RFC: JEP JDK-8229358: ZGC: Support for macOS

[Roman Kennke]

I personally wouldn't bother to file a JEP for it, and go through The 
Process. We certainly didn't for Shenandoah new features in JDK13 
(elimination of fwdptr, new arches, maybe LRB, maybe concurrent roots), 
and likely won't do for JDK14 (concurrent class-unloading,...) either. A 
whole new GC: sure. New GC features: not so sure. It just seems to much 
hassle for too little benefit. Time's better spent on actual coding and 
fixing ;-)

my 2c

Cheers,
Roman


> Hi,
> 
> I prepared a new JEP [1], about adding support in ZGC for macOS. 
> Implementing this is fairly straight forward now, after the work to have 
> HotSpot deal with discontiguous heap reservations has completed. The 
> reason this discontiguous heap reservation support was necessary is that 
> macOS ASLR may put things in "our" address space, making the previously 
> large and contiguous memory reservation fail. So now that the carpet has 
> been rolled out, it will be a matter of using POSIX shared memory 
> objects for ZGC bindings on macOS.
> 
> Feedback is more than welcome.
> 
> Thanks,
> /Erik
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8229358