RFR: 8351187: Add JFR monitor notification event [v5]

[Markus Grönlund]

On Thu, 13 Mar 2025 09:44:04 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> We have `JavaMonitorWait` event, but no symmetric `JavaMonitorNotify` event. Notifications are important/interesting to track as well, for example to correlate the delay between notification and eventual wake up.
>> 
>> Providing this event would also replace one of of the RT counters that are going away in [JDK-8348829](https://bugs.openjdk.org/browse/JDK-8348829).
>> 
>> This counter is disabled by default to keep any potential impact low. We can consider flipping it to enabled by default later.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, `jdk_jfr`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:
> 
>  - Merge branch 'master' into JDK-8351187-jfr-monitor-notify
>  - Only emit event when notification happened
>  - Merge branch 'master' into JDK-8351187-jfr-monitor-notify
>  - Rewrite test to RecordingStream
>  - Drop threshold to 0ms
>  - Merge branch 'master' into JDK-8351187-jfr-monitor-notify
>  - Disable by default
>  - Fix

Marked as reviewed by mgronlun (Reviewer).

Okay, Aleksey, it looks good.

It was good to look at this stuff again. I realized some things we can do to improve all the monitor-related events, but I will attempt that after you put this in.

Cheers.

-------------

PR Review: https://git.openjdk.org/jdk/pull/23901#pullrequestreview-2692185809
PR Comment: https://git.openjdk.org/jdk/pull/23901#issuecomment-2731030090