JRuby: Enhancing Java Developers Lives

JRuby:
Enhancing Java Developers' Lives
Hiro Asari
@hiro_asari
JRuby Support Engineer
Engine Yard
@engineyard
Wednesday, November 16, 11

JRuby: a Brief
History
Where it came from, and where it is now


History
• September 10, 2001
Source:(Wikipedia


History


History
• 10+ years old
• Led by Charles Nutter and
Tom Enebo
• 14.800+ commits


Project Status
• Current Stable Release:
1.6.5
• Compatible with Ruby
1.8.7 and 1.9.2
• Supports Rails 3.1


Getting JRuby

h0p://jruby.org/download


Trying JRuby
h0p://jruby.org/tryjruby


Book


Quick Tour of
Ruby
A brief overview of the language


Classes

public class Circle extends Shape { class Circle < Shape
private final int radius; def initialize(radius)
@radius = radius
public Circle(int radius) { end
this.radius = radius;
} attr_reader :radius
public int getRadius() {
return radius; def area
} Math::PI*(@radius **
public double getArea() { 2)
return Math.PI * Math.pow(radius,2); end
} end
public static void main(String[] a) {
double area=new Circle(2).getArea(); puts Circle.new(2).area
System.out.println(area);
}
}


Single Inheritance
Same Thing
@radius = radius
} end
}
}


Constructor

@radius = radius
} end
}
}


No Type Declarations

@radius = radius
} end
}
}


Instance Variables
‘@’ == ‘this.’ and is mandatory
@radius = radius
} end
}
}


Working with Instance Variables
Common tasks are easy
@radius = radius
} end
}
}


Symbols
:identifier

• Prefixed with a colon
• Uniquely defined in a runtime


Point of No Return
Last Expression is always return value
@radius = radius
} end
}
}


.new is just a class method

@radius = radius
} end
}
}


Blocks/Closures
• Pass an anonymous function to a method call
# Look mom...no boilerplate!
my_open(file) do |io| letters.group_by {|b| b.zip_code }
first_line = io.gets
# ...
end

def my_open(file, mode='r')
io = File.open(file)
yield io button.action_performed do
ensure exit
io.close end
end


Modules
module Enumerable class MyTree
def find(if_none = nil) include Enumerable
each { |o| return o if yield(o) }
if_none # tree impl not shown :)
end
def each
# Many other methods not shown # yield each element
# in tree
def collect end
ary = [] end
each { |o| ary << yield(o) }
ary
end
end

dude = people.find { |person| person.id == 123 }

floats = [1,2].collect { |int| int.to_f } # => [1.0, 2.0]


Everything is an Expression

class Color
COLORS = {:red => 0xff0000, :green => 0x00ff00, :blue => 0x0000ff}

COLORS.each do |name, value|
define_method(name) do
value
end
end
end


Classes/Modules are open

class MyTree
def each
#...
end
end

#... later in source
#... maybe even different file

class MyTree
def debug
#...
end
end


Pure OO Language
• Everything is an object
MyTree.foo #=> method call
12 + 8 #=> here, '+' is a method on Fixnum, 12.
12.to_s(8) #=> "14"
puts 11.odd? #=> true


JRuby on Rails
Ruby's Killer app


Java Web Frameworks

Devoxx 2010


Java Web Frameworks
h0p://j.mp/raible<jvm<frameworks

COMPARING JVM WEB
FRAMEWORKS
Matt Raible
http://raibledesigns.com

Images by Stuck in Customs - http://www.ﬂickr.com/photos/stuckincustoms
© 2010, Raible Designs
© 2010 Raible Designs


Install Rails
$ jruby -S gem install rails
Fetching: multi_json-1.0.3.gem (100%)
⋮
Fetching: bundler-1.0.21.gem (100%)
Fetching: rails-3.1.1.gem (100%)
Successfully installed multi_json-1.0.3
Successfully installed activesupport-3.1.1
⋮
Successfully installed thor-0.14.6
Successfully installed rack-ssl-1.3.2
Successfully installed json-1.6.1-java
Successfully installed rdoc-3.11
Successfully installed railties-3.1.1
Successfully installed bundler-1.0.21
Successfully installed rails-3.1.1
31 gems installed


