RFR: 8366865: Allocation GC Pauses Triggered after JVM has started shutdown [v9]

[David Holmes]

On Mon, 22 Sep 2025 05:56:58 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 18 commits:
> 
>  - Merge remote-tracking branch 'upstream/master' into shutting_down_gcs
>  - Remove lock
>  - remove assert
>  - make universal
>  - Merge remote-tracking branch 'upstream/master' into shutting_down_gcs
>  - 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
>  - ... and 8 more: https://git.openjdk.org/jdk/compare/cc65836d...87c80194

src/hotspot/share/gc/shared/collectedHeap.cpp line 625:

> 623:   //   - short enough to avoid excessive stall time if the shutdown itself
> 624:   //     triggers a GC.
> 625:   JavaThread::current()->sleep(2 * MILLIUNITS);

I prefer this to the Monitor::wait too. Thanks

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PR Review Comment: https://git.openjdk.org/jdk/pull/27190#discussion_r2367032872