RFR: Full GC should cleanup earlier/bad version of redefined classes

[Zhengyu Gu]

>>>
>>> Yes, we do unload classes during full gc. However, if the flag =
>>> false, it won't do the cleanup within full gc cycle, and those classes
>>> can still be seen after full gc, which fails the test.
>> In other words, it expects full gc to cleanup those classes, cause
>> cleanup tasks may run much later.
> 
> So what if we call the parallelcleaning from full-gc instead? What you
> propose enables serial cleaning, which might impact our (good) full-gc
> performance.

We do parallel cleaning from full-gc, but it is not enough and "defer 
cleaning" is misleading.

Without do_cleaning = true, metadata is not walked and clean 
(ClassLoaderDataGraph::do_unloading()), previous versions of redefined 
classes are not cleaned.

It is potential costly, but only if there are redefined classes. 
Otherwise, it is the same as do_cleaning = false.

Thanks,

-Zhengyu





> 
> Roman
>