This document summarizes the lessons learned from migrating a Ruby on Rails codebase to JRuby. Some key points covered include choosing a deployment strategy like Warbler or TorqueBox, addressing issues with forking and signals in JRuby, using thread-safe patterns to avoid sharing mutable state between threads, and alternatives to C extensions and OpenSSL in JRuby. Tuning aspects like connection pools, thread pools, and JVM memory are also discussed.

1. Migrate to
JRuby
What We Learned

2. ian yang
@doitian

3. Agenda
• Background
• How to Migrate
• What We Learned

4. Background

5. Breadcrumb Payments

6. The Codebase
• 4 Ruby on Rails applications
• Ruby 1.9.2 and Rails 3.2.1

7. Why JRuby?
• Multithreading
• Memory Leak
• Easy integration of libraries on
JVM

8. How to Migrate

9. Choose a Deploy
Strategy

10. Archive File
Capistrano
Scheduler
Background Jobs
Clustering
Warbler
✔
Trinidad
✔
✔
✔
✔
TorqueBox
✔
✔
✔
✔
✔

11. Archive File
Capistrano
Scheduler
Background Jobs
Clustering
Warbler
✔
Trinidad
✔
✔
✔
✔
TorqueBox
✔
✔
✔
✔
✔

12. JRuby-Lint
https://github.com/jruby/jruby-lint

13. What We Learned

14. Gems Alternatives

15. Wiki: C Extension
Alternatives
https://github.com/jruby/jruby/wiki/C-ExtensionAlternatives

16. Lock Compatible
Version

17. gem 'rubyzip', '<1.0.0'

18. *nix to JVM

19. •
Cannot trap all signals
•
No Kernel#fork

20. Kernel#fork → Thread.new

21. Thread-safety

22. Avoid Sharing Mutable
State Between Threads

23. Global Variable
Class Variable
Class Instance Variable

24. Lazy Initialization →
Preload

25. class Cvv
✘
def self.redis
@@redis ||= Redis.new(...)
end
end

26. class Cvv
def self.redis
@@redis
end
def self.redis=(r)
@@redis = r
end
end
✔
!
# config/initializers/cvv.rb
Cvv.redis = Redis.new(...)

27. Thread Local Storage

28. class Processor
class_attribute :skip
✘
!
def execute
do_something unless self.class.skip
end
end

29. ✔
class Processor
def self.skip
Thread.current['Processor.skip']
end
def self.skip=(s)
Thread.current['Processor.skip'] = s
end
end

30. Atomic Variable

31. class Airlock
class_variable :enabled
end
✘

32. # gem 'atomic'!
✔
class Airlock!
@@enabled = Atomic.new(false)!
def self.enabled!
@@enabled.value!
end!
def self.enabled=(e)!
@@enabled.update { e }!
end!
end

33. Locks
require 'thread'!
mutex = Mutex.new!
!
Thread.new do!
mutex.synchronize do!
...!
end!
end

34. Reference:
Concurrency in JRuby
https://github.com/jruby/jruby/wiki/Concurrency-injruby

35. Reference: Ruby
Mutithreading
http://www.tutorialspoint.com/ruby/
ruby_multithreading.htm

36. Resque

37. •
Jobs run in the same process
•
Free the resources
•
No Fork

38. OpenSSL

39. Full OpenSSL Support
gem 'jruby-openssl'

40. Different Cryptography
Implementations
https://github.com/jruby/jruby/issues/931

42. Cryptography Adapter
• Use OpenSSL in CRuby
• Use JCE directly in JRuby
(java_import)

43. Tuning

44. TorqueBox + JBoss

45. Connection Pool Size

46. Thread Pool Size

47. JVM Memory

48. How To?
• Benchmark
• Monitoring

49. References

50. Deploying with
JRuby

51. JRuby Wiki
https://github.com/jruby/jruby/wiki