VarAccessor - VarHandle alternative?

Rémi Forax forax at univ-mlv.fr
Sun Aug 16 08:41:27 UTC 2015


Hi Paul,
the thing is that if VarHandle is wrapped, you control the callsites so you don't need the VarHandle methods to use polymorphic signatures anymore.

cheers,
Rémi 

Le 16 août 2015 07:41:34 CEST, Paul Sandoz <paul.sandoz at oracle.com> a écrit :
>HI Peter,
>
>Sorry for the late reply, got sucked into JVMLS, and travel back, and
>now holiday (back on 27th).
>
>Thanks for experimenting with this. We pulled back from the
>Field/Array-specific handle experiments in a previous revision of the
>variable handle JEP because we knew we could do similar kinds of
>wrapping as you have shown. The idea being a VarHandle could be wrapped
>in a class that encapsulates the specific shape associated with a
>variable kind, and VarHandle becomes the primary place where unsafe
>access is corralled.
>
>Paul.
>
>On 8 Aug 2015, at 02:28, Peter Levart <peter.levart at gmail.com> wrote:
>
>> Hi,
>> 
>> @PolymorphicSignature methods in VarHandle (combined with generics in
>FieldHandle) are a way to expose an API that does not explode in the
>number of different public classes for different primitive types. But
>aren't any-fied (specialized) generics doing just the same? I know:
>VarHandles are  proposed for JDK9 and any-fied generics aren't there
>yet.
>> 
>> Anyway, I tried to see if current state of any-fied generics allows
>me to build an API that is similar in footprint as VarHandle but fully
>compile-time type safe:
>> 
>>
>http://cr.openjdk.java.net/~plevart/misc/valhala-hacks/vaccess/VarAccessor.java
>> 
>> With some tricks (type tokens and manual specialization by
>sub-classing), it can be done as a type-safe wrapper over Unsafe. This
>implementation is missing proper access checks. It's just a proof of
>concept.
>> 
>> While playing with this, I noticed a javac inconsistency. The
>following diamond:
>> 
>> public abstract class VarAccessor<T, any V> {
>> 
>>    private static final Map<Class<?>, BiFunction<Class<?>, String,
>VarAccessor<?, any>>> factories
>>        = new HashMap<>();
>> 
>> ... does not work. I had to re-specify the full types in the HashMap
>constructor:
>> 
>>    private static final Map<Class<?>, BiFunction<Class<?>, String,
>VarAccessor<?, any>>> factories
>>        = new HashMap<Class<?>, BiFunction<Class<?>, String,
>VarAccessor<?, any>>>();
>> 
>> 
>> Regards, Peter
>> 



More information about the valhalla-dev mailing list