RFR: 8324067: GenShen: Isolate regulator thread to generational mode [v5]

[Kelvin Nilsen]

On Tue, 13 Feb 2024 01:23:25 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Shenandoah's generational mode uses a second thread to evaluate heuristics. This is necessary so that the heuristics may interrupt a control thread which is running an old cycle in order to run a young cycle.
>> 
>> The changes here move the regulator thread into `ShenandoahGenerationalHeap`. The generational version of the control thread is also now instantiated only by the generational heap. The upstream version of the control thread has more or less been restored. To  summarize:
>> * An abstract base class called `ShenandoahController` has been introduced as the base class for the original and generational control threads. It has just one virtual method and it is not on a fast path. Much of the common code has been pulled up into this class.
>> * The respective control threads no longer need to check what mode they are in. They also no longer need to select which global generation they need to use.  The regulator thread is now only used by the generational mode so it no longer supports running only global cycles.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix zero build some more

Thanks for separating this out.

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Marked as reviewed by kdnilsen (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/391#pullrequestreview-1879187203