From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: ludo@gnu.org (Ludovic =?iso-8859-1?Q?Court=E8s?=) Newsgroups: gmane.lisp.guile.devel Subject: Re: Race condition in threading code? Date: Sun, 31 Aug 2008 21:39:19 +0200 Message-ID: <87myitynx4.fsf@gnu.org> References: <2bc5f8210808161142n2b415569y8499f3efafb4a@mail.gmail.com> <87prnu293y.fsf@gnu.org> <2bc5f8210808270614s3ddc6e9fued2ed9f95da15303@mail.gmail.com> <2bc5f8210808301605v5a6376ffs98b58c848c2f64fa@mail.gmail.com> <877i9x9w8j.fsf@gnu.org> <2bc5f8210808310805p34f88f9em8f8d9c16fbf42df@mail.gmail.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1220211587 14886 80.91.229.12 (31 Aug 2008 19:39:47 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 31 Aug 2008 19:39:47 +0000 (UTC) To: guile-devel@gnu.org Original-X-From: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Sun Aug 31 21:40:42 2008 Return-path: Envelope-to: guile-devel@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.50) id 1KZsmu-0006TU-64 for guile-devel@m.gmane.org; Sun, 31 Aug 2008 21:40:40 +0200 Original-Received: from localhost ([127.0.0.1]:37562 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KZslv-0008Ui-Ba for guile-devel@m.gmane.org; Sun, 31 Aug 2008 15:39:39 -0400 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KZsls-0008U8-3P for guile-devel@gnu.org; Sun, 31 Aug 2008 15:39:36 -0400 Original-Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KZslq-0008TW-Fu for guile-devel@gnu.org; Sun, 31 Aug 2008 15:39:35 -0400 Original-Received: from [199.232.76.173] (port=33027 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KZslq-0008TR-92 for guile-devel@gnu.org; Sun, 31 Aug 2008 15:39:34 -0400 Original-Received: from main.gmane.org ([80.91.229.2]:36175 helo=ciao.gmane.org) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1KZslp-0005Q9-Oi for guile-devel@gnu.org; Sun, 31 Aug 2008 15:39:34 -0400 Original-Received: from list by ciao.gmane.org with local (Exim 4.43) id 1KZsln-0000BL-7M for guile-devel@gnu.org; Sun, 31 Aug 2008 19:39:31 +0000 Original-Received: from reverse-83.fdn.fr ([80.67.176.83]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 31 Aug 2008 19:39:31 +0000 Original-Received: from ludo by reverse-83.fdn.fr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 31 Aug 2008 19:39:31 +0000 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 61 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: reverse-83.fdn.fr X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 15 Fructidor an 216 de la =?iso-8859-1?Q?R=E9volutio?= =?iso-8859-1?Q?n?= X-PGP-Key-ID: 0xEA52ECF4 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 821D 815D 902A 7EAB 5CEE D120 7FBA 3D4F EB1F 5364 X-OS: i686-pc-linux-gnu User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) Cancel-Lock: sha1:YG1zahH0n/5k811ANKMHaSOijDc= X-detected-kernel: by monty-python.gnu.org: Linux 2.6, seldom 2.4 (older, 4) X-BeenThere: guile-devel@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Developers list for Guile, the GNU extensibility library" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Errors-To: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.lisp.guile.devel:7560 Archived-At: Hey! "Julian Graham" writes: > Thread A wants to lock fat_mutex M. It seizes the administrative lock > M->lock and examines the state of M. M is held by thread B, so thread > A prepares to put itself onto the blocking queue for M by calling > `SCM_TICK'. In order to call `SCM_TICK', thread A must temporarily > release M->lock. > > When it does this, thread B, the owner of M, seizes M->lock and > releases M, which involves waking up the next waiting thread on the > blocking queue for M -- but thread A hasn't finished doing the tick > and so isn't on the blocking queue. Thread B releases M->lock and > goes about its business. > > Thread A finishes the tick and seizes M->lock again and adds itself to > the blocking queue for M without re-examining M's state. The only way > thread A can ever wake up after this is if another thread locks and > releases M. Thanks for the clarification, that's what I was trying to express. ;-) I just pushed it to `master'. >> I guess it can be applied to 1.8 as well? > > I would say so, yes. I'll make a patch against it if you tell me how > to do that with git. :) The easiest way is to "cherry-pick" the change. So, assuming the commit is at the tip of `master', you'd do: $ git checkout branch_release-1-8 $ git cherry-pick master ... resolve conflicts... $ git commit -a -c THE-ID-THAT-GIT-TOLD-YOU-BEFORE And that's it! >> Another question: why is there this mixture of `scm_i_pthread' and >> `scm_i_scm_pthread' calls? > > The scm_i_pthread_* functions are actually preprocessor #defines that > map directly onto pthreads API functions. The scm_i_scm_pthread_* > functions are wrappers around pthreads functions that could block -- > the wrappers leave Guile mode before calling into pthreads. > pthread_mutex_lock can block, so from Guile mode (e.g., from > fat_mutex_lock), it needs to be called via > scm_i_scm_pthread_mutex_lock; but pthread_mutex_unlock can't block, so > it can be called directly via scm_i_pthread_mutex_unlock. > > Is that what you were asking? Yes, exactly. I had overlooked this. Thanks! Ludo'.