Integrated: 8369048: GenShen: Defer ShenFreeSet::available() during rebuild

[Kelvin Nilsen]

On Thu, 2 Oct 2025 17:58:48 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

> This code introduces a new rebuild-freeset lock for purposes of coordinating the freeset rebuild activities and queries as to memory available for allocation in the mutator partition.
> 
> This addresses a problem that results if available memory is probed while we are rebuilding the freeset.
> 
> Rather than using the existing global heap lock to synchronize these activities, a new more narrowly scoped lock is introduced.  This allows the available memory to be probed even when other activities hold the global heap lock for reasons other than rebuilding the freeset, such as when they are allocating memory.  It is known that the global heap lock is heavily contended for certain workloads, and using this new lock avoids adding to contention for the global heap lock.

This pull request has now been integrated.

Changeset: 0d19d91b
Author:    Kelvin Nilsen <kdnilsen at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/0d19d91b44e5232dbd99d34dcdf6500f892e3048
Stats:     113 lines in 7 files changed: 60 ins; 29 del; 24 mod

8369048: GenShen: Defer ShenFreeSet::available() during rebuild

Reviewed-by: wkemper, ysr

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PR: https://git.openjdk.org/jdk/pull/27612