fun) -> pid()
• Spawns out a new process and returns the
Process Identifier <0.13.1>
• Normally we assign the PID to a variable
• Pid = hello_world:start()

18. The *Real* Erlang "Hello, World!"
http://egarson.blogspot.com/2008/03/real-erlang-hello-world.html

19. Pattern Matching
, 29.09.2012

20. Tail recursion
@tailrec

21. Tail recursion
tail recursion as seen here is not making the memory grow
because when the virtual machine sees a function calling
itself in a tail position (the last expression to be evaluated in a
function), it eliminates the current stack frame.

22. Scala react or receive
• React is the “normal” actor, lightweight process
• Receive spins out a new Java thread
• In the paper *
– 1.80GHz Intel Pentium M processor with 1024 MB
memory, running Sun’s Java HotSpot™VM 1.5.0 under Linux
2.6.15
– Max heap size set to 512 MB
– 5000 threads
– 600 000 processes (1 200 000 actors)
• React uses partial functions to send the process to the
heap, react has return type Nothing
• Receive runs on the stack and is heavyweight JVM threads
(like Java)
*Actors That Unify Threads and Events P. Haller, M. Odersky

23. Area server Erlang

24. Area server in Scala

25. Remote processes Erlang

26. Remote actors Scala

27. Supervisors in Erlang/OTP and
AKKA
Supervisor
Process
Process
Process
Page
, 29.09.2012
Actor model baksia

28. Supervising supervisors
Root
Supervisor
Supervisor
Supervisor
Process
Process
Process Process
Process Process
Page
, 29.09.2012
Actor model baksia