Newsgroups: comp.lang.dylan,comp.lang.functional,comp.lang.scheme
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From: "Eric Jeschke" <jeschke@cs.indiana.edu>
Subject: Re: (debunk-myth '(debunk-myth '(<-efficient gc malloc/free)))
Message-ID: <1995Oct25.100928.7396@news.cs.indiana.edu>
Organization: Computer Science, Indiana University
References: <QOBI.95Oct22061418@qobi.ai> <rzqpwfob5v9.fsf@dlpx1.dl.ac.uk> <LTH.95Oct23083525@blackrabbit.cs.uoregon.edu>
Date: Wed, 25 Oct 1995 10:09:19 -0500 (EST)
Lines: 29
Xref: glinda.oz.cs.cmu.edu comp.lang.dylan:5587 comp.lang.functional:6578 comp.lang.scheme:14116

lth@blackrabbit.cs.uoregon.edu (Lars Thomas Hansen) writes:


:In article <rzqpwfob5v9.fsf@dlpx1.dl.ac.uk> Dave Love <d.love@dl.ac.uk> writes:

:>In-place updating seems
:>orthogonal to issues of alloc/free v. GC, though. 

:This is not entirely correct.  Generational collectors impose penalties
:on assignments to pointer-containing structures: if the assigned (rhs)
:object is in a younger generation than the assigned-to (lhs) object, the
:assignment must typically be recorded for processing during GC.  The
:cost of recording and processing the assignment (not including tracing
:the pointer during GC) is probably on the order of 10-20 cycles; the
:cost of filtering out assignments which do not create cross-generational
:pointers is fairly small but not zero.  A system which uses explicit
:alloc/free does not have to pay these costs.

Interestingly, I've heard that generational collectors are not well-suited
to lazy languages for this reason.  Namely, there are many such assignments
as suspensions (futures, delays, etc.) are resolved.  Same principle for
graph reduction as redexes are overwritten with results.

Unfortunately, I can't supply a reference for this.  Does anyone else
have any anecdotal evidence?

-- 
Eric Jeschke                      |          Indiana University
jeschke@cs.indiana.edu            |     Computer Science Department
