RFR: 8231269: CompileTask::is_unloaded is slow due to JNIHandles type checks [v2]

[Aleksey Shipilev]

On Fri, 28 Mar 2025 22:01:43 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> What do you think about making 1 step further and encapsulating weak/strong reference handling into a helper class?

Yes. I think @veresov would want to have some of this for persistent profiles JEP and `TrainingData`.
 
I pushed the WIP thing into PR. That only covers the "method unload blocker" part. But I think it should _really_ go further, and encapsulate `Method*` completely, since it is not safe to touch `Method*` when its holder is not blocked for unload. We dodge the problems now by obsessively checking `is_unloading()` all over the place, but we need to guarantee this more mechanically. I'll take a look at that tomorrow. 

> Also, as an optimization idea: seems like weak + strong handles form a union (none -> weak -> strong). So, once a strong reference is captured, corresponding weak handle can be cleared straight away.

It turns out to be necessary to avoid touching `peek()` when in the wrong thread state, when we encapsulate `Method*` as well.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/24018#issuecomment-2767098568