From owner-freebsd-threads@FreeBSD.ORG Thu Nov 19 17:09:35 2009 Return-Path: Delivered-To: threads@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 56AD21065670; Thu, 19 Nov 2009 17:09:35 +0000 (UTC) (envelope-from deischen@freebsd.org) Received: from mail.netplex.net (mail.netplex.net [204.213.176.10]) by mx1.freebsd.org (Postfix) with ESMTP id F1D548FC18; Thu, 19 Nov 2009 17:09:34 +0000 (UTC) Received: from sea.ntplx.net (sea.ntplx.net [204.213.176.11]) by mail.netplex.net (8.14.3/8.14.3/NETPLEX) with ESMTP id nAJH9XYw021276; Thu, 19 Nov 2009 12:09:33 -0500 (EST) X-Virus-Scanned: by AMaViS and Clam AntiVirus (mail.netplex.net) X-Greylist: Message whitelisted by DRAC access database, not delayed by milter-greylist-4.2.2 (mail.netplex.net [204.213.176.10]); Thu, 19 Nov 2009 12:09:33 -0500 (EST) Date: Thu, 19 Nov 2009 12:09:33 -0500 (EST) From: Daniel Eischen X-X-Sender: eischen@sea.ntplx.net To: John Baldwin In-Reply-To: <200911191202.30738.jhb@freebsd.org> Message-ID: References: <200911191030.14151.jhb@freebsd.org> <200911191202.30738.jhb@freebsd.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: threads@freebsd.org Subject: Re: Using pthread_once() in libc X-BeenThere: freebsd-threads@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Daniel Eischen List-Id: Threading on FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 Nov 2009 17:09:35 -0000 On Thu, 19 Nov 2009, John Baldwin wrote: > On Thursday 19 November 2009 11:48:54 am Daniel Eischen wrote: >> On Thu, 19 Nov 2009, John Baldwin wrote: >> >>> I would like to provide a pthread_once()-like facility in libc that library >>> bits can use to initialize data safely rather than trying to home-roll their >>> own variants (see the recent commit to stdtime in libc). Ideally what I >>> would like to do is have libc use the "real" pthread_once() when libthr is >>> linked in and fall back to a simple stub without libthr linked in. I know we >>> already do something like this for _spinlock() and friends. My question is >>> what is the most correct way to do this? Should libc grow a new _once() >>> symbol ala _spinlock() that is a weak symbol to a stub version and >>> pthread_once() in thr_once.c would override that, or should there be a >>> _pthread_once() in libc that is a stub in place of the current stub_zero? I >>> noticed a comment in thr_spinlock.c saying the spinlock stuff is kept for >>> backwards compat. Does this mean that for the future we would like to expose >>> pthread symbols directly in libc? Meaning would we rather have libc export a >>> pthread_once() and that ideally libc would be using pthread_mutex_lock/unlock >>> instead of _spinlock/unlock? >> >> pthread_once() is already a stub in libc that gets overloaded with the >> real thing when libthr is linked. See libc/gen/_pthread_stubs.c. >> Isn't that what you want or does it not serve your purpose? > > Hmm, the libc stub will never run the init routine. I would like to do > something like this: Well, I suppose you could do that. But what happens if libthr gets dlopen()'d and your once function needs to initialize a mutex or something that can only be properly done by a real threads library? Can we envision a scenario where that would be a problem? -- DE