RFR: 8344320: GenShen: Possible null pointer usage in shGenerationalHeapFix plab nullptr

[Kelvin Nilsen]

On Tue, 19 Nov 2024 16:01:10 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

> Certain threads, including the vm thread and Shenandoah's control thread, do not have PLABs.  There are scenarios where each may need to allocate old-gen memory on the slow-path of the load reference barrier.  This PR fixes an assumption in the allocator that assumed all threads have plabs.

Currently running regression tests.  Will not integrate until all tests succeed.

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PR Comment: https://git.openjdk.org/shenandoah/pull/543#issuecomment-2486121575