Presented at EMRubyConf 2011 alongside RailsConf/BohConf.

1. JRuby
Concurrency
Nick Sieger
EMRubyConf @ RailsConf 2011

2. Mental
Model
http://www.flickr.com/photos/solar_decathlon/4524503892/

3. http://twitter.com/RoflscaleTips/status/61135427813384192

4. Uncertainty
/* ruby/struct.c */
static VALUE rb_struct_equal(VALUE s, VALUE s2) {
/* ... */
if (RSTRUCT_LEN(s) != RSTRUCT_LEN(s2)) {
rb_bug("inconsistent struct"); /* should never happen */
}
/* ... */
}
O RLY?!

5. How could this code fail?
class ExpensiveToCreate
def self.instance
@instance ||= ExpensiveToCreate.new
end
end

6. How could this code fail?
class ExpensiveToCreate
def self.instance
unless defined?(@instance)
@instance = ExpensiveToCreate.new
end
end
end

7. How could this code fail?
class ExpensiveToCreate
def self.instance
T2 unless defined?(@instance)
@instance = ExpensiveToCreate.allocate
T1 @instance.initialize # big pause here
@instance
end
end
end

8. Avoid shared mutable state,
lazy initialization
MutableConstant.merge! :key => value
class MemoryCache
def self.cache
@cache ||= {} $global_lock.do_something!
end
end

9. Difficult to observe
with green threads

10. data = []
M.times do |m|
Thread.new do
N.times do |n|
data << m * n
end
end
end

11. OK NOT OK
instance vars
method def
String
class def
Array
class vars
Hash

12. class WorkerTask
def run
@thread = Thread.new do
50.times do
digest = Digest::MD5.new
@range.step(1024) do |idx|
digest.update(@data[idx...idx+1024])
end
end
end
end
end

13. Other Concurrency
Approaches

14. java.util.concurrent

15. require 'java'
java_import java.util.concurrent.Executors
@count = java.util.concurrent.atomic.AtomicInteger.new
def send_email(executor)
executor.submit do
puts "email #{@count.incrementAndGet} sent"
end
end

16. executor = Executors.newCachedThreadPool
send_email(executor)
executor =
Executors.newFixedThreadPool(2)
loop do
send_email(executor)
end

17. jetlang/jretlang
http://code.google.com/p/jetlang/
https://github.com/reevesg/jretlang

18. require 'jretlang'
fiber = JRL::Fiber.new
channel = JRL::Channel.new
fiber.start
channel.subscribe_on_fiber(fiber) do |msg|
puts msg
end
channel.publish "Hello"

19. Akka
http://akka.io
http://j.mp/jruby-akka

20. require 'akka'
class HelloWord
def hi
puts "hello actor world"
end
end
Actors.actorOf(HelloWord.new).hi
puts "initiating shutdown..."
Actors.delayedShutdown 1