jmx-dev RFR: 8368527: JMX: Add an MXBeans method to query GC CPU time [v2]

[Jonas Norlinder]

On Wed, 15 Oct 2025 10:14:21 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

>> Jonas Norlinder has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Move from j.l.management to com.sun.management etc.
>
> Or:
> 
> 
>      * @implNote Time calculation is implementation-specific, and may include details
> 	 * such as CPU time for driver threads, workers, VM Operations and string deduplication. 
> 	 * The return value can be -1 if called when measurement is not possible, such as during shutdown.

@kevinjwalls 

> Particularly on this method about GC time, I don't really follow the reasoning for not accepting the method in java.lang.MemoryMXBean.
>
> The most generic Java API can admit that Java is Garbage-Collected, and that doing that work can take some CPU time.

I think I'm leaning towards jdk.lang/com.sun over java.lang since there are GC algorithms out there (which we don't have in HotSpot), that make this method sometimes less useful. A method in java.lang may need to consider the most generic situation. For instance, GCs that pushes out most of its work onto mutators. It may be hard to accurately measure this at mutator level and we don't want to force JDK implementors to do so. As such this should be categorized as a JDK-specific method. I understand we would prefer jdk.lang over com.sun for new additions?

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PR Comment: https://git.openjdk.org/jdk/pull/27537#issuecomment-3433172604