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

[Jonas Norlinder]

On Tue, 16 Sep 2025 09:26:19 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 incrementally with one additional commit since the last revision:
> 
>   Revert

I think we want either `log_cpu_time` or `gc_threads_do` (which we might want to avoid for performance reasons?) to check `is_shutting_down()` such that we can't query terminated GC workers.

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PR Comment: https://git.openjdk.org/jdk/pull/27190#issuecomment-3297922874