RFR: Cleanups, TODOs, asserts (part 1) [v2]

[William Kemper]

On Wed, 5 Apr 2023 16:36:01 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> I have been reading the `openjdk/shenandoah` vs `openjdk/jdk` diff and these are the simple code massages we can do to improve and bullet-proof the code, hopefully without changing the semantics. This would continue with more parts later.
>> 
>> Additional testing:
>>  - [x] macos-aarch64-server-fastdebug (some pre-existing failures)
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   New assert fires, but instead of fixing it, remove useless live_memory completely

src/hotspot/share/gc/shenandoah/shenandoahConcurrentGC.cpp line 125:

> 123:     // Concurrent remembered set scanning
> 124:     entry_scan_remembered_set();
> 125:     // TODO: When RS scanning yields, we will need a check_cancellation_and_abort() degeneration point here.

We need to be really careful when transitioning to a degenerated cycle after RS scan is complete. Logically, the RS scan is part of the concurrent root scan, but it didn't get implemented with that pattern.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/245#discussion_r1160059174