RFR: 8335358: [premain] Explore alternative ways to trigger the end of training run [v15]

[Mat Carter]

On Thu, 21 Nov 2024 17:36:20 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> > Nice work, Mat!
> > Speaking of proposed API, there's a lot of complexity around `-XX:AOTEndTrainingOnMethodEntry=`. What's the primary use case for it? Does it add much for uncooperative case (no application changes) compared to `jcmd`?
> > For cooperative case, a dedicated method in JDK an application can call seems more appropriate.
> 
> I think this PR has its benefits:
> 
> * JCMD triggers are imprecise. If you using jcmd to trigger the end of training based on time, or based on parsing the app's log, it may capture too much or too little profile.
> * An API would require modifying the app.
> 
> So this PR allows precise timing (for apps that have a well-known Java method that's called during important state transition) without modifying the app itself.

Following our premain discussion I've added two methods to the System class.  AOTEndTraining() as discussed as well as AOTIsTraining() which may also be of use for those willing to modify their application.  As with the -XX:EndTrainingOnMethodEntry we'll review workflows in premain and settle on an approach before any commit to tip

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PR Comment: https://git.openjdk.org/leyden/pull/21#issuecomment-2494626228