RFR: 8338939: Simplify processing of hidden class names

[Chen Liang]

On Sun, 25 Aug 2024 18:29:47 GMT, Markus Grönlund <mgronlun 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?

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PR Review Comment: https://git.openjdk.org/jdk/pull/20708#discussion_r1730424838