headius

We had a good discussion while I was in the informal meetup today, and I'm putting together a summary of action items we might want to consider for outreach (more blog posts, more content on short-form video sites, refreshing old articles and projects). One of the ideas I had that I really want to dig into is that new developers aren't looking for their next "enterprise application" language. They want to run something small, quickly. Java is not known for being small or quick.

I wanted to try playing with the "small" hello world, since it was mentioned that other language fans still use this as a way to dunk on Java.

I believe the smallest we can get right now in 25 (as a readable one-liner without golfing) is:

void main() { IO.println("Hello!"); }

headius

diff --git a/ext/java/org/jruby/ext/stringio/StringIO.java b/ext/java/org/jruby/ext/stringio/StringIO.java
index f3ab1cf..9c58077 100644
--- a/ext/java/org/jruby/ext/stringio/StringIO.java
+++ b/ext/java/org/jruby/ext/stringio/StringIO.java
@@ -79,27 +79,17 @@ import static org.jruby.util.RubyStringBuilder.types;
 @JRubyClass(name="StringIO")
 @SuppressWarnings("serial")
 public class StringIO extends RubyObject implements EncodingCapable, DataType {
-    static class StringIOData {
-        /**

headius

// This code was generated by AI. It's completely wrong.
public static RubyFixnum newFixnum(Ruby runtime, long value) {
    if (value < Byte.MIN_VALUE || value > Byte.MAX_VALUE) {
        return newFixnum(runtime, (byte) value);
    } else if (value < Short.MIN_VALUE || value > Short.MAX_VALUE) {
        return newFixnum(runtime, (short) value);
    } else if (value < Integer.MIN_VALUE || value > Integer.MAX_VALUE) {
        return newFixnum(runtime, (int) value);
    }

headius

$ ruby -e 'files = Dir["code/**/*.rb"]; files.each_with_index {|file, i| puts "#{i+1}/#{files.size}: #{file}"; system "jruby #{file}"; system "/Users/headius/.rubies/ruby-3.4.7/bin/ruby --jit #{file}" }'
1/68: code/array/array-concat-vs-+.rb
jruby 10.0.3.0-SNAPSHOT (3.4.5) 2025-11-04 d74cb7a2e0 OpenJDK 64-Bit Server VM 21.0.8+9-LTS on 21.0.8+9-LTS +indy +jit [arm64-darwin]
Warming up --------------------------------------
        Array#concat   289.000 i/100ms
             Array#+     1.000 i/100ms
Calculating -------------------------------------
        Array#concat      3.037k (± 1.1%) i/s  (329.29 μs/i) -     15.317k in   5.044432s
             Array#+     13.653 (± 0.0%) i/s   (73.24 ms/i) -     69.000 in   5.059999s

headius

sidekiq $ export RAILS_VERSION=7.1                               
sidekiq $ bundle
...
Bundle complete! 21 Gemfile dependencies, 88 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
sidekiq $ warble                                                 
rm -f sidekiq.jar
Creating sidekiq.jar
sidekiq $ export JDK_JAVA_OPTIONS=-Djava.net.preferIPv4Stack=true
sidekiq $ java -jar sidekiq.jar -r ./examples/por.rb             

headius

[] image_voodoo_demo $ jruby -Ilib exe/voodoo PXL_20250802_162259596.jpg 
wrote demo files to /Users/headius/work/image_voodoo_demo/PXL_20250802_162259596/
[] image_voodoo_demo $ ls PXL_20250802_162259596
border.jpg		cropped_thumb.jpg	cropped.jpg		reduced.jpg		resized.jpg		resized.png		thumb.jpg
[] image_voodoo_demo $ rm -rf PXL_20250802_162259596
[] image_voodoo_demo $ gem install warbler
Fetching warbler-2.1.0.gem
Successfully installed warbler-2.1.0
Parsing documentation for warbler-2.1.0
Installing ri documentation for warbler-2.1.0

headius

] jdk25 $ rm /Users/headius/work/jruby/lib/jruby-java25.jsa
[] jdk25 $ /Library/Java/JavaVirtualMachines/zulu-25.jdk/Contents/Home/bin/java @/Users/headius/work/jruby/bin/.jruby.java_opts @/Users/headius/work/jruby/bin/.jruby.module_opts -Xss2048k -Djffi.boot.library.path=/Users/headius/work/jruby/lib/jni -Djava.security.egd=file:/dev/urandom -XX:+AutoCreateSharedArchive -XX:SharedArchiveFile=/Users/headius/work/jruby/lib/jruby-java25.jsa --enable-native-access=org.jruby.dist --sun-misc-unsafe-memory-access=allow --module-path /Users/headius/work/jruby/lib/jruby.jar -classpath : -Djruby.home=/Users/headius/work/jruby -Djruby.lib=/Users/headius/work/jruby/lib -Djruby.script=jruby -Djruby.shell=/bin/sh -Xlog:aot,cds org.jruby.Main -e 1
[0.007s][info][cds] Specified shared archive file not found (/Users/headius/work/jruby/lib/jruby-java25.jsa)
[0.012s][info][cds] trying to map /Library/Java/JavaVirtualMachines/zulu-25.jdk/Contents/Home/lib/server/classes.jsa
[0.012s][info][cds] Opened shared archive file /Librar

headius

This is an experiment to pre-train and AOT enough of JRuby to get startup time for "gem list" down to a reasonable speed. I've tried various combintions and so far this seems to be the best, but the timings are highly variable.

Step 1: Perform a gem list while dumping IR. This saves the compiled IR for all loaded files to disk, to skip parsing and compiling in future runs.

jruby --dev -Xir.writing -S gem list > /dev/null

Step 2: Train AOT by running the following script repeatedly with the given JRuby arguments. Requires a small JRuby patch because IR reading breaks for any script has not been written (like the training script).

headius

Native Memory Tracking:

(Omitting categories weighting less than 1KB)

Total: reserved=1341322KB, committed=143578KB
       malloc: 30682KB #118112, peak=33492KB #117863
       mmap:   reserved=1310640KB, committed=112896KB

-                 Java Heap (reserved=57344KB, committed=32768KB)
                            (mmap: reserved=57344KB, committed=32768KB, at peak)

headius

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGBUS (0xa) at pc=0x0000000103e8e604, pid=4379, tid=35331
#
# JRE version: OpenJDK Runtime Environment (23.0+1) (build 23-valhalla+1-90)
# Java VM: OpenJDK 64-Bit Server VM (23-valhalla+1-90, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, bsd-aarch64)
# Problematic frame:
# V  [libjvm.dylib+0x9ce604]  SystemDictionaryShared::ArchiveInfo::lookup_lambda_proxy_class(LambdaProxyClassKey*)+0x5c
#