RFC: Refactoring SystemABI

[Jorn Vernee]

Maurizio Cimadamore schreef op 2018-12-04 16:07:
> On 04/12/2018 14:23, Jorn Vernee wrote:
>> We have Scope::allocateCallback to replace step 2. and 3., but that 
>> requires an annotated functional interface object. What if a user just 
>> has a MethodHandle?
> 
> Not sure I follow - a Callback is based on the idea that you _do have_
> a functional interface.

The scenario I'm talking about still uses a functional interface _type_. 
But the Scope::allocateCallback api expects _an instance_ of such a 
functional interface type; So if you just have a MethodHandle you would 
first have to turn it into an instance of this functional interface type 
and then call Scope::allocateCallback. This adds a level of indirection, 
and AFAIK there's no straight forward API for wrapping a MethodHandle in 
a functional interface in the JDK (MethodHandleProxies comes close but 
it relies on reflection, so it's slow).

So what I'm talking about is that a user can use System::upcallStub to 
make the MethodHandle callable from native, but if they have some other 
method that accepts a Callback there still needs to be a way to convert 
the value returned from upcallStub into a Callback.

> I don't think it makes sense to mix the abstraction levels - the
> binder will represent all callbacks using Callback, so I don't expect
> a user of the high-level binder to mess with SystemABI interface to
> allocate stubs.

I was thinking about the inverse; we have a user who is using the 
low-level SystemABI, and wants to have the high-level addition of 
Callback. This also makes sense where low-level code has to interact 
with high-level code.

Jorn