RFR: 8366865: Allocation GC Pauses Triggered after JVM has started shutdown [v6]

[David Holmes]

On Wed, 17 Sep 2025 14:59:05 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> 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 with a new target base due to a merge or a rebase. The pull request now contains 13 commits:
> 
>  - Merge remote-tracking branch 'upstream/master' into shutting_down_gcs
>  - Merge remote-tracking branch 'upstream/master' into shutting_down_gcs
>  - Revert
>  - Thomas Review
>  - return on timeout
>  - Merge remote-tracking branch 'upstream/master' into shutting_down_gcs
>  - timed wait
>  - Merge remote-tracking branch 'upstream/master' into shutting_down_gcs
>  - space
>  - remove debug logs
>  - ... and 3 more: https://git.openjdk.org/jdk/compare/d7eeacf2...ab94789c

As this doesn't seem to perturb the general shutdown process I have no further comment and will leave it to GC folk to approve.

Though I still wonder if this aspect of shutdown should be part of "Heap" (or Universe) rather than G1 specific.

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PR Review: https://git.openjdk.org/jdk/pull/27190#pullrequestreview-3237321918