need little help for class loading & invokeDynamics

[Rémi Forax]

On 01/14/2011 09:59 AM, Marvin Hansen wrote:
> Thansk you Rene,

I think i prefer Rémi or Rémy.

run is declared (int,int,String) and you lookup (int,String,int).

Also the line:
   methodHandle.invokeWithArguments(21, "+", 21);
will raise a runtime exception because you forget to pass an instance of 
SimpleMath
as first argument (run is not static).

Rémi

> visibility is not an issue, since both class&  method are declared
> public and a normal static call works just fine. I'm sorry
> I've forgotten to add the simpleMath source but for the sake of
> completeness I've copied the class
> at the bottom of the mail.
>
> However, it looks much more that I've run into the problem that java
> cannot directly emit invokedynamic.
> I understant that the main purpose for invokedynamic was and still is
> the support of dynamic languages but
> this limitation seams arbitrary for me. Is there any intention to
> change it or is that the way invokedynamic should
> be released?
>
> Anyway, thanks for the link I will read it carefully and hopefully I
> will find a work-around to do an
> invokedynamic call from my loaded class.
>
> Thanks for your helpful advice;
>
>
>
>
>
> public class SimpleMath {
>
>      public SimpleMath() {
>      }
>
>      /**
>       * @param a
>       * @param b
>       * @param op
>       * @return int
>       */
>      public int run(int a, int b, String op) {
>
>          int returnvalue = calculate(a, b, op);
>
>          return returnvalue;
>      }
>
>
>      private int calculate(int a, int b, String op) {
>
>          int ret = null;
>
>              switch (op) {
>                  case "+":
>                      ret = a + b;
>                      break;
>                  case "-":
>                      ret = a - b;
>                      break;
>                  case "/":
>                      ret = a / b;
>                      break;
>                  case "*":
>                      ret = a * b;
>                      break;
>                  default:
>                      System.err.println("No valid paramter given. Use
> only :  '+' ; '-' ; '/' ; '*' (String)
>                                                    as operator and
> interger as numbers");
>                      break;
>              }
> }
>
>
>
> http://www.marvin-hansen.tel
>
>
>
>
> On 14 January 2011 21:04, Rémi Forax<forax at univ-mlv.fr>  wrote:
>> On 01/14/2011 06:15 AM, Marvin Hansen wrote:
>>> Hi Folks,
>>>
>>> I've started to work on invokeDynamics but I need a little help to
>>> understand how to use it right. For learning purpose, I've written a
>>> little class, that loads another class, does the method look-up and
>>> (should) execute the located method. The example in the methodHandle
>>> JavaDoc was my starting point but as usual it's not that easy since it
>>> works well for JDK classes but not with loading my own class which
>>> causes a “NoAccessException”.
>>>
>>> I suppose that I need to deal with CallSite&    Bootstraping but I've
>>> not yet figured out how to patch class-loading, methodHandle,
>>> Bootstraping&    invocation together in order to make it work. The
>>> JavaDoc says, that before an invokedynamic instruction can be executed
>>> a CallSite must be linked  via boostrap method that produces a
>>> methodHandle. That makes sense for me.
>>>
>>> However, the CallSite JavaDoc is a little bit short on illustrating
>>> how to use it together with class-loading.
>>> The given example bootstrap Method:
>>>
>>> private static CallSite bootstrapDynamic(MethodHandles.Lookup caller,
>>> String name, MethodType type) {
>>>     // ignore caller and name, but match the type:
>>>     return new ConstantCallSite(MethodHandles.collectArguments(printArgs, type));
>>> }
>>>
>>> looks fine but this method is neither used nor linked or registered
>>> in the sample code of the JavaDoc so here are my related questions:
>>>
>>> 1) What is needed in a bootstrap method to produce a working callSite
>>> for a loaded class?
>>>
>>> 2) How is the bootstrap method linked to  an invokedynamic instruction?
>>> The spec does not have the @BootstrapMethod anymore so what's the
>>> current way of linking?
>> The bootstrap method is know encoded as argument of the invokedynamic
>> instruction.
>> So each invokedynamic can have its own bootstrap method.
>>
>> The main problem is that there is no way currently to emit an
>> invokedynamic in Java,
>> see
>> http://weblogs.java.net/blog/forax/archive/2011/01/07/call-invokedynamic-java
>>
>>> 3) Should the class-loading be done by the bootstrap method or  is it
>>> fine to do it before?
>> Fine to do it before.
>>
>>> I really appriciate any input, since I'm new to InvokeDynamics and not
>>> familiar with all concepts.
>>>
>>> marvin
>> Rémi
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