RFR: 8192647: GClocker induced GCs can starve threads requiring memory leading to OOME [v2]

[Albert Mingkun Yang]

> Here is an attempt to simplify GCLocker implementation for Serial and Parallel.
> 
> GCLocker prevents GC when Java threads are in a critical region (i.e., calling JNI critical APIs). JDK-7129164 introduces an optimization that updates a shared variable (used to track the number of threads in the critical region) only if there is a pending GC request. However, this also means that after reaching a GC safepoint, we may discover that GCLocker is active, preventing a GC cycle from being invoked. The inability to perform GC at a safepoint adds complexity -- for example, a caller must retry allocation if the request fails due to GC being inhibited by GCLocker.
> 
> The proposed patch uses a readers-writer lock to ensure that all Java threads exit the critical region before reaching a GC safepoint. This guarantees that once inside the safepoint, we can successfully invoke a GC cycle. The approach takes inspiration from `ZJNICritical`, but some regressions were observed in j2dbench (on Windows) and the micro-benchmark in [JDK-8232575](https://bugs.openjdk.org/browse/JDK-8232575). Therefore, instead of relying on atomic operations on a global variable when entering or leaving the critical region, this PR uses an existing thread-local variable with a store-load barrier for synchronization.
> 
> Performance is neutral for all benchmarks tested: DaCapo, SPECjbb2005, SPECjbb2015, SPECjvm2008, j2dbench, and CacheStress.
> 
> Test: tier1-8

Albert Mingkun Yang 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 four additional commits since the last revision:

 - Merge branch 'master' into gclocker
 - review
 - Merge branch 'master' into gclocker
 - gclocker

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23367/files
  - new: https://git.openjdk.org/jdk/pull/23367/files/6283a19c..1b6f908b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23367&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23367&range=00-01

  Stats: 20456 lines in 569 files changed: 9369 ins; 6708 del; 4379 mod
  Patch: https://git.openjdk.org/jdk/pull/23367.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23367/head:pull/23367

PR: https://git.openjdk.org/jdk/pull/23367