From: Eli Zaretskii <eliz@gnu.org>
To: dick.r.chiang@gmail.com
Cc: larsi@gnus.org, politza@hochschule-trier.de, pipcet@gmail.com,
36609@debbugs.gnu.org
Subject: bug#36609: 27.0.50; Possible race-condition in threading implementation
Date: Sun, 06 Jun 2021 19:35:31 +0300 [thread overview]
Message-ID: <83wnr7gdd8.fsf@gnu.org> (raw)
In-Reply-To: <87fsxv8182.fsf@dick> (dick.r.chiang@gmail.com)
> From: dick.r.chiang@gmail.com
> Cc: Pip Cet <pipcet@gmail.com>, larsi@gnus.org, 36609@debbugs.gnu.org,
> Eli Zaretskii <eliz@gnu.org>
> Date: Sun, 06 Jun 2021 11:25:01 -0400
>
> #1. Want to revert commit 9c62ffb
This will bring back bug#36609, so we cannot do that without
discussing first why you think that commit was wrong.
> #2. Fails on tip of master, succeeds after patch in #1.
Please explain what does "fails" mean, and why do you think the above
commit is the culprit. (A much simpler test case will be
appreciated, btw.)
> Fails not necessarily because xgselect.c is wrong, but rather because
> channel-recv blocks on a mutex before channel-send can get its act together.
You mean, in this code:
(let ((channel (make-channel 1)))
(make-thread
(lambda nil
(channel-send (car channel) 42))
"produce")
(channel-recv (cdr channel))
(ignore-errors (enable-command 'list-threads))
(call-interactively #'list-threads))
? Here, channel-send is called by a new thread, created by
make-thread. In this code, it is _expected_ that channel-recv will be
called (by the main thread) _before_ channel-send is called by the new
thread, because make-thread creates a thread, but the newly created
thread doesn't run until it can acquire the global lock. Meanwhile,
the main thread continues running and calls channel-recv. The new
thread will not begin running, AFAIU, until the main thread calls
condition-wait inside channel-recv.
By "blocks on a mutex", did you mean that channel-recv blocks trying
to acquire the mutex here:
(cl-defgeneric channel-recv ((sink channel-terminal))
(with-mutex (oref sink mutex) <<<<<<<<<<<<<<<<<<<<<<<<<<
(with-slots (condition msg-queue) sink
If so, which thread holds that mutex at this point?
> #4. What #3 probably intended, succeeds after patch in #1.
Yes, race conditions can be solved by using sleep-for, but that's not
really a clean solution, at least not in my book.
next prev parent reply other threads:[~2021-06-06 16:35 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 20:51 bug#36609: 27.0.50; Possible race-condition in threading implementation Andreas Politz
2019-07-12 7:47 ` Eli Zaretskii
2019-07-12 8:05 ` Eli Zaretskii
2019-07-12 9:02 ` Pip Cet
2019-07-12 12:42 ` Eli Zaretskii
2019-07-12 12:57 ` Pip Cet
2019-07-12 13:31 ` Eli Zaretskii
2019-07-12 13:51 ` Pip Cet
2019-07-12 15:05 ` Eli Zaretskii
2019-07-12 18:06 ` Pip Cet
2019-07-12 18:27 ` Eli Zaretskii
2019-07-12 18:34 ` Eli Zaretskii
2019-07-12 19:24 ` Pip Cet
2019-07-12 19:57 ` Eli Zaretskii
2019-07-13 14:37 ` Pip Cet
2019-07-13 15:03 ` Eli Zaretskii
2019-07-13 15:13 ` Eli Zaretskii
2019-07-13 15:54 ` Eli Zaretskii
2019-07-13 15:57 ` Pip Cet
2019-07-13 16:02 ` Eli Zaretskii
2019-07-13 18:17 ` Pip Cet
2020-08-21 12:57 ` Lars Ingebrigtsen
2019-07-13 15:04 ` Andreas Politz
2019-07-12 12:44 ` Pip Cet
2019-07-12 12:55 ` Eli Zaretskii
2019-07-12 13:40 ` Pip Cet
2019-07-12 13:51 ` Eli Zaretskii
2019-07-12 14:34 ` Pip Cet
2019-07-12 15:02 ` Eli Zaretskii
2019-07-12 19:30 ` Pip Cet
2019-07-13 6:50 ` Eli Zaretskii
2021-06-06 15:50 ` dick.r.chiang
[not found] ` <87fsxv8182.fsf@dick>
2021-06-06 16:35 ` Eli Zaretskii [this message]
2021-06-06 19:10 ` dick.r.chiang
2021-06-06 19:27 ` Eli Zaretskii
2021-06-09 21:40 ` dick.r.chiang
2021-06-10 6:46 ` Eli Zaretskii
2021-06-10 11:52 ` dick.r.chiang
2021-06-10 14:18 ` Eli Zaretskii
2021-06-10 14:55 ` dick.r.chiang
2021-06-10 15:04 ` Eli Zaretskii
2021-06-10 21:36 ` dick.r.chiang
2021-06-11 6:00 ` Eli Zaretskii
2021-06-19 17:53 ` Eli Zaretskii
2021-06-19 19:14 ` dick.r.chiang
2021-06-19 19:18 ` Eli Zaretskii
2021-06-19 21:12 ` dick.r.chiang
2021-06-20 11:39 ` Eli Zaretskii
2021-06-20 14:01 ` dick.r.chiang
2021-06-20 15:53 ` Eli Zaretskii
2021-06-25 13:54 ` Eli Zaretskii
2021-06-10 15:35 ` Andreas Schwab
2021-06-10 15:39 ` Eli Zaretskii
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/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=83wnr7gdd8.fsf@gnu.org \
--to=eliz@gnu.org \
--cc=36609@debbugs.gnu.org \
--cc=dick.r.chiang@gmail.com \
--cc=larsi@gnus.org \
--cc=pipcet@gmail.com \
--cc=politza@hochschule-trier.de \
/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.
Code repositories for project(s) associated with this public inbox
https://git.savannah.gnu.org/cgit/emacs.git
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).