RFR: 8338939: Simplify processing of hidden class names

[Markus Grönlund]

On Sun, 25 Aug 2024 20:23:15 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Greetings,
>> 
>> The name symbol for hidden (anonymous) classes has evolved. Initially, it consisted of only a base class name, e.g., "java/lang/invoke/LambdaForm$BMH", so JFR had to introduce a scheme for disambiguating one anonymous class from another.
>> 
>> The scheme (which still exists in JFR) appends the Java class mirror's hashcode to the base class name, e.g., "java/lang/invoke/LambdaForm$BMH/22626602".
>> 
>> With [JDK-8238358](https://bugs.openjdk.org/browse/JDK-8238358), the disambiguation of hidden class names is now intrinsic to the processing by the ClassFileParser. This is done by appending the InstanceKlass address to the base class name, e.g., "java/lang/invoke/LambdaForm$BMH+0x000000001d190000".
>> 
>> An argument can be made that JFR specialization for hidden (anonymous) classes may no longer be necessary. Indeed, the result now involves a "double" disambiguation: e.g., "java/lang/invoke/LambdaForm$BMH+0x000000001d190000/231202600".
>> 
>> It is now possible to simplify the handling of hidden (anonymous) class names, which avoids using the Java mirror oop. We might want to keep the "/" construct as that might be an implicit invariant on users' expectations (quickly done by replacing "+" with "/").
>> 
>> Testing: jdk_jfr
>> 
>> Thanks
>> Markus
>
> src/hotspot/share/jfr/support/jfrSymbolTable.cpp line 259:
> 
>> 257:   const size_t len = static_cast<size_t>(name->utf8_length());
>> 258:   char* hidden_klass_name = NEW_RESOURCE_ARRAY(char, len + 1);
>> 259:   strncpy(hidden_klass_name, name->as_klass_external_name(), len + 1);
> 
> Can't you use the `k->external_name()` which performs this plus to slash replacement already?

Good point, turns out this support already exists.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20708#discussion_r1730985016