JRuby, Windows, and C Extensions

You've found a really useful RubyGem but can't use it on your JRuby Windows machine because it's a native C extension. And yes, it's only available in source. And if you did get it to compile, you'd slam face first into the well-known fact that JRuby doesn't work with native RubyGems.

Fahrvergn├╝gen!

"No problem, I'll just port it to Java" says your always-optimistic-but-clueless other self. "Great, another one-off to support" you mutter as reality saunters back into view.

Just about to call it quits, you find this post about some cool Ruby Summer of Code work by Tim Felgentreff. Oddly, you stumble upon the DevKit toolchain for Windows systems, it falls into place, and everything begins to look a little brighter.

But why would anyone do that? Well, one of the JRuby guys has a few words on the matter.

Always the sceptic realist, you decide to see how The Pipe Dream works out with a few of the well-known native RubyGems from the ether.

Turns out, it's as easy as:

  1. Clone JRuby's GitHub repository
  2. Download and install the DevKit
  3. Build JRuby with C extension support
  4. RubyGem install-o-rama!
  5. Smoke test the RubyGems

Cloning JRuby's Repository

Using your existing msysgit installation, type

C:\>git clone git://github.com/jruby/jruby.git jruby-dev
Cloning into jruby-dev...
done.

C:\>

Installing the DevKit

First, download the DevKit and install it to a directory without spaces, say C:\DevKit. Next, run the following after you've updated the DevKit's config.yml file to point to the JRuby repository you just cloned. For more detailed instructions check out the DevKit installation and DevKit upgrade wiki pages.

C:\DevKit>type config.yml
# ...SNIP...
#
---
- C:/jruby-dev

C:\DevKit>ruby dk.rb install
[INFO] Installing 'C:/jruby-dev/lib/ruby/site_ruby/1.8/rubygems/defaults/operating_system.rb'
[INFO] Installing 'C:/jruby-dev/lib/ruby/site_ruby/shared/devkit.rb'

C:\DevKit>

Building JRuby with C Extension Support

Make sure you've setup your Ant+JDK build environment correctly, bring the DevKit's build tools and git onto PATH, and build JRuby via

C:\DevKit>devkitvars
Adding the DevKit to PATH...

C:\DevKit>cd \jruby-dev

C:\jruby-dev>echo %PATH%
C:\DevKit\bin;C:\DevKit\mingw\bin;C:\git\cmd;C:\ant\bin;C:\Program Files\Java\jdk1.6.0_22\bin;
C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem

C:\jruby-dev>ant clean jar cext
...SNIP...
cext:

BUILD SUCCESSFUL
Total time: 2 minutes 5 seconds
C:\jruby-dev>

Installing Some RubyGems

Ensure your setup is correct by opening a new shell, adding your newly built JRuby to PATH, and running a quick smoke test via

C:\>echo %PATH%
C:\jruby-dev\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem

C:\>jruby --version
jruby 1.6.0.dev (ruby 1.8.7 patchlevel 249) (2010-11-30 88ad204) (Java HotSpot(TM)
Client VM 1.6.0_22) [Windows 7-x86-java]

C:\>jruby -e "puts 'Hello from Ruby-on-%s' % RUBY_PLATFORM.capitalize"
Hello from Ruby-on-Java

C:\>jruby -S gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.7
  - RUBY VERSION: 1.8.7 (2010-11-30 patchlevel 249) [java]
  - INSTALLATION DIRECTORY: C:/jruby-dev/lib/ruby/gems/1.8
  - RUBY EXECUTABLE: C:/jruby-dev/bin/jruby.exe
  - EXECUTABLE DIRECTORY: C:/jruby-dev/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - universal-java-1.6
  - GEM PATHS:
     - C:/jruby-dev/lib/ruby/gems/1.8
     - C:/Users/Jon/.gem/jruby/1.8

  ...SNIP...

C:\>

Now, let's install the rdiscount and curb gems.

rdiscount is simple enough, but to install curb you need to have already installed curl's header and library development artifacts. As the DevKit is based upon MinGW, a great place to get these development artifacts is from Guenter Knauf who distributes Curl's Windows binaries. Thank him when you get a moment.

Although I use jruby -S gem you can also use just gem if the JRuby bindir is the only (or first) Ruby on your PATH. Note, the --platform=ruby option forces RubyGems to attempt to build the native gem rather than trying to install a gem specifically built for JRuby. For example, EventMachine has a Java specific gem in addition other platform specific gems and a source gem. But that is a topic for a future post.

Moving on...

C:\>jruby -S gem install rdiscount --platform=ruby
JRuby limited openssl loaded. http://jruby.org/openssl
gem install jruby-openssl for full support.
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
Successfully installed rdiscount-1.6.5
1 gem installed

C:\>jruby -S gem install curb --platform=ruby -- --with-curl-lib="c:/curl/bin" --with-curl-include="c:/curl/include"
JRuby limited openssl loaded. http://jruby.org/openssl
gem install jruby-openssl for full support.
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
Successfully installed curb-0.7.8
1 gem installed

C:\>jruby -S gem list

*** LOCAL GEMS ***

curb (0.7.8)
rdiscount (1.6.5)
sources (0.0.1)

C:\>

Smoke Test the RubyGems

Make sure the directory you used with --with-curl-lib containing the curl DLL is on PATH.

C:\>jruby -rubygems -e "require 'rdiscount'; puts RDiscount.new('**Hello JRuby**').to_html"
calling init (63288dd6)
<p><strong>Hello JRuby</strong></p>

C:\>type curbee.rb
require 'rubygems'
require 'curb'

c = Curl::Easy.perform("http://www.google.com")
puts 'URL: %s' % c.url
puts 'IP: %s' % c.primary_ip
puts 'Request Size: %s' % c.request_size

C:\>jruby curbee.rb
calling init (63fc1560)
URL: http://www.google.com
IP: 72.14.204.103
Request Size: 53

C:\>

Yeh!

Conclusion

So what does it all mean? Simply put, a wider spectrum of code reuse options for you as both a developer and user of JRuby on Windows.

One of the more interesting options is the ability to defer, perhaps completely, custom development by enabling you to focus your limited resources on the areas of your product in which you add real value, thereby getting you to 'go-live' faster. For me, JRuby's C extension support is a compelling code reuse and aggregation technology that enhances JRuby's existing integration capabilities.

From that perspective, take another read of both Tim and Charles posts.

Future Post Spoiler

Is it really always this easy? Well, most of the times yes, but sometimes no. There are a few caveats, but they're for a future post. For example, why is the first "failure" not really a failure?

C:\>jruby -S gem install eventmachine --platform=ruby --pre
JRuby limited openssl loaded. http://jruby.org/openssl
gem install jruby-openssl for full support.
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing eventmachine:
        ERROR: Failed to build gem native extension.

...SNIP...

cmain.cpp:752:20: error: 'fstat' was not declared in this scope
g++.exe: unrecognized option '-EHs'
g++.exe: unrecognized option '-GR'
make: *** [cmain.o] Error 1

C:\>jruby -s gem install eventmachine --pre
JRuby limited openssl loaded. http://jruby.org/openssl
gem install jruby-openssl for full support.
Successfully installed eventmachine-1.0.0.beta.2-java
1 gem installed

C:\>
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