JRuby Embed (Red Bridge) Gotchas: on jirb

I haven't used like that before, but there are people who want to use JRuby Embed API on jirb. I fixed a bug, http://jira.codehaus.org/browse/JRUBY-4521, and tried what I could do on jirb.

At first, I instantiated ScriptingContainer and checked what initial parameters were set.

irb(main):001:0> require 'java'
=> true
irb(main):002:0> container = org.jruby.embed.ScriptingContainer.new
=> org.jruby.embed.ScriptingContainer@ea7549
irb(main):003:0> p container.get_home_directory                    
"/Users/yoko/DevSpace/jruby~main"
=> nil
irb(main):004:0> p container.load_paths
[/Users/yoko/DevSpace/jruby~main/lib/profile.jar, /Users/yoko/NetBeansProjects/cirrus/build/classes]
=> nil
irb(main):005:0> p container.class_loader
org.jruby.util.JRubyClassLoader@5e2075
=> nil
irb(main):006:0> p container.current_directory
"/Users/yoko/NetBeansProjects/cirrus"
=> nil
irb(main):007:0> p container.compat_version
RUBY1_8
=> nil
irb(main):008:0> p container.supported_ruby_version
"jruby 1.5.0.dev (ruby 1.8.7 patchlevel 174) (2010-02-02 0505fb1) (Java HotSpot(TM) Client VM 1.5.0_22) [i386-java]"
=> nil

Hmmm.... interesting. Of course, no compilation at all. Perhaps, ScriptingContainer's API is useful to see jirb internal settings.

Then, how evaluations go?

irb(main):009:0> script = "puts \"Hello World\""
=> "puts \"Hello World\""
irb(main):010:0> container.run_scriptlet(script)
Hello World
=> nil
irb(main):011:0> message = "Hi, there!"
=> "Hi, there!"
irb(main):012:0> container.put("message", message)
=> nil
irb(main):013:0> container.run_scriptlet("puts \"message: #{message}\"")
message: Hi, there!
=> nil

OK, evaluations as well as sharing variables between Java(?) (or jirb?) and Ruby seem to work.
How about method call?

irb(main):014:0> script = "def say\nputs \"oh!\"\nend"
=> "def say\nputs \"oh!\"\nend"
irb(main):015:0> recv = container.run_scriptlet(script)
=> nil
irb(main):016:0> container.call_method(recv, "say", java.lang.Object.class)
:1:in `say': wrong # of arguments(1 for 0) (ArgumentError)
 from :1
NativeException: org.jruby.embed.InvokeFailedException: wrong # of arguments(1 for 0)
 from org/jruby/embed/internal/EmbedRubyObjectAdapterImpl.java:387:in `call'
 from org/jruby/embed/internal/EmbedRubyObjectAdapterImpl.java:326:in `callMethod'
 from org/jruby/embed/ScriptingContainer.java:1268:in `callMethod'
 from :1

No, it failed. This is because jirb chose "public Object callMethod(Object receiver, String methodName, Object... args)" for callMethod. Unfortunately, in this case, Ruby doesn't know the difference of several callMethod methods.
Ok, then, no argument for "say" method. Will it work?

irb(main):017:0> container.call_method(recv, "say")                        
CallableSelector.java:196:in `assignableOrDuckable': java.lang.ArrayIndexOutOfBoundsException: 2
 from CallableSelector.java:22:in `access$200'
 from CallableSelector.java:163:in `accept'
 from CallableSelector.java:101:in `findCallable'
 from CallableSelector.java:86:in `findMatchingCallableForArgs'
 from CallableSelector.java:39:in `matchingCallableArityN'
 from RubyToJavaInvoker.java:170:in `findCallable'
 from InstanceMethodInvoker.java:29:in `call'
 from InstanceMethodInvoker.java:67:in `call'
 from AliasMethod.java:66:in `call'
 from CachingCallSite.java:329:in `cacheAndCall'
...
...

Oh dear, jirb was blown up.

So far, ScriptingContainer on jirb doesn't work enough but might be fun for quick hack.

........

Wrap this up.

We have java_send method and can specify exact Java method by its argument, but this also didn't work well. When I tried to run "volume" method of this Ruby code:

def volume(r)
  4.0 / 3.0 * Math::PI * r ** 3.0
end

irb(main):008:0> ret = container.run_scriptlet(org.jruby.embed.PathType::CLASSPATH, "ruby/sphere.rb")
=> nil
irb(main):009:0> container.java_send :callMethod, [java.lang.Object, java.lang.String, java.lang.Class], self, "volume", java.lang.Integer.new(3)
TypeError: for method ScriptingContainer.callMethod expected [class java.lang.Object, class java.lang.String, class java.lang.Class]; got: [org.jruby.RubyObject,java.lang.String,java.lang.Integer]; error: argument type mismatch
 from :1

like in the above, I got TypeError. A receiver object was the problem. Java program could cast java.lang.RubyObject to java.lang.Object, but jirb could not.

........

Wrap up, part 2.

While testing ScriptingContainer on jirb, I found a bug. Singleton model didn't see the same RubyInstanceConfig when Ruby runtime had already instantiated preceding ScriptingContainer. After the fix, some of runtime configurations can be changed through ScriptingContainer's methods. For example, I could change Ruby version to be used. The Ruby code below uses a block local variable introduced in Ruby 1.9.

# This snippet is borrowed from http://gihyo.jp/dev/serial/01/ruby/0003
# defines local variable x
x = "bear"

# A block local variable x is used in this block. (Two "x"s work together)
["dog", "cat", "panda"].each do |x|
  # This x is a block local variable.
  p x
  break if x == "cat"
end

# This x is a local variable since it is used outside of the block.
p x

When I tried this code by setting both Ruby 1.8 and 1.9, I got appropriate outputs for both mode on jirb.

irb(main):001:0> require 'java'
=> true
irb(main):002:0> container = org.jruby.embed.ScriptingContainer.new
=> org.jruby.embed.ScriptingContainer@ea7549
irb(main):003:0> container.compat_version
=> RUBY1_8
irb(main):004:0> container.run_scriptlet(org.jruby.embed.PathType::CLASSPATH, "ruby/block-param-scope.rb")
"dog"
"cat"
"cat"
=> nil
irb(main):005:0> container.set_compat_version(org.jruby.CompatVersion::RUBY1_9)
=> nil
irb(main):006:0> container.compat_version
=> RUBY1_9
irb(main):007:0> container.run_scriptlet(org.jruby.embed.PathType::CLASSPATH, "ruby/block-param-scope.rb")
"dog"
"cat"
"bear"
=> nil

So, again, SciprtingContainer on jirb is interesting. :)