Generate Rails app
$ jruby -S rails new awesomeapp
create
⋮
create vendor/plugins
create vendor/plugins/.gitkeep
run bundle install
Fetching source index for http://rubygems.org/
Using rake (0.9.2.2)
⋮
Using json (1.6.1)
Using rdoc (3.11)
Using thor (0.14.6)
Using railties (3.1.1)
Installing coffee-rails (3.1.1)
Installing jquery-rails (1.0.16)
Installing jruby-openssl (0.7.4)
Using rails (3.1.1)
Installing sass (3.1.10)
Installing sass-rails (3.1.4)
Installing uglifier (1.0.4)
Your bundle is complete! Use `bundle show [gemname]` to see
where a bundled gem is installed.


Rails Scaffolding
$ jruby -S rails generate scaffold person name:string
email:string
invoke active_record
create db/migrate/20111107052142_create_people.rb
create app/models/person.rb
⋮
create app/views/people/show.html.erb
create app/views/people/new.html.erb
create app/views/people/_form.html.erb
invoke test_unit
create test/functional/people_controller_test.rb
invoke helper
create app/helpers/people_helper.rb
invoke test_unit
create test/unit/helpers/people_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/people.js.coffee
invoke scss
create app/assets/stylesheets/people.css.scss
invoke scss
create app/assets/stylesheets/scaffolds.css.scss


Migrate Database
$ jruby -S rake db:migrate
== CreatePeople: migrating ====================================
-- create_table(:people)
-> 0.0040s
-> 0 rows
== CreatePeople: migrated (0.0040s) ===========================


Start Server
$ jruby -S rails server
=> Booting WEBrick
=> Rails 3.1.1 application starting in development on http://
0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2011-11-07 00:26:30] INFO WEBrick 1.3.1
[2011-11-07 00:26:30] INFO ruby 1.8.7 (2011-11-05) [java]
[2011-11-07 00:26:30] INFO WEBrick::HTTPServer#start: pid=40454
port=3000


First Page


app/controllers/people_controller.rb
class PeopleController < ApplicationController
# GET /people
# GET /people.json
def index
@people = Person.all

respond_to do |format|
format.html # index.html.erb
format.json { render :json => @people }
end
end
⋮
end


JSON out of the box


app/models/person.rb
class Person < ActiveRecord::Base
end


Rails Deployment


Rails IDE and text editors

jetbrains.com/ruby/

redcareditor.com netbeans.org

•emacs
•vi(m)
•TextMate

JRuby in Java web app
Requests

JRuby

/ /vets /rack/ Java/
Spring

App

JRuby in Java web app
diff --git a/src/main/webapp/WEB-INF/web.xml b/src/main/webapp/WEB-INF/web.xml
index 8d02684..60ed6cb 100644
--- a/src/main/webapp/WEB-INF/web.xml
+++ b/src/main/webapp/WEB-INF/web.xml
@@ -87,6 +87,21 @@
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
+
+ <listener>
+ <listener-class>org.jruby.rack.RackServletContextListener</listener-class>
+ </listener>
+
+ <servlet>
+ <servlet-name>rack</servlet-name>
+ <servlet-class>org.jruby.rack.RackServlet</servlet-class>
+ </servlet>
+
+ <servlet-mapping>
+ <servlet-name>rack</servlet-name>
+ <url-pattern>/rack/*</url-pattern>
+ </servlet-mapping>
+

<!--
Defines the 'default' servlet (usually for service static resources).

Rails in Java web app
Requests

/ /vets JRuby

/owners Java/
/ /vets /owners /1/pets Spring

App

Rails in Java web app
diff --git a/src/main/webapp/WEB-INF/web.xml b/src/main/webapp/WEB-INF/web.xml
index 60ed6cb..f64b34d 100644
--- a/src/main/webapp/WEB-INF/web.xml
+++ b/src/main/webapp/WEB-INF/web.xml
@@ -92,16 +92,6 @@
<listener-class>org.jruby.rack.RackServletContextListener</listener-class>
</listener>

- <servlet>
- <servlet-name>rack</servlet-name>
- <servlet-class>org.jruby.rack.RackServlet</servlet-class>
- </servlet>
-
- <servlet-mapping>
- <servlet-name>rack</servlet-name>
- <url-pattern>/rack/*</url-pattern>
- </servlet-mapping>
-

<!--
Defines the 'default' servlet (usually for service static resources).
@@ -162,6 +152,16 @@
<url-pattern>/</url-pattern>
</servlet-mapping>

+ <filter>
+ <filter-name>RackFilter</filter-name>
+ <filter-class>org.jruby.rack.RubyFirstRackFilter</filter-class>
+ </filter>
+
+ <filter-mapping>
+ <filter-name>RackFilter</filter-name>
+ <url-pattern>/*</url-pattern>
+ </filter-mapping>
+
<filter>
<filter-name>httpMethodFilter</filter-name>
<filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>

More…

h0p://bit.ly/refactoring<to<rails
h0p://vimeo.com/25410705


Testing Libraries
Test-Driven Development


Testing
Number of Tests Written (1000's)

100

75

50

25

Easy Hard
Ease of Writing Tests

Test files
$ jruby -S rails g scaffold person name:string email:string
invoke active_record
create db/migrate/20111107052142_create_people.rb
create app/models/person.rb
⋮
create app/views/people/show.html.erb
create app/views/people/new.html.erb
create app/views/people/_form.html.erb
invoke test_unit
create test/functional/people_controller_test.rb
invoke helper
create app/helpers/people_helper.rb
invoke test_unit
create test/unit/helpers/people_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/people.js.coffee
invoke scss
create app/assets/stylesheets/people.css.scss
invoke scss
create app/assets/stylesheets/scaffolds.css.scss


DeepThought.java
class DeepThought {
public static int answerToEverything(Object obj) {
return 42;
}

public static String getName() {
return "DeepThought";
}
}


RSpec
require 'rspec'
require 'java'

java_import 'DeepThought'

describe 'DeepThought' do
describe '.answerToEverything' do
it "should return 42, given any input" do
DeepThought.answerToEverything(nil).should == 42
DeepThought.answerToEverything(true).should == 42
end
end

describe '.getName' do
it "should return 'DeepThought'" do
DeepThought.name.should == "DeepThought"
end
end
end


RSpec
$ javac DeepThrought.java

$ jruby -rubygems deep_thought_spec.rb
..

Finished in 0.013 seconds
2 examples, 0 failures


Cucumber
Feature: AnswerToEverything
Ask DeepThought the answer to everything

Scenario: Ask a question
Given nil as input
Then the result should be 42

Feature: getName
Ask DeepThought what its name is

Scenario: get name
When asked the name
Then it answers the name as "DeepThought"


Cucumber
$ jruby -S cucumber
Feature: AnswerToEverything
Ask DeepThought the answer to everything

Scenario: Ask a question # features/answer.feature:4
Given nil as input # features/step_definitions…
Then the result should be 42 # features/step_definitions…

Feature: getName
Ask DeepThought what its name is

Scenario: get name # features/…
When asked the name # features/…
Then it answers the name as "DeepThought" # features/…

2 scenarios (2 passed)
4 steps (4 passed)
0m0.065s


JTestr
• Bridge for Java to make use of Ruby testing
• Integrates with both Ant and Maven
• Allows mocking of non-final Java class/method
• Written by Ola Bini


JTestr Example
my_project/
build.xml!
test/
test_hashmap.rb
hashmap_spec.rb
lib/
jtestr.jar
src/
<your source ;) >


JTestr in Ant
<?xml version="1.0" encoding="UTF-8"?>

<project basedir="." default="jar" name="JRuby">
<target name="test" description="Runs all tests">
<taskdef name="jtestr"
classname="org.jtestr.ant.JtestRAntRunner"
classpath="lib/jtestr.jar"/>
<jtestr/>
</target>
</project>


