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Java Forum / General / January 2006setting a reference count to zero
Is there a quick way to set a reference count to zero manually, instead of waiting for the GC to do it for you? I know that System.gc() will perform a quick garbage collection which is great, but i have some objects I would like to set reference count to zero before this happens to make sure they go. Many thanks in advance. > Is there a quick way to set a reference count to zero manually, instead of > waiting for the GC to do it for you? I know that System.gc() will perform a > quick garbage collection which is great, but i have some objects I would > like to set reference count to zero before this happens to make sure they > go. There is no reference count. (Imagine that spoken in a Matrix-like "there is no spoon" tone.) Garbage collection by reference counting is practically never done in modern implementations of Java, or of any other garbage collected environment. It's not done because it is slow and it doesn't work. There are variations that do work; they are not just slow but unimaginably slow. The ONLY good reasons to use reference counting are if you need deterministic object destruction (and don't mind paying for it in correctness, as well as speed), or if you're trying to explain garbage collection to someone who is unlikely to understand more realistic algorithms. What's more often done is copy collection, or more rarely mark-and- sweep. Neither has a reference count. Even if reference counting were used, the virtual machine wouldn't let you set one automatically to zero, because you would be able to circumvent the platform security model and create errors that lead to undefined (and potentially non-portable) behavior.  Signaturewww.designacourse.com The Easiest Way To Train Anyone... Anywhere. Chris Smith - Lead Software Developer/Technical Trainer MindIQ Corporation > Garbage collection by reference counting is > practically never done in modern implementations of Java, or of any > other garbage collected environment. There's the Unix file system, of course. >> Garbage collection by reference counting is >> practically never done in modern implementations of Java, or of any >> other garbage collected environment. > > There's the Unix file system, of course. Which is guaranteed to be acyclic (no hardlinks to directories) and thus doesn't suffer from the cycle problem reference-counted systems can have. >>> Garbage collection by reference counting is >>> practically never done in modern implementations of Java, or of any [quoted text clipped - 4 lines] > Which is guaranteed to be acyclic (no hardlinks to directories) and thus > doesn't suffer from the cycle problem reference-counted systems can have. Sure; that's one reason reference-couting is appropriate. Another place you might see it is in distributed-object systems, where the reference and object may live on different nodes of a network. Creating and deleting references is less common (and already expensive), so the expense of counting is insignificant, and the cost of distributed true GC is high. > Another place you might see it is in distributed-object systems, where the > reference and object may live on different nodes of a network. And, of course, RC is the basis of object lifetime management in COM. -- chris Chris Smith sez: >> Is there a quick way to set a reference count to zero manually, instead of >> waiting for the GC to do it for you? I know that System.gc() will perform a [quoted text clipped - 5 lines] > "there is no spoon" tone.) Garbage collection by reference counting is > practically never done in modern implementations of Java, There's a rumour that IBM has a reference-counting JVM and they use it for busy-server type programs -> >... The ONLY good reasons to use reference > counting are if you need deterministic object destruction -> for precisely that reason: non-deterministic GCs are not very suitable for certain tasks. Dima Signature...the mainstream products of major vendors largely ignore these demonstrated technologies... [Instead, their customers] are left with several ineffective solutions collected under marketing titles like "defense in depth". -- Thirty Years Later: Lessons from the Multics Security Evaluation > Chris Smith sez: >>> Is there a quick way to set a reference count to zero manually, instead [quoted text clipped - 12 lines] > There's a rumour that IBM has a reference-counting JVM and they > use it for busy-server type programs -> Programs where it's important to run out of memory? > > There's a rumour that IBM has a reference-counting JVM and they > > use it for busy-server type programs -> > > Programs where it's important to run out of memory? If such a beast existed (which is possible, at least as a research project), then it wouldn't use /pure/ reference counting. -- chris Chris Uppal sez: >> > There's a rumour that IBM has a reference-counting JVM and they >> > use it for busy-server type programs -> >> >> Programs where it's important to run out of memory? Programs where it's important to have upper bound on suckage. > If such a beast existed (which is possible, at least as a research project), > then it wouldn't use /pure/ reference counting. No, apparently there's some cycle-detecting magic in there. Of course, I saw it on the web somewhere and as we all know everything one sees on the web is true. Dima SignatureThe most horrifying thing about Unix is that, no matter how many times you hit yourself over the head with it, you never quite manage to lose consciousness. It just goes on and on. -- Patrick Sobalvarro On Sun, 8 Jan 2006 23:38:08 +0000 (UTC), Peter Jones <ant_on_line@hotmail.REMOVEHERE.com> wrote, quoted or indirectly quoted someone who said : >Is there a quick way to set a reference count to zero manually, instead of >waiting for the GC to do it for you? I know that System.gc() will perform a >quick garbage collection which is great, but i have some objects I would >like to set reference count to zero before this happens to make sure they >go. >Many thanks in advance. There are no reference counts. See http://mindprod.com/jgloss/garbagecollection.html SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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