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AW: [Caml-list] The tag bit
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Date: 2004-08-13 (14:28)
From: skaller <skaller@u...>
Subject: Re: AW: [Caml-list] The tag bit
On Fri, 2004-08-13 at 22:58, Christophe Raffalli wrote:

> Does anyone have  a comparison between two identical GC except one 
> should have a tag bit and the other be conservative ?

The Boehm collector is quite efficient: if you compare it
to hand written encodings such as reference counting
for example.

The main problem with it is that it has to 'stop the world'
whilst it is doing its thing, and so isn't useful for
real time applications such as a game where you can easily
pay 20% of all CPU for the GC -- but you simply can't freeze
up the game for 10 seconds every few minutes.

The Ocaml generational collector is likely to be much better
at this -- some of the workload is spread over time, and
the remaining major collection when needed will also be
faster, and can be called manually at appropriate points.

A second point is -- Boehm cannot defragment memory.
Ocaml can (although the compaction is 'world stop').

So .. i don't think the 'overall CPU use' of the two collector
kinds is actually what you need to compare: the real time
performance and/or ability to operate with C/C++ code
are the likely issues.

John Skaller,
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language

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