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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Extending C with GC? |
| Date | 2016-08-01 12:46 -0700 |
| Organization | None to speak of |
| Message-ID | <lnlh0g46hk.fsf@kst-u.example.com> (permalink) |
| References | <60b33d17-71b7-4ecf-a821-dc641e2673ba@googlegroups.com> <lninvl5sjx.fsf@kst-u.example.com> <87bn1cxrqp.fsf@news.bourguet.org> |
Jean-Marc Bourguet <jm@bourguet.org> writes:
> Keith Thompson <kst-u@mib.org> writes:
>
>> GC depends on the ability to detect that a chunk of memory is no
>> longer in use, and can be recovered. There are various methods
>> to do this, but basically if there's currently nothing pointing to
>> a chunk of memory, it's considered safe to assume that that chunk
>> can be reclaimed.
>>
>> In standard C, it's perfectly legal to take a pointer value, write
>> it to a file, set the pointer variable to NULL, and later read the
>> original pointer value back from the file.
>
> Without writing pointers to files, which I've never met, there are at least
> three techniques which I've met in the wild which don't play nice with GC:
>
> - the old trick of using the or of the next and prev pointers as unique
> sibling link in a doubly linked list (to iterate, you need to keep the
> current and the previous node); AFAIK you don't even need to be
> implementation dependent for that
You mean xor, yes?
Storing the result of xor'ing two pointer values in a pointer object
could (in principle) cause problems if the result is a trap
representation. I believe it's harmless in practice on most common
systems.
> - the old trick of using low order bits of aligned pointers or high order
> bits when there is a large adress space to keep additional information
> (you depend of your implementation alignment structure for the first
> variant, you'll be cursed by the future maintainer of your code with the
> second -- ask those who have succeeded IBM 360 and MC68000 programmers)
This also makes assumptions about how pointers are represented. I've
worked on systems (Cray vector systems) where C pointers contained a
byte offset in the high-order 3 bits.
> - offsetting a pointer. There are non-conformant variant (offsetting by
> negative value) and conformant one (offsetting by a positive value but
> staying in the allocated region)
Offsetting by a negative value is perfectly valid if the result still
points into the same object. As for positive offsets, I can imagine
that something like:
unsigned char *ptr = malloc(1024);
assert(ptr != NULL);
ptr += 32;
might cause headaches for a GC system. (I don't know whether it does so
in practice.)
[...]
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Extending C with GC? luser droog <luser.droog@gmail.com> - 2016-07-31 15:31 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-07-31 15:52 -0700
Re: Extending C with GC? Tim Rentsch <txr@alumni.caltech.edu> - 2016-07-31 17:21 -0700
Re: Extending C with GC? Jean-Marc Bourguet <jm@bourguet.org> - 2016-08-01 20:34 +0200
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-01 12:14 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-01 12:46 -0700
Re: Extending C with GC? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-08-01 15:56 -0400
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-01 14:28 -0700
Re: Extending C with GC? Jean-Marc Bourguet <jm@bourguet.org> - 2016-08-01 23:37 +0200
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-01 15:03 -0700
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-02 00:11 +0200
Re: Extending C with GC? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-08-01 18:19 -0400
Re: Extending C with GC? BGB <cr88192@hotmail.com> - 2016-08-02 12:46 -0500
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-03 15:26 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-03 15:49 -0700
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-04 14:07 +1200
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-03 19:26 -0700
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-04 14:55 +1200
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-03 20:38 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-04 05:10 -0700
Re: Extending C with GC? Siri Cruise <chine.bleu@yahoo.com> - 2016-08-04 05:57 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-04 06:13 -0700
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-05 07:24 +1200
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-04 12:47 -0700
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-04 23:32 -0700
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-05 10:09 +0100
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-05 20:32 +1200
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-05 06:14 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 04:14 -0700
Re: Extending C with GC? Melzzzzz <mel@zzzzz.com> - 2016-08-06 13:23 +0200
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 04:38 -0700
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-06 04:34 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 05:28 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 06:05 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 06:12 -0700
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-06 14:02 +0100
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-06 06:11 -0700
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-06 14:50 +0100
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-06 07:57 -0700
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-06 17:02 +0100
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-06 19:20 +0200
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-06 14:27 +0100
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-06 14:45 +0100
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 09:59 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-06 19:38 +0100
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 17:03 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 09:54 +0100
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-07 21:53 +1200
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 11:34 +0100
Re: Extending C with GC? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-07 12:06 +0000
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-07 14:10 +0100
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 15:38 +0100
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-07 14:32 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 23:44 +0100
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-07 16:12 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 01:42 +0100
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-07 18:56 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 10:20 +0100
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-08 09:39 -0700
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-08 02:30 +0100
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 20:15 +0100
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-08 01:24 +0100
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 02:08 +0100
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-07 18:49 -0700
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-08 03:28 +0100
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 12:14 +0100
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 07:37 +1200
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 20:56 +0100
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 08:11 +1200
Re: Extending C with GC? Melzzzzz <mel@zzzzz.com> - 2016-08-07 22:19 +0200
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 22:23 +0100
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-07 14:29 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-07 22:36 +0100
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-07 15:04 -0700
Re: Extending C with GC? jameskuyper@verizon.net - 2016-08-07 15:19 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 00:04 +0100
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-07 16:20 -0700
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 15:21 +1200
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 10:35 +0100
Re: Extending C with GC? Gareth Owen <gwowen@gmail.com> - 2016-08-08 18:13 +0100
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-08 11:53 -0700
Re: Extending C with GC? raltbos@xs4all.nl (Richard Bos) - 2016-08-10 12:58 +0000
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-10 07:05 -0700
Re: Extending C with GC? Ken Brody <kenbrody@spamcop.net> - 2016-08-10 12:29 -0400
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 21:15 +0100
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-08 08:57 -0700
Re: Extending C with GC? luser droog <luser.droog@gmail.com> - 2016-08-07 15:37 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-07 14:58 -0700
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 15:26 +1200
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-08 10:26 +0200
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 21:13 +1200
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-08 10:41 +0100
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-08 12:00 +0200
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 22:07 +1200
Re: Extending C with GC? David Brown <david.brown@hesbynett.no> - 2016-08-08 12:57 +0200
Re: Extending C with GC? Gareth Owen <gwowen@gmail.com> - 2016-08-08 18:12 +0100
Re: Extending C with GC? Ian Collins <ian-news@hotmail.com> - 2016-08-08 21:25 +1200
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-08 02:57 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-07 13:28 -0700
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-07 05:42 -0700
Re: Extending C with GC? Florian Weimer <fw@deneb.enyo.de> - 2016-08-07 11:49 +0200
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-06 19:18 +0200
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-06 12:35 -0700
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-06 19:27 +0200
Re: Extending C with GC? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-06 10:55 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-06 12:31 -0700
Re: Extending C with GC? James Kuyper <jameskuyper@verizon.net> - 2016-08-03 22:36 -0400
Re: Extending C with GC? David Brown <david.brown@hesbynett.no> - 2016-08-04 10:57 +0200
Re: Extending C with GC? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-04 04:09 -0700
Re: Extending C with GC? David Brown <david.brown@hesbynett.no> - 2016-08-04 14:01 +0200
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-04 07:52 -0700
Re: Extending C with GC? Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-04 08:57 -0700
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-04 09:19 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-04 12:30 -0700
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-04 15:21 -0700
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-04 16:50 -0700
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-05 07:31 -0700
Re: Extending C with GC? Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-05 16:01 -0700
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-04 21:00 +0200
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-04 20:26 +0100
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-05 10:37 +0200
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-05 15:52 +0100
Re: Extending C with GC? antispam@math.uni.wroc.pl - 2016-08-21 00:09 +0000
Re: Extending C with GC? Gareth Owen <gwowen@gmail.com> - 2016-08-21 08:58 +0100
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-21 10:48 +0200
Re: Extending C with GC? "Pascal J. Bourguignon" <pjb@informatimago.com> - 2016-08-21 19:58 +0200
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-22 08:46 -0700
Re: Extending C with GC? Öö Tiib <ootiib@hot.ee> - 2016-08-26 02:24 -0700
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-26 13:37 -0700
Re: Extending C with GC? Melzzzzz <mel@zzzzz.com> - 2016-08-27 00:41 +0200
Re: Extending C with GC? Öö Tiib <ootiib@hot.ee> - 2016-08-28 06:12 -0700
Re: Extending C with GC? BartC <bc@freeuk.com> - 2016-08-05 10:06 +0100
Re: Extending C with GC? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-05 15:26 +0100
Re: Extending C with GC? Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-05 08:11 -0700
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-05 17:43 +0200
Re: Extending C with GC? Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-05 15:28 -0700
Re: Extending C with GC? BGB <cr88192@hotmail.com> - 2016-08-04 17:11 -0500
Re: Extending C with GC? Tim Rentsch <txr@alumni.caltech.edu> - 2016-07-31 17:35 -0700
Re: Extending C with GC? jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-01 07:45 +0200
Re: Extending C with GC? Keith Thompson <kst-u@mib.org> - 2016-08-01 08:49 -0700
Re: Extending C with GC? supercat@casperkitty.com - 2016-08-01 09:06 -0700
Re: Extending C with GC? Aleksandar Kuktin <akuktin@gmail.com> - 2016-08-05 18:11 +0000
Re: Extending C with GC? luser droog <luser.droog@gmail.com> - 2016-08-05 11:24 -0700
Re: Extending C with GC? "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-08-08 22:12 -0700
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