RFR: 8254001: [Metrics] Enhance parsing of cgroup interface files for version detection [v4]

[Harold Seigel]

On Tue, 9 Feb 2021 13:31:25 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> This is an enhancement which solves two issues:
>> 
>> 1. Multiple reads of relevant cgroup interface files. Now interface files are only read once per file (just like Hotspot).
>> 2. Proxies creation of the impl specific subsystem via `determineType()` as before, but now reads all relevant interface files: `/proc/cgroups`, `/proc/self/mountinfo` and `/proc/self/cgroup`. Once read it passes the parsed information to the impl specific subsystem classes for instantiation. This allows for more flexibility of testing as interface files can be mocked and, thus, more cases can be tested that way without having access to these specific systems. For example, proper regression tests for JDK-8217766 and JDK-8253435 have been added now with this in place.
>> 
>> * [x] Tested on Linux x86_64 on cgroups v1 and cgroups v2. Container tests pass.
>
> Severin Gehwolf has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Fix jcheck
>  - Add documentation and reduce code running in the critical section
>  - Add some documentation
>  - Merge branch 'master' into jdk-8254001-enhance-file-parsing-java-metrics
>  - Merge branch 'master' into jdk-8254001-enhance-file-parsing-java-metrics
>  - Merge branch 'master' into jdk-8254001-enhance-file-parsing-java-metrics
>  - 8254001: [Metrics] Enhance parsing of cgroup interface files for version detection

Hi Severin,
Thanks for doing this!  Sorry for taking so long to review this change.  The change looks good.  Before pushing it, could you add a comment explaining what the code in lines 185-194 of CgroupSubsystemFactory.java is doing?  Also, please don't overwrite the fix for JDK-8257746.
Thanks again! Harold

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Marked as reviewed by hseigel (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1393