Slides from the Introduction to JRuby work

1. Introduction to JRuby
Anthony Juckel
ajuckel@gmail.com
@ajuckel

2. What is Ruby?
• Dynamic/duck-typed language
• Strongly object oriented
• Open class definitions
• Closures, blocks, and generators, oh my!

3. What is JRuby?

4. What is JRuby?
• JRuby == Ruby

5. What is JRuby?
• JRuby == Ruby
• JRuby != Ruby

6. What is JRuby?
• JRuby == Ruby
• JRuby != Ruby
• JRuby == Ruby++

7. How to install it?
• Download from jruby.org
• Install via rvm (but not on this wifi)

8. What can I do with it?
• Run Ruby code (1.8 or 1.9)
• Access Java libraries from Ruby
• Embed Ruby within a Java application

9. Lab 1: Install it!
• $ jruby -e ‘puts “Hello, World!”’
• $ jruby hello.rb
• $ jruby --1.9 hello.rb
• $ jirb
• $ jruby --1.9 -S irb
• $ JRUBY_OPTS=”--1.9” jirb

10. RubyGems
• Gems are units of software reuse in the
Ruby world
• Most Gems will work the same in JRuby as
in MRI
• Gems with native code _may_ work, but
seek alternatives

11. RubyGems
• Gems can install library files
• $ gem install json
• require ‘json’
• Gems can install scripts
• $ gem install rspec
• $ jruby --1.9 -S rspec

12. RubyGems
• Some gems are only of interest on JRuby
• jruby-openssl
• activerecord-jdbc-adapter

13. RubyGems
• Others have JRuby-specific versions
• nokogiri
• Uses libxml on MRI
• Uses Java XML libraries on JRuby

14. Lab 2: Gems
• $ gem search -r [gem] • jruby-openssl
• $ gem install [gem] • rspec
• $ gem list • json
• $ gem rdoc • bundler
• $ gem server • $ cd lab02
• $ rspec

15. Launch Time
• Yes, it can be a problem
• MRI: Quick to start, speed remains constant
• JVM: Slow to start, faster as hotspots are
optimized

16. Launch Time
• What to do about it?
• Tweak startup options to make JVM
startup as fast as possible

17. Launch Time
• JVM Options (prefixed with -J with jruby)
• -client (-J-client)
• -XX:+TieredCompilation
• -Xshare:dump / -Xshare:on

18. Launch Time
• JRuby Options
• -X-C (turn off compilation)
• --ng-server / --ng
• --ng will get faster after several
executions while the JVM optimizes

19. Launch Time
ITERATIONS=1000 rspec
1000
1.9.3
JRuby
100 JRuby -X-C
JRuby NailGun
10
1
0.1
1000 100000 10000000

20. Lab 3: Try it out
• -J-client
• -J-XX:+TieredCompilation
• -J-Xshare:on
• -X-C (turn off compilation)
• --ng-server / --ng

21. Launch Time (cont.)
• Can be improved, but for small tasks
cannot (yet?) match MRI
• What options are left?
• Guard
• Spork

22. Launch Time (cont.)
• Iterate using MRI
• Quickly verify small changes
• Integrate using JRuby
• Less frequent
• May have longer test suites, perhaps more
work, can afford to pay the start up cost

23. ActiveRecord
• An Object-Relational Mapping (ORM)
library
• Developed as part of Rails
• Maps database data to Ruby classes

24. ActiveRecord
• activerecord: Core functionality
• activerecord-*-adapter: Database-specific
adapter layer

25. ActiveRecord
• MRI’s activerecord-*-adapters use native
database libraries.
• JRuby can use JDBC drivers
• Must have JDBC adapter on classpath
• activerecord-jdbc*-adapters

26. Lab 4: ActiveRecord
• $ gem install activerecord-jdbc-adapter
• $ gem install activerecord-jdbcpostgresql-adapter
• $ gem install activerecord-jdbcsqlite3-adapter
• $ gem install activerecord-derby-adapter

27. Converting Rails App
• Rails itself (aside from ActiveRecord) is
very compatible with JRuby
• Gems used in any given project may or may
not be.
• jruby-lint can help identify potential issues.

28. Converting Rails App
• What are some known issues?
• Some ObjectSpace methods disabled by
default
• Native code use
• Kernel#fork / backtick operator / system
usage

29. Lab 5: Convert an App
• $ cd graphy # Rails app targeting MRI 1.9.3
• If you’ve got MRI installed, look at current
app
• bundle install
• rake db:create db:migrate db:seed
• rails s

30. Lab 5: Convert an App
• $ jrlint
• Update Gemfile
• :platforms => :jruby
• activerecord-jdbc*-adapter
• :platforms => :ruby
• pg, sqlite3

31. Lab 5: Convert an App
• After performing the updates, test the app
in JRuby
• Also test the app in MRI, if available
• Having dependencies properly scoped
should allow you to execute the app in
either environment

32. Lab 5: Convert an App
• Have an app along with you? Try
converting it now!
• Install/Run jrlint
• Update Gemfile (if necessary)
• bundle install
• Run your tests/specs or rails s.
• Ask questions!

33. Web App Deployment
• A Rails app is no good without a solid
deployment environment
• MRI deployment strategies leverage MRI
strengths
• Need JVM deployment options to leverage
JVM strengths

34. Web App Deployment
• MRI: HTTP server -> Ruby process(es)
• Mongrel / Unicorn
• Passenger
• JRuby: HTTP server -> JRuby threads
• Rails app: config.threadsafe!
• Be mindful of the threadsafety of your
dependencies

35. Web App Deployment
• Deploying in Java Application Server
• Most self-contained option: WARbler!
• JRuby web app -> deployable WAR
• Other options
• Trinidad / Glassfish Gem
• Torquebox

36. Lab 6: Deploy it
• We’ve ported an app to JRuby. Now
deploy it!
• $ gem install warbler
• $ warble config
• Browse/edit config/warble.rb
• $ warble war # builds WAR
• $ cp app.war [tomcat-home]/webapps

37. Questions?
• https://github.com/ajuckel/intro-to-jruby
• @ajuckel
• ajuckel@gmail.com