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Re: reference count size

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On 6/7/2012 11:23 AM, BartC wrote:
>
>
> "bob" <bob@coolfone.comze.com> wrote in message
> news:233b32fd-bdfc-4ffb-a9da-320abb11c07d@googlegroups.com...
>> What is the typical size of a reference count? 32 bits? So, does this
>> add 4 bytes to the size of every object?
>
> Reference counts are typically used with heap-allocated objects, which
> may already have overheads beyond the size of the object, might have a
> minimum size anyway, and are generally used for objects bigger then
> 32-bits. So the few extra bytes is usually not significant.
>

FWIW, my GC uses considerably fewer bits, more around 3, and in the case 
where more than about 6 references exist, it counts as a "many" 
reference, where ref-counts no longer apply (only mark/sweep can free 
such an object).

probably 8 or 16 bits would be plenty, provided it saturates in the off 
chance the limit is reached.


note that objects in this GC have an 8 byte object header, which also 
encodes the size, type, and some other information about the object 
(note that small objects have their space managed by a bitmap, whereas 
large objects use a free-list allocator).

but, doing stuff this way results in considerable memory savings for 
objects < 100 bytes or so (albeit costs are still a bit steep for 
objects <=16 bytes).

efficiently allocating lots of 4-16 byte objects would likely require 
some sort of slab allocator though.

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reference count size bob <bob@coolfone.comze.com> - 2012-06-07 08:42 -0700
  Re: reference count size "BartC" <bc@freeuk.com> - 2012-06-07 17:23 +0100
    Re: reference count size BGB <cr88192@hotmail.com> - 2012-06-07 23:55 -0500
      Re: reference count size "BartC" <bc@freeuk.com> - 2012-06-08 16:52 +0100
        Re: reference count size BGB <cr88192@hotmail.com> - 2012-06-09 09:11 -0500
  Re: reference count size Robert Wessel <robertwessel2@yahoo.com> - 2012-06-07 11:32 -0500
    Re: reference count size "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-06-09 10:29 +0100
      Re: reference count size Ian Collins <ian-news@hotmail.com> - 2012-06-09 21:43 +1200
  Re: reference count size JJ <jaejunks@googlemail.com> - 2012-06-08 01:46 +0700
    Re: reference count size Willem <willem@toad.stack.nl> - 2012-06-07 18:52 +0000

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