RFR: Coalesce and fill objects immediately after final mark

[Kelvin Nilsen]

On Tue, 1 Feb 2022 22:06:17 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Before this change, an allocation failure during a global concurrent cycle _after_ final mark would resume the degenerate cycle for evacuation. However, the degenerated cycle cleans up unmarked old objects during the marking phase. This scenario would leave pointers from unmarked objects into reclaimed memory and could lead to a crash when scanning the remembered set.

Marked as reviewed by kdnilsen (Committer).

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PR: https://git.openjdk.java.net/shenandoah/pull/108