RFR: 8343064: ClassFormatError: Illegal class name from InnerClassLambdaMetafactory [v2]

[Chen Liang]

On Tue, 5 Nov 2024 19:21:58 GMT, Chen Liang <liach at openjdk.org> wrote:

>> After the ClassFile API migration, when serializable lambdas are requested for hidden class callers, illegal class name is generated for the serialization methods, which previously had legal yet unusable class names, as hidden classes cannot be described by a `CONSTANT_Class_info`.
>> 
>> This patch restores a similar older behavior of using legal yet unusable class names.  Previously, the invalid `.` in hidden class names was replaced by a `/` as if a package separator; this patch changes it to a `_` like that in the generated lambda's class name.
>> 
>> The bug report shows some unintended and erroneous usages of `LambdaMetafactory`.  To clarify and to persuade against misuse, I added a paragraph of API notes to `LambdaMetafactory`, describing the impact of this API being designed to support Java language features.  In particular, I used the scenario where people assumed LMf generates weak hidden classes, which happened in this issue report and in #12493, that misuse can lead to resource leaks.
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add a test to ensure serializable lambda creation and basic execution in hidden classes

I have updated the documentation.

The API note has been simplified to a simple warning about the intended uses and the resource leak risk.

A new implementation note is added, mentioning the notorious "can't be unloaded" behavior #12493 in the reference implementation explicitly, and describe its implications.

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PR Comment: https://git.openjdk.org/jdk/pull/21912#issuecomment-2471218170