The curious case of MHS.Lookup.unreflect on MethodHandle.invoke/invokeExact

[Vladimir Ivanov]

Paul,
> A call to the following:
>
>    Object o = rmh.invokeExact((MethodHandle) null, new Object[]{});
>
> Will result in a:
>
>    java.lang.UnsupportedOperationException: cannot reflectively invoke MethodHandle
>
> However, the stack trace corresponds to the stack where the call to "unreflect" was performed and not where the invocation occurs.
The reason is that the preconstructed exception is thrown and not 
created on every invocation:
   mh = mh.bindTo(new UnsupportedOperationException("cannot reflectively 
invoke MethodHandle"));

> Further it does "mh.withInternalMemberName(method, false)", that i cannot explain. Why do we need to re-associate the MH throwing the USO with the member name corresponding to the MH.invokeExact/invoke method?
I think the main reason is to keep direct method handle cracking API 
(MethodHandles.revealDirect()) working for MethodHandle.invoke*.

Actual method handle structure in this case is more complex than a 
simple DMH, so additional trick with WrappedMember is needed to preserve 
an illusion an ordinary direct method handle is returned.

> For such edge cases perhaps caching is not required.
Agree, caching shouldn't be important for such cases.

Best regards,
Vladimir Ivanov