RFR: 8351187: Add JFR monitor notification event [v4]

[Markus Grönlund]

On Fri, 14 Mar 2025 18:17:40 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> It is not like we cannot enable it by default. We just don't know yet what is the actual overhead of doing so. My initial thought was to not enable it by default to give us extra safety.

Yes, this is what I meant with not being able to enable it by default. It can depend on a lot of things, overhead in performance, too much data, to much noise etc etc. In general, if we cannot enable an event by default, it is an indication there is something in the design that needs to be reconsidered - i.e. how could it be made to work by default? Throttling, caching, thresholds, others?

That said, events that can help support and performance engineers to troubleshoot faster and reduce time to issue resolution has high value in and of itself, even if it means turning on something extra.

I also like also your argument that we get the stacktrace of the notifier thread - that is valuable context indeed.

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PR Comment: https://git.openjdk.org/jdk/pull/23901#issuecomment-2728995679