From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org
X-Spam-Level: 
X-Spam-Status: No, score=-3.4 required=5.0 tests=DKIM_SIGNED,DKIM_VALID,
	DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A,RCVD_IN_DNSWL_MED,
	RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,T_SCC_BODY_TEXT_LINE autolearn=ham
	autolearn_force=no version=3.4.4
Received: (qmail 2711 invoked from network); 26 Feb 2022 11:39:09 -0000
Received: from mother.openwall.net (195.42.179.200)
  by inbox.vuxu.org with ESMTPUTF8; 26 Feb 2022 11:39:09 -0000
Received: (qmail 23978 invoked by uid 550); 26 Feb 2022 11:39:07 -0000
Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm
Precedence: bulk
List-Post: <mailto:musl@lists.openwall.com>
List-Help: <mailto:musl-help@lists.openwall.com>
List-Unsubscribe: <mailto:musl-unsubscribe@lists.openwall.com>
List-Subscribe: <mailto:musl-subscribe@lists.openwall.com>
List-ID: <musl.lists.openwall.com>
Reply-To: musl@lists.openwall.com
Received: (qmail 23945 invoked from network); 26 Feb 2022 11:39:07 -0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zhasha.com;
	s=wirbelwind; t=1645875535;
	bh=BV5wcpdfJVxk92AkgyiHt567gu6jw/aSKESb0DOtoww=;
	h=Date:From:To:Subject:In-Reply-To:References;
	b=TZPsyTyHdvwBYUzJwz5FvU2QeeAqvvuO6ICattUE8dCtBE598jppQB7Q/aacabAKx
	 A0oQb/NVD33W05XPQJ3XtgqCWMw3YjyTQuC0+OqyRydIZHbTZpzSjECjwifii+rTTa
	 flyvgyvWhL0g+kRFaAIAlGIXrA6zibzWdFHzHB4I=
Date: Sat, 26 Feb 2022 12:38:55 +0100
From: Joakim Sindholt <opensource@zhasha.com>
To: musl@lists.openwall.com
Message-Id: <20220226123855.392c22acb208a966210c7af2@zhasha.com>
In-Reply-To: <CAOZ3c1rkxt3SgTvpzb4g+HJi1+rwhhbnDP_wE8+aZyREA8dyZg@mail.gmail.com>
References: <CAOZ3c1rUN24Arx5iy+Zm-4gYajfBthQsgL9q-iiNQpAo1aZL8w@mail.gmail.com>
	<20220221174223.GA2079@voyager>
	<CAOZ3c1p8R00oxar+nRUPTxAzLqAxwpNfWfMVfkZ0dQLnmOZVeA@mail.gmail.com>
	<20220223185746.GB2079@voyager>
	<CAOZ3c1rkxt3SgTvpzb4g+HJi1+rwhhbnDP_wE8+aZyREA8dyZg@mail.gmail.com>
X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu)
Mime-Version: 1.0
Content-Type: multipart/mixed;
 boundary="Multipart=_Sat__26_Feb_2022_12_38_55_+0100_BfJMqo2k.wNQmd=4"
Subject: Re: [musl] Suggestion for thread safety

This is a multi-part message in MIME format.

--Multipart=_Sat__26_Feb_2022_12_38_55_+0100_BfJMqo2k.wNQmd=4
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Sat, 26 Feb 2022 09:56:04 +0000, Lee Shallis <gb2985@gmail.com> wrote:
> On Wed, 23 Feb 2022 at 18:58, Markus Wichmann <nullplan@gmx.net> wrote:
> >
> > On Wed, Feb 23, 2022 at 12:30:43AM +0000, Lee Shallis wrote:
> > > think of the lock as the same as a mutex, just simpler,
> >
> > It isn't really simpler than a fast mutex, but a lot buggier.
> >
> There are no bugs, I made sure to test this after all, I deliberately
> created a situation where any bugs would show them selves, the only
> thing that was a potential problem I've now fixed (after doing some
> research to find out if 0 is ever a valid thread id), the concept
> remains the same, just with support for developer calling LockSiData
> twice:

Did I use it wrong then?

zhasha@wirbelwind /home/zhasha ; gcc -lpthread buglock.c
zhasha@wirbelwind /home/zhasha ; ./a.out
var = 1, expected 0
zhasha@wirbelwind /home/zhasha ; ./a.out
var = 1, expected 0
zhasha@wirbelwind /home/zhasha ; ./a.out
var = 2, expected 1
zhasha@wirbelwind /home/zhasha ; ./a.out
var = 2, expected 1
var = 1, expected 0
zhasha@wirbelwind /home/zhasha ; ./a.out
var = 1, expected 0

--Multipart=_Sat__26_Feb_2022_12_38_55_+0100_BfJMqo2k.wNQmd=4
Content-Type: text/plain;
 name="buglock.c"
Content-Disposition: attachment;
 filename="buglock.c"
Content-Transfer-Encoding: 7bit

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <stdint.h>
#include <errno.h>

static void NoPause(void *ud)
{
    (void)ud;
}

typedef int dint;
typedef const char* LOCK;
void (*pauseCB)(void *) = NoPause;

static void LockSiData( LOCK **shared, LOCK *ptr )
{
    while ( *shared != ptr )
    {
        if ( !(*shared) )
            *shared = ptr;
        pauseCB( ptr );
    }
}

static dint FreeSiData( LOCK **shared, LOCK *ud )
{
    if ( *shared == ud )
    {
        *shared = NULL;
        return 0;
    }
    return EPERM;
}

static LOCK *l = 0;
static volatile int var = 0;

static void *thread(void *arg)
{
    int i;
    while (1) {
        LockSiData(&l, arg);
        i = var++;
        if (i != 0) {
            printf("var = %d, expected 0\n", i);
            exit(1);
        }
        i = var--;
        if (i != 1) {
            printf("var = %d, expected 1\n", i);
            exit(1);
        }
        FreeSiData(&l, arg);
    }
    return 0;
}

int main(void)
{
    pthread_t pt;
    uintptr_t i;

    for (i = 1; i <= 2; i++) {
        if ((errno = pthread_create(&pt, 0, thread, (void *)i)) != 0) {
            printf("pthread_create failed: %m\n");
            return 1;
        }
    }
    pthread_exit(0);
    return 0;
}

--Multipart=_Sat__26_Feb_2022_12_38_55_+0100_BfJMqo2k.wNQmd=4--