RFR: 8333105: Shenandoah: Results of concurrent mark may be lost for degenerated cycle

[William Kemper]

On Tue, 28 May 2024 18:01:56 GMT, William Kemper <wkemper at openjdk.org> wrote:

> If Shenandoah does not detect a cancellation after completing concurrent mark, but before completing final mark it will fall through the concurrent cycle without collecting anything. This will shortly lead to a degenerated cycle which will _not_ use the results from the nearly complete concurrent mark. This will result in an unnecessarily longer degenerated cycle.

I'll try to trim it down. I shot myself in the foot after being confused by the original comment and deleting this check. Not having this check is not so serious for non-generational modes, but it is necessary to avoid heap corruption and crashes in the generational mode.

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PR Comment: https://git.openjdk.org/jdk/pull/19434#issuecomment-2138084507