Ruby’s test/unit
test/test_hashmap.rb

class HashMapTests < Test::Unit::TestCase
def setup
@map = java.util.HashMap.new
end

def test_that_an_entry_can_be_added
@map.put "foo", "bar"
assert_equal "bar", @map.get("foo")
end

def test_empty_key_set_iterator_throws_exception
assert_raises(java.util.NoSuchElementException) do
@map.key_set.iterator.next
end
end
end


RSpec revisited
test/hashmap_spec.rb
require 'java'
java_import java.util.HashMap

describe "An empty", HashMap do
before :each do
@hash_map = java.util.HashMap.new
end

it "should be able to add an entry to it" do
@hash_map.put "foo", "bar"
@hash_map.get("foo").should == "bar"
end

it "should not be empty after an entry has been added to it" do
@hash_map.put "foo", "bar"
@hash_map.should_not be_empty
end

it "should be empty" do
@hash_map.should be_empty
end
end

Results
$ ant test
Buildfile: /Users/asari/Development/projects/jtestr-example/
build.xml

test:
[jtestr] Other TestUnit: 2 tests, 0 failures, 0 errors
[jtestr]
[jtestr] Other Spec: 3 examples, 0 failures, 0 errors
[jtestr]
[jtestr] Total: 5 tests, 0 failures, 0 errors, 0 pending
[jtestr]

BUILD SUCCESSFUL
Total time: 7 seconds


Ant-Rake
Integration


Problem…
NUL

Windows

dev.null

/dev/null dev_null

Un*x everything else


Ant…
<condition property="dev.null" value="/dev/null">
<os family="unix"/>
</condition>
<condition property="dev.null" value="NUL">
<os family="windows"/>
</condition>
<condition property="dev.null" value="dev_null">
<not>
<or>
<os family="unix"/>
<os family="windows"/>
</or>
</not>
</condition>


Ruby
if os.family == 'unix'
:dev_null = '/dev/null'
elsif os.family == 'windows'
:dev_null = 'NUL'
else
:dev_null = 'dev_null'
end


Ant…
<macrodef name="run-junit-1.8-short">
<attribute name="compile.mode" default="OFF"/>
<attribute name="jit.threshold" default="20"/>
<attribute name="jit.maxsize" default="1000000000"/>
<attribute name="reflection" default="false"/>
<attribute name="thread.pooling" default="false"/>
<attribute name="jvm.flags" default=""/>
⋮
</macrodef>
⋮
<target name="run-junit-compiled-short">
<run-junit-1.8-short compile.mode="JIT" jit.threshold="0"/>
</target>


Ruby
def run_junit_18_short(opts={})
compile_mode = opts[:compile_mode] || 'OFF'
jit_threshold = opts[:jit_threshold] || 20
jit_maxsize = opts[:jit_maxsize] || 1000000000
reflection = opts[:reflection] || false
thread_pooling = opts[:thread_pooling] || false
jvm_flags = opts[:jvm_flags] || ""
⋮
end

def run_junit_compiled_short
run_junit_18_short :compile_mode => 'JIT', :jit_threshold => 0
end


Ant tasks from Rake
<path id="build.classpath">
<fileset dir="${build.lib.dir}" includes="*.jar"/>
</path>

<path id="jruby.execute.classpath">
<path refid="build.classpath"/>
<pathelement path="${jruby.classes.dir}"/>
</path>

task :initialize_paths do
ant.path(:id => "build.classpath") do
fileset :dir => BUILD_LIB_DIR, :includes => "*.jar"
end

ant.path(:id => "jruby.execute.classpath") do
path :refid => "build.classpath"
pathelement :path => JRUBY_CLASSES_DIR
end
end


Rake tasks as Ant targets
<project name="foobar" default="top-level" basedir=".">
<description>Builds, tests, and runs foobar.</description>

