This document discusses the pros and cons of using JRuby, a Ruby implementation that runs on the Java Virtual Machine. Some key advantages of JRuby include access to the vast Java library ecosystem, better performance compared to MRI Ruby due to improvements in the JVM, and the ability to leverage Java deployment infrastructure. However, JRuby also has disadvantages like potential issues with Ruby gems that use C extensions and lack of thread safety in some Ruby libraries. The document concludes that JRuby is worth considering if access to Java libraries, performance, or deployment options are important factors for a project.

1. Why JRuby?
Fiona Tay
@msfionatay
Engineer, Pivotal Labs

2. This is for the
person who just
wants to make web
apps.

3. This is about the
Good, The Bad, and
The Ugly.

4. I’m a Rubyist
4

5. I’m also a JRubyist
http://github.com/GreenplumChorus/chorus
5

6. An Introduction

7. It’s a Ruby implementation
1. Install it
2. Write Ruby code
7

8. It’s a Ruby implementation
8

9. Ruby implementations
Interchangeable to an extent
Popular implementations:
• MRI
• JRuby
• Rubinius
• MacRuby
9

10. Under the hood
10

11. Under the hood
secret sauce
11

12. Interchangeability
1+1 should be 2 in all implementations
12

13. Implementation differences
Some implementations are more equal than others
Differences:
• Speed of execution
• Support for libraries
• Implementation bugs
13

14. History of JRuby
Around since 2002
Has had traction in real projects since ~2005
14

15. JRuby in the real world
15

16. JRuby in the real world
16

17. The Good

18. Access to Java libraries
Incredibly powerful tool
Everyone and his/her dog writes Java
18

19. Java libraries: NLP
Stanford Parser is the NLP library of choice
19

20. Java libraries: Email
JavaMail is a better alternative to ActionMailer
20

21. Access to Java libraries
JRuby has deep integration with Java
Directly call Java code from Ruby
21

22. Directly calling Java code
22

23. Using other languages
Other languages built on the JVM
• Scala - special support
• Clojure
• Groovy
23

24. Using Ruby gems
If you’re lucky, someone has made a Ruby gem that
wraps the Java library
Also wrapping a gem is a good idea
24

25. Easier app deployment
Not easier than git push heroku master
Only relevant if you’re deploying to large server system
25

26. Easier app deployment
Leverage existing Java-based deployment infrastructure
26

27. Leverage infrastructure
Warbler packages everything into a single WAR file
Standard file format for Java deploys
27

28. Other deployment options
TorqueBox provides additional services
28

29. Better performance
Better compiler than MRI
Benefits from improvements to JVM
29

30. Better performance
Access to highly optimized Java libraries
30

31. The Bad

32. Gem availability
32

33. Gem availability
Gems written in pure Ruby work with JRuby
Gems with C extensions don’t work with JRuby
Typically, these are older, less-maintained gems
33

34. Fixing gems
Sometimes, you can fix the existing gem
Could be as simple as replacing its dependencies
Or could be complex
34

35. Fixing gems
Patched a job queueing system
Took more work than we expected
YMMV
35

36. Long app startup time
Inhibits test-driven development
Due to Rails startup time
Difficult to set up Spork with JRuby
36

37. Long app startup time
C’est la vie
37

38. Less mature technology
MRI still the default
Though JRuby has matured
Libraries developed against MRI
38

39. The Ugly

40. Concurrency
“Concurrency is when several computations are
executing simultaneously, and potentially interacting
with each other.” - Wikipedia
40

41. Concurrency
JRuby has real threads
MRI Ruby has threads with Global Interpreter Lock
41

42. Concurrency and Ruby
Threads are a major innovation
But MRI has never really had a focus on concurrency
42

43. Concurrency is great
Cheaper to scale
Good multi-threaded web servers
43

44. More bang for your buck
One server: MRI runs two Ruby processes
One server: JRuby runs two Ruby processes with 4
threads each
Can use JRuby on Heroku
44

45. Concurrency is not free
Bugs in non-thread safe libraries
• Rails
• Airbrake
Libraries developed without a focus on concurrency
45

46. Concurrency is not free
Writing thread-safe code is difficult
Even for Java developers with experience
But concurrency is the new sexy
46

47. Concurrency is worth it
Huge performance improvements
Some features would be much easier with threads
Threads is the future
47

48. The Decision

49. JRuby is a non-
standard choice.

50. Should you use JRuby?
Do you want to use Java libraries?
50

51. Should you use JRuby?
Do you want to leverage Java-based deployment
infrastructure?
51

52. Should you use JRuby?
Do you need good performance?
52

53. Should you use JRuby?
Otherwise, no
53

54. Should you use JRuby?
Not to worry - you can always switch to JRuby later
Lots of people switch for performance reasons
54

55. Getting started with JRuby
jruby-lint checks how ready your code is to run on
JRuby
55

56. Acknowledgments
Pivotal Labs
JRuby team
56

57. Thanks!
@MsFionaTay