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

[Nils Eliasson]

Hi Erik,

Looks good!

// Nils

On 2019-02-14 12:08, Erik Österlund 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