From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755819AbYCKEVh (ORCPT ); Tue, 11 Mar 2008 00:21:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751623AbYCKEV3 (ORCPT ); Tue, 11 Mar 2008 00:21:29 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:35807 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751083AbYCKEV3 (ORCPT ); Tue, 11 Mar 2008 00:21:29 -0400 Date: Mon, 10 Mar 2008 21:21:08 -0700 From: Andrew Morton To: Nick Piggin Cc: Akinobu Mita , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/5] lib: introduce call_once() Message-Id: <20080310212108.5882011e.akpm@linux-foundation.org> In-Reply-To: <200803111510.52761.nickpiggin@yahoo.com.au> References: <20080310145704.GA6396@APFDCB5C> <20080310204853.3108d21c.akpm@linux-foundation.org> <200803111510.52761.nickpiggin@yahoo.com.au> X-Mailer: Sylpheed 2.3.1 (GTK+ 2.10.11; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 11 Mar 2008 15:10:52 +1100 Nick Piggin wrote: > On Tuesday 11 March 2008 14:48, Andrew Morton wrote: > > On Mon, 10 Mar 2008 23:57:05 +0900 Akinobu Mita > wrote: > > > call_once() is an utility function which has similar functionality of > > > pthread_once(). > > > > > > +/* > > > + * call_once - call the initialization function only once > > > + * > > > + * @once_control: guarantee that the init_routine will be called only > > > once + * @init_routine: initialization function > > > + * > > > + * The first call to call_once(), with a given once_control, shall call > > > the + * init_routine with no arguments and return the value init_routine > > > returned. + * If the init_routine returns zero which indicates the > > > initialization + * succeeded, subsequent calls of call_once() with the > > > same once_control shall + * not call the init_routine and return zero. > > > + */ > > > + > > > +static inline int call_once(struct once_control *once_control, > > > + int (*init_rouine)(void)) > > > +{ > > > + return likely(once_control->done) ? 0 > > > + : call_once_slow(once_control, init_rouine); > > > +} > > > > I don't believe that this shold be described in terms of an "init_routine". > > This mechanism can be used for things other than initialisation routines. > > > > It is spelled "routine", not "rouine". > > > > > > Would it not be simpler and more general to do: > > > > #define ONCE() \ > > ({ \ > > static long flag; \ > > \ > > return !test_and_set_bit(0, flag); \ > > }) > > > > and then callers can do > > > > if (ONCE()) > > do_something(); > > > > ? > > Isn't this usually going to be buggy if you have concurrent access > here? I'd prefer to keep synchronisation details in the caller and > not have this call_once at all. Well, I'm a bit dubious about the calue of all of this (althoug I didn't review the callers). But the above code is guaranteed race-free ;)