[9] RFR (XXS): 8058309: Unsafe.defineAnonymousClass deoptimization checks scale devastatingly poorly

[Vladimir Ivanov]

Aleksey,

> Sorry for not being clear earlier, but I am a bit concerned with the bug
> synopsis: we have sure worked around the issue with LambdaForms, but are
> we sure this fixed the general problem? John asked me to follow up on
> that with more concrete benchmark, and I will do that later. In other
> words, I would like to see the separate issue submitted for this
> workaround, and record the fix under that issue.
It depends on what do you mean by general problem here.

I don't see anything obviously wrong either with U.dAC() or with 
dependency tracking in VM. What we stumbled upon is an inherent 
limitation of current dependency tracking implementation.

It's not specific to U.dAC(). Regular class loaders can hit similar 
problem as well.

With compiled LFs we ended up in relatively polluted context. 
Considering how many classes we spin for LFs, validating this context 
over and over again takes considerable amount of time.

The question is how common polluted contexts are and how frequently do 
we need to validate them.

We could think of improving dependency tracking in VM by increasing 
granularity and narrowing contexts, thus making polluted contexts less 
likely.

If you want to use 8058309 for dependency tracking improvments in VM, 
let me know. So far, I got an impression it is about LFs & JSR292 mostly.

Best regards,
Vladimir Ivanov