RFR: 8294961: Convert java.base/java.lang.reflect.ProxyGenerator to use the Classfile API to generate proxy classes [v5]

[Adam Sotona]

On Sun, 24 Dec 2023 03:14:44 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   minor StackCounter fix
>
> src/java.base/share/classes/java/lang/reflect/ProxyGenerator.java line 737:
> 
>> 735:         private void generateMethod(ClassBuilder clb, ClassEntry className) {
>> 736:             var cp = clb.constantPool();
>> 737:             var desc = new StringJoiner("", "(", ")" + returnType.descriptorString());
> 
> We should just use an MTD here; the MTD will be passed to StackCounter so we don't have to recompute a MTD.
> 
> The MT to MTD conversion shouldn't be too costly; the overhead probably comes from Optional, which we have to wait until Valhalla, as proxy generation is unlikely to be hot and compiled by C2.

Original code has been significant in profiler.


MethodTypeDesc desc = MethodTypeDesc.of(toClassDesc(returnType),
                    Arrays.stream(parameterTypes).map(ProxyGenerator::toClassDesc).toArray(ClassDesc[]::new));


1. each `toClassDesc` builds `descriptorString` and parses/validates it while constructing `ClassDesc`
2. `Arrays.stream(...).map(...).toArray(...)` allocates an array
3. `MethodTypeDesc.of(...)` clones the array and iterates params to check for void
4. `desc.descriptorString()` then finally use the `StringJoiner` 

Optimized code only joins `descriptorString`, no validations, no streaming, no arrays, no cloning.


I suggest this patch as this code is considered as performance critical.
However we can go through `ClassDesc` and `MethodTypeDesc` if not performance critical or if the conversions would be optimized.

For example better (trusted) paths from `MethodType` to `MethodTypeDescriptor` and from `Class` to `ClassDesc`, avoiding at least validations.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17121#discussion_r1440395021