1. InvokeDynamic
Java 7 dynamically typed language support
arkadi.shishlov@gmail.com

3. Statically typed languages
Java
Scala
C#
C
C++
F#
Haskel

4. Dynamic languages
Groovy
Clojure
JavaScript
Perl
Python
Ruby
PHP

5. Dynamic language
object runtime alteration (open program code)
metaobject protocol
eval
functional programming, closures, macros

6. Dynamically typed language
type checking performed at runtime
variable does not have a type
value is associated with a type
duck typing

7. The program must be compiled
to bytecode to achieve Java
level performance

8. Use case
groovy:000> f = { it + it }
===> groovysh_evaluate$_run_closure1@dc737be
groovy:000> f(1)
===> 2
groovy:000> f("qw")
===> qwqw
groovy:000> [2, "qwe"].collect(f)
===> [4, qweqwe]
groovy:000>

9. collect (list, func) {
foreach (list)
push (result, func (it))
}

10. The problem
invokevirtual
some/class/Name.func(Ljava/lang/String)Z,
objectref,
arg1, arg2, ...
invokespecial
invokestatic has similar calling convention
invokeinterface

11. The solution
Reflection is (relatively) slow
There are others possibilities

12. Java 7 approach - JSR292
invokedynamic (indy)
boostrapFuncRef,
NameLiteral(Lorg/jruby/runtime/builtin/IRubyObject)
Lorg/jruby/runtime/builtin/IRubyObject,
arg1, arg2, ...

13. java.lang.invoke.*
MethodHandle
CallSite
ConstantCallSite
MutableCallSite
VolatileCallSite
MethodType

14. public static CallSite bootstrap (
MethodHandles.Lookup lookup,
String dynMethodName,
MethodType dynMethodType) throws Throwable {
MethodHandle handle = lookup.findStatic(
SomeClosure.class,
"func",
MethodType.methodType(
Integer.class, Object.class, Object.class));
if (!dynMethodType.equals(handle.type()))
handle = handle.asType(dynMethodType);
return new ConstantCallSite(handle);
}

15. MutableCallSite.setTarget(MethodHandle newTarget)

16. Advantages
fast
JIT-ted
inlined
signature polymorphism, arguments adaptation

19. Work in Progress
JRuby - works, sort of; Mirah
Rhino (JavaScript) - J.Rose experiment, V8 for
performance freaks
Groovy - proposed for 1.9, no impl
Jython (Python) - different priorities: PyPy, Cython,
language features upgrade
Clojure - many features not applicable to Indy
PHP.reboot

20. Learn more
http://download.java.net/jdk7/docs/technotes/guides/vm/multiple-language-support.html
JDK 7 JSR-292 java.lang.invoke.* API
JRuby source: src/org/jruby/compiler/impl/*.java
http://code.google.com/p/jsr292-cookbook/
http://mail.openjdk.java.net/pipermail/mlvm-dev/
http://www.oracle.com/technetwork/issue-archive/2010/10-may/o30java-099612.html
http://blog.headius.com/2008/09/first-taste-of-invokedynamic.html