Hi Jochen,
On 06/01/2016 05:46 PM, Jochen Theodorou wrote:
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.
Ah, sorry to hear there are other obstacles...
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.
No, for obtaining reflection objects you don't need language access
rights. You need security permissions if security manager is installed,
but that's independent of language access checks. Language access checks
are performed when you call Method::invoke or Field::get, etc... or when
you do Lookup::unreflect, but the later is performed against the "caller
class" that is captured inside the Lookup object.
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.
So you can use normal Class.getDeclaredMethods() and choose among them
for yourself. When you have resolved THE Method, you call
Lookup::unreflect with it and decorate the resulting MH with needed
transformations.
bye Jochen
Regards, Peter
