RFR: 8252103: Parallel heap inspection for ParallelScavengeHeap [v4]

[Lin Zang]

On Wed, 21 Oct 2020 20:56:01 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

>> Lin Zang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.
>
> src/hotspot/share/gc/parallel/parallelScavengeHeap.hpp line 318:
> 
>> 316:   static const uint eden_index = 0;
>> 317:   static const uint survivor_index = 1;
>> 318:   static const uint num_inseparable_spaces = 2;
> 
> One more comment. These should be CamelCase, and I have an idea to get rid of `num_inseparable_spaces`. 
> 
> If we make `_claimed_index` a signed integral type we could define `EdenIndex = -2` and `SurvivorIndex = -1`. If we then initialize `_claimed_index = EdenIndex` the old gen indices will be correct without needing a decrease.

Good idea! I also suggest to rename _n_blocks to _max_iteratable_block_index in HeapBlockClaimer, To avoid incorrectly considering _n_blocks to be "total number of blocks to be iterated".

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PR: https://git.openjdk.java.net/jdk/pull/25