Why JRuby?Fiona Tay @msfionatayEngineer, Pivotal Labs

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

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

I’m a Rubyist

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I’m also a JRubyist

http://github.com/GreenplumChorus/chorus

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An Introduction

It’s a Ruby implementation1. Install it2. Write Ruby code

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It’s a Ruby implementation

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Ruby implementationsInterchangeable to an extentPopular implementations:• MRI• JRuby• Rubinius • MacRuby

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Under the hood

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Under the hood

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secret sauce

Interchangeability1+1 should be 2 in all implementations

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Implementation differencesSome implementations are more equal than others Differences:• Speed of execution• Support for libraries• Implementation bugs

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History of JRubyAround since 2002Has had traction in real projects since ~2005

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JRuby in the real world

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JRuby in the real world

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The Good

Access to Java librariesIncredibly powerful toolEveryone and his/her dog writes Java

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Java libraries: NLPStanford Parser is the NLP library of choice

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Java libraries: EmailJavaMail is a better alternative to ActionMailer

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Access to Java librariesJRuby has deep integration with JavaDirectly call Java code from Ruby

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Directly calling Java code

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Using other languagesOther languages built on the JVM• Scala - special support• Clojure• Groovy

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Using Ruby gemsIf you’re lucky, someone has made a Ruby gem that wraps the Java libraryAlso wrapping a gem is a good idea

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Easier app deploymentNot easier than git push heroku masterOnly relevant if you’re deploying to large server system

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Easier app deploymentLeverage existing Java-based deployment infrastructure

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Leverage infrastructureWarbler packages everything into a single WAR fileStandard file format for Java deploys

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Other deployment optionsTorqueBox provides additional services

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Better performanceBetter compiler than MRIBenefits from improvements to JVM

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Better performanceAccess to highly optimized Java libraries

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The Bad

Gem availability

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Gem availabilityGems written in pure Ruby work with JRubyGems with C extensions don’t work with JRubyTypically, these are older, less-maintained gems

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Fixing gemsSometimes, you can fix the existing gemCould be as simple as replacing its dependenciesOr could be complex

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Fixing gemsPatched a job queueing systemTook more work than we expectedYMMV

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Long app startup timeInhibits test-driven developmentDue to Rails startup timeDifficult to set up Spork with JRuby

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Long app startup timeC’est la vie

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Less mature technologyMRI still the defaultThough JRuby has maturedLibraries developed against MRI

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The Ugly

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

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ConcurrencyJRuby has real threadsMRI Ruby has threads with Global Interpreter Lock

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Concurrency and RubyThreads are a major innovation But MRI has never really had a focus on concurrency

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Concurrency is greatCheaper to scaleGood multi-threaded web servers

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More bang for your buckOne server: MRI runs two Ruby processesOne server: JRuby runs two Ruby processes with 4 threads eachCan use JRuby on Heroku

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Concurrency is not freeBugs in non-thread safe libraries• Rails• AirbrakeLibraries developed without a focus on concurrency

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Concurrency is not freeWriting thread-safe code is difficultEven for Java developers with experienceBut concurrency is the new sexy

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Concurrency is worth itHuge performance improvementsSome features would be much easier with threadsThreads is the future

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The Decision

JRuby is a non-standard choice.

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

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

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Should you use JRuby?Do you need good performance?

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Should you use JRuby?Otherwise, no

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Should you use JRuby?Not to worry - you can always switch to JRuby laterLots of people switch for performance reasons

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Getting started with JRubyjruby-lint checks how ready your code is to run on JRuby

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AcknowledgmentsPivotal LabsJRuby team

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Thanks!@MsFionaTay