RFR: 8259862: MutableSpace's end should be atomic

[Albert Mingkun Yang]

On Sat, 30 Jan 2021 05:51:38 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to MutableSpace, making its _end member volatile
> and using Atomic operations to access the _top and _end members.  Some
> unused accessor functions that would otherwise need updating are removed.
> 
> Testing:
> mach5 tier1

Marked as reviewed by ayang (Author).

src/hotspot/share/gc/parallel/mutableSpace.hpp line 62:

> 60:   HeapWord* _bottom;
> 61:   HeapWord* volatile _top;
> 62:   HeapWord* volatile _end;

Maybe add some comments explaining how `_top` and `_end` are used in the concurrent setting.

-------------

PR: https://git.openjdk.java.net/jdk/pull/2323