The document discusses the challenges and progress of porting JRuby to mobile platforms, particularly Java ME, emphasizing the need for a viable subset of Ruby for mobile usage. It highlights the differences between native Ruby VM and JRuby, outlines the porting process, and lists obstacles faced during development. Future goals include enhancing JRuby for mobile and adapting to mobile constraints while attracting developers from diverse backgrounds.

1. Introduction to JRubME
Roy Ben Hayun
Engineering Services
CSG
1

2. Topics
• Requirements for mobile Ruby
• Port of the native Ruby VM (MRI)
• Porting JRuby to Java ME
> CLDC
> CDC
• More things to do..
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3. Requirements for mobile Ruby
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4. Possible usages for mobile Ruby
• Simple application development
• Prototyping
• Development tools
• Education
• Not Ruby on Rails.
• Not much usage today.
• Possibly in few years when/if scripting languages
gain more traction in mobile space
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5. Requirements from JRubyME
• What do we actually want to get?
> The power of Ruby language
> JRuby's Java bindings
> An acceptable working subset
• What can we keep for later?
> Ruby to JVM bytecode compilation
> Threading
> Any advanced feature
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6. Port of the native Ruby VM (MRI)
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7. Porting the native Ruby MRI
• See
http://developer.symbian.com/main/tools/opensrc/ruby
• Native porting effort is lengthy
• Need to port per OS
• Requires additional effort for API access
> Mobile APIs
> GUI
• MRI port gives only barebones Ruby language
> No mobile APIs
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8. Comparing native MRI vs JRuby port
• Porting involved:
> Hybrid of C, K&R C, Symbian C++ vs Java only
• Porting time:
> Weeks vs Days
• Value achieved in those ports:
> Interpreter – approximately same in both
> No OS APIs vs Java APIs via JRuby Java binding
> Required customization vs platform independent
> JRubME is easier to extend and enhance
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9. Porting JRuby to Java ME
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10. Choosing the Java ME plaform
• CLDC based solution
> The current Java ME de-facto standard
> MIDP provides rich mobile APIs
> Requires build-time modifications to replace reflection
> Requires source modifications to JRuby
• CDC based solution
> e.g., Sony Ericsson P990, M600
> Closer to a desktop Java environment
> Requires source modifications to JRuby
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11. Choosing the JRuby baseline
• Newer versions (v0.9.8 from 2007)
> Closer to the main JRuby branch for easy integration
> Has more advanced features
• Taking an older version (v0.8.2 from 2006)
> Has less advanced features
> Minimize the porting effort to get a working subset
– Less code, fewer dependencies, fewer libraries
> Provides the interpreter and Java bindings
– Which is what we need for now
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12. Various options for JRuby on Java ME
• Newer JRuby mainlines (X axis)
> More language and VM features
> Better Maintainability
• Java platform power (Y axis)
> Less porting effort
> More usability
features
Effort
/ JRuby 0.8.2 / JRuby 0.9.8
CDC CDC Maintainability
Java platform
closer to desktop Usability
/ JRuby 0.8.2 / JRuby 0.9.8 trade-off line
CLDC CLDC
Newer JRuby mainlines
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13. JRuby 0.9.8 on CLDC
• Initial exploration to get some hands-on feeling
• Minor obstacles
> Missing classes/packages (i.e. collections, nio, regex)
> Missing methods in existing classes
> Migrating to GCF
> Obstacles accumulate
/ JRuby 0.9.8
CLDC
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14. JRuby 0.9.8 on CLDC main obstacles
• Obstacles accumulate
• Java bindings require reflection capability
• Possible solutions:
> Pseudo reflection mechanism
> Hard wired code support for specific classes
– LCDUI, PIM, connectivity, persistance etc.
> Same process as using the C API for the native Ruby
VM
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15. Usability obstacle on CLDC
• Sandboxing limits the usage of JRuby on mobiles
> Limits usage to MIDP APIs
> Can not jump out of the sandbox
> Limits options of development tools
– i.e. Limits dynamic extensions of testing frameworks
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16. Summary of obstacles on CLDC
• CLDC porting effort becomes a handcrafted port
> Although, it’s not a full rewrite
> But big enough to diverge from the mainline JRuby
• Need to have a CLDC version.
• A more powerful JRuby on CDC should come first
> Provide a proof of concept
> Prototype for mobile usage
> Attract developers
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17. Porting process to CDC
• Avoid “We don’t need all that!”
• Avoid the big bang blind port
• Decremental iterations to downgrade JRuby mainline and platform
> Ensure it is running on Java SE 1.X
> Regress down to Java SE 1.X-1
• Move to CDC
> And tell the world!
/ JRuby 0.8.2 / JRuby 0.9.8
CDC CDC
• Incremental iterative steps
> Integrate with newer JRuby mainlines / JRuby 0.8.2 / JRuby 0.9.8
> Migrate to CLDC CLDC CLDC
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18. Regress on Java SE 1.4
• Ensuring it runs on Java SE 1.5 and 1.4
• Less libraries to remove then newer JRuby mainlines
> junit.jar
> bsf.jar and javasupport.bsf.*
> ant.jar and the AST serialization
• Remove asserts
• No java.nio.*
• (No autoboxing in the source..)
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19. Regress on Java SE 1.3
• Chained exceptions
• Few more minor removals
> Missing methods i.e. String.split(), Boolean.valueOf()
> Missing classes i.e. StackTraceElement
> Restricted access i.e. java.util.Calendar.setTimeInMills()
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20. Regress on Java SE 1.3
• Bigger obstacle is that there is no java.util.regex.*
• Solution
> Find a replacement package e.g.,Java 1.4
> Paste into a new package jrubyme.poc.[package]
> Modifications as required to package and client code
– e.g., sun.text.Normalizer silently commented out.
• And do the same for other dependencies
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21. Move to CDC
• Introspection support incompatible
> java.beans.Introspector required by BeanExtender Ruby
class
• Solution:
> Disable the Ruby beans extension
> Serialize Abstract Syntax Tree and redeploy *.ast.ser
files
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22. Evaluating the CDC port
• How does downgrading JRuby to 0.8.2 simplify things?
> i.e. Less than 40 locations of java.util.Regex package usage
> Less code e.g., 318 source files compared to 574 in 0.9.8
• How does porting to CDC via Java SE simplify things?
> Moving closer to CDC gradually
> Much fewer new APIs or API differences
– No need for handcrafted porting
• Remember: we’re trying to get to a working subset
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23. Demo on a real device
• AWT UI
• Can load, modify and launch a script
• On device programming
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24. Demo on a real device
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25. Demo on a real device
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26. There's a lot to do from here..
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27. Bringing JRuby to the mobile space
• Co-existence of the native and Java options
> Attracts developers from different backgrounds
> No reason to limit the hosting platform options
• Anatomy of free open source success
> Governance and decision making capability
> Tools for collaboration
> Strong community values and commitment
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28. Bringing JRuby to the mobile space
• JRubME ‘TODO’ list
> Create a mobile spec (desktop too)
> Adapt to mobile constraints (ROM, performance, ..)
> Rectify the initial porting
> Move upwards in the JRuby versions
> Migrate to CLDC as well
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29. Bringing JRuby to the mobile space
• JRubME ‘Wish-list’
> Scripting languages gain more traction in the mobile
space
> CDC (or embedded Java SE flavour) to become the
mobile Java de-facto standard
> Dual compilation and JSR-292 (invokedynamic)
– Moore’s law will take care of speed
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30. Thank you
Roy Ben Hayun
Engineering Services
CSG
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