<taskdef name="rakeimport"
classname="org.jruby.ant.RakeImport"/>
<rakeimport/>

<target name="top-level" depends="its_in_rake" />

<target name="its_in_ant">
<echo message="ant: its_in_ant"/>

build.xml
</target>
</project>

task :its_in_rake => [:setup, :its_in_ant] do
puts "it's in Rake"
end

task :setup do
puts "setup in Rake"
end Rakefile


<rakeimport/>



build.xml
</target>
</project>

puts "it's in Rake"
end

task :setup do
end



<rakeimport/>


</target>
</project>

puts "it's in Rake"
end

task :setup do
end Rakefile


<rakeimport/>


</target>
</project>

puts "it's in Rake"
end

task :setup do
end


Buildfile: build.xml
[rakeimport] (in /tmp/example2)

<taskdef name="rakeimport" setup:
<rakeimport/>


</target>
</project>

puts "it's in Rake"
end

task :setup do
end



setup in Rake
<rakeimport/>


</target>
</project>

puts "it's in Rake"
end

task :setup do
end



setup in Rake
<rakeimport/>
its_in_ant:

</target>
</project>

puts "it's in Rake"
end

task :setup do
end



setup in Rake
<rakeimport/>
its_in_ant:
<target name="top-level" depends="its_in_rake" ant: its_in_ant
[echo] />

</target>
</project>

puts "it's in Rake"
end

task :setup do
end



setup in Rake
<rakeimport/>
its_in_ant:
[echo] />

<target name="its_in_ant"> its_in_rake:
</target>
</project>

puts "it's in Rake"
end

task :setup do
end



setup in Rake
<rakeimport/>
its_in_ant:
[echo] />

it's in Rake
</target>
</project>

puts "it's in Rake"
end

task :setup do
end



setup in Rake
<rakeimport/>
its_in_ant:
[echo] />

it's in Rake
</target>
</project> top-level:

BUILD SUCCESSFUL
task :its_in_rake => [:setup, :its_in_ant] time: 7 seconds
Total do
puts "it's in Rake"
end

task :setup do
end


More…

http://bit.ly/rake_ant


Maven and
RubyGems


JRuby via Maven
• Group ID: org.jruby
• Artifact IDs: jruby, jruby-complete
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.jruby</groupId>
<artifactId>jruby</artifactId>
<version>1.6.5</version>
</dependency>
</dependencies>


Maven artifacts as gems
jruby -S gem install mvn:org.clojure:clojure

maven



group ID



artifact ID



Successfully installed mvn:org.clojure:clojure-1.4.0.a.2-java
1 gem installed

Some restrictions apply


$ jruby -S irb
irb(main):001:0> require 'mvn:org.clojure:clojure'
=> true
irb(main):002:0> java_import Java::clojure.lang.PersistentHashMap
=> Java::ClojureLang::PersistentHashMap
irb(main):003:0> phm = PersistentHashMap.create({:a => 100, :b =>
200, :c => 300})
=> {:c=>300, :a=>100, :b=>200}
irb(main):004:0> phm.delete_if {|k,v| k == :b}
Java::JavaLang::UnsupportedOperationException:
from clojure.lang.APersistentMap.remove(APersistentMap.java:273)
from org.jruby.java.proxies.MapJavaProxy
$RubyHashMap.internalDelete(MapJavaProxy.java:154)
from org.jruby.RubyHash.delete(RubyHash.java:1407)
from org.jruby.RubyHash$22.visit(RubyHash.java:1464)
from org.jruby.java.proxies.MapJavaProxy
$RubyHashMap.visitAll(MapJavaProxy.java:182)
⋮


Foreign Function
Interface
Calling native functions


Gamma function

∞
Γ(z) = ∫ t
0
z-1e-1 dt


Apache Commons?
org.apache.commons.math.special
Class Gamma
java.lang.Object
org.apache.commons.math.special.Gamma

public class Gamma
extends java.lang.Object
This is a utility class that provides computation methods related
to the Gamma family of functions.

Version:
$Id: Gamma.java 1131229 2011-06-03 20:49:25Z luc $


Apache Commons?
org.apache.commons.math.special
Class Gamma

ize
?
java.lang.Object

e
org.apache.commons.math.special.Gamma

s

Rs
public class Gamma
en
extends java.lang.Object
Lic
This is a utility class that provides computation methods related

JA
to the Gamma family of functions.

