RFR: JDK-8298597 : HdrSeq: support for a merge() method [v3]

[Kelvin Nilsen]

On Mon, 19 Dec 2022 17:46:18 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> A merge functionality on stats (distributions) was needed for the remembered set scan that I was using in some companion work. This PR implements a first cut at that, which is sufficient for our first (and only) use case.
>> 
>> Unfortunately, for expediency, I am deferring work on decaying statistics, as a result of which users that want decaying statistics will get NaNs instead (or trigger guarantees).
>> 
>> In the sort term, before I open this draft for review, I'll:
>> 
>> - [x] add tests
>> - [x] ensure that if a merge action has been taken on a distribution, then any attempt to access a decayed statistic causes an error
>> - [x] open a linked ticket to take care of the decayed statistics
>> 
>> An important goal here was to have an API that would be efficient and correct. The API shape may change when we have considered how to handle decaying statistics.
>
> Y. Srinivas Ramakrishna has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:
> 
>  - Merge branch 'master' into stats_merge
>  - Merge branch 'master' into stats_merge
>  - Safety tests for decayed stats, until implemented.
>  - gtest for merge.
>  - Vanilla merge test for ShenandoahNumberSeq; needs to be extended some.
>  - Changes based on experience with uses in RS scan stats.
>    Fixed some bugs.
>    
>    -- We still need to implement a few vanilla tests for the merge method.
>    -- Planning to defer the work on decayed stats (which will be delivered
>    separately in a lower-priority sibling ticket)
>  - Merge branch 'master' into stats_merge
>  - More merge() implementation.
>    -- Need to think about merge of decaying stats in AbsSeq.
>    -- Need to add tests.
>  - Interim checkin of code w/beginnings of merge() support. Some
>    implementations are still stubbed out and need to be written.
>  - First cut at merge. More changes to come. May not build yet.

Marked as reviewed by kdnilsen (Committer).

Marked as reviewed by kdnilsen (Committer).

-------------

PR: https://git.openjdk.org/shenandoah/pull/184