DKIM-Filter: OpenDKIM Filter v2.11.0 delorie.com 452ERll83409633
Authentication-Results: delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=YBl3vhxR
X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 45E6F389A129
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1717338465;
	bh=3vzyjmeWgWzAaolEQ5jZ8Ysh5elgJOy9JJPqpjb3l7Y=;
	h=Date:To:Cc:Subject:In-Reply-To:References:List-Id:
	 List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe:
	 From:Reply-To:From;
	b=YBl3vhxRH1R6U7C4zi6ReWgfkO24gPBFbQkrwctT20cwBfBuj6evV22hZI548ITLX
	 ar5imfQw/5yh32GfcoEK4F/SX3sZmzDXbBvXu9fQdltn8SA2yxWwmcOz6sLQeesaw5
	 xpiKEfmfSgQrkdZa4LvNsa3fh/np7k8AWBrvQA7k=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 54B26389909A
ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 54B26389909A
ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1717338444; cv=none;
 b=N90jb77Smpk9aIsgh3PNMpoR1t41phlaWHAzPzCHSECoIrDoc3boupif61J3J/dsvweSx7VL4I/HHPfBih9g0CLAiPrJNQGyTFLijoXlrsb/PsHuo1bseBLssHfbfS8JTpptHfXyaiJ+FZkcKG0diyky2C4gwny6PdG5B8mXOQI=
ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key;
 t=1717338444; c=relaxed/simple;
 bh=TrK3c90sakmEsMH4WQFuVBDbcH/kfRP/tayJg1ZhzRA=;
 h=Date:From:To:Subject:Message-Id:Mime-Version:DKIM-Signature;
 b=Rzp1fEN0de4jTXY1QycJDxA3x4PoFgRgV6G83kPxuGZXXLLOhMyt2GylS4pZx0q+RInVa+FvdT17a8ylaiHvHL2qHA0DrfA9j5p1lOnNHnOldsuNdrO2QY9b3+ZxlD9XFzOU6DWHEOR/3d8kYd4erpHpt1/ubpCQne1dwt621Fo=
ARC-Authentication-Results: i=1; server2.sourceware.org
Date: Sun, 2 Jun 2024 23:27:17 +0900
To: Bruno Haible <bruno AT clisp DOT org>
Cc: cygwin AT cygwin DOT com
Subject: Re: [PATCH v2] Cygwin: pthread: Fix a race issue introduced by the
 commit 2c5433e5da82
Message-Id: <20240602232717.25baf1bdfe7ac283dea96899@nifty.ne.jp>
In-Reply-To: <1904124.oxc7TNfbsn@nimes>
References: <20240530050538 DOT 53724-1-takashi DOT yano AT nifty DOT ne DOT jp>
 <4338587 DOT 3DMzsUbDvx AT nimes>
 <20240601231830 DOT 882dc56aadb9c3087bcf4b9c AT nifty DOT ne DOT jp>
 <1904124 DOT oxc7TNfbsn AT nimes>
X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.30; i686-pc-mingw32)
Mime-Version: 1.0
X-Spam-Status: No, score=-4.3 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_NUMSUBJECT, NICE_REPLY_A,
 RCVD_IN_DNSWL_NONE, SPF_HELO_PASS, SPF_PASS, TXREP,
 T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
 server2.sourceware.org
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
Content-Type: text/plain; charset="iso-2022-jp"
Content-Transfer-Encoding: 7bit
Errors-To: cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

On Sun, 02 Jun 2024 15:14:51 +0200
Bruno Haible wrote:
> Hi Takashi Yano,
> 
> > The result is as follows (submitted as v4 patch).
> > 
> > int
> > pthread::once (pthread_once_t *once_control, void (*init_routine) (void))
> > {
> >   /* Sign bit of once_control->state is used as done flag.
> >      Similary, the next significant bit is used as destroyed flag. */
> >   const int done = INT_MIN;		/* 0b1000000000000000 */
> >   const int destroyed = INT_MIN >> 1;	/* 0b1100000000000000 */
> >   if (once_control->state & done)
> >     return 0;
> > 
> >   /* The type of &once_control->state is int *, which is compatible with
> >      LONG * (the type of the pointer argument of InterlockedXxx()). */
> >   if ((InterlockedIncrement (&once_control->state) & done) == 0)
> >     {
> >       pthread_mutex_lock (&once_control->mutex);
> >       if (!(once_control->state & done))
> > 	{
> > 	  init_routine ();
> > 	  InterlockedOr (&once_control->state, done);
> > 	}
> >       pthread_mutex_unlock (&once_control->mutex);
> >     }
> >   InterlockedDecrement (&once_control->state);
> >   if (InterlockedCompareExchange (&once_control->state,
> > 				  destroyed, done) == done)
> >     pthread_mutex_destroy (&once_control->mutex);
> >   return 0;
> > }
> > ...
> > I believe both codes are equivalent. Could you please check?
> 
> Yes, they are equivalent. This code is free of race conditions. (Let's
> hope I am not making a mistake again.)
> 
> For legibility I would write the constant values as bit masks:
>   0x80000000
>   0xc0000000
> and - following the habit that constant integers should have names in
> upper case - I would rename
>   done → DONE
>   destroyed → DESTROYED

Thanks for checking. I'll push the patch after the modification.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple