From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Daniel Colascione <dancol@dancol.org>
Cc: emacs-devel@gnu.org
Subject: Re: Conservative GC isn't safe
Date: Mon, 28 Nov 2016 14:33:13 -0500 [thread overview]
Message-ID: <jwvk2bnmmx9.fsf-monnier+Inbox@gnu.org> (raw)
In-Reply-To: <f56b45c5-7248-ed09-1f9f-92c134dc4a71@dancol.org> (Daniel Colascione's message of "Mon, 28 Nov 2016 11:18:32 -0800")
> It's not just strings and buffers and intervals.
The case of intervals is different because pointers to them from the
stack aren't recognized by our conservative stack scanner (CSS), so they're
more at risk, regardless of funny compiler shenanigans.
> What about cons cells? There's nothing wrong with getting a cons from
> something, doing something that might GC with its car, then doing
> something that might GC with its cdr. There's nothing stopping the
> compiler from keeping a pointer to the cdr instead of the car and
> indexing when it's time to dereference the cons and get the cdr out
> of it.
Read Boehm&Chase's article: indeed, it's legal for compilers to do that.
But Emacs is not the only program using CSS, so there is some amount of
pressure to try and make sure C compilers don't make life impossible
for CSS.
> Let me ask again: we already have all the runtime data we need for more
> conservative GC. Where is the resistance to the idea coming from?
A few reasons I can think of for this inertia:
- The problem is hypothetical.
- Even if you pay attention to internal pointers, there are still
(hypothetical) cases that won't be caught.
- Noone volunteered to write it.
- It will likely increase the CPU cost of stack scanning.
- It will likely increase the amount of garbage we erroneously keep alive.
Stefan
next prev parent reply other threads:[~2016-11-28 19:33 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-26 8:11 Conservative GC isn't safe Daniel Colascione
2016-11-26 8:30 ` Paul Eggert
2016-11-26 8:33 ` Daniel Colascione
2016-11-26 9:01 ` Eli Zaretskii
2016-11-26 9:04 ` Daniel Colascione
2016-11-26 9:24 ` Eli Zaretskii
2016-11-26 15:05 ` Stefan Monnier
2016-11-26 15:21 ` Camm Maguire
2016-11-28 17:51 ` Daniel Colascione
2016-11-28 18:00 ` Eli Zaretskii
2016-11-28 18:03 ` Daniel Colascione
2016-11-28 18:50 ` Eli Zaretskii
2016-11-28 18:03 ` Stefan Monnier
2016-11-28 19:18 ` Daniel Colascione
2016-11-28 19:33 ` Stefan Monnier [this message]
2016-11-28 19:37 ` Eli Zaretskii
2016-11-28 19:40 ` Daniel Colascione
2016-11-28 20:03 ` Eli Zaretskii
2016-11-28 20:09 ` Daniel Colascione
2016-11-28 19:26 ` Andreas Schwab
2016-11-28 19:34 ` Stefan Monnier
2016-11-26 15:03 ` Stefan Monnier
2016-11-26 15:12 ` Eli Zaretskii
2016-11-26 16:29 ` Stefan Monnier
2016-11-26 16:42 ` Eli Zaretskii
2016-11-26 18:43 ` Stefan Monnier
2016-11-27 6:17 ` Ken Raeburn
2016-11-27 15:39 ` Eli Zaretskii
2016-11-28 9:50 ` Ken Raeburn
2016-11-28 15:55 ` Eli Zaretskii
2016-11-27 16:15 ` Paul Eggert
2016-11-28 9:36 ` Ken Raeburn
2016-11-28 15:55 ` Eli Zaretskii
2016-11-28 16:15 ` Stefan Monnier
2016-11-28 17:37 ` Eli Zaretskii
2016-11-28 17:49 ` Stefan Monnier
2016-11-28 17:57 ` Eli Zaretskii
2016-11-28 18:05 ` Stefan Monnier
2016-11-28 19:09 ` Ken Raeburn
2016-11-28 19:33 ` Eli Zaretskii
2016-11-29 8:49 ` Ken Raeburn
2016-11-28 17:03 ` Björn Lindqvist
2016-11-28 16:13 ` Paul Eggert
2016-11-27 16:52 ` Stefan Monnier
2016-11-26 19:08 ` Pip Cet
2016-11-27 0:24 ` Paul Eggert
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