The document discusses concurrency and the actor model. It notes that as processors are no longer getting significantly faster, programs need to be parallelized to run faster. The actor model is introduced as a way to build concurrent programs where actors communicate asynchronously by message passing and have no shared state, avoiding issues like race conditions. Several Ruby libraries and frameworks for implementing the actor model are described, including Celluloid and Akka. The advantages of the actor model like encapsulation and decentralization are highlighted, though issues like potential for livelocks are also noted.

1. Ruby
goes to
@elise_huard Euruko 2011
Monday 30 May 2011

2. Why Concurrency?
Monday 30 May 2011

3. “... for the first time in history, no one is
building a much faster sequential processor.
If you want your programs to run
significantly faster (...) you’re going to have to
parallelize your program.”
Hennessy and Patterson
“Computer Architectures” (4th edition, 2007)
Monday 30 May 2011

4. Concurrency !=
Parallellism
Monday 30 May 2011

5. 3 threads, 2 cores
1 1 2
2 3
1
3 3
2
1
core1 core2 core1 core2
Monday 30 May 2011

6. Your program
language VM
OS
(kernel processes, other processes)
multicore - multiCPU
Monday 30 May 2011

7. Concurrency will melt
your brain
non-determinism
mutable AND shared state
Monday 30 May 2011

8. Actor Model
Monday 30 May 2011

9. Hewitt et al. 1973
no shared state
in response to a message, an actor can:
make local decisions
create more actors
send more messages
determine how to respond to the next message
received
Monday 30 May 2011

10. Hewitt et al. 1973
Generalization of the lambda
calculus
Monday 30 May 2011

11. Inspiration
artificial intelligence
‘quantum mechanics’ - observing details
by which the order of arrival of
messages for an actor is determined
can affect result
Monday 30 May 2011

12. The point
only actors - no global state
partial order of execution
from http://pragprog.com/titles/vspcon/programming-concurrency-on-the-jvm
Monday 30 May 2011

13. Implementations
• using threads/processes
• async messaging - mailbox
• pattern matching on incoming messages
• actors = state machines.
Monday 30 May 2011

14. Lifecycle
from http://pragprog.com/titles/vspcon/programming-concurrency-on-the-jvm
Monday 30 May 2011

15. Sleeping barber
shop with x chairs
1 barber
no customer: sleep. customers: cut hairs
customer
if barber is sleeping: wake him up
else if enough chairs take a chair
else leave
Monday 30 May 2011

16. Monday 30 May 2011

17. Actors in Ruby
Monday 30 May 2011

18. Concurrent gem
theoretical - different concurrency
models
https://github.com/mental/concurrent
Monday 30 May 2011

19. Rubinius Actors
require 'actor'
actor = Actor.spawn(Actor.current) do |master|
msg = Actor.receive
master.send msg
end
actor.send "test"
msg = Actor.receive
# msg == "test"
Monday 30 May 2011

20. Revactor
concurrent I/O for networking
apps
Evented rather than parallel
https://github.com/tarcieri/revactor
Monday 30 May 2011

21. Celluloid
thread-based actors
based on erlang
https://github.com/tarcieri/celluloid
Monday 30 May 2011

22. No true parallelism
with MRI
Monday 30 May 2011

23. Cheat on Ruby
Monday 30 May 2011

24. Erlang
light-weight processes
= actors
Monday 30 May 2011

25. Erlang
blocking receives
timeouts
supervision trees: fault-tolerance
Monday 30 May 2011

26. Erlectricity
require 'rubygems'
require 'erlectricity'
receive do |f|
f.when([:echo, String]) do |text|
f.send!([:result, "You said: #{text}"])
f.receive_loop
end
end
https://github.com/mojombo/erlectricity
Monday 30 May 2011

27. Reia or Elixir
languages on erlang vm
friendlier, more ruby-like, OO
Monday 30 May 2011

28. Scala
“We also included enhancements to make it
easier to call from Ruby into Scala libraries,
which has enabled the Lift web framework to
offer support for Ruby.” Charles Nutter, ‘JRuby 1.6 released,
now what ?’
http://www.engineyard.com/blog/2011/jruby-1-6-released-now-what/
Actors in standard library
Monday 30 May 2011

29. Akka
actor model + software transactional memory
java and scala
Monday 30 May 2011

30. Akka
• sending: reply is possible or not, sync or
async
• supervision: several strategies
• as library or as framework
• local and distributed
Monday 30 May 2011

31. JRuby!
Monday 30 May 2011

32. Caveat
Monday 30 May 2011

33. Advantages
easy to grasp
real encapsulation -
separation of concerns
highly decentralized
Monday 30 May 2011

34. But
many messages (bandwidth)
livelocks are still possible
Monday 30 May 2011

35. Back to Ruby
Monday 30 May 2011

36. Time to control
shared state ?
Change RubySpec:
default: variables not shared between
threads?
integrate better concurrency primitives
into the Ruby stdlib ?
Monday 30 May 2011

37. Let’s think about it.
Monday 30 May 2011

38. Thanks
@elise_huard
http://www.delicious.com/elisehuard/concurrency
Monday 30 May 2011

39. Ruby
goes to
Hollywood
Elise Huard LRUG 11-04-2011
Monday 30 May 2011

40. Ruby
goes to
Hollywood
Elise Huard LRUG
Monday 30 May 2011

41. Monday 30 May 2011