RFR: 8159746: (proxy) Support for default methods [v3]
Peter Levart
plevart at openjdk.java.net
Wed Sep 30 21:34:33 UTC 2020
On Wed, 30 Sep 2020 19:14:28 GMT, Mandy Chung <mchung at openjdk.org> wrote:
>> This proposes a new static `Proxy::invokeDefaultMethod` method to invoke
>> the given default method on the given proxy instance.
>>
>> The implementation looks up a method handle for `invokespecial` instruction
>> as if called from with the proxy class as the caller, equivalent to calling
>> `X.super::m` where `X` is a proxy interface of the proxy class and
>> `X.super::m` will resolve to the specified default method.
>>
>> The implementation will call a private static `proxyClassLookup(Lookup caller)`
>> method of the proxy class to obtain its private Lookup. This private method
>> in the proxy class only allows a caller Lookup on java.lang.reflect.Proxy class
>> with full privilege access to use, or else `IllegalAccessException` will be
>> thrown.
>>
>> This patch also proposes to define a proxy class in an unnamed module to
>> a dynamic module to strengthen encapsulation such that they are only
>> unconditionally exported from a named module but not open for deep reflective
>> access. This only applies to the case if all the proxy interfaces are public
>> and in a package that is exported or open.
>>
>> One dynamic module is created for each class loader that defines proxies.
>> The change changes the dynamic module to contain another package (same
>> name as the module) that is unconditionally exported and is opened to
>> `java.base` only.
>>
>> There is no change to the package and module of the proxy class for
>> the following cases:
>>
>> - if at least one proxy interface is non-public, then the proxy class is defined
>> in the package and module of the non-public interfaces
>> - if at least one proxy is in a package that is non-exported and non-open,
>> if all proxy interfaces are public, then the proxy class is defined in
>> a non-exported, non-open package of a dynamic module.
>>
>> The spec change is that a proxy class used to be defined in an unnamed
>> module, i.e. in a exported and open package, is defined in an unconditionally
>> exported but non-open package. Programs that assume it to be open unconditionally
>> will be affected and cannot do deep reflection on such proxy classes.
>>
>> Peter Levart contributed an initial prototype [1] (thanks Peter). I think
>> the exceptions could be simplified as more checking should be done prior to
>> the invocation of the method handle like checking the types of the arguments
>> with the method type. This approach avoids defining a public API
>> `protected Proxy::$$proxyClassLookup$$` method. Instead it defines a
>> private static method that is restricted for Proxy class to use (by
>> taking a caller parameter to ensure it's a private lookup on Proxy class).
>>
>> javadoc/specdiff:
>> http://cr.openjdk.java.net/~mchung/jdk16/webrevs/8159746/api/
>> http://cr.openjdk.java.net/~mchung/jdk16/webrevs/8159746/specdiff/
>>
>> [1] http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-June/041629.html
>
> Mandy Chung has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev
> excludes the unrelated changes brought in by the merge/rebase. The pull request contains 17 additional commits since
> the last revision:
> - Merge branch 'master' of https://github.com/openjdk/jdk into proxy-default-method
> - minor tweak to the spec wording and impl
> - Merge pull request #1 from plevart/proxy-default-method-performance
>
> Performance improvements for Proxy::invokeDefaultMethod
> - Add test case for InvocationTargetException
> - Revert the thrown exceptions spec to be consistent with Method::invoke
> - Speed up Proxy.invokeDefaultMethod while also changing its spec regarding exception types thrown
> - Merge branch 'master' of https://github.com/openjdk/jdk into proxy-default-method
> - fix regression tests due to proxy name change
> - minor bug fix
> - Merge branch 'master' of https://github.com/openjdk/jdk into proxy-default-method
> - ... and 7 more: https://git.openjdk.java.net/jdk/compare/3112f91d...db6cfc13
src/java.base/share/classes/java/lang/reflect/Proxy.java line 1256:
> 1254: * {@code args} elements cannot be assigned to the corresponding
> 1255: * method parameter type.</li>
> 1256: * </ul>
After trying it in practice, I see your words are correct. 1st unboxing happens and then assignment.
-------------
PR: https://git.openjdk.java.net/jdk/pull/313
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