JRuby runs Ruby code on the Java Virtual Machine. This allows Ruby programs to access Java libraries and tools like Swing, and take advantage of features like the JVM's garbage collection and just-in-time compilation. JRuby is compatible with Ruby 1.8.7 and 1.9.2 and runs on multiple platforms. While it has some missing or disabled features compared to MRI Ruby, JRuby programs typically see improved performance due to the JVM. JRuby also enables building scalable, concurrent server applications using Java servers and tools.

1. What's Different About JRuby?
Charles Oliver Nutter
@headius

2. What's Different About JRuby?
(and why should you care?)

3. JRuby
Ruby on the JVM

4. JRuby
Started in 2001

5. JRuby
Fast and compatible

6. JRuby
Contributors all over the world

7. JRuby
Awesomesauce!

8. Install JRuby
rvm install jruby ; rvm use jruby

9. Install JRuby
Download tar/zip from jruby.org
Unpack archive
Add to PATH

10. Install JRuby
Windows installer at jruby.org

11. Get the Book

12. What's Different?

13. The Bad

14. Memory Footprint

15. Memory Footprint
Base memory size is larger
(Footprint over time is smaller)

16. Memory Footprint
Objects are larger

17. Memory Footprint
Objects are larger
(But instance var table is smaller)

18. Missing or Disabled Features

19. Missing or Disabled Features
No Kernel#fork

20. Missing or Disabled Features
No continuations (callcc)

21. Missing or Disabled Features
No continuations (callcc)
(except for specific forms)

22. Missing or Disabled Features
ObjectSpace off by default
(-X+O to enable)

23. Missing or Disabled Features
set_trace_func off by default
(--debug to enable)

24. C Extensions
Shipped in JRuby 1.6,
still considered experimental

25. The Good

26. Ruby Itself

27. Ruby Itself
Ruby 1.8.7 and 1.9.2 in the box

28. 28

29. 29

30. Ruby Itself
Multi-VM support
(many apps in one process)

31. 31

32. Ruby Itself
Solid across platforms

33. Ruby Itself
Solid across platforms
(Best Ruby on Windows?)

34. Ruby Itself
Solid across platforms
(Best Ruby on OpenVMS?)

35. Ruby Itself
Solid across platforms
(Best Ruby on zLinux?)

36. Java Virtual Machine (JVM)

37. Java Virtual Machine (JVM)
Java libraries like Swing
(or Scala, Groovy, Clojure, etc)

38. 38

39. 39

40. 40

41. 41

42. Java Virtual Machine (JVM)
Tools like VisualVM

43. 43

44. 44

45. 45

46. 46

47. 47

48. 48

49. 49

50. Java Virtual Machine (JVM)
Best garbage collectors

51. Java Virtual Machine (JVM)
Optimizing JIT compiler

52. Java Virtual Machine (JVM)
Concurrent threading

53. 53

54. 54

55. 55

56. 56

57. 57

58. 58

59. Java Virtual Machine (JVM)
New dynamic dispatch support
(invokedynamic)

60. 60

61. 61

62. Ruby = Method Calls
Lots and lots and lots and lots...

63. def foo
bar
end
def bar
baz foo bar baz
end
def baz
# ...
end

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

65. def foo
JRuby on Java 7
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

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

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

68. Benchmarks!
You know you love them.

69. A “Better” fib bench
bench_fib_complex.rb 5 35

70. “Richards”
bench_richards.rb 1000000

71. Red/Black Tree
github.com/headius/redblack

72. Wait for it...
Benchmarks are benchmarks.
If you don’t like them, give us yours!

74. App Development

75. App Development
Trinidad for command-line server
gem install trinidad

76. App Development
Torquebox for "Enterprise"

77. App Development
Warbler for WAR/JAR files
gem install warbler

78. App Development
Engine Yard AppCloud
engineyard.com/products/appcloud

79. App Development
Other Java servers using Warbler

80. What It Means For You

81. What It Means For You
Faster Ruby applications

82. What It Means For You
Better tool ecosystem

83. What It Means For You
Solid concurrent servers

84. What It Means For You
A better Ruby experience!

85. Thank You!
Charles Oliver Nutter
@headius