Lazy Events

[Michael Bien]

Hello,

I was wondering if it was ever considered to implement lazy evaluation 
of event attributes?

commit() must happen close to the time the event happens since it stores 
the time and thread id. Instead of storing all fields on commit using 
the client Thread, JFR could potentially append additional fields by 
calling event methods before its written to the repository on the JFR 
Thread.

class LazyEvent extends Event {

     @Label("Normal Field")
     String msg1;  // taken on commit()

     @Lazy
     @Label("Lazy Field")
     String msg2() { return /** called by JFR thread before its written to repo **/; }

}

Another (simpler) way to allow the same functionality could be a 
Event::writeHeader() which would only store eventThread + 
startTime/duration values, while the actual Event::commit() would store 
the fields without altering the exiting event "header" and could be 
called from a different thread later.

I am mostly asking since I wrote a tiny library called JFRLog[1] which 
lets you log directly to JFR records using normal logging APIs. While a 
traditional logger impl can be usually configured to do potentially 
expensive stuff like message formatting or calling toString() on objects 
asynchronously (e.g the Thread which writes the message to a file could 
do this), JFRLog has to do everything in the caller Thread before 
event.commit(). If i would try to put that into its own thread, the 
eventThread IDs and startTime would be all wrong.


its mostly just a thought i got while writing the lib - the performance 
is sufficient for my needs, I avoid using complex log msgs anyway which 
makes it just as fast as loggers which format in their own Threads. JFR 
does all the heavy lifting anyway.

best regards,

michael

ps: thank you for the flush-interval flag :)


[1] https://mbien.dev/blog/entry/jfrlog-logging-directly-to-the