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

[Y. Srinivas Ramakrishna]

On Thu, 15 Dec 2022 19:33:36 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.

test/hotspot/gtest/gc/shenandoah/test_shenandoahNumberSeq.cpp line 1:

> 1: /*

An earlier version of this test is in tip for an earlier bug fix. I am happy to consult if there is any confusion during a merge from tip. In this specific case, the contents of this file should take precedence.

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