X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 7D91A3889823
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1699892490;
	bh=BQgq5Xwf7T6K7/l1yDEzOd004g/Jqtzl/n+QmTlyzBw=;
	h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:
	From;
	b=RV70nBBkL6wq2oF10BwTbDnn1K5AKu2lauPZKNitp+fcaBGmSi6qQdBqUrhTwSFiV
	++onI8P3teeUDkDBUccJIIpNl7bRWXwdGMUA55CpPeTILdg8fAmpdroe47z36eEGOu
	OpBOlHWGRDpc1mK5MCfOTPOdG/16f22+n7bD4DVk=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.4.2 sourceware.org D3B3A3853315
ARC-Filter:	OpenARC Filter v1.0.0 sourceware.org D3B3A3853315
ARC-Seal:	i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699892477; cv=none;
	b=Kj7ovMnTTeo+sFRSsDGLQq+C2yjtYEMfmCUZpp6VgZMah33TvTpRgD8Pdqt6nDAABLuEVzND1PYH8EJKSGf+dClVGrcnr4bgocsJu8u9T+oYHsP/lck7T/BHZTOoXjE6t31TlQOqjtWj8f+hHgrtflV4r97jU79czfXo9WiHS4k=
ARC-Message-Signature:	i=1; a=rsa-sha256; d=sourceware.org; s=key;
	t=1699892477; c=relaxed/simple;
	bh=TdQotI1OeS+/0Meim+UhirUXlJAI0dGdIag53iUHRDs=;
	h=DKIM-Signature:Date:From:To:Subject:Message-ID:MIME-Version;
	b=VlUZiiXuHJjCbTucZhhMDylAYLyO1ZiqH6avF8GvcrcWSc7bTo75feADfoyS10y8LkfsD7CxIZ0uhdGYIkCeWWzGQ+YF3TXMYUr7N4KqkRkyTmqfEr0WfSNaP/PZDrbFLIVNY4/nnd3q6C23ZwdeYLfbs4EpjXP+WEELtYBHmNY=
ARC-Authentication-Results:	i=1; server2.sourceware.org
X-MC-Unique:	25usbKz4MsiHfx9S7j3YVw-1
Date:	Mon, 13 Nov 2023 17:21:02 +0100
To:	Bruno Haible <bruno AT clisp DOT org>
Subject:	Re: rand is not ISO C compliant in Cygwin
Message-ID:	<ZVJM7g9smHGMN7QH@calimero.vinschen.de>
Mail-Followup-To:	Bruno Haible <bruno AT clisp DOT org>, newlib AT sourceware DOT org,
	cygwin AT cygwin DOT com
References:	<9938355 DOT c9vzh5UkMf AT nimes> <ZVIv3oq8UU6GTa0n AT calimero DOT vinschen DOT de>
	<4746602 DOT Hd9D3QOfv1 AT nimes> <ZVI06HnJE+r1CwFB AT calimero DOT vinschen DOT de>
MIME-Version:	1.0
In-Reply-To:	<ZVI06HnJE+r1CwFB@calimero.vinschen.de>
X-Scanned-By:	MIMEDefang 3.4.1 on 10.11.54.6
X-Mimecast-Spam-Score:	0
X-Mimecast-Originator:	redhat.com
X-Spam-Status:	No, score=-5.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH,
	DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_NONE,
	RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP,
	T_SCC_BODY_TEXT_LINE autolearn=unavailable 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
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:	Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	newlib AT sourceware DOT org
Cc:	Corinna Vinschen <vinschen AT redhat DOT com>, newlib AT sourceware DOT org,
	cygwin AT cygwin DOT com
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 Nov 13 15:38, Corinna Vinschen wrote:
> On Nov 13 15:25, Bruno Haible wrote:
> > Corinna Vinschen wrote:
> > > The rand() function would still not use locking but AFAICS that's
> > > not actually required by POSIX or ISO C.
> > 
> > Correct. Those who want an MT-safe rand-like function need to use random(),
> > not rand().

I took a look into POSIX and I'm a bit puzzled now.  From
https://pubs.opengroup.org/onlinepubs/9699919799/functions/rand.html

RATIONAL

  The ISO C standard rand() and srand() functions allow per-process
                                                  ^^^^^ (not requires)

  pseudo-random streams shared by all threads. Those two functions need
  not change, but there has to be mutual-exclusion that prevents
  interference between two threads concurrently accessing the random
  number generator.

Ok, so, *iff* rand/srand share per-process state, then they have to
use locking to prevent MT interference.  POSIX continues:

  With regard to rand(), there are two different behaviors that may be
  wanted in a multi-threaded program:

  1. A single per-process sequence of pseudo-random numbers that is
     shared by all threads that call rand()

  2. A different sequence of pseudo-random numbers for each thread that
     calls rand()
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I read this as the newlib technique being one way of correctly
implementing rand/srand, no?


Corinna


-- 
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

- Raw text -