RFR(S): 8157225: adopt method handle for array length getter in BeanLinker

[Attila Szegedi]

There’s a bit of an issue with this. Namely, the old GET_ARRAY_LENGTH being the unreflection of j.l.reflect.Array.getLength() worked for any array type, so it was always accompanied with ValidationType.IS_ARRAY. I believe this is wrong now and can cause ClassCastException at runtime (I say “believe” as I can’t currently build jdk 9 so can’t confirm). This could be caught by a test that handles two arrays of different types in the same call site, e.g. with Nashorn:

  var intArray = Java.type(“int[]”)
  var doubleArray = Java.type(“double[]”)
  var arrs = [new intArray(0), new doubleArray(0)]
  for (var i in arrs) arrs[i].length

Since the MethodHandles.arrayLength is typed to the concrete array class, it should be used with ValidationType.EXACT_CLASS. 

This will obviously cause call sites taking length of different kinds of arrays more polymorphic… FWIW, the IS_ARRAY validation type is probably obsolete now as it was only used for array length getters anyway.

The polymorphism could be somewhat alleviated by having stable validation for all arrays of reference types. Maybe have one MethodHandles.arrayLength(Object[].class) handle cached to use with all arrays of reference types, and use a Validator(Object[].class, ValidationType.INSTANCE_OF) with it. Then you’d have stable linkage that can take the length of any reference-typed array, but you’d still trigger relinking for primitive-typed arrays.

Attila.
 
> On 18 May 2016, at 11:25, Michael Haupt <michael.haupt at oracle.com> wrote:
> 
> Dear all,
> 
> please review this change.
> RFE: https://bugs.openjdk.java.net/browse/JDK-8157225
> Webrev: http://cr.openjdk.java.net/~mhaupt/8157225/webrev.00/
> 
> Thanks,
> 
> Michael
> 
> -- 
> 
> <http://www.oracle.com/>
> Dr. Michael Haupt | Principal Member of Technical Staff
> Phone: +49 331 200 7277 | Fax: +49 331 200 7561
> Oracle Java Platform Group | LangTools Team | Nashorn
> Oracle Deutschland B.V. & Co. KG | Schiffbauergasse 14 | 14467 Potsdam, Germany
> 
> ORACLE Deutschland B.V. & Co. KG | Hauptverwaltung: Riesstraße 25, D-80992 München
> Registergericht: Amtsgericht München, HRA 95603
> 
> Komplementärin: ORACLE Deutschland Verwaltung B.V. | Hertogswetering 163/167, 3543 AS Utrecht, Niederlande
> Handelsregister der Handelskammer Midden-Nederland, Nr. 30143697
> Geschäftsführer: Alexander van der Ven, Jan Schultheiss, Val Maher
> <http://www.oracle.com/commitment>	Oracle is committed to developing practices and products that help protect the environment
>