[crac] RFR: 8364554: [CRaC] Improve CRaC VM options' docs [v2]

[Timofei Pushkin]

On Mon, 4 Aug 2025 14:19:47 GMT, Radim Vansa <rvansa at openjdk.org> wrote:

>> Timofei Pushkin has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Improve wording for CRaCMinPid
>
> src/hotspot/share/runtime/globals.hpp line 2006:
> 
>> 2004:           "use -Djdk.crac.resource-policies=...")                           \
>> 2005:                                                                             \
>> 2006:   product(bool, CRaCSkipCheckpoint, false, DIAGNOSTIC,                      \
> 
> Shouldn't we rather deprecate/obsolete the option altogether? Sounds like a predecessor to `simengine`, that is the preferred way. Looking into the implementation it seems that this will keep `jcmd` hanging if invoked from that, won't it?

I used it recently when doing performance investigations: it allowed to rule out influence of the engine on checkpoint/restore performance. So it still can be useful. But I agree, some tests wouldn't harm.

> it seems that this will keep jcmd hanging if invoked from that, won't it?

No, the connection is closed after the JCMD operation is finished, as for any other JCMD operation. `report_ok_to_jcmd_if_any` is needed when we use an engine to close the socket before checkpointing.

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PR Review Comment: https://git.openjdk.org/crac/pull/256#discussion_r2253467617