RFR: 8306825: Monitor deflation might be accidentally disabled by zero intervals

[Aleksey Shipilev]

On Tue, 25 Apr 2023 09:55:10 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Found this mistake while backporting [JDK-8305994](https://bugs.openjdk.org/browse/JDK-8305994): if we put GuaranteedAsyncDeflationInterval=0 (defined as "disable guaranteed deflation"), then the MonitorDeflationThread would call `wait(0)`, that is, wait indefinitely for the notify. This breaks triggering the threshold heuristics!
> 
> But what is even more concerning, the same thing would happen even prior to [JDK-8305994](https://bugs.openjdk.org/browse/JDK-8305994), if we put GuaranteedSafepointInterval=0 too. Which means users who kept GSI=0 as the way to dodge excess safepoints, now effectively disable monitor deflation!
> 
> New test cases capture most of the interesting paths/combinations. Since I needed to add more test cases, I ended up refactoring the test for more clarity. The test is also renamed, because now it tests not only GADI, but other intervals too.

@dcubed-ojdk, you might be interested in the continuation of this small saga :)

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PR Comment: https://git.openjdk.org/jdk/pull/13635#issuecomment-1523835789