From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
To: 70474@debbugs.gnu.org
Subject: bug#70474: Possible bug with `atomic-box-swap!` on OSX/M3 (?!?!)
Date: Fri, 19 Apr 2024 12:54:32 +0200 [thread overview]
Message-ID: <825897f1-19fa-4f6a-b459-8db93791d1c3@leastfixedpoint.com> (raw)
Hello all,
I'm seeing some very strange behaviour from `atomic-box-swap!` (but not
`atomic-box-compare-and-swap!`) on Guile 3.0.9 from Homebrew on OSX
Sonoma using an M3 Pro cpu. The issue does not seem to manifest on
x86_64. Could it be some interaction between Guile and M3 CPUs?
Or am I just doing something very silly that shouldn't work at all and
just happens to look like it works on x86_64?
Here's the program that fails. It will run for a few hundred million
rounds and then yield "q null in get". Note that using CAS seems to
work, but plain old swap doesn't.
;;--
;; Eventually this fails with "q null in get" if `atomic-box-swap!` is
;; used where marked (*) below. It takes usually between hundreds of
;; millions and a few billion increments to fail.
;;
;; It does NOT fail if the line marked (*) is commented out and the line
;; below it mentioning `atomic-box-compare-and-swap!` is uncommented and
;; used instead.
;;
;; The failure happens on OSX Sonoma 14.4.1 on a MacBook Pro running an
;; M3 Pro CPU using Guile version 3.0.9 from Homebrew as of 2024-04-17.
;;
;; It does NOT happen on AMD x86_64 Debian linux with Guile 3.0.9 from
;; Debian packaging.
(use-modules (ice-9 atomic))
(define r (make-atomic-box '(0)))
(let loop ()
(let ((v (let ((q (atomic-box-ref r)))
(when (null? q) (error "q null in get"))
(unless (eq? (atomic-box-compare-and-swap! r q (cdr q)) q)
(error "CAS failed in get"))
(car q))))
(when (zero? (remainder v 10000000)) (write v) (newline))
(unless (null?
(atomic-box-swap! r (list (+ v 1))) ;; (*)
;; (atomic-box-compare-and-swap! r '() (list (+ v 1)))
)
(error "swap failed in put"))
(loop)))
next reply other threads:[~2024-04-19 10:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-19 10:54 Tony Garnock-Jones [this message]
2024-04-19 12:14 ` bug#70474: Also manifests on an M1 running 14.1.1 and with newer Guile versions Tony Garnock-Jones
2024-04-19 13:19 ` bug#70474: Possible bug with `atomic-box-swap!` on OSX/M3 (?!?!) Christopher Baines
2024-04-19 20:46 ` bug#70474: [PATCH 1/2] Including the cast makes Apple clang 15.0.0 happy; without it, clang is sad Tony Garnock-Jones
2024-04-19 20:48 ` bug#70474: [PATCH 2/2] Replace aarch64 CAS and atomic-swap generated JIT code with CASAL and SWPAL instructions Tony Garnock-Jones
2024-04-22 7:52 ` bug#70474: Just adding DMB doesn't help Tony Garnock-Jones
2024-04-22 8:18 ` bug#70474: [PATCH] Move the spin loop target to the LDAXR instruction Tony Garnock-Jones
2024-04-22 11:23 ` Tony Garnock-Jones
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/guile/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=825897f1-19fa-4f6a-b459-8db93791d1c3@leastfixedpoint.com \
--to=tonyg@leastfixedpoint.com \
--cc=70474@debbugs.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).