RFR: 8319867: GenShen: Make old regions parseable at end of concurrent cycles [v2]

[Y. Srinivas Ramakrishna]

On Sat, 11 Nov 2023 00:44:35 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahOldGeneration.cpp line 448:
>> 
>>> 446:       break;
>>> 447:     case EVACUATING:
>>> 448:       assert(_state == WAITING_FOR_BOOTSTRAP || _state == MARKING, "Cannot have old collection candidates without first marking, state is '%s'", state_name(_state));
>> 
>> FWIW, the ASCII art state-transition-diagram doesn't show the transition from WAITING_FOR_BOOTSTRAP directly into EVACUATING, without passing through an intermediate MARKING.
>
> Yes, that can only happen at the end of a _GLOBAL_ collection. This is explained in the comment above the diagram. I will add it to the diagram.

Got it. One way to manage this and still get stronger checking during all, but in particular non-global, collections, might be to organize the state transition checks per collection type, and make assertions specific to the kind of collection in which the transition is happening/being checked. But perhaps that is overkill, and in any case not necessary in this PR.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/355#discussion_r1391304232