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

[Jonas Norlinder]

On Tue, 30 Sep 2025 10:41:41 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> I don't think this is appropriately placed in MemoryMXBean. I will discuss in the CSR request
>
>> I don't think this is appropriately placed in MemoryMXBean. I will discuss in the CSR request
> 
> The CSR is probably a bit premature as this one is going to require seeing if the existing MXBeans are the best place for this (at least some of the original modelling assumed STW collectors) or whether a new management interface is needed.
> 
> It will need think about whether should be a standard or JDK-specific API. Right now, the draft API spec makes it sounds very HotSpot VM specific.
> 
> If added to an existing interface then it will need to be a default method and specifies to have default behavior when not implemented.

@AlanBateman

> The CSR is probably a bit premature ...

Sorry if I broke protocol (first time I submit a PR requiring a CSR). Are you saying that I should had sent out this suggestion on a mailing list for a pre-discussion before actually submitting the CSR?

> Right now, the draft API spec makes it sounds very HotSpot VM specific.

Could you elaborate on what makes this HotSpot VM specific? I think driver threads and workers are a generic concept but I do see your point that VM operations and string deduplication tends to be more HotSpot VM specific. Is that what you meant? I added these specific pointers in an effort to be helpful for a user to understand what parts the metric could include (but for actual details they would need to go to the VM implementation). To avoid being HotSpot VM specific I prefaced with "In general, ...". Should I remove these specialized pointers?

> If added to an existing interface then it will need to be a default method and specifies to have default behavior when not implemented.

Great point. Should have added a default behavior. Will include that in an updated PR (if we reach a consensus that we should add it to an existing interface).

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PR Comment: https://git.openjdk.org/jdk/pull/27537#issuecomment-3351513274