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From Etienne Gagnon <egag...@sablevm.org>
Subject Re: [drlvm] Class unloading support - tested one approach
Date Thu, 09 Nov 2006 15:49:10 GMT
Alexey Varlamov wrote:
>> > My proposal already argued that vtable bit/byte/word marking is
>> > unnecessary for "nursery allocations".  You only need to mark the
>> vtable
>> > of objects that survive collection and pretenured objects.
> 
> 
> I may have missed it, but I only recall you argued that we just need
> to collect mature space for the *final unloading* as CL and classes
> are unlikely to die young, which I agree. But chances that a live
> object of a candidate class appeared in the nursery are higher.
> Otherwise I just do not grok how this algorithm can be proven for
> correctness.
> 

OK.  My latest proposal (a few messages ago) was assuming that the
nursery was empty when the "end of epoch collection" is launched.

If it is not, you can do 2 things:

a) do a minor collection to empty it, or

b) i  - use a finalization-like list of references to class loader
        objects
   ii - launch gc, which might mark a previously unmarked vtable
   iii- do a finalization-like rescuing for resuscitated class loaders

"b)" should really have a minimal performance impact.  As for its
"apparent complexity", I would say that this is a non-issue; similar
code must already exist in drlvm for implementing finalization.

Etienne

-- 
Etienne M. Gagnon, Ph.D.            http://www.info2.uqam.ca/~egagnon/
SableVM:                                       http://www.sablevm.org/
SableCC:                                       http://www.sablecc.org/

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