RFR: 8254877: GCLogPrecious::_lock rank constrains what locks you are allowed to have when crashing [v2]

[Stefan Karlsson]

On Wed, 28 Oct 2020 15:27:57 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review 1
>
> Looks good.

In the latest update I added two new helper classes: `SemaphoreLock` and `SemaphoreLocker`. I think this makes the code nicer. Since those classes are more broadly used, I'll go a head and split them out into a separate PR.

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PR: https://git.openjdk.java.net/jdk/pull/903