RFR: 8277397: ZGC: Add JFR event for temporary latency measurements [v3]

[Stefan Karlsson]

On Fri, 19 Nov 2021 08:49:14 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> I often measure latencies and stalls using JFR events. I'd like to add an event that can be used for these ad-hoc measurements during development and debugging.
>
> Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rename ZThreadEvent to ZThreadDebug

> 

No, this is more likely to be used in release builds to identify and measure performance issues in ZGC. It is intended for us during debugging and development of various features in ZGC.

Think of this similar to the UseNewCode flag.

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PR: https://git.openjdk.java.net/jdk/pull/6454