RFR: 8310994: Add JFR event for selection operations

[Daniel Fuchs]

On Fri, 17 Nov 2023 16:22:55 GMT, Tim Prinzing <tprinzing at openjdk.org> wrote:

> Added mirror event with static methods: jdk.internal.event.SelectionEvent that provides the duration of select calls and the count of how many keys are available.
> 
> Emit the event from SelectorImpl::lockAndDoSelect
> 
> Test at jdk.jfr.event.io.TestSelectionEvents

src/java.base/share/classes/jdk/internal/event/SelectionEvent.java line 35:

> 33:  * {@link #commit(long, long, int)} method
> 34:  * must be the same as the order of the fields.
> 35:  */

You should probably define what a "selection operation" is and put a link to `Selector::select`.

src/java.base/share/classes/jdk/internal/event/SelectionEvent.java line 38:

> 36: public class SelectionEvent extends Event {
> 37: 
> 38:     public int count;

It could also be interesting to provide the `timeout` that was given to the selection operation.

src/java.base/share/classes/sun/nio/ch/SelectorImpl.java line 150:

> 148:         long duration = SelectionEvent.timestamp() - start;
> 149:         if (SelectionEvent.shouldCommit(duration)) {
> 150:             SelectionEvent.commit(start, duration, n);

Maybe the value of `timeout` should be provided here?

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PR Review Comment: https://git.openjdk.org/jdk/pull/16710#discussion_r1401948063
PR Review Comment: https://git.openjdk.org/jdk/pull/16710#discussion_r1401950078
PR Review Comment: https://git.openjdk.org/jdk/pull/16710#discussion_r1401951825