RFR: 8255231: Avoid upcalls when initializing the statSampler [v4]

[David Holmes]

On Mon, 26 Oct 2020 12:49:43 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Current implementation of the statSampler does upcalls to System.getProperty to collect values for a number of properties that are all provided by the VM itself. And since the sampling starts before any user code run then no property can have changed.
>> 
>> I suggest refactoring the code so that no upcalls are made normally - while asserting this invariant holds using assert-only upcalls. 
>> 
>> This is a small startup optimization - reducing the startup sequence by approx. 300k instructions and 70k branches in my linux-x64 setup.
>
> Claes Redestad 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 21 additional commits since the last revision:
> 
>  - Address review comments from David Holmes
>  - Merge branch 'master' into com_ns
>  - Refactor to remove stable_java_property_counters and clarify comments
>  - Merge branch 'master' into com_ns
>  - Revert unrelated changes to perfData
>  - Merge branch 'master' into com_ns
>  - Improve comments
>  - typo
>  - Missing definition
>  - Extract the shorthand java.version from VersionProps and use it in StatSampler
>  - ... and 11 more: https://git.openjdk.java.net/jdk/compare/145a3876...8572159f

Thanks for making the suggested changes.

I think we need a further RFE to add some error checking for the sizes of the various property strings in relation to the fixed size arrays that have been allocated to them.

Thanks,
David

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/802