RFR: 8310994: Add JFR event for selection operations [v3]

[Daniel Fuchs]

On Thu, 11 Apr 2024 16:08:31 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> We should probably find a way to not emit the event if n == 0 and the operation was interrupted by `Selector.wakeUp`. Since we have another issue logged to emit a spin event, I wonder if we should only commit the event here if `n != 0`? The case where n == 0 would be handled by the spin event (added later) 
>> @AlanBateman what do you think?
>
> I think it's okay for now. If there is another phase of this work to help diagnose spinning issues then it will need to re-visited. I'm very concerned about the possible changes for that second phase, but this first phase of instrumentation is not disruptive.

OK. I am a little concerned about how often this event will be fired when using the HttpClient - given that it's enabled by default. Idle connections sitting in the pool will fire it at least once per connection every 1500ms. That may not be too bad.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16710#discussion_r1561313983