Kim, Thanks for sending this out. I like the 1-line fix in hotspot - simple and sweet.
Mandy > On Dec 2, 2015, at 10:37 AM, Kim Barrett <kim.barr...@oracle.com> wrote: > > Please review this change to PhantomReference processing, changing the > GC-based notification to automatically clear the referent. > > This change provides performance benefits by eliminating the work > involved in keeping the otherwise inaccessible referent objects alive, > as required by the existing specification. This not only immediately > removes some work, but may enable further performance improvements. > It also allows the referent objects to be immediately reclaimed in > the GC cycle in which they were determined to be inaccessible, rather > than lingering as a form of floating garbage until the application > deals with the notified reference. > > This change results in a behavioral change to application code, as > demonstrated by the associated test. Under the old specification, a > reference R with referent X may be kept alive because it is referenced > by an otherwise inaccessible referent Y of phantom reference P. This > will result in X being treated as strongly referenced and prevent R > from being notified, even if R is a phantom reference and X has become > inaccessible to the application. With this change, Y is reclaimed > when it becomes inaccessible and P is notified, and no longer prevents > X from itself becoming a candidate for reclaimation once it is no > longer accessible to the application. While this is a change in > behavior, it seems unlikely to affect applications negatively. > > CR: > https://bugs.openjdk.java.net/browse/JDK-8071507 > > Webrevs: > http://cr.openjdk.java.net/~kbarrett/8071507/jdk.05/ > http://cr.openjdk.java.net/~kbarrett/8071507/hotspot.05/ > > Testing: > jprt, aurora ad hoc (defaults, GC/Runtime nightly, JCK) >
