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From "Aleksey Ignatenko" <aleksey.ignate...@gmail.com>
Subject Re: [drlvm] Class unloading support - tested one approach
Date Wed, 08 Nov 2006 06:04:21 GMT
Hi, Robin.
I do really like this proposed idea of marking VTables from objects via
additional word field in VTable.

But I have one question about detecting reachability of the classloaders
("sweep the vtables and check the reachability of the classloaders").
Possibly I missed something, but here is my view of the current model of
drlvm: all j.l.Classes and j.l.Classloaders are enumerated as strong roots
(strong references). Therefore we meet situation when all j.l.Classes and
j.l.Classloaders are always reachable (marked). And no sweep will help to
detect classloaders reachability.
I see the single way to distinguish if j.l.Classloader or j.l.Class was
marked not by strong root from VM but by some reference from heap - is
to write unique object value into VTable. Then we can detect if some
jlClasloader was marked from rootset (strong root from VM) or from some live

I also want to say that 1-st proposed design from me assumed addtional
mark&scan phase without enumeration of jlClasses and jlClassloaders to be
able to detect their reachability.

Could you, please, clarify this moment.
Thanks, Aleksey.

On 11/3/06, Rana Dasgupta <rdasgupt@gmail.com> wrote:
> On 11/2/06, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> >
> > >Robin, thanks for all the clarifications. Now it seems clear to me >and
> > >I am convinced by this proposal. :-)
> Yes, this proposal is the simplest and has the least perf impact. Thanks
> Robin.

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