RFR: 8371369: Parallel: Relax precondition of PSOldGen::expand_and_allocate

[Axel Boldt-Christmas]

On Wed, 5 Nov 2025 19:29:13 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Use more precise precondition for heap/old-gen expansion; the same precondition is also used in its sole caller.
> 
> Test: tie1-5

We currently also need to hold `PSOldGenExpand_lock` to do expansion in old gen (when not doing it from a safepoint, or is just `Thread::current()->is_VM_thread()` right now, maybe a bit scary). I cannot really see that we take it in the`!!is_init_completed()` path. Think we also need to either take this lock or loosen the invariant to only require the lock when `is_init_completed() && !Thread::current()->is_VM_thread()` 

See `MutableSpace::needs_expand` and `PSOldGen::expand`.

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PR Comment: https://git.openjdk.org/jdk/pull/28162#issuecomment-3501053430