[nestmates] JDK-8235602: Re-examine if a hidden class should trust final non static fields

[Remi Forax]

Hi Mandy,
Good idea.
Patch is fine.

Rémi

----- Mail original -----
> De: "mandy chung" <mandy.chung at oracle.com>
> À: "valhalla-dev" <valhalla-dev at openjdk.java.net>
> Envoyé: Lundi 27 Janvier 2020 22:08:28
> Objet: [nestmates] JDK-8235602: Re-examine if a hidden class should trust final non static fields

> Deserialization is the primary use case for core reflection to allow
> writing to final fields after object construction.  Serializable hidden
> classes are required to use its own custom serialization mechanism.
> With the properties of hidden classes, "non-discoverable" and
> "non-modifiable", I propose to make hidden classes final fields
> not-writeable via reflection and enables frameworks and language
> implementors to benefit from the final fields optimization with the use
> of hidden classes.   Core platform classes like lambdas will not have to
> pay for the price just because a few libraries (e.g. mocking) might want
> to write to final fields.
> 
> java.lang.reflect.Field::set and Lookup::unreflectSetter already
> disallow the write-access to static final fields regardless of the
> accessible flag.  This proposes to disallow write-access to final
> non-static fields declared in a hidden class.
> 
> There is no change to AccessibleObject::setAccessible that can be used
> to suppress language access control check.   Most frameworks use
> setAccessible to break encapsulation and access a member and they should
> not be impacted.
> 
> I see that this spec change sets a precedence for JDK-8233873 [1] "final
> field values should be trusted constants", the general fix.
> 
> Webrev:
> http://cr.openjdk.java.net/~mchung/valhalla/webrevs/8235602/webrev.01/
> 
> This patch also puts a stop in using sun.misc.Unsafe to find field
> offsets of hidden class.  jdk.internal.misc.Unsafe::objectFieldOffset is
> used by reflection machinery that I will follow up next.
> 
> Mandy
> [1] https://bugs.openjdk.java.net/browse/JDK-8233873