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

[David Holmes]

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

LGTM2. One nit.

Thanks

src/hotspot/share/runtime/objectMonitor.cpp line 2005:

> 2003: static void post_monitor_notify_event(EventJavaMonitorNotify* event,
> 2004:                                     ObjectMonitor* monitor,
> 2005:                                     int notified_count) {

```suggestion - indent is off
static void post_monitor_notify_event(EventJavaMonitorNotify* event,
                                      ObjectMonitor* monitor,
                                      int notified_count) {

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23901#pullrequestreview-2692804394
PR Review Comment: https://git.openjdk.org/jdk/pull/23901#discussion_r2000128558