JRuby Everywhere! Bringing a world of opportunities to the Ruby community

Delivered remotely at RubyJam in Taipei, April 14 2026

1. JRuby Everywhere! Bringing a world of opportunities to the Ruby community
2. @headius headius.com 㟬޷ʂ • Charles Oliver Nutter • "headius" on all the socials! • JRuby core developer since 2005 • Founder of Headius Enterprises • "The JRuby Company" • Thank you RubyJam! I hope I can visit in person again soon!
3. @headius headius.com
4. @headius headius.com What is JRuby? • Ruby on the Java Virtual Machine • Ruby implementation fi rst, JVM language second • Many bene fi ts from JVM ecosystem • Ruby code should "just work" • Try your code, your library • If something doesn't work, let us know!
5. @headius headius.com $ java -version openjdk version "26" 2026-03-17 OpenJDK Runtime Environment Zulu26.28+59-CA (build 26+35) OpenJDK 64-Bit Server VM Zulu26.28+59-CA (build 26+35, mixed mode, sharing) $
6. @headius headius.com $ java -version openjdk version "26" 2026-03-17 OpenJDK Runtime Environment Zulu26.28+59-CA (build 26+35) OpenJDK 64-Bit Server VM Zulu26.28+59-CA (build 26+35, mixed mode, sharing) $ ruby-install jruby-10.0.5.0 >>> Updating jruby versions ... >>> Installing jruby 10.0.5.0 into /Users/headius/.rubies/jruby-10.0.5.0 ... >>> Downloading https://repo1.maven.org/maven2/org/jruby/jruby-dist/10.0.5.0/jruby- dist-10.0.5.0-bin.tar.gz into /Users/headius/src ... >>> Verifying jruby-dist-10.0.5.0-bin.tar.gz ... >>> Extracting jruby-dist-10.0.5.0-bin.tar.gz to /Users/headius/src/jruby-10.0.5.0 ... >>> Installing jruby 10.0.5.0 ... >>> Symlinking bin/ruby to bin/jruby ... >>> Successfully installed jruby 10.0.5.0 into /Users/headius/.rubies/jruby-10.0.5.0
7. @headius headius.com $ irb >> RUBY_VERSION => "3.4.5" >> JRUBY_VERSION => "10.0.5.0" >> runtime = java.lang.Runtime.runtime => #<Java::JavaLang::Runtime:0x64a896b0> >> runtime.available_processors => 10 >> runtime.free_memory => 385494344
8. @headius headius.com Ruby Compatibility • JRuby 10 supports Ruby 3.4 • Language and core specs: 98% passing • Pure-Ruby standard library shared with CRuby • JRuby support for most native stdlib • Rails 8.x support is just about ready to release
9. @headius headius.com Deploying JRuby • Puma works just fi ne! • Warbler: package app + libraries + JRuby in single fi le • WAR fi les for app servers, JAR fi les for standalone apps • Obfuscate code for commercial release • jruby-rack: Run any Rack-based app on any JVM app server • Embedding APIs: Script existing JVM app using Ruby
10. @headius headius.com The JVM Advantage
11. @headius headius.com JVM Language • JRuby is a fi rst-class JVM language • Extensions are written in Java, not insecure C code • JVM can optimize Ruby code just like Java • JVM garbage collector is concurrent and ef fi cient • We write Java so you don't have to! • But you can if you want to! (or Scala, Clojure, Kotlin...)
12. @headius headius.com JVM GC • Many options to tune JVM GCs • Heap size: small or large? • Throughput: faster allocations or shorter pause times? • Several GC algorithms in OpenJDK • G1, ZGC, Shenandoah, Parallel, Concurrent
13. @headius headius.com Visual VM
14. @headius headius.com JVM Performance • JRuby depends on JVM for most optimization • JVM has world-class JIT compilers, garbage collectors • Similar design to ZJIT, but with 30 years of work in it • JRuby itself has an IR, basic block-based interpreter and JIT • Similar design to ZJIT starting in JRuby 9.0 (2015)
15. @headius headius.com Object.new 0M 3.5M 7M 10.5M 14M Object.new allocations per second 0M 13M 10.3M Ruby 3.4 + YJIT Ruby 4.0 + opt_new JRuby 10
16. @headius headius.com Object.new 0M 56.25M 112.5M 168.75M 225M Object.new allocations per second 217.5M 13M 10.3M Ruby 3.4 + YJIT Ruby 4.0 + opt_new JRuby 10 🤯
17. @headius headius.com JVM Concurrency • Ractors are designed to bring concurrency to Ruby • You must write Ractor-friendly code (immutable objects) • High overhead crossing Ractor boundary • Threads in JRuby are already 100% parallel • Immutable objects FTW • Low overhead for threads and shared memory
18. @headius headius.com if THREADS queues = CONCURRENT.times.map { Queue.new } threads = CONCURRENT.times.map do |i| Thread.new do queue = queues[i] data_chunk = queue.pop data_chunk.each { |item| JSON.parse(item) } end end end
19. @headius headius.com Threads vs Ractors 0 1.25 2.5 3.75 5 times faster than linear 4.2x 1.2x 1.1x CRuby threads CRuby ractors JRuby threads
20. @headius headius.com A World of Libraries • JVM ecosystem has tens of thousands of libraries • Graphics, GUIs, servers, document formats, AI/LLM • One of the largest collections in the dev world • All available to JRuby users! • Easy integration into Ruby apps and code • "Magic" to make Java APIs look like Ruby
21. @headius headius.com Example: 3D Bar Chart with JFreeChart • Chart-generating library with support for document output • Easily used from JRuby • https://blog.headius.com/ 2025/05/3d-charts-and-more-with- jruby-and-jfreechart.html
22. @headius headius.com java_import org.jfree.chart3d.data.StandardCategoryDataset3D java_import org.jfree.chart3d.data.DefaultKeyedValues ... require 'json' data = JSON.load(File.read("data/app_monitoring_revenue.json")) dataset = StandardCategoryDataset3D.new data.each do |name, subset| values = DefaultKeyedValues.new subset.each { values.put(_1, _2) } dataset.add_series_as_row name, values end
23. @headius headius.com
24. @headius headius.com JRuby Users Say... "We use [JRuby] for running Ruby in environments without Ruby!" "[JRuby was] chosen to overcome MRI Ruby's lack of multithreading and to leverage the vast and mature ecosystem of Java" "JRuby has been integral to Poshmark's stack for over a decade and remains a cornerstone of scalability and innovation" - Quantum Inventions - LogStash - Poshmark "The JRuby team has been amazingly responsive and helpful!" - SubstituteAlert
25. @headius headius.com JRuby Future
26. @headius headius.com JRuby 10.1 and Beyond • Many more optimizations coming! • Now that we are caught up, we can work on fun stuff • Reduced memory use, better JIT, better Java integration • JVM features to improve startup, fast native library integration • Liliput shrinks all objects • Leyden pre-JITs (AOT) JRuby and Ruby code • Upgrade JVM, your JRuby code runs faster!
27. HEADIUS.COM
28. @headius headius.com Headius Enterprises • Expert support for your JRuby apps • New dev, migrations, upgrades • Bug prioritization, security SLAs • Help with your code under NDA • headius.com/welcome • Site by
29. @headius headius.com Thank You! • Please contact me! • @headius on all the socials • headius@headius.com • JRuby Matrix chat • headius.com/welcome