On 08/08/2014 11:55 AM, Jaroslav Tulach wrote: > Dne Pá 8. srpna 2014 10:01:14, Andrew Haley napsal(a): > >> On 08/08/14 09:01, Jaroslav Tulach wrote: >> > Given the fact that WeakReference & co. has been introduced in JDK >> > 1.2 and that version was released at the end of 1998, I bet it was >> > just a communication problem, as Andrew must have been talking about >> > something else than WeakReference + ReferenceQueue behavior. >> >> You don't have to believe me, read this: >> >> http://thevirtualmachinist.blogspot.co.uk/2011/07/subtle-issue-of-reachability.html > > Interesting, but not really related.
Your question was "Why is finalize wrong?" This is one reason that I consider finalization (which includes finalizers, weak references, and phantom references) to be wrong, so it is a direct answer to your question. That, and the fact that finalizable objects may end up in a region which is never collected. So: finalization can happen too early, too late, or never. It is difficult to use and error-prone, so much so that I suspect that most finalizers out in the wild are broken. > Maybe a topic for the memory management group to require a receiver > of an instance method call to be considered GC root while the method > is running. I think that one has been considered and rejected. It would add pressure to register-straved machines (think x86). > Btw. if anyone really gets into problems described in the article, this: Yes, people really do get into those problems. There are lots of things one can do to defer finalization, some of them more lightweight than using a logger. We've tried many of them. My current favourite is AtomicIntegerFieldUpdater.lazySet(), which I think cannot be optimized away, but a smart compiler may realize that the object is not reachable from other threads and eliminate it. Maybe. > My assumption is that the Logger.log call is so polymorphic that it > won't be possible for a VM to inline it and/or optimize away - even > it is usually a no-op. But would you bet the farm on that assumption? HotSpot is very good at inlining polymorphic calls. Andrew.
