Integrated: 8355789: GenShen: assert(_degen_point == ShenandoahGC::_degenerated_unset) failed: Should not be set yet: Outside of Cycle

[William Kemper]

On Mon, 28 Apr 2025 22:57:09 GMT, William Kemper <wkemper at openjdk.org> wrote:

> When old generation marking is cancelled to run a young collection. we still set a `_degen_point ` for reasons that became vestigial after [JDK-8349094](https://bugs.openjdk.org/browse/JDK-8349094). When old marking is cancelled, the `_degen_point` should only be set if the marking was cancelled because of an allocation failure (and it should still only be set to "outside of cycle"). The following sequence could lead to this assertion failure:
> 1. Control thread is marking old
> 2. Young GC preempts it
> 3. Control thread sets the degen point because the old GC was "cancelled"
> 4. The concurrent young GC fails and attempts to set a degenerated point
> 5. This trips the assert because we already (incorrectly) set the degen point in `3`.

This pull request has now been integrated.

Changeset: 5e27547e
Author:    William Kemper <wkemper at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/5e27547e2d577e17316ae1a91f83e4091e9729c5
Stats:     11 lines in 1 file changed: 0 ins; 3 del; 8 mod

8355789: GenShen: assert(_degen_point == ShenandoahGC::_degenerated_unset) failed: Should not be set yet: Outside of Cycle

Reviewed-by: kdnilsen, ysr

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PR: https://git.openjdk.org/jdk/pull/24940