RFR: Allow old collections to span degenerated young collections

[Kelvin Nilsen]

On Wed, 16 Mar 2022 18:11:26 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Prior to this change, a degenerated young cycle would cause an old collection effort to be abandoned. 
> 
> Summary of changes:
> * Resetting state of old GC during cancellation has been consolidated
> * When old marking is in progress, SATB queues are serviced during init mark of concurrent cycles (bug fix)
> * Old GC cannot be interrupted between end of final mark and final roots (bug fix)

Marked as reviewed by kdnilsen (Committer).

-------------

PR: https://git.openjdk.java.net/shenandoah/pull/124