[crac] RFR: Correct System.nanotime() value after restore [v2]

[Ashutosh Mehra]

On Thu, 30 Mar 2023 11:07:31 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Correct time since restore
>
> Crac-criu does not use restore timens [1]  since once a bug in kernel or criu caused timedwait to return immediatelly everytime that is called after restore. I don't remember the bug exactly (already fixed), but I believe it was discussed on this maillist.
> 
> In general, we should not to depend on very obscure linux abillities, as this reduce chances we'd be able to run on something rather than linux. Having the code in the JVM provides better control for the implementation the java spec.
> 
> [1] https://github.com/CRaC/criu/commit/1cb2f4a518a4ae471a1df7a9b540203c1efaf1ba

@AntonKozlov 

> Crac-criu does not use restore timens [1] since once a bug in kernel or criu caused timedwait to return immediatelly everytime that is called after restore. I don't remember the bug exactly (already fixed), but I believe it was discussed on this maillist

https://github.com/CRaC/criu/commit/1cb2f4a518a4ae471a1df7a9b540203c1efaf1ba commit is dated July 14, 2020, but the crac-dev archives has earliest mailing list from Sept 2021. Is there some other mailing list this was discussed on? I am interested in understanding the problem that prompted not to use timens in criu.
Since you mention it was a bug in kernel or criu and it has been almost 3 years since your commit, may be it is worth enabling the criu changes again to see if the timedwait problem still exists, unless you have already done that.

> In general, we should not to depend on very obscure linux abillities, as this reduce chances we'd be able to run on something rather than linux.

I don't think timens can be put in the category of obscure linux ability. It has even made its way into container runtime spec: https://github.com/opencontainers/runtime-spec/pull/1151.

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PR Comment: https://git.openjdk.org/crac/pull/53#issuecomment-1490262494