RFR: 8242888: Convert dynamic proxy to hidden classes

[Chen Liang]

Hmm, I think Proxy being hidden in stacktraces might be an advantage; the
same happens for lambdas.
The main advantage of hidden classes compared to an explicit class with
classData is that it supports flexible unloading, which might be useful for
Proxy.
I still believe the flexible unloading advantage justifies the migration to
hidden classes.

Chen

On Thu, May 23, 2024 at 6:43 AM Remi Forax <forax at univ-mlv.fr> wrote:

> ----- Original Message -----
> > From: "Chen Liang" <liach at openjdk.org>
> > To: "core-libs-dev" <core-libs-dev at openjdk.org>, "hotspot-dev" <
> hotspot-dev at openjdk.org>, kulla-dev at openjdk.org
> > Sent: Thursday, May 23, 2024 1:28:01 PM
> > Subject: Re: RFR: 8242888: Convert dynamic proxy to hidden classes
>
> > On Thu, 23 May 2024 03:28:30 GMT, Chen Liang <liach at openjdk.org> wrote:
> >
> >> Please review this change that convert dynamic proxies implementations
> to hidden
> >> classes, intended to target JDK 24.
> >>
> >> Summary:
> >> 1. Adds new implementation while preserving the old implementation
> behind
> >> `-Djdk.reflect.useLegacyProxyImpl=true` in case there are compatibility
> issues.
> >> 2. ClassLoader.defineClass0 takes a ClassLoader instance but discards
> it in
> >> native code; I updated native code to reuse that ClassLoader for Proxy
> support.
> >> 3. ProxyGenerator changes mainly involve using Class data to pass
> Method list
> >> (accessed in a single condy) and removal of obsolete setup code
> generation.
> >>
> >> Testing: tier1 and tier2 have no related failures.
> >>
> >> Comment: Since #8278, Proxy has been converted to ClassFile API, and
> >> infrastructure has changed; now, the migration to hidden classes is much
> >> cleaner and has less impact, such as preserving ProtectionDomain and
> dynamic
> >> module without "anchor classes", and avoiding java.lang.invoke package.
> >
> > A CSR targeting 24 describing the compatibility concerns and behavioral
> > differences is here, somehow not linked by skara:
> > https://bugs.openjdk.org/browse/JDK-8332770
> > The incompatibilities were much greater in the previous iterations of
> this
> > issue, such as in dynamic modules, serialization, and in proxy class
> protection
> > domain. Now these aspects are addressed by this patch, the only real one
> left
> > is the change in stack trace. Feel free to raise other incompatibilities
> you
> > have discovered.
>
> I wonder if instead of using hidden classes, we should not use usual named
> classes and add a new Lookup.defineClass() that takes a classData as
> parameter.
> This will solve the both the problem of the stacktrace and the problem of
> the roundtrip proxyClass != Class.forName(proxyClass.getName()).
>
> Rémi
>
> >
> > -------------
> >
> > PR Comment:
> https://git.openjdk.org/jdk/pull/19356#issuecomment-2126869679
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/core-libs-dev/attachments/20240523/4c32512f/attachment-0001.htm>