RFR: Simplify crossing map implementation [v2]

[Kelvin Nilsen]

On Tue, 1 Feb 2022 21:30:45 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Respond to reviewer feedback
>>   
>>   null out object_starts reference in ShenandoahCardCluster destructor.
>
> src/hotspot/share/gc/shenandoah/shenandoahScanRemembered.hpp line 570:
> 
>> 568:   ~ShenandoahCardCluster() {
>> 569:     if (object_starts != nullptr)
>> 570:       free(object_starts);
> 
> I know `ShenandoahCardCluster` is a singleton so this is a nit pick, but we should set `object_starts` to `nullptr` here to avoid double deletes.

fixed.

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PR: https://git.openjdk.java.net/shenandoah/pull/107