question on exports to

[Jochen Theodorou]

On 01.06.2016 14:43, Peter Levart wrote:
[...]
> I also don't wish to cause further confusion, but I have a feeling that
> Jochen might have the following situation:
>
> - MyOtherLib contains classes and code that is using these classes
> (invoking their methods), but it wishes to call those methods via an
> indirection through a GeneralInvoker that happens to live in another module
> - MyOtherLib is also using classes (invoking methods) from other modules
> that it already has direct access to, but it wishes to call those
> methods via an indirection through a GeneralInvoker too

in the end I am trying to figure out step-by-step what I have to do for 
the Groovy runtime to make it fully module compatible. That job is 
similar to what is to be done for Nashorn or JRuby.

In Groovy we have 2 callsite caching mechanisms, one is based on 
invokedynamic, the other is using reflection and runtime class 
generation. At least the later one will have to change a lot... up to 
the point that I am wondering if we should not ditch it... which again 
is difficult, because legacy code will still use it. Replacing the old 
code to do internally MethodHandles might be an option though.. but then 
again, the old API does not provide me with a Lookup object... which is 
where things fall apart again.

Anyway... the groovy runtime would be almost something like java.base, 
but instead of being like a root element, this one will have to sit in 
the middle, because we depend on java as well.

> If that is true, then perhaps there is a simpler solution that doesn't
> require modifying the exports of any module.
>
> Make your TheInvoker take another argument of type MethodHandles.Lookup:
>
> public class TheInvoker{
>      public static Object invoke(MethodHandles.Lookup lookup, Object
> receiver, String name, Object... args) throws Throwable {
>          Method m = receiver.getClass().getDeclaredMethod(name,
> toClass(args));
>          MethodHandle mh = lookup.unreflect(m).bindTo(receiver);
>          return mh.invokeWithArguments(args);
>      }
> ...
> }
>
> Then pass the appropriate lookup to it from where you call
> TheInvoker.invoke (from MyOtherLib):
>
> TheInvoker.invoke(MethodHandles.lookup(), receiver, "methodName",
> arguments...);

receiver.getClass().getDeclaredMethod would fail, if I cannot access the 
class of the receiver. So if "MyOtherLib is also using classes (invoking 
methods) from other modules that it already has direct access to, but it 
wishes to call those methods via an indirection through a GeneralInvoker 
too", then this will fail without further precautions.

In theory Lookup#findvirtual could be used in my example, but in the 
real code I will most probably have to get all methods of that name, to 
then filter the most fitting one, considering the argument types, as 
well as potentially transforming arguments. And Lookup does not provide 
me anything like MethodHandle[] for a given name.

bye Jochen