Version:
$Id: Gamma.java 1131229 2011-06-03 20:49:25Z luc $


for the coe cients in the series and estimate the error. After the
Read academic paper
our new formula with some classical results. The numerical comp
equal number of ’correction’ terms the new formula is the most acc
recommended for computing the Gamma function for large real arg

Theorem 1. Let x 1, unction every n
then for 1, the following express
( x) f
or the !!x r
sion f n 1
X Gk 2⇡
expan x
ptotic (x) = + Rn (x)
1
Neme
s ,
New asym G ˝
ergo e x2k x
8
er 7, 200 05
k=0
ecemb t h08.0
D sl2ma
7/
0.324
wherex.don.o = O
d
R i (x) rg/1 1
x2n
and the Gk coe cients are given by
-
// ap
http: otic series ter
ract
re as ympt with bet -
Abst
, St
-De Moiv a new one se of Stir
irling erted into X wit h tho nd turns Y 1 ✓
k
B2r
◆mr
ation n is conv pared than 0.5 a rior to
sform G = io k com
s tran ma funct formula is ts greater ically sup ed up
e ,
U
serie m n
sing a to the Ga The new al argume rms, num on has tu maxi-
er rn m ! 2r (2r 1)r
atio n ertie s. for re n’ te m1 ,m2 ,...,msk( 0 al
ima ti ing’
r=1
p roxim nce prop amanujan ’correctio 2m p+4mer+...+2kmu =2k p rox rd Stirl r or eq
e f rm a 1 e
co nverg lace and R number o closed-fo d as 3rd o nts great to which 2 k
Lap ual t, a goo ume e [7]
ling, be, for eq side beneﬁ about as al arg n older on
or re
o ut to em. As a ich is an 1e-10 f ersion th of a
where B denotes the r
th si
all of the analy r rmall
g o
s wh er th
s ne xtend
ed v Bernoulli number [4]. Moreover, if x n
durin elative err article is a mainder.
r s e
mum Note: thi te of the r !
). a
to 10 the estim
8e1/5 the ⇣ n ⌘2
adds n for a
it
|Rn (x)|  mptot+expxpeci+ormu ed
(n ic 1) li t f ansio l
2n
n w as y an e mnr(2n
pa 1) (2⇡) x
uctio nt a n
e e give of, we co for
Introd se
pre
ct, we ual than
one.
W ro
the p n shows
tha t
hly
1 esult
nr a
abstr r or eq . After pariso is hig
Wednesday, November 16, 11 1 i
e ma in the ate error com and i
t

…and implement
if (Double.isNaN(x)) {
value = Double.NaN;
return;
}

double int_part = (int) x;
sign = (int_part % 2 == 0 && (x - int_part) != 0.0 && (x < 0)) ? -1 : 1

!
if ((x - int_part) == 0.0 && 0 < int_part && int_part <= FACTORIAL.leng
value = Math.log(FACTORIAL[(int) int_part - 1]);

d
}

r
else if (x < 10) {
double rising_factorial = 1;

a
for (int i = 0; i < (int) Math.abs(x) - int_part + 10; i++) {
rising_factorial *= (x + i);

H
}
NemesLogGamma l = new NemesLogGamma(x + (int) Math.abs(x) - int_par
value = l.value - Math.log(Math.abs(rising_factorial));
} else {
double temp = 0.0;
for (int i = 0; i < NEMES_GAMMA_COEFF.length; i++) {
temp += NEMES_GAMMA_COEFF[i] * 1.0 / Math.pow(x, i);
}

value = x * (Math.log(x) - 1 + Math.log(temp)) +
(Math.log(2) + Math.log(Math.PI) - Math.log(x)) / 2.0;
}


man…
man gamma


Not reinventing the wheel
TGAMMA(3) BSD Library Functions Manual TGAMMA(3)

NAME
tgamma, lgamma, gamma -- gamma and log of gamma

SYNOPSIS
#include <math.h>

double
tgamma(double x);
⋮

DESCRIPTION
tgamma() calculates the gamma function of x. lgamma()
calculates the natural logorithm of the absolute value of the
gamma function of x. gamma() is the same function as tgamma.
Its use is deprecated.

⋮


JNI Workflow
javah
Example.java Example.h

cc
gamma.c libgamma.dylib
javac

Example.class

$ java Example


Example.java
import java.util.*;

class Example {
native static double gamma(double x);

static {
System.loadLibrary("gamma");
}

public static void main(String args[]) {
System.out.println(gamma(0.5));
}
}


Example.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Example */

#ifndef _Included_Example
#define _Included_Example
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Example
* Method: gamma
* Signature: (D)D
*/
JNIEXPORT jdouble JNICALL Java_Example_gamma
(JNIEnv *, jclass, jdouble);

#ifdef __cplusplus
}
#endif
#endif


gamma.c
#include "Example.h"
#include <math.h>

JNIEXPORT jdouble JNICALL Java_Example_gamma(JNIEnv* env,
jclass jclass, jdouble jdbl) {
return tgamma(jdbl);
}


Voilà!
$ javah Example.java
$ javac Example.java
$ gcc -shared gamma.c -o libgamma.dylib
-I /Library/Java/JavaVirtualMachines/1.6.0_29-b11-397.jdk/
Contents/Headers/

$ java Example
1.772453850905516


gamma.rb
require 'ffi'

module Gamma
extend FFI::Library
ffi_lib FFI::Library::LIBC
attach_function :tgamma, [:double], :double
end

puts Gamma::tgamma(0.5)


Same result*!
$ jruby gamma.rb
1.77245385090552

$ jruby --1.9 -e 'p Math::gamma(0.5)'
1.77245385090552


Benchmark
$ jruby --1.9 bench_gamma.rb
Rehearsal
----------------------------------------------------------------
pure_java 3.432000 0.000000 3.432000
( 3.432000)
JNI 0.409000 0.000000 0.409000
( 0.409000)
FFI 0.281000 0.000000 0.281000
( 0.281000)
-------------------------------------------------------- total:
4.122000sec

user system total
real
pure_java 2.849000 0.000000 2.849000
( 2.849000)
JNI 0.288000 0.000000 0.288000
( 0.289000)
FFI 0.219000 0.000000 0.219000
( 0.219000)


But…

d y?
I n
ut
a b o
ha t
W
h0p://www.ﬂickr.com/photos/evablue/5665409533/


Invokedynamic!
• Only mainstream
alternative JVM language
• Worked closely with
Hotspot team
• JRuby master/1.7
• Waiting for Java 1.7.0u2
release
• What does it mean for
you?


Benchmark
Times faster than Ruby 1.9.3
16
14.2x

12

8 7.4x

5.5x
4.4x
4 2.7x
3.6x 3.5x 3.2x
1.7x 1.8x 1.6x 1.9x

0
fib +calls +consts +both richardsredblack
JRuby on Java 6
JRuby on invokedynamic

Benchmark
0.300

0.225

0.150

0.075

0
currentTimeMillis Thread#name
No indy With indy

Indy TODOs
• Remaining invocation paths
–varargs, super, all Java paths
• Per-type specialization
–Faster block-receiving calls
–Faster module methods
• More code in Ruby!


Thank you!
• Twitter: @hiro_asari
• Github: BanzaiMan
– Code examples:
• jtestr-example
• jni-gamma
• test_example_deepthought
• http://github.com/jruby/jruby

http://www.engineyard.com/tryjruby

References
• http://ruby-lang.org
• http://jruby.org
• http://pragprog.com/book/jruby/using-jruby
• http://rubyonrails.org
• http://torquebox.org
• http://tomcat.apache.org
• http://jetty.codehause.org
• http://glassfish.java.net
• https://www.relishapp.com/rspec
• http://cukes.info

References
• http://jtestr.codehaus.org/
• http://www.ebyte.it/library/docs/math07/
GammaApproximation.html
• http://download.oracle.com/javase/6/docs/
technotes/guides/jni/
• http://jcp.org/en/jsr/detail?id=292


JRuby: Enhancing Java Developers Lives

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