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.
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)
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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
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10. Hewitt et al. 1973
Generalization of the lambda
calculus
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11. Inspiration
artificial intelligence
‘quantum mechanics’ - observing details
by which the order of arrival of
messages for an actor is determined
can affect result
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12. The point
only actors - no global state
partial order of execution
from http://pragprog.com/titles/vspcon/programming-concurrency-on-the-jvm
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13. Implementations
• using threads/processes
• async messaging - mailbox
• pattern matching on incoming messages
• actors = state machines.
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14. Lifecycle
from http://pragprog.com/titles/vspcon/programming-concurrency-on-the-jvm
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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
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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
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27. Reia or Elixir
languages on erlang vm
friendlier, more ruby-like, OO
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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
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29. Akka
actor model + software transactional memory
java and scala
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30. Akka
• sending: reply is possible or not, sync or
async
• supervision: several strategies
• as library or as framework
• local and distributed
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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
