JDK-6824466 java.lang.reflect.Method should use java.lang.invoke.MethodHandle

[Mandy Chung]

Hi Johannes,

I believe you are aware of the prototype I'm working on:
     https://github.com/mlchung/jdk/tree/method-invoke

My prototype so far replaces method and fields but not constructors 
yet.   You are welcome to contribute.

My main motivation of doing this is to get rid of the old clunky 
bytecode generator and core reflection will be built atop on method 
handles.   This would greatly simplify the work to add support for a new 
feature for example Valhalla primitive classes only in method handles.  
   I plan to keep the native method accessor  for startup use (or switch 
to method handles when module system is initialized).

Mandy

On 2/1/21 6:50 AM, Johannes Kuhn wrote:
> While implementing a prototype for JDK-8242888 (Convert dynamic proxy 
> to hidden classes) I came across the problem that hidden classes can't 
> be mentioned in the constant pool, breaking the constructor for 
> serialization.
>
> To remedy that problem, I used a MHConstructorAccessor which delegates 
> the actual work to MethodHandles - not unlike what JDK-6824466 suggests.
>
> As there has been previous work in that area, (I am aware of at least 
> 3 independently developed prototypes for that bug/enchantment) I would 
> like to ask a few questions around it:
>
>
>
> 1) What are the challenges?
>
> From the bug I could infer, that it's cold start is slower than 
> NativeMethodAccessor, but still faster than the generated (bytecode 
> spinning) accessors.
>
> 2) Are there any roadblocks that prevent replacing the 
> MethodAccessorGenerator with accessors that use MethodHandles?
>
> From my limited tests, it appears to work well enough.
>
> 3) Should I try to implement it?
>
>
>
> From my POV, replacing MethodAccessorGenerator with accessors that 
> delegate to MethodHandles has a few benefits:
>
> * Support for hidden classes. (Currently fallback to native accessors)
> * Removal of MethodAccessorGenerator (which is old and clunky)
>
> - Johannes