RFR: 8218969: Free JVMCI native structures in nmethod::flush

[Doug Simon]

Hi Eric,

This seems sensible to me and I cannot recall any special reason it wasn’t done this way to begin with. Tom, do you have any recollections about this?

-Doug

> On 14 Feb 2019, at 12:08, Erik Österlund <erik.osterlund at oracle.com> wrote:
> 
> Hi,
> 
> An nmethod goes from being is_alive() to being !is_alive() and eventually being freed in nmethod::flush. Native structures for nmethods are freed in nmethod::flush when we free the nmethod. Except for a few things, including JVMCI handles, that are freed already when becoming !is_alive (and some logic to deal with this potentially happening twice for a given nmethod), and finally asserting during flush that it was already cleared.
> 
> This enhancement proposes to treat these JVMCI handles like we treat any other native structure and simply free it in nmethod::flush, when we free the nmethod, so that the nmethod and handles have a 1:1 mapping for their life cycles.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8218969
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8218969/webrev.00/
> 
> Thanks,
> /Erik