From owner-freebsd-threads@FreeBSD.ORG Thu Jan 29 01:43:42 2004 Return-Path: Delivered-To: freebsd-threads@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id F2A3316A4CE for ; Thu, 29 Jan 2004 01:43:41 -0800 (PST) Received: from telecom.net.et (sparrow.telecom.net.et [213.55.64.38]) by mx1.FreeBSD.org (Postfix) with ESMTP id 1691E43D1F for ; Thu, 29 Jan 2004 01:43:33 -0800 (PST) (envelope-from mtm@identd.net) Received: from [213.55.65.234] (HELO pool-151-200-10-97.res.east.verizon.net) by telecom.net.et (CommuniGate Pro SMTP 3.4.8) with ESMTP-TLS id 35385611; Thu, 29 Jan 2004 12:37:54 +0300 Received: from mobile.acsolutions.com (localhost [127.0.0.1]) ESMTP id i0T9hJXT002615; Thu, 29 Jan 2004 12:43:24 +0300 (EAT) (envelope-from mtm@mobile.acsolutions.com) Received: (from mtm@localhost) by mobile.acsolutions.com (8.12.10/8.12.10/Submit) id i0T8LMMX001482; Thu, 29 Jan 2004 11:21:22 +0300 (EAT) (envelope-from mtm) Date: Thu, 29 Jan 2004 11:21:22 +0300 From: Mike Makonnen To: Daniel Eischen Message-ID: <20040129082122.GA1439@mobile.acsolutions.com> References: <20040128165031.GA3461@mobile.acsolutions.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i X-Operating-System: FreeBSD/5.2-CURRENT (i386) cc: threads@FreeBSD.org cc: Peter Kostouros Subject: Re: pthread_mutex_trylock() should never block X-BeenThere: freebsd-threads@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Threading on FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 29 Jan 2004 09:43:42 -0000 On Wed, Jan 28, 2004 at 12:01:27PM -0500, Daniel Eischen wrote: > On Wed, 28 Jan 2004, Mike Makonnen wrote: > > > On Sun, Dec 07, 2003 at 01:34:31AM -0500, Daniel Eischen wrote: > > > > > > The man page may not mention it, and that may be a bug, but I > > > think a pthread_mutex_trylock() on a non-recursive mutex is allowed > > > to return EDEADLK. > > > > > > http://www.opengroup.org/onlinepubs/007904975/functions/pthread_mutex_trylock.html > > > > > > If the mutex type is PTHREAD_MUTEX_ERRORCHECK, then error > > > checking shall be provided. If a thread attempts to relock a > > > mutex that it has already locked, an error shall be returned. > > > If a thread attempts to unlock a mutex that it has not locked > > > or a mutex which is unlocked, an error shall be returned. > > > > > > ... > > > > If you look further down in the spec you will see: > > > > The pthread_mutex_trylock() function shall be equivalent to > > pthread_mutex_lock(), except that if the mutex object referenced > > by mutex is currently locked (by any thread, including > > the current thread), the call shall return immediately... > > Yes, but the implementation has to use internal locks to > keep the mutex in a consistent state. There is no problem > here. Apologies, I was commenting on the EDEADLK vs. EBUSY issue, not the "is an internal lock allowed to block in pthread_mutex_trylock" issue. I should have also explained better instead of just throwing out the quote. EDEADLK is returned by pthread_mutex_lock() only on error checking mutexes that would otherwise deadlock if they were not error checking. Since pthread_mutex_trylock() must return immediately whether the mutex is error-checking or not, I think for consistency sake it should return EBUSY regardless of what type of mutex it is operating on. Also, the 'ERRORS' section lists EDEADLK as a _possible_ return value only for pthread_mutex_lock(). I'm not a standards expert but I think it is permissable for an implementation to return EDEADLK from pthread_mutex_trylock(). However, I think it's better to always return EBUSY, rather than EDEADLK in some cases and EBUSY in others. Cheers. -- Mike Makonnen | GPG-KEY: http://www.identd.net/~mtm/mtm.asc mtm@identd.net | Fingerprint: 00E8 61BC 0D75 7FFB E4D3 6BF1 B239 D010 3215 D418 mtm@FreeBSD.Org| FreeBSD - Unleash the Daemon !