Inserting pre and post-call logic around a handle?

[Charles Oliver Nutter]

On Thu, May 19, 2011 at 3:53 PM, John Rose <john.r.rose at oracle.com> wrote:
> Your sketch seems good, except that you cannot handle both the return value and the thrown exception in one place.  (API limitation.)  So if your post logic wants to see the return value, you have more work to do.
>
> Suggestion:  Make the direct MH be a free variable, by doing the fancy transform on MethodHandles.exactInvoker(dmh.type()).  That is, instead of mh = T(dmh); mh.invoke(a*); do inv = T(exactInvoker(dmh.type()));  if (?) inv.invokeExact(dmh, a*) else { mh = inv.bindTo(dmh); mh.invoke(a*); }.

Ok, I thought I understood this, but I don't. Where is my pre/post
logic supposed to live? Something like this?

static Object invokeWithPrePost(MethodHandle mh, Object arg1, Object arg2) {
  pre(arg1, arg2);
  try {
    return mh.invokeExact(arg1, arg2);
  } finally {
    post(arg1);
  }
}

And then bind that into a handle, currying in the handle to invoke?
Perhaps I'm not following how to use exactInvoker in this case?

- Charlie