RFR: 8305994: Guarantee eventual async monitor deflation [v4]

[Volker Simonis]

On Mon, 17 Apr 2023 13:26:30 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See discussion in the bug. This PR introduces a safety rail that kicks in when the threshold heuristics fails, and it is cleanly backportable to JDK 17, where the problem manifests as apparent memory leak. There are other options to resolve this (see the bug), but I think this one is the easiest in the interim. 
>> 
>> Additional testing:
>>  - [x] Linux x86_64 `tier1`
>>  - [x] Linux x86_64 `tier2`
>>  - [x] `runtime/Monitor` tests
>>  - [x] Ad-hoc experiments (see example in the bug)
>>  - [x] New feature test
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Volker is right again (fixing unsigned underflow)

Looks good now. Thanks!

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Marked as reviewed by simonis (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13474#pullrequestreview-1388203421