RFR: 8351187: Add JFR monitor notification event

[Aleksey Shipilev]

On Wed, 5 Mar 2025 07:26:13 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> Do I read this correctly that this is a duration event and will only be recorded if the notify takes >= 10ms? When I read David's comment then I assumed it was an instant event but it seems not. Given the "address" field then I assume this is intended to be part of a troubleshooting recipe, maybe with threshold set to 0ms, is that right?

Good catch, copy-paste error, really. 

I am arguing separately in #23891 that monitor-related JFR events that do not actually block should not have a high threshold. Otherwise we filter most of them in practice. (JFR tests do not see this, because they override the thresholds to 0ms themselves). Notification event is one of those events as well. See new version, where I dropped the threshold to `0ms`.

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PR Comment: https://git.openjdk.org/jdk/pull/23901#issuecomment-2700796156