RFR: 8366865: Allocation GC Pauses Triggered after JVM has started shutdown [v4]

[Ivan Walulya]

> Please review this patch to skip VM_GC_Collect_Operations  if initiated after the VM shutdown process has begun. We add a _is_shutting_down flag to CollectedHeap, which is set while holding the Heap_lock. This ensures mutual exclusion with VM_GC_Collect_Operations, which also require the Heap_lock.
> 
> Skipping VM_GC_Collect_Operation would otherwise cause allocation requests to fail (resulting in OutOfMemoryError) if requesting daemon threads were allowed to continue, we instead block these threads on a monitor. They remain stalled until they are terminated as part of the VM shutdown sequence.
> 
> Testing: Tier 1-7

Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:

  Revert

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27190/files
  - new: https://git.openjdk.org/jdk/pull/27190/files/0e45912b..2ebff06c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27190&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27190&range=02-03

  Stats: 5 lines in 2 files changed: 3 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27190.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27190/head:pull/27190

PR: https://git.openjdk.org/jdk/pull/27190