Path: utzoo!attcan!uunet!mcsun!ukc!dcl-cs!aber-cs!pcg
From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.object
Subject: Re: C++ and garbage collection
Message-ID: <2030@aber-cs.UUCP>
Date: 23 Sep 90 01:42:38 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 37

In article <57605@microsoft.UUCP> jimad@microsoft.UUCP (Jim ADCOCK) writes:

  |The efficiency of conservative garbage collection, measured as the
  |percentage of garbage that is not reclaimed, has been proven to be quite
  |high; this is because on many common os/architecture pairs only few
  |words that are not pointers into the heap look like they were, even
  |without taking a lot of care, so that little garbage is left
  |unreclaimed.
  |
  |	Why? because on many machines the heaps are segments in fairly
  |	high storage addresses, the typical heap address being often a
  |	bit pattern like
  |
  |		0x0a00d1fc0
  
  "Just to make things clearer" -- you're assuming you're running on machines
  with 32-bit integers, and 32-bit linear addresses.

You are assuming this -- I have written 'on many common os/architecture
pairs'.

  There's at least one large interesting class of machines on which these
  assumptions fail miserably.

Maybe one can be clever enough to find a storage managemen scheme by which
integer, string or float values are not easily mistaken with addresses also
for this one large interesting (for marketing departments only, I surmise
:->) class of machines -- or may be not.

I guess that for the large interesting class of machines and pseudo os
architectures you might be thinking about this can be done with fairly good
efficiency. Especially if you can make the storage allocator and compiler
cooperate.
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcsun!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk