RFR: 8364638: Refactor and make accumulated GC CPU time code generic [v10]

[Jonas Norlinder]

On Tue, 19 Aug 2025 11:27:53 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Jonas Norlinder has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove unused
>
> src/hotspot/share/services/cpuTimeUsage.hpp line 47:
> 
>> 45:     static jlong gc_threads();
>> 46:     static jlong vm_thread();
>> 47:     static jlong stringdedup();
> 
> I feel the API surface contains some redundancy.
> 
> For example, the GC-part API design exposes two ways to query and they are essentially the same -- for the sake of simplicity, I'd suggest keeping only one.
> 
> The calculation of `total` should be done by users of this API, I believe, when/if total is desirable.

The motivation for `total()` is that this is probably what most users want, but in case anyone want a sub-component I also expose each one of them. It also serves as documentation as what we currently consider to be "total", so I would prefer keeping it.

If you look at e.g. `WeakProcessor::CountingClosure`  the following is defined

  size_t dead() const { return _old_dead + _new_dead; }
  size_t new_dead() const { return _new_dead; }
  size_t total() const { return dead() + _live; }


so having such convenience method in hotspot is not unprecedented and I would prefer keeping it.

`statistics()` is a less important convenience method that can be removed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26621#discussion_r2285510749