JRuby is Ruby for the JVM, right? But what does that really mean? What do you get out of the deal? We'll explore what makes JRuby unique among Ruby implementations, and why the JVM is a Rubyist's dream come true. Using JRuby means you have the best GC, real threads, easy and scalable deployment, high performance, no-compile cross-platform libraries, and the best monitoring and profiling tools of any VM. And you get it all without leaving Ruby behind. If you're not using JRuby already, this talk will convince you to give it a try.

1. JRuby!

2. Me
• Charles Oliver Nutter
• @headius
• Java developer since 1996
• JRuby developer since 2006
• Starting at Red Hat on Monday!

3. Red Hat FAQ
• Primary job still JRuby
• Expanding to help other languages
• Working with OpenJDK team
• Continuing to support EY JRuby efforts

4. What is JRuby?

5. Ruby on JVM
• Core classes and runtime in Java
• Moving parts to Ruby over time
• Standard command line
• 1.8 and 1.9 compatible
• 1.9 default in JRuby 1.7
• Drop in replacement for MRI*

6. *caveats
• Weak low-level UNIX stuff
• Improving over time
• Poor C extension support
• Not maintained...off by default in 1.7
• Some features differ or unavailable
• ObjectSpace, trace funcs, callcc...

7. JRuby 1.7 (preview)
• Ruby 1.9.3 mode by default
• Many 1.9 compat fixes
• Numerous perf improvements
• Java 7 invokedynamic support
• Beginning of new optimizing compiler

8. Getting Started
• Need a JVM...
• rvm install jruby
• rvm install jruby-1.7.0-preview1
• Download manually
• Unpack, edit PATH, done

9. Try it Out

10. JRuby is the best*
Ruby runtime

11. The Team

12. JRuby Team

13. JRuby Team
Charlie

14. JRuby Team
Charlie Tom
Nick Hiro Marcin Nahi Wayne Subbu Douglas Douglas
Douglas
Contribs

15. JRuby Team
Charlie Tom
Nick Hiro Marcin Nahi Wayne Subbu Douglas Douglas
Douglas
Contribs
Douglas
Douglas Douglas
Douglas Douglas
Douglas Douglas
Other
Douglas
OpenJDK Android J9
JVMs

16. JRuby Structure
JRuby
Bytecode Core Java
Parser
JIT Classes Integ
JVM
Native
Threads GC C API
JIT

17. JRuby Structure
JRuby
Bytecode Core Java
Parser
JIT Classes Integ
JRuby team can focus on implementing JRuby.

18. JRuby Team Doesn’t
Have to Work On*
• Memory allocation • Native JIT
• Garbage collectors • Tooling
• Native threading • Server environments
• Cross-platform • Native extensions
• Mobile/Embedded VMs

19. We could stop working
on JRuby and it would
continue to get faster.

20. Google Summer
of Code
• JRuby accepted as an organization
• Eight students!
• Shoes, Krypt, evented IO, fibers, Ruboto,
IR dumping, IR to Dalvik, benchmarking
• Three more from C42

21. Platforms

22. Systems
• Best Ruby on Windows?
• Exotic platforms: zLinux, OpenVMS, AS/400
• Android’s Dalvik
• Embedded JVMs

23. Ruboto

24. Servers
• Any Java server can host Ruby
• Trinidad
• Ruby-style CLI server atop Tomcat
• Torquebox
• Full Ruby stack atop JBossAS

25. Torquebox
• Rack-compatible • Server management
• Database connectivity • Clustering
• Background daemons • In and out-process cache
• Scheduled jobs • Web sockets
• Messaging • Authentication
• Asynchronous tasks • XA Transactions

26. Torquebox
• Rack-compatible • Server management
• Database connectivity • Clustering
• All R
Background daemons • In and out-process cache
• Scheduled jobs
uby • Web sockets
• Messaging
APIs
• Authentication
• Asynchronous tasks • ! XA Transactions

27. Libraries

28. Libraries
• 340k versioned jars in Maven central
• Compare to 35k gems in RubyGems.org
• Vast majority have no native code
• All usable from JRuby

31. Midi Example

32. GC

33. JVM GC
• Wide array of options
• Generation size, worker threads,
concurrency, tenuring...
• Many GCs to choose from
• Scales up to massive heaps
• Best GCs in the world!

34. class Simple
attr_accessor :next
end
top = Simple.new
puts Benchmark.measure {
outer = 10
total = 100000
per = 100
outer.times do
total.times do
per.times { Simple.new }
s = Simple.new
top.next = s
top = s
end
end
}

35. 15
GC time %
11.25
7.5
3.75
0
JRuby Ruby 1.9.3

36. Threads

37. Real Parallellism
• Ruby thread = JVM thread = native thread
• One process can use all cores
• One server can handle all requests

38. require 'benchmark'
ary = (1..1000000).to_a
loop {
puts Benchmark.measure {
10.times {
ary.each {|i|}
}
}
}

39. require 'benchmark'
ary = (1..1000000).to_a
loop {
puts Benchmark.measure {
(1..10).map {
Thread.new {
ary.each {|i|}
}
}.map(&:join)
}
}

41. Ruby 1.9
unthreaded

42. Ruby 1.9 Ruby 1.9
unthreaded threaded

43. Ruby 1.9 Ruby 1.9
unthreaded threaded
JRuby
unthreaded

44. Ruby 1.9 Ruby 1.9
unthreaded threaded
JRuby JRuby
unthreaded threaded

45. threaded_reverse
0.8
0.65
0.5
0.35
0.2
one thread two threads three threads four threads

46. Nonlinear?
• More work means more objects
• More objects needs memory bandwidth
• No different from multi-process

47. Performance

48. Performance
• JRuby compiles Ruby to JVM bytecode
• JVM compiles bytecode to native
• Best JIT technology in the world
• Getting even better with invokedynamic

49. def foo
bar
end
def bar
baz foo bar baz
end
def baz
# ...
end

50. JRuby on Java 5/6
def foo
bar
end
def bar JRuby JRuby
baz foo call bar call baz
end logic logic
def baz
# ...
end
Kills many JVM optimizations

51. JRuby on Java 7
def foo
bar
X X
end
def bar JRuby JRuby
baz foo call bar call baz
end logic logic
def baz
# ...
end
Dynamic call logic built into JVM

52. JRuby on Java 7
def foo
bar
end
def bar
baz foo bar baz
end
def baz
# ...
end
Straight through dispatch path

53. JRuby on Java 7
def foo
bar
end
def bar
baz foo bar baz
end
def baz
# ...
end
Optimizations (like inlining) can happen!

55. JRuby/Java 6 JRuby/Java 7

56. JRuby/Java 6 JRuby/Java 7
Times Faster than Ruby 1.9.3
5
3.75
2.5
1.25
0
base64 richards neural mandelbrot redblack

57. JRuby/Java 6 JRuby/Java 7
Times Faster than Ruby 1.9.3
5
3.75
2.5
1.914 1.806
1.538 1.565
1.25 1.346
0
base64 richards neural mandelbrot redblack

58. JRuby/Java 6 JRuby/Java 7
Times Faster than Ruby 1.9.3
5
4.226 4.32
3.75
3.66
3.44
2.5 2.658
1.914 1.806
1.538 1.565
1.25 1.346
0
base64 richards neural mandelbrot redblack

60. Tools

61. Profiling
• Java profilers
• VisualVM,YourKit, NetBeans, JXInsight
• jruby [--profile | --profile.graph]
• jruby -Xreify.classes=true
• JVM command-line profilers

62. Monitoring
• Java Management Extensions (JMX)
• Gems available for clients and servers
• jconsole and VisualVM
• Most servers provide additional tools
• New Relic, etc have JVM support

63. VisualVM
• CPU, memory, thread monitoring
• CPU and memory profiling
• VisualGC
• Heap analysis

66. Your Turn
• Try your apps on JRuby and tell us
• Turn on JRuby in @travisci
• Let us know what you think of JRuby
• Help us make JRuby even better!

67. Thank you!
• @headius
• jruby.org
• torquebox.org