Immediate closing of iterators

Chris Hansen renselp at gmail.com
Fri Dec 22 01:23:25 PST 2006


You're right, non-conservative GC is still possible.

I thought the guarantee was that an unreachable generator will
eventually be closed.  If you're using a conservative GC you may not
be able to discover whether or not an object is dead and hence may
keep dead objects alive indefinitely.  With a generational GC you may
keep objects alive long after they're dead but at least you can, if
you want, determine with certainty whether or not an object is dead.
If you had a policy that caused a full collection to be run of all
generations with some regularity (and the spec could mandate that) a
generational GC could offer (what I thought was) the guarantee.

If, on the hand, the guarantee is that a generator will be closed
before its space is reclaimed then using a conservative GC is still
fine because the guarantee doesn't deal with generators that are not
discovered to be garbage.  But then is that a guarantee that is really
useful to anyone?


-- Chris

On 12/22/06, Lars T Hansen <lth at acm.org> wrote:
> Chris Hansen writes:
>
> > Also, having finalization will mandate a non-conservative GC.
>
> I assume you're trying to guarantee that the finalizer is run once the
> object becomes garbage.  But non-conservative generational GCs in general
> do not make any guarantees about the promptness of collection of any
> particular object, thus also do not guarantee anything about the running
> of finalizers.  A generational GC that maintains an set of independently
> collectable generations and guesses which ones of them are the best to
> collect may never collect particular generations if it believes those
> generations contain very little garbage.  A very quick scan of the work by
> Detlefs et al on "Garbage-first" GC suggests that this collector might
> behave like that, for example.
>
> --lars
>
>



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