RFR: 8334147: Shenandoah: Avoid taking lock for free set logging [v2]

[Xiaolong Peng]

> Hi all, 
> This pull request propose a fix for the issue https://bugs.openjdk.org/browse/JDK-8334147
> 
>> There are multiple places in Shenandoah where we take heap lock for potential free set diagnostics. There is no point in taking that lock if we do not report anything. We should at very least take the lock only when logging is actually needed.
> 
> Basically it moves the ShenandoahHeapLocker into ShenandoahFreeSet::log_status and only acquire heap lock when log is actually enabled. Since the lock is not a reentrant lock, re-arrangement of code related to ShenandoahFreeSet::rebuild is needed. 
> 
> The change for ShenandoahFreeSet::rebuild is probably debatable, ShenandoahFreeSet::log_status will acquire lock again after ShenandoahFreeSet::rebuild is executed, hence the metrics/information in log may not be always consistent, but it might be fine. 
> 
> Additional test:
> - [x] `make test TEST=hotspot_gc_shenandoah`
> 
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR   
>    jtreg:test/hotspot/jtreg:hotspot_gc_shenandoah      259   259     0     0   
> ==============================
> TEST SUCCESS
> 
> 
> Best,
> Xiaolong.

Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:

  Add method log_status_with_heap_lock and make log_status private

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19915/files
  - new: https://git.openjdk.org/jdk/pull/19915/files/597ded38..a8c07f96

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19915&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19915&range=00-01

  Stats: 26 lines in 6 files changed: 16 ins; 5 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/19915.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19915/head:pull/19915

PR: https://git.openjdk.org/jdk/pull/19915