RFR: 8344320: GenShen: Possible null pointer usage in shGenerationalHeap

[Y. Srinivas Ramakrishna]

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.

Marked as reviewed by ysr (Committer).

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PR Review: https://git.openjdk.org/shenandoah/pull/543#pullrequestreview-